ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 03 Apr 2020 21:47:17 GMT2020-04-03T21:47:17Z50591- Mass transport in a microchannel bioreactor with a porous wallhttps://scholarbank.nus.edu.sg/handle/10635/73585Title: Mass transport in a microchannel bioreactor with a porous wall
Authors: Low, H.-T.; Chen, X.; Yu, P.; Winoto, S.
Abstract: A two-dimensional flow model, incorporating mass transport, has been developed to simulate flow in a microchannel bioreactor with a porous wall. A two-domain method was implemented which was based on finite volume method. For the porous-fluid interface, a stress jump condition was used with continuity of normal stress; and the mass interfacial conditions were continuities of mass and mass flux. Two parameters are defined to characterize the mass transports in the fluid and porous regions. The porous Damkohler number is the ratio of consumption to diffusion of the substrates in the porous medium. The fluid Damkohler number is the ratio of substrate consumption in the porous medium to substrate convection in the fluid region. The concentration results are found to be well correlated by the use of a reaction-convection distance parameter which incorporates the effects of axial distance, substrate consumption and convection. © (2012) Trans Tech Publications, Switzerland.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/735852012-01-01T00:00:00Z
- Lattice Boltzmann method for flows in porous and homogenous fluid domains coupled at the interface by stress jumphttps://scholarbank.nus.edu.sg/handle/10635/60638Title: Lattice Boltzmann method for flows in porous and homogenous fluid domains coupled at the interface by stress jump
Authors: Bai, H.; Yu, P.; Winoto, S.H.; Low, H.T.
Abstract: A numerical method was developed for flows involving an interface between a homogenous fluid and a porous medium. The numerical method is based on the lattice Boltzmann method for incompressible flow. A generalized model, which includes Brinkman term, Forcheimmer term and nonlinear convective term, was used to govern the flow in the porous medium region. At the interface, a shear stress jump that includes the inertial effect was imposed for the lattice Boltzmann equation, together with a continuity of normal stress. The present method was implemented on three cases each of which has a porous medium partially occupying the flow region: channel flow, plug flow and lid-driven cavity flow. The present results agree well with the analytical and/or the finite-volume solutions. Copyright © 2008 John Wiley & Sons, Ltd.
Tue, 30 Jun 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/606382009-06-30T00:00:00Z
- A numerical method for forced convection in porous and homogenous fluid domains coupled at interface by stress jumphttps://scholarbank.nus.edu.sg/handle/10635/84805Title: A numerical method for forced convection in porous and homogenous fluid domains coupled at interface by stress jump
Authors: Chen, X.; Yu, P.; Winoto, S.H.; Low, H.-T.
Abstract: A numerical method was developed for flows involving an interface between a homogeneous fluid and a porous medium. It is based on the finite volume method with body-fitted and multi-block grids. The Brinkman-Forcheimmer extended model was used to govern the flow in the porous medium region. At its interface, the flow boundary condition imposed is a shear stress jump, which includes the inertial effect, together with a continuity of normal stress. The thermal boundary condition is continuity of temperature and heat flux. The forced convection through a porous insert over a backward-facing step is investigated. The results are presented with flow configurations for different Darcy numbers, 10-2 to 10-5, porosity from 0.2 to 0.8, Reynolds number from 10 to 800, and the ratio of insert length to channel height from 0.1 to 0.3. The heat transfer is improved by using porous insert. To enhance the heat transfer with minimal frictional losses, it is preferable to have a medium length of insert with medium Darcy number, and larger Reynolds number. The interfacial stress jump coefficients β and β1 were varied from - 1 to 1, and within this range the average and local lower-wall Nusselt numbers are not sensitive to the parameters. Copyright © 2007 John Wiley & Sons, Ltd.
Sun, 30 Mar 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/848052008-03-30T00:00:00Z
- Transition of boundary layer flows in the presence of Goertler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/58855Title: Transition of boundary layer flows in the presence of Goertler vortices
Authors: Winoto, S.H.; Low, H.T.
Abstract: Transition of boundary layer flows in the presence of longitudinal counter-rotating Goertler vortices was experimentally investigated on a concave surface of 1.0 m radius of curvature in a perspex (plexiglass) curved rectangular duct connected to a low speed wind tunnel for a free-stream velocity range of 5.7-11.8 m/s. Quantitative measurements were carried out using a single sensor hot-wire anemometer, while the boundary layer transitions were detected using frequency spectrum method. The results confirm that in the presence of Goertler vortices, transition is initiated at the boundary layer upwash regions, and also agree well with the predicted values obtained using the two existing empirical transition criteria for concave surface boundary layer flows. © 1989 Springer-Verlag.
Sun, 01 Oct 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/588551989-10-01T00:00:00Z
- Secondary instability in forced wavelength Görtler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/61269Title: Secondary instability in forced wavelength Görtler vortices
Authors: Mitsudharmadi, H.; Winoto, S.H.; Shah, D.A.
Abstract: From an experimental study on the onset of secondary instability in forced wavelength Görtler vortices, it is found that the breakdown process of the Görtler vortices is due to the development of varicose and sinuous mode instabilities. The development of the varicose mode is characterized by the formation of horseshoe vortices that evolve downstream to form mushroom-like structures. This phenomenon is then followed by meandering of the vortices as an indication of the onset of sinuous mode instability, prior to turbulence. The spectrum analysis applied to the fluctuating velocity component shows the occurrence of peak frequency of about 150Hz, which is attributed to the fundamental secondary instability mode with its wavelength comparable to the spanwise wavelength of the primary Görtler vortices, at the location where the mushroom-like structures are clearly depicted in the mean velocity contours on the y-z plane. This confirms that the secondary instability is of the varicose type at the onset that is followed by the sinuous type downstream, prior to the breakdown of the vortices that will lead the boundary layer flow to turbulence. It is also found that the growth rate of the secondary instability observed is about 6.5 times higher than that of the Görtler instability, which leads to a breakdown of the streamwise structures and hence to turbulence. © 2005 American Institute of Physics.
Fri, 01 Jul 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/612692005-07-01T00:00:00Z
- Development of boundary-layer flow in the presence of forced wavelength Görtler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/84984Title: Development of boundary-layer flow in the presence of forced wavelength Görtler vortices
Authors: Mitsudharmadi, H.; Winoto, S.H.; Shah, D.A.
Abstract: Hot-wire measurements in the boundary layer developing on a concave surface of 2.0 m radius of curvature in the presence of forced wavelength Görtler vortices have been conducted for a free-stream velocity of 3.0 m/s. The wavelengths of vortices were preset by vertical perturbation wires of 0.2 mm diameter located 10 mm upstream of the concave surface leading edge. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices that are similar to those found in the transitional flow field. It shows the occurrence of the second instability mode that is indicated by the formation of small horseshoe eddies generated between the two neighboring vortices traveling in the streamwise direction to form mushroom-like structures as a consequence of the nonlinear growth of the Görtler vortices. The breakdown of these structures before the boundary-layer flow becomes turbulent is also shown to qualitatively predict the start of the transition in the flow. The Görtler number where the start of the transition was predicted is found to be within the range of transitional Görtler numbers previously reported for naturally developed Görtler vortices. The average of the spanwise wavelength after being normalized by v/u τ, is comparable with the generally quoted value of 100 for turbulent boundary layers. © 2004 American Institute of Physics.
Mon, 01 Nov 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/849842004-11-01T00:00:00Z
- Visualizing Görtler Vorticeshttps://scholarbank.nus.edu.sg/handle/10635/74008Title: Visualizing Görtler Vortices
Authors: Winoto, S.H.; Mitsudharmadi, H.; Shah, D.A.
Abstract: The development of Görtler vortices with pre-set wavelength of 15 mm has been visualized in the boundary-layer on a concave surface of 2.0 m radius of curvature at a free-stream velocity of 3.0 m/s. The wavelength of vortices was pre-set by vertical wires of 0.2 mm diameter located 10 mm upstream of the concave surface leading edge. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on different growth rate of the vortices. The occurrence of a secondary instability mode is indicated by the formation of a small horseshoe eddies generated between the two neighboring vortices traveling streamwise, to form mushroom-like structures as a consequence of the non-linear growth of the Görtler vortices. © 2005 The Visualization Society of Japan and Ohmsha, Ltd.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/740082005-01-01T00:00:00Z
- On the development of concave surface boundary layer flowshttps://scholarbank.nus.edu.sg/handle/10635/73708Title: On the development of concave surface boundary layer flows
Authors: Winoto, S.H.; Tandionol; Shah, D.A.; Mitsudharmadi, H.
Abstract: The development of concave surface boundary-layer flows is characterized by the formation of streamwise counterrotating Görtler vortices and has been experimentally investigated for concave surfaces of 1 m and 2 m radius of curvature. For this study, the wavelengths of the vortices were pre-set or "forced" by thin perturbation wires placed upstream and perpendicular to the concave surface leading edge. This method was used to obtain uniform vortex wavelengths. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified wavelengths of the vortices can be pre-set by the spanwise spacing of the thin wires and free-stream velocity. The velocity contours on the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of Görtler vortices. Measurements of wall shear stress on concave surface of 1 m radius of curvature reveal that the spanwise-averaged wall shear stress increases well beyond the flat plate boundary layer values. By presetting much larger or much smaller vortex wavelength than the most amplified one, the splitting or merging of Görtler vortices can be respectively observed. © 2010 American Institute of Physics.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/737082010-01-01T00:00:00Z
- A bi-directional rotating fluid bearing systemhttps://scholarbank.nus.edu.sg/handle/10635/73003Title: A bi-directional rotating fluid bearing system
Authors: Zhang, Q.D.; Chen, S.X.; Yang, J.P.; Winoto, S.H.
Abstract: Most fluid bearing systems with grooves on the journal/thrust bearing surfaces were designed to rotate in a specified direction and cannot be reversed. This feature of such fluid bearings limits their application range and hence, a bi-directional rotating fluid bearing system is proposed. The results of numerical simulation on the dynamic characteristics of such bearing system are presented and compared with those of one-directional rotating fluid-bearing system. It shows that for the same load capacity and stiffness requirement, the bi-directional rotating fluid bearing system has a higher power consumption than that of the one-directional counterpart. However, the bidirectional rotating fluid bearing system provides the freedom of rotating spindle motor in either direction and widens the application range of fluid bearing spindle motors.
Thu, 01 Aug 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/730032002-08-01T00:00:00Z
- Visualizing shear stress in görtler vortex flowhttps://scholarbank.nus.edu.sg/handle/10635/61682Title: Visualizing shear stress in görtler vortex flow
Authors: Tandiono; Winoto, S.H.; Shah, D.A.
Abstract: Shear stress distributions were obtained from velocity measurements in a concave surface boundary layer flow in the presence of Görtler vortices by means of a single hot-wire probe for several streamwise (x) locations. A set of vertical wires of 0.20 mm diameter were positioned at a distance of 10 mm upstream from the leading edge of a concave surface of radius of curvature R = 1.0 m to pre-set the wavelength of the vortices so to obtain the most amplified wavelength Görtler vortices. Consequently, the wavelength of the vortices was set equal to the wire spacing and preserved downstream. In addition to the high shear regions near the wall, one positive peak at the head of the mushroom-like structures and two relatively weak negative peaks at the vicinity of the low-speed streaks are found in the iso-∂u/∂y contours. They are believed to be related to the formation of the inflectional point in the velocity profile across boundary layer. The occurrence of the inflection points in the spanwise distributions of streamwise velocity component u is associated with the appearance of the second peak of the ∂u/∂z shear near the boundary layer edge. The nonlinear effect of Görtler instability is to increase the wall shear stress, and further enhancement beyond the turbulent values is due to the presence of secondary instability.© 2009 The Visualization Society of Japan.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/616822009-01-01T00:00:00Z
- Pressure distributions along vertical hydrodynamic herringbone-grooved journal bearingshttps://scholarbank.nus.edu.sg/handle/10635/61147Title: Pressure distributions along vertical hydrodynamic herringbone-grooved journal bearings
Authors: Rondonuwu, C.C.; Winoto, S.H.
Abstract: The pressure distributions generated along vertical hydrodynamic herringbone-grooved journal bearings were experimentally and numerically investigated at rotational speeds ranging from 203 to 2110 rpm. A test rig was designed and constructed for this purpose and four journals (shafts) with different herringbone-grooved patterns and radial gaps were tested: Journal 1 (with symmetrical and discontinuous grooves and 0.25-mm clearance gap), Journal 2 (with symmetrical and discontinuous grooves and 0.35-mm clearance gap), Journal 3 (with symmetrical and four continuous grooves), and Journal 4 (with asymmetrical and three continuous grooves). The journals were made of aluminum with diameters of 46.00 mm, and the sleeve was made of a transparent Plexiglas pipe for visual observation of the lubricant in the gap between the journal and the sleeve. Pressure taps were installed along the sleeve to obtain the pressure distributions using a pressure transducer. Numerical simulations were performed for these four herringbone-grooved journal bearings using commercially available computational fluid dynamic software. The computational simulations agree in trends with the experimental results and theoretical expectations. Copyright © Society of Tribologists and Lubrication Engineers.
Sat, 01 Apr 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/611472006-04-01T00:00:00Z
- Splitting and merging of Görtler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/61351Title: Splitting and merging of Görtler vortices
Authors: Mitsudharmadi, H.; Winoto, S.H.; Shah, D.A.
Abstract: The splitting and merging of Görtler vortices are experimentally studied by varying the spacings of vertical wires located 10mm upstream of a concave surface leading edge of 2.0m radius of curvature subjected to a free-stream velocity of 3.0m/s. The splitting and merging as the result of the linear instability of the vortices with respect to spanwise perturbation (Eckhaus instability), occurred when the wire spacing was set to respectively twice and half of the dominant or most amplified wavelength of Görtler vortices. These show the susceptibility of Görtler vortices to wavelengths greater and smaller than the most amplified wavelength of the vortices. The spectral study shows that the values of the dimensionless frequency parameter for the wire spacings of 7.5, 15.0, and 30.0mm are nearly constant (of about 0.5) for the streamwise locations where the mushroom-like structures dominate the flow. It is also found that the dimensionless wavelength parameter is more sensitive than the Reynolds number of the vertical wires as a threshold identification of transition from one pair to two pairs of vortex configurations. © 2005 American Institute of Physics.
Thu, 01 Dec 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/613512005-12-01T00:00:00Z
- Investigation of Intermittency Measurement Methods for Transitional Boundary Layer Flowshttps://scholarbank.nus.edu.sg/handle/10635/58418Title: Investigation of Intermittency Measurement Methods for Transitional Boundary Layer Flows
Authors: Zhang, D.H.; Chew, Y.T.; Winoto, S.H.
Abstract: Three turbulent intermittency methods, namely the ū, TERA (turbulent energy recognition algorithm), and M-TERA (modified turbulent energy recognition algorithm) methods, for identifying the intermittent flow characteristics associated with boundary layer transition from laminar to turbulent were considered and compared. The data used were obtained from hot-wire measurements in transitional boundary layer flows on a concave surface with a 2-m radius of curvature and on a flat plate. Comparisons show that the ū and TERA methods are more sensitive to the choice of threshold constants than the M-TERA method. In terms of the intermittency distribution across the boundary layer, the values obtained by the ū and TERA methods are unrealistically high in the near-wall region, while those obtained by the M-TERA method are more realistic. In the outer boundary layer region and outside the boundary layer, the ū and M-TERA methods give reasonable intermittency values, whereas the TERA method produces unrealistically high values in the region outside the boundary layer. In addition, the M-TERA method provides a sharper definition of the end of transition.
Wed, 01 May 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/584181996-05-01T00:00:00Z
- A piecewise parabolic method for barotropic and nonbarotropic two-fluid flowshttps://scholarbank.nus.edu.sg/handle/10635/54708Title: A piecewise parabolic method for barotropic and nonbarotropic two-fluid flows
Authors: Zheng, J.G.; Lee, T.S.; Winoto, S.H.
Abstract: Purpose - The aim of the study is to present a piecewise parabolic method (PPM) for numerical simulation of barotropic and nonbarotropic two-fluid flows in more than one space dimension. Design/methodology/approach - In transition layers of two components, a fluid mixture model system is introduced. Besides, conserving the mass, momentum and energy for the mixture, the model is supplemented with an advection equation for the volume fraction of one of the two fluid components to recover the pressure and track interfaces. The Tait and stiffened gas equations of state are used to describe thermodynamic properties of the barotropic and nonbarotropic components, respectively. To close the model system, a mixture equation of state is derived. The classical third-order PPM is extended to the two-fluid case and used to solve the model system. Findings - The feasibility of this method has been demonstrated by good results of sample applications. Each of the material interfaces is resolved with two grid cells and there is no any pressure oscillation on the interfaces. Research limitations/implications - With the mixture model system, there may be energy gain or loss for the nonbarotropic component on the material interfaces. Practical implications - The method can be applied to a wide range of practical problems. Originality/value - The method is simple. It not only has the advantage of Lagrangian-type schemes but also keeps the robustness of Eulerian schemes. © Emerald Group Publishing Limited.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/547082008-01-01T00:00:00Z
- Pressure/flow behaviour in collapsible tube subjected to forced downstream pressure fluctuationshttps://scholarbank.nus.edu.sg/handle/10635/58637Title: Pressure/flow behaviour in collapsible tube subjected to forced downstream pressure fluctuations
Authors: Low, T.H.; Chew, Y.T.; Winoto, S.H.; Chin, R.
Abstract: An experimental investigation, has been made into the pressure/flow behaviour of a collapsible tube subjected to downstream pressure fluctuations. These downstream pressure waves are observed to be transmitted upstream beyond the point of collapse. The mean flow rate is not significantly affected by the amplitude or frequency of pressure fluctuations. However, the oscillatory flow amplitude is reduced at the higher frequency. The mean flow rate also remains independent of the mean driving pressure.
Sat, 01 Jul 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/586371995-07-01T00:00:00Z
- Design of high-speed magnetic fluid bearing spindle motorhttps://scholarbank.nus.edu.sg/handle/10635/73323Title: Design of high-speed magnetic fluid bearing spindle motor
Authors: Zhang, Q.; Chen, S.; Winoto, S.H.; Ong, E.-H.
Abstract: A high-speed magnetic-fluid bearing spindle motor for hard disk drive is introduced. Some design challenges and considerations of its load capacity, stiffness, power consumption, lubricant leakage and shock resistant capability are addressed. The prototypes were fabricated and the test results of the prototypes are presented and discussed. The results show that the magnetic-fluid bearing spindle motor is very promising for use in future hard disk drives.
Sun, 01 Jul 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/733232001-07-01T00:00:00Z
- Free convection in a porous wavy cavity based on the Darcy-Brinkman- Forchheimer extended modelhttps://scholarbank.nus.edu.sg/handle/10635/60365Title: Free convection in a porous wavy cavity based on the Darcy-Brinkman- Forchheimer extended model
Authors: Chen, X.B.; Yu, P.; Winoto, S.H.; Low, H.T.
Abstract: A numerical investigation is carried out for steady, free convection inside a cavity filled with a porous medium. The cavity has vertical wavy walls which are isothermal. The top and bottom horizontal straight walls are kept adiabatic. The numerical method is based on the finite-volume method with body-fitted and nonorthogonal grids. A generalized model, which includes a Brinkman term, a Forcheimmer term, and a nonlinear convective term, is used. Studies are carried out for a range of wave ratio =0-1.8, aspect ratio A=1-5, Darcy number Da=10-1-10-6, and Darcy-Rayleigh number Ra*=10-105. Results are presented in the form of streamlines, isotherms, and local and average Nusselt numbers. The generalized model which considers viscous, inertia, and convective effects enables results to be obtained for a wider range of Darcy and Rayleigh numbers.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/603652007-01-01T00:00:00Z
- An interface-capturing method for resolving compressible two-fluid flows with general equation of statehttps://scholarbank.nus.edu.sg/handle/10635/59487Title: An interface-capturing method for resolving compressible two-fluid flows with general equation of state
Authors: Lee, T.S.; Zheng, J.G.; Winoto, S.H.
Abstract: In this study, a stable and robust interface-capturing method is developed to resolve inviscid, compressible two-fluid flows with general equation of state (EOS). The governing equations consist of mass conservation equation for each fluid, momentum and energy equations for mixture and an advection equation for volume fraction of one fluid component. Assumption of pressure equilibrium across an interface is used to close the model system. MUSCL-Hancock scheme is extended to construct input states for Riemann problems, whose solutions are calculated using generalized HLLC approximate Riemann solver. Adaptive mesh refinement (AMR) capability is built into hydrodynamic code. The resulting method has some advantages. First, it is very stable and robust, as the advection equation is handled properly. Second, general equation of state can model more materials than simple EOSs such as ideal and stiffened gas EOSs for example. In addition, AMR enables us to properly resolve flow features at disparate scales. Finally, this method is quite simple, time-efficient and easy to implement. © 2009 Global-Science Press.
Sun, 01 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/594872009-11-01T00:00:00Z
- Efficiency of jet pumpshttps://scholarbank.nus.edu.sg/handle/10635/58243Title: Efficiency of jet pumps
Authors: Winoto, S.H.; Li, H.; Shah, D.A.
Abstract: A theoretical analysis and an experimental study on the efficiency of water jet pumps, where water is used for both the primary and secondary flows, are presented in this paper. The theoretical efficiency equations for such jet pumps were first derived based on one-dimensional formulation, and the theoretical maximum ideal efficiency of 100% was obtained. An experimental rig was designed and constructed to conduct the experimental study in which a commercial water jet pump was used. The effects of different area ratios of nozzle to mixing throat as well as different nozzle cross sections, which include square and triangular nozzles, on the jet pump performance were then investigated. The best nozzle cross section for the jet pump was found to be circular, and for high efficiency, the area ratio was found to be around 0.30.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/582432000-01-01T00:00:00Z
- Mass transport in a microchannel enzyme reactor with a porous wall: Hydrodynamic modeling and applicationshttps://scholarbank.nus.edu.sg/handle/10635/89360Title: Mass transport in a microchannel enzyme reactor with a porous wall: Hydrodynamic modeling and applications
Authors: Chen, X.B.; Sui, Y.; Cheng, Y.P.; Lee, H.P.; Yu, P.; Winoto, S.H.; Low, H.T.
Abstract: A two-dimensional flow model, incorporating mass transport, has been developed to simulate a microchannel enzyme reactor with a porous wall. A two-domain approach based on the finite volume method was implemented. Two parameters are defined to characterize the mass transports in the fluid and porous regions: the porous Damkohler number and the fluid Damkohler number. For reactions close to first-order type (enzyme reactor), the concentration results are found to be well correlated by the use of a reaction-convection distance parameter which incorporates the effects of axial distance, substrate consumption and convection. The reactor efficiency reduces with reaction-convection distance parameter because of reduced reaction (or flux) due to the lower concentration. Increased fluid convection improves the efficiency but it is limited by the diffusion in the fluid region. The correlated results can find applications for the design of enzyme reactors with a porous wall. © 2010 Elsevier B.V.
Mon, 15 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/893602010-11-15T00:00:00Z
- Numerical flow simulation in a centrifugal pump at design and off-design conditionshttps://scholarbank.nus.edu.sg/handle/10635/85498Title: Numerical flow simulation in a centrifugal pump at design and off-design conditions
Authors: Cheah, K.W.; Lee, T.S.; Winoto, S.H.; Zhao, Z.M.
Abstract: The current investigation is aimed to simulate the complex internal flow in a centrifugal pump impeller with six twisted blades by using a three-dimensional Navier-Stokes code with a standard k-ε two-equation turbulence model. Different flow rates were specified at inlet boundary to predict the characteristics of the pump. A detailed analysis of the results at design load, Qdesign, and off-design conditions, Q = 0.43 Qdesign and Q = 1.45 Qdesign, is presented. From the numerical simulation, it shows that the impeller passage flow at design point is quite smooth and follows the curvature of the blade. However, flow separation is observed at the leading edge due to nontangential inflow condition. The flow pattern changed significantly inside the volute as well, with double vortical flow structures formed at cutwater and slowly evolved into a single vortical structure at the volute diffuser. For the pressure distribution, the pressure increases gradually along streamwise direction in the impeller passages. When the centrifugal pump is operating under off-design flow rate condition, unsteady flow developed in the impeller passage and the volute casing.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/854982007-01-01T00:00:00Z
- Boundary conditions at the interface between fluid layer and fibrous mediumhttps://scholarbank.nus.edu.sg/handle/10635/59650Title: Boundary conditions at the interface between fluid layer and fibrous medium
Authors: Bai, H.X.; Yu, P.; Winoto, S.H.; Low, H.T.
Abstract: The flow through a channel partially filled with fibrous porous medium was analyzed to investigate the interfacial boundary conditions. The fibrous medium was modeled as a periodic array of circular cylinders, in a hexagonal arrangement, using the boundary element method. The area and volume average methods were applied to relate the pore scale to the representative elementary volume scale. The permeability of the modeled fibrous medium was calculated from the Darcy's law with the volume-averaged Darcy velocity. The slip coefficient, interfacial velocity, effective viscosity and shear jump coefficients at the interface were obtained with the averaged velocities at various permeabilities or Darcy numbers. Copyright © 2008 John Wiley & Sons, Ltd.
Fri, 10 Jul 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/596502009-07-10T00:00:00Z
- Mass transport for mixed co-culture applications in a perfusion bioreactor partially filled with a porous layerhttps://scholarbank.nus.edu.sg/handle/10635/85375Title: Mass transport for mixed co-culture applications in a perfusion bioreactor partially filled with a porous layer
Authors: Bai, H.X.; Yu, P.; Zeng, Y.; Winoto, S.H.; Low, H.T.
Abstract: A simplified analysis is carried out to derive the analytical solution of the mass transfer equation in a microchannel bioreactor, which has a porous wall for the co-culture of two types of cells distributed randomly and uniformly. Based on the analysis, a group of dimensionless parameters is proposed, which can be applied to correlate the numerical data and characterize the mass transfer in the bioreactor. The normalized numerical data, for the concentration at the porous-fluid interface and concentration difference between the interface and the base, show satisfactory correlation when presented as a function of the effective distance parameter. Two cell culture examples are presented to demonstrate the general applications of the correlated results in the design of a co-culture microchannel bioreactor with a porous wall. © 2014 by Begell House, Inc.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/853752014-01-01T00:00:00Z
- Measurement in laminar and transitional boundary-layer flows on concave surfacehttps://scholarbank.nus.edu.sg/handle/10635/92737Title: Measurement in laminar and transitional boundary-layer flows on concave surface
Authors: Zhang, D.H.; Winoto, S.H.; Chew, Y.T.
Abstract: Measurements of streamwise mean and fluctuating velocities in laminar and transitional boundary-layer flows on a concave surface of 2.0 m radius of curvature have been performed using hot-wire anemometry technique. A new turbulent intermittency detector method was used to calculate the intermittency factor. In addition to the spanwise distributions of mean velocity, the profiles of mean, fluctuating velocities and intermittency across the boundary layer at two different spanwise positions; namely, the upwash and downwash, are also presented. The experimental results show that the normal and spanwise distributions of mean velocity, normal turbulence intensity u′rms/U0 profiles experience different streamwise evolutions in the laminar and transition regions. Significant velocity profile distortion, saturated growth of Goertler vortices, and the existence of two peaks in u′rms/U0 profiles are the main features of the boundary-layer low at the onset of transition. The intermittency profiles in the early stages of transition t the two spanwise positions have some similar characteristics and are not consistent vith each other on some other aspects. Comparisons of the y profiles at the two spanwise positions confirm that the transition first starts at the low-speed regions. © 1995 Elsevier Science Inc.
Sat, 01 Apr 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927371995-04-01T00:00:00Z
- Development of most amplified wavelength Görtler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/59939Title: Development of most amplified wavelength Görtler vortices
Authors: Mitsudharmadi, H.; Winoto, S.H.; Shah, D.A.
Abstract: The development of most amplified wavelength Görtler vortices is studied by means of varying the spanwise spacing of thin vertical wires located upstream of the leading edge of a concave surface. The free-stream velocity is set so as to provide the value of the dimensionless parameter of that for the most amplified vortex wavelength. The resulting uniform vortex wavelengths were determined by the wire spacings and they were preserved downstream prior to turbulence. The spectrum study of the fluctuating velocity component was able to detect the fundamental frequency of the secondary instability mode with the streamwise wavelengths comparable to the wire spacing, which confirm that the wavelength of the vortices observed is the most amplified one. The intermittency study of the boundary layer flow in the presence of the most amplified wavelength Görtler vortices of 15.0 mm using Turbulent Energy Recognition Algorithm method shows the transition onset in the upwash regions, which coincides with the onset of the secondary instability obtained from the spectrum method. The intermittency factor distributions obtained agree with the single universal distribution with an error of about 5%. The transition Görtler number was also found within the range of that of the boundary layers in the presence of naturally developed Görtler vortices reported earlier. © 2006 American Institute of Physics.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/599392006-01-01T00:00:00Z
- Natural convection in a cavity filled with porous layers on the top and bottom wallshttps://scholarbank.nus.edu.sg/handle/10635/85473Title: Natural convection in a cavity filled with porous layers on the top and bottom walls
Authors: Chen, X.B.; Yu, P.; Sui, Y.; Winoto, S.H.; Low, H.T.
Abstract: Natural convection in a partially filled porous square cavity is numerically investigated using SIMPLEC method. The Brinkman-Forchheimer extended model was used to govern the flow in the porous medium region. At the porous-fluid interface, the flow boundary condition imposed is a shear stress jump, which includes both the viscous and inertial effects, together with a continuity of normal stress. The thermal boundary condition is continuity of temperature and heat flux. The results are presented with flow configurations and isotherms, local and average Nusselt number along the cold wall for different Darcy numbers from 10-1 to 10-6, porosity values from 0.2 to 0.8, Rayleigh numbers from 103 to 107, and the ratio of porous layer thickness to cavity height from 0 to 0.50. The flow pattern inside the cavity is affected with these parameters and hence the local and global heat transfer. A modified Darcy-Rayleigh number is proposed for the heat convection intensity in porous/fluid filled domains. When its value is less than unit, global heat transfer keeps unchanged. The interfacial stress jump coefficients β1 and β2 were varied from -1 to +1, and their effects on the local and average Nusselt numbers, velocity and temperature profiles in the mid-width of the cavity are investigated. © Springer Science+Business Media B.V. 2008.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/854732009-01-01T00:00:00Z
- Numerical analysis for the flow past a porous square cylinder based on the stress-jump interfacial-conditionshttps://scholarbank.nus.edu.sg/handle/10635/85492Title: Numerical analysis for the flow past a porous square cylinder based on the stress-jump interfacial-conditions
Authors: Chen, X.; Yu, P.; Winoto, S.H.; Low, H.-T.
Abstract: Purpose - The purpose of this paper is to report on the flow past a porous square cylinder, implementing the stress jump treatments for the porous-fluid interface. Design/methodology/approach - The numerical method was developed for flows involving an interface between a homogenous fluid and a porous medium. It is based on the finite volume method with body-fitted and multi-block grids. The Brinkman-Forcheimmer extended model was used to govern the flow in the porous medium region. At its interface, a shear stress jump that includes the inertial effect was imposed, together with a continuity of normal stress. Findings - The present model is validated by comparing with those for the flow around a solid circular cylinder. Results for flow around porous square cylinder are presented with flow configurations for different Darcy number, 10-2 to 10 -5, porosity from 0.4 to 0.8, and Reynolds number 20 to 250. The flow develops from steady to unsteady periodic vortex shedding state. It was found that the stress jump interface condition can cause flow instability. The first coefficient β has a more noticeable effect whereas the second coefficient β1 has very small effect, even for Re=200. The effects of the porosity, Darcy number, and Reynolds number on lift and drag coefficients, and the length of circulation zone or shedding period are studied. Originality/value - The present study implements the numerical method based on finite volume method with a collocated variable arrangement to treat the stress jump condition. © Emerald Group Publishing Limited.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/854922008-01-01T00:00:00Z
- Flow past a wind-assisted ship propulsion devicehttps://scholarbank.nus.edu.sg/handle/10635/58296Title: Flow past a wind-assisted ship propulsion device
Authors: Low, H.T.; Luo, S.C.; Winoto, S.H.
Abstract: An experimental investigation has been carried out on a wind-assisted ship propulsion device (WASP), consisting of a cylinder-flap wing with boundary layer suction. Measurements of the pressure distribution, lift and drag have been presented for various angular locations of the suction area and flap. It was found that a lift coefficient of 4.2 is obtained, with suction coefficient of 0.09, when the suction area and flap are symmetrically placed at angular locations of 110° from the relative wind axis; the corresponding lift-drag ratio is 6. Also presented is a polar plot which ascertained that the propulsion force is not significantly affected by small variations (±10°) in the angular position of the flap. However, a corresponding variation in the suction location will significantly affect the propulsion force. © 1991.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/582961991-01-01T00:00:00Z
- Experimental investigation of pulsatile flows in tubeshttps://scholarbank.nus.edu.sg/handle/10635/58265Title: Experimental investigation of pulsatile flows in tubes
Authors: Shi, Z.D.; Winoto, S.H.; Lee, T.S.
Abstract: Based on cam-piston-valve arrangement, a mechanical pulsatile flow generator is designed to investigate sinusoidal flow and other types of pulsatile flow in straight rigid tube. Measurement reveals the relation between pressure gradient and flow rate. Numerical simulation using the k-ε turbulence model are carried out to compare the pulsatile flow produced by the generator with a sinusoidal flow and a physiological flow in a rigid tube. The results show that the pulsatile flow generated has similar dynamic properties to the physiological flow. Hence, the present setup can be used for in-vitro investigation of biofluid phenomena.
Thu, 01 May 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/582651997-05-01T00:00:00Z
- Numerical studies of transitional turbulent pulsatile flow in pipes with ring-type constrictionshttps://scholarbank.nus.edu.sg/handle/10635/92755Title: Numerical studies of transitional turbulent pulsatile flow in pipes with ring-type constrictions
Authors: Lee, T.S.; Shi, Z.D.; Winoto, S.H.
Abstract: Pulsatile flows in the vicinity of mechanical ring-type constrictions in pipes were studied for transitional turbulent flow with a Reynolds number (Re) of the order of 104. The Womersley number (Nw) is in the range 30-50, with a corresponding Strouhal number (St) range of 0·0143-0·0398. The pulsatile flows considered are a pure sinusoidal flow, a physiological flow and an experimental pulsatile flow profile for mechanical aortic valve flow simulations. Transitional laminar and turbulent flow characteristics in an alternating manner within the pulsatile flow fields were studied numerically. It was observed that fluid accelerations tend to suppress the development of flow disturbances. All the instantaneous maximum values of turbulent kinetic energy, turbulent viscosity and turbulent shear stress are smaller during the acceleration phase than during the deceleration period. Various parametric equations have been formulated through numerical experimentation to better describe the relationships between the instantaneous flow rate (Q), the pressure loss (ΔP), the maximum velocity (Vmax), the maximum vorticity (ζmax), the maximum wall vorticity (ζw,max), the maximum shear stress (τmax) and the maximum wall shear stress (τw,max) for turbulent pulsatile flow in the vicinity of constrictions in the vascular tube. An elliptic relationship has been found to exist between the instantaneous flow rate and the instantaneous pressure gradient. Other linear and quadratic relations between various flow parameters were also obtained.
Sun, 30 Jun 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927551996-06-30T00:00:00Z
- Performance of a viscous pump with radial pumping grooves©https://scholarbank.nus.edu.sg/handle/10635/92766Title: Performance of a viscous pump with radial pumping grooves©
Authors: Winoto, S.H.
Abstract: A disk-type viscous pump with radial pumping grooves on its stator has been previously shown to have linear pressure-flow rate relationships. However, the gradual increase of the working fluid temperature in practice makes the pressure-flow rate relations no longer linear. For this reason, a prototype of such a pump has been retested for rotor speeds ranging from 600 to 1800 rpm, and a few methods for comparing the test data with the analytical predictions have been suggested. The comparisons show very good agreement for all the rotor speeds tested.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927661998-01-01T00:00:00Z
- Prediction of pressure drop in non-woven filter mediä using a hagen-poiseuille modelhttps://scholarbank.nus.edu.sg/handle/10635/92772Title: Prediction of pressure drop in non-woven filter mediä using a hagen-poiseuille model
Authors: Biswas, S.; Winoto, S.H.
Abstract: An accurate estimation of the pressure drop across filter media is not an eajy task considering the randomness of pore size and shape] and complexity in geometry of flow paths, particularly for non-woven depth filters. The pioneering work of Darcy laid the foundation of pressure flow characteristics through sand beds. This was followed by the work ofKozeny who proposed a theory to determine the pore size using porosity as a parameter. Carman modified the porosity-permeability relationship further to suit experimental results more closely. The pressure drop relationship using this expression is known as Kozeny-Carman equation. In the present work, the prediction results of Kozeny and KozenyCarman equations have been compared with those obtained from the Hagen-Poiseuille model which include the effect of tortuosity. The results indicate that the introduction of tortuosity effect alone can improve the prediction based on the Hagen-Poiseuille model over the Kozeny model, which underestimates the pressure drop across the filter media.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927722000-01-01T00:00:00Z
- A proposed intermittency measurement method for transitional boundary layer flowshttps://scholarbank.nus.edu.sg/handle/10635/54742Title: A proposed intermittency measurement method for transitional boundary layer flows
Authors: Zhang, D.H.; Chew, Y.T.; Winoto, S.H.
Abstract: A new turbulent intermittency detector method, based on the Turbulent Energy Recognition Algorithm (TERA), has been proposed. Its performance was compared with two other available methods using the data obtained from hot-wire measurements in a developing boundary layer flow on a concave surface with constant radius of curvature of 2 m. Comparisons show that this new method is better than the other two as a turbulent detector under the same flow conditions, especially in the near-wall and in the outer and outside regions of the boundary layer. © 1995 Springer-Verlag.
Sun, 01 Oct 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/547421995-10-01T00:00:00Z
- Transition in boundary layers on a concave surfacehttps://scholarbank.nus.edu.sg/handle/10635/58854Title: Transition in boundary layers on a concave surface
Authors: Winoto, S.H.; Zhang, D.H.; Chew, Y.T.
Abstract: Transition from laminar to turbulent flow has been investigated in boundary layers along a concave surface of 2.0 m radius of curvature for a freestream velocity range of 6.0-15.0 m/s. Velocity and turbulent intermittency measurements were made using a single sensor hot-wire anemometer. Intermittency profiles at the so-called upwash and downwash regions were obtained at some streamwise positions to help determine the transition starts and ends at the regions. The experimental results show that, at both upwash and downwash regions for all of the free-stream velocities tested, the intermittency profiles at different transition stages exhibit similar behaviors. The difference between the upwash and downwash intermittency profiles obtained at the same streamwise locations decreases with increasing freestream velocity. For all of the freestream velocities, transition starts and ends earlier at the upwash regions than at the downwash regions. The transition lengths in the upwash regions are slightly longer than those in the downwash regions and decrease with increasing freestream velocity. The starts of transition at the upwash regions agree well with the transition prediction Goertler number of 6, whereas at the ends of transition for both upwash and downwash regions, the Goertler number ranges front 7.90 to 9.30.
Sat, 01 Jul 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/588542000-07-01T00:00:00Z
- Transition of boundary layer flows in the presence of Goertler vorticeshttps://scholarbank.nus.edu.sg/handle/10635/58856Title: Transition of boundary layer flows in the presence of Goertler vortices
Authors: Winoto, S.H.; Low, H.T.
Abstract: Further experimental results on transition of boundary layer flows in the presence of streamwise counter-rotating Goertler vortices were obtained on concave test surface of 3.0 m radius of curvature. The test surface was mounted in a perspex (plexiglass) curved rectangular section duct connected to a low speed, blow down type, wind tunnel for a free-stream velocity range of 2.0 to 13.1 m/s. Velocity measurements were made using a single sensor hot-wire anemometer and boundary layer flow transitions were detected by a frequency spectrum method. The experimental results show a simple linear relationship between transition start position and free-stream velocity, and lie well between the limit lines of Goertler number transition criteria. It is found that the onset of transition at the flow upwash region occurs when the Goertler number based on the boundary layer momentum thickness reaches a value of about 7.5. © 1991 Springer-Verlag.
Fri, 01 Feb 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/588561991-02-01T00:00:00Z
- Visualization in water jet pump throat under limiting flow conditionhttps://scholarbank.nus.edu.sg/handle/10635/58911Title: Visualization in water jet pump throat under limiting flow condition
Authors: Winoto, S.H.; Shah, D.A.; Li, H.
Abstract: The effects of varying suction and delivery pressures on the so-called limiting flow condition in a water jet pump have been experimentally investigated. Reducing the delivery pressure may lead to this limiting flow condition, in which the secondary flow will no longer respond to any further reduction in the delivery pressure, accompanied by a drastic drop in the pump efficiency. The measurement results show that the limiting flow condition will not occur when the jet pump suction pressure is reduced, but it will occur earlier at lower suction pressure when the delivery pressure is reduced. However, the jet pump operation was observed to remain stable under this limiting flow condition. Flow visualizations in the jet pump mixing throat revealed that cavitation bubbles were formed well before this condition. Copyright © 1998 by Begell House, Inc.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/589111998-01-01T00:00:00Z
- Visualization in the interface of a noncontacting mechanical face seal with spiral groove patternhttps://scholarbank.nus.edu.sg/handle/10635/58910Title: Visualization in the interface of a noncontacting mechanical face seal with spiral groove pattern
Authors: Rasaei, M.; Winoto, S.H.
Abstract: A noncontacting mechanical face seal with spiral groove pattern had been designed and tested under relatively low pressures by means of visualization in its interface. The visualizations not only demonstrated its principle of operation, but also revealed the successive stages of the fluid film formation from the start-up, transition state to dynamically stable operating condition. The tests also showed that for properly aligned seal faces, the generated fluid film was stable, ensuring lubrication around the interface and hence the noncontacting and zero leakage condition, whereas for misaligned seal faces, the fluid film was not uniform, resulting In leakage even at relatively high speeds. Copyright © 1997 by Begell House, Inc.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/589101997-01-01T00:00:00Z
- Flow in a pipe with a ring-type obstaclehttps://scholarbank.nus.edu.sg/handle/10635/92707Title: Flow in a pipe with a ring-type obstacle
Authors: Shi, Z.D.; Lee, T.S.; Winoto, S.H.
Abstract: Turbulent calculations have been carried out to investigate flows in a circular pipe with a ring-type obstacle attached to the wall for Reynolds numbers from 102 to 105. The numerical procedure is based on the solution of the primitive variable formulation of the Reynolds-averaged Navier-Stokes governing equations and the k - ε turbulence model in axisymmetric co-ordinate system and with a non-staggered grid. The obstacle opening ratio (d/D) is 0.5, and the obstacle thickness ratio (h/D) is 0.13. The numerical results reveal the effect of the Reynolds number on the flow fields. With the Reynolds number varying from 102 to 105, the reattachment length (Zr/D) increases to a maximum of 3.1 at Re = 5 × 102 and then decreases gradually to a value of 2.1. The velocity profiles of the fully developed flow change from parabolic to power-law curves. The non-dimensional maximum turbulent shear stress (τmax) varies in a range from 0.2 to 0.4 and the pressure loss (fioss) across the obstacle varies between 8.0 and 11.0, while the maximum vorticity (Ωmax) remains unchanged at a value of 16.2. At Re = 5 × 102 and 103, laminar cores exist downstream of the obstacle. For the cases of Re>3 × 104, the τmax and Ploss remain unchanged at 0.32 and 10.5, respectively. The flow field structures are similar. The distributions of the centreline turbulent kinetic energy, velocity and pressure along axial distance remain unchanged.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927071996-01-01T00:00:00Z
- Estimation of turbulent shear stress in free jets: Application to valvular regurgitationhttps://scholarbank.nus.edu.sg/handle/10635/92698Title: Estimation of turbulent shear stress in free jets: Application to valvular regurgitation
Authors: Winoto, S.H.; Shah, D.A.; Liu, H.
Abstract: In an attempt to better assess the severity of valvular regurgitation, an in-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress (ūv̄/U(m)/2) were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of ūv̄/U(m)/2 independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m2, corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.
Fri, 01 Mar 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/926981996-03-01T00:00:00Z
- The 7th Asian Symposium on Visualizationhttps://scholarbank.nus.edu.sg/handle/10635/86092Title: The 7th Asian Symposium on Visualization
Authors: Winoto, S.H.
Abstract: The 7th Asian Symposium on Visualization (7ASV) was successfully held in Singapore from 3rd to 7th November 2003. This event was originally scheduled from 26th to 30th May 2003, but had to be postponed because of the outbreak of SARS (Severe Acute Respiratory Syndrome) in some parts of the world. A total number of 122 participants attended the Symposium of which, 107 were foreign participants from 16 countries (excluding Singapore) worldwide. There were 104 papers covering broad range of topics presented at the Symposium which were delivered in 2 × 7 long sessions, and 9 keynote papers.
Thu, 01 Jan 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/860922004-01-01T00:00:00Z
- Some experimental techniques to detect transition in boundary layer flowhttps://scholarbank.nus.edu.sg/handle/10635/58712Title: Some experimental techniques to detect transition in boundary layer flow
Authors: Winoto, S.H.; Shah, D.A.; Ang, S.G.; Bin Ishak, M.Kamil
Abstract: In this work, in an attempt to quantify the extent of the transition region, some experimental techniques to detect the start and end of transition in boundary layer flows over solid surfaces are employed. The techniques considered are: the (surface) Pitot tube technique the hot-wire intermittency technique as used by Hachem and Johnson; and the hot-wire frequency spectrum method as demonstrated by Winoto and Low. The purpose of the present work is to test the effectiveness of these three techniques in detecting the transition region of a boundary layer developing on a flat plate under a mild favorable pressure gradient.
Wed, 01 Sep 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/587121993-09-01T00:00:00Z
- Velocity measurements within confined turbulent jets: Application to cardiovalvular regurgitationhttps://scholarbank.nus.edu.sg/handle/10635/58888Title: Velocity measurements within confined turbulent jets: Application to cardiovalvular regurgitation
Authors: Liu, H.; Winoto, S.H.; Shah, D.A.
Abstract: An expression for centerline mean velocity distributions for circular and noncircular confined turbulent jets has been obtained by assuming self- preservation of flow downstream of the jet potential core. It was assumed that the velocity decay was not only dependent on the streamwise distance x in terms of x/d, as in the case of free jets, but also on the ratio of the orifice diameter d to the confining pipe diameter D. To Validate the expression and to determine the empirical constants, measurements of the centerline velocities within the confined jets issuing from different size circular orifices and various noncircular orifices of different shapes were conducted. The results indicate that the validity of the expression is restricted to d/D ≤0.25 and is weakly dependent on the particular orifice shape. It is suggested that, as for the case of free turbulent jets reported earlier, that this expression may be used potentially to predict the valvular lesion size or to estimate the volume of valvular regurgitation for confined jets provided the value of D, which corresponds to the 'atrial diameter,' is known or statistically available.
Sat, 01 Nov 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/588881997-11-01T00:00:00Z
- Analysis and test of a viscous pump with radial pumping grooveshttps://scholarbank.nus.edu.sg/handle/10635/57902Title: Analysis and test of a viscous pump with radial pumping grooves
Authors: Winoto, S.H.; Yohanand, K.
Abstract: A new disk-type viscous pump utilizing multi-radial pumping grooves on its stator has been designed, analyzed and subsequently fabricated and tested. Analyses show that this new design pump exhibits higher flow rate characteristics than the recently reported multi-lobe design for the same pump size and rotor-stator clearances. Test results at rotor speeds of 600, 900, 1200 and 1500 rpm for a nominal rotor-stator clearance of 135 μm show the linear relationship between flow rate and discharge pressure for each speed, even though gradual increase in the working fluid temperature occurred during each test. This temperature increase can be the main practical problem in operating such a pump, along with maintaining very small rotor-stator clearances at high rotor speeds. Comparisons between the test results and the analytical predictions show good qualitative and quantitative agreements, especially for pump speeds of 600, 900 and 1200 rpm. For the present set-up, only low flow rate readings were obtained at a higher pump speed of 1500 rpm, since air entrainment occurred for higher flow rates at this speed. However, the experiment has shown that his new type of viscous pump is practically feasible.
Sat, 01 Oct 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/579021994-10-01T00:00:00Z
- Performance simulations of Tesla microfluidic valveshttps://scholarbank.nus.edu.sg/handle/10635/51640Title: Performance simulations of Tesla microfluidic valves
Authors: Zhang, S.; Winoto, S.H.; Low, H.T.
Abstract: A three-dimensional (3-D) parametric model of Tesla-type valves is proposed. A geometrical relationship is derived for optimization study, and based on the model, performance investigations in terms of diodicity and pressure-flow rate characteristics of the valve are numerically carried out with same hydraulic diameter and different aspect ratios (of the model cross-sectional dimensions) ranging from 0.5 to 4. The 3-D computational simulations show that, for the same hydraulic diameter, the unity aspect ratio gives higher diodicity at Reynolds number less than 500 and higher will be achieved with bigger aspect ratio when the Reynolds number is above 500. Investigations of pressure-flow rate characteristics of the Tesla valve show that Tesla valve with high aspect ratio gives more flow control ability. Copyright © 2007 by ASME.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/516402007-01-01T00:00:00Z
- Visualization of counter-rotating streamwise vortices in a rectangular channel with one-sided wavy surfacehttps://scholarbank.nus.edu.sg/handle/10635/51666Title: Visualization of counter-rotating streamwise vortices in a rectangular channel with one-sided wavy surface
Authors: Budiman, A.C.; Mitsudharmadi, H.; Low, H.T.; Winoto, S.H.
Abstract: Counter-rotating streamwise vortices in a rectangular cross-section channel with a wavy surface on one side were visualized by smoke-wire flow visualization technique. The use of six equilateral triangle patterns cut at the leading edge of the wavy surface results in relatively uniform spanwise wavelengths of these vortices. Visualization results show that these vortex structures remained visible until the second peak of surface waviness in the channel for Re = 3350, while for Re = 5300 more engulfment occurs in the spanwise structures of the vortices at the first peak of the surface waviness. The more engulfment could increase the mixing which results in early breakdown of the streamwise vortices prior to turbulence. It is also revealed that the evolution of these counter-rotating streamwise vortices is confined within the boundary layer. It causes the spanwise variation of the boundary layer thickness indicated by the spanwise wavy pattern at the edge of the boundary layer.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/516662013-01-01T00:00:00Z
- LDA MEASUREMENT WITHIN A VORTEX BOUNDARY LAYER GENERATED IN A ROTATING DRUM.https://scholarbank.nus.edu.sg/handle/10635/75027Title: LDA MEASUREMENT WITHIN A VORTEX BOUNDARY LAYER GENERATED IN A ROTATING DRUM.
Authors: Khoo, B.C.; Winoto, S.H.
Abstract: Atmospheric vortices like tornadoes, whirlwinds and watersprouts have attracted the interest of many people because of their destructive nature. The essential data regarding distribution of velocity, pressure and energy are lacking as tornadoes destroy all standard measuring instruments. A detailed study is usually confined to a laboratory simulated natural vortex. The objective of the present work is to study the flow field of such a three-dimensional vortex boundary layer and effusing core at various Reynolds numbers Re (based on disk radius and free stream velocity of the edge of disk) which range from 5,000 to 30,000. This is done by measuring the three velocity components (tangential, radial and axial) in the flow field using a non-disturbing laser Doppler anemometer (LDA). From these measurements, a quantitative assessment of the flow characteristics and flow development is possible.
Thu, 01 Jan 1987 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/750271987-01-01T00:00:00Z
- CORRECTION OF LDA READINGS FOR STREAMWISE VELOCITY MEASUREMENT IN CURVED RECTANGULAR CHANNEL FLOWS.https://scholarbank.nus.edu.sg/handle/10635/74976Title: CORRECTION OF LDA READINGS FOR STREAMWISE VELOCITY MEASUREMENT IN CURVED RECTANGULAR CHANNEL FLOWS.
Authors: Winoto, S.H.
Abstract: In an investigation of fluid flow in curved rectangular channels using a fringe mode laser Doppler anemometer (LDA), it is necessary to make correction for streamwise velocity readings due to refraction of the laser beams at the curved wall interfaces. This paper is written to introduce a correction factor which will increase the accuracy of such streamwise velocity measurement.
Wed, 01 Jan 1986 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/749761986-01-01T00:00:00Z
- Numerical analysis for the flow past a porous trapezoidal-cylinder based on the stress-jump interfacial-conditionshttps://scholarbank.nus.edu.sg/handle/10635/60908Title: Numerical analysis for the flow past a porous trapezoidal-cylinder based on the stress-jump interfacial-conditions
Authors: Chen, X.B.; Yu, P.; Winoto, S.H.; Low, H.T.
Abstract: Purpose - The paper aims to report on the flow past a porous trapezoidal-cylinder, in which the porous-fluid interface was treated by implementing the stress jump boundary conditions. Design/methodology/approach - The numerical method was based on the finite-volume method with body-fitted and multi-block grids. The Brinkman-Forcheimmer extended model was used to govern the flow in the porous medium region. At its interface, a shear stress jump that includes the inertial effect was imposed, together with a continuity of normal stress. Findings - The present model was validated by comparing with those for the flow around a solid circular cylinder. Results for flow around porous expanded trapezoidal cylinder are presented with flow configurations for different Darcy number, 10UP-2/UP to 10UP-7/UP, porosity from 0.4 to 0.8, and Reynolds number 20 to 200. The flow develops from steady to unsteady periodic vortex shedding state. The first coefficient IT/IT has a more noticeable effect, whereas the second coefficient IT/ITDN1/DN has very small effect, even for ITRe/IT ? = ? 200. Originality/value - The effects of the porosity, Darcy number and Reynolds number on lift and drag coefficients, and the length of circulation zone or shedding period are studied. Copyright © 2009 Emerald Group Publishing Limited. All rights reserved.
Fri, 27 Mar 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/609082009-03-27T00:00:00Z
- Numerical simulation of Richtmyer-Meshkov instability driven by imploding shockshttps://scholarbank.nus.edu.sg/handle/10635/60953Title: Numerical simulation of Richtmyer-Meshkov instability driven by imploding shocks
Authors: Zheng, J.G.; Lee, T.S.; Winoto, S.H.
Abstract: In this paper, the classical piecewise parabolic method (PPM) is generalized to compressible two-fluid flows, and is applied to simulate Richtmyer-Meshkov instability (RMI) induced by imploding shocks. We use the compressible Euler equations together with an advection equation for volume fraction of one fluid component as model system, which is valid for both pure fluid and two-component mixture. The Lagrangian-remapping version of PPM is employed to solve the governing equations with dimensional-splitting technique incorporated for multi-dimensional implementation, and the scheme proves to be non-oscillatory near material interfaces. We simulate RMI driven by imploding shocks, examining cases of single-mode and random-mode perturbations on the interfaces and comparing results of this instability in planar and cylindrical geometries. Effects of perturbation amplitude and shock strength are also studied. © 2008 IMACS.
Mon, 01 Dec 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/609532008-12-01T00:00:00Z
- Steady and pulsating flow through collapsible tubeshttps://scholarbank.nus.edu.sg/handle/10635/29487Title: Steady and pulsating flow through collapsible tubes
Authors: Low, H.T.; Chew, Y.T.; Winoto, S.H.; Lee, C.N.
Sun, 01 Jan 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/294871989-01-01T00:00:00Z