ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 24 Sep 2019 09:15:08 GMT2019-09-24T09:15:08Z5071- Force analysis of underwater object with supercavitation evolutionhttps://scholarbank.nus.edu.sg/handle/10635/85219Title: Force analysis of underwater object with supercavitation evolution
Authors: Khoo, B.C.; Zheng, J.G.
Abstract: Supercavitation generally occurs as a result of flow acceleration along underwater body surface and is numerically investigated in this study using a compressible Navier-Stokes equations solver. Here, the supercavitating flow is assumed to be the homogeneous mixture of pure liquid water and vapour which are in kinematic and thermodynamic equilibrium. Liquid phase and cavitation are modeled by Tait equation of state (EOS) and isentropic one-fluid formulation, respectively. Convective terms of the governing equations are numerically integrated using Godunov-type, cell-centered finite volume MUSCL scheme on unstructured triangular mesh, whereas time integration is handled with the second-order accurate Runge-Kutta approach. Our interest is focused on the force analysis of traveling object with the formation, growth, evolution and even collapse of supercavity enveloping the object. It is found that skin friction drag exerted on the object can be reduced significantly by the formation of supercavity where viscosity of vapour is much smaller than that of liquid water. It is also observed that form drag acting on the object is influenced by the supercavitation. Collapse of supercavity over the body due to external perturbation not only damages underwater object but also alters form drag on it.
Sun, 01 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/852192013-12-01T00:00:00Z
- 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
- A piecewise parabolic method for barotropic two-fluid flowshttps://scholarbank.nus.edu.sg/handle/10635/54709Title: A piecewise parabolic method for barotropic two-fluid flows
Authors: Zheng, J.G.; Lee, T.S.; Ma, D.J.
Abstract: In this paper, a third-order Piecewise Parabolic Method for barotropic two-fluid flows with Tait equation of state is presented. In transition layers between two different fluids, a mixture model system based on the assumption of equilibrium pressure is introduced. It conserves the mass of each fluid, the total momentum and energy of the mixture and is supplemented with an advection equation for the volume fraction of one of the two fluids. To close the model and recover the pressure, a nonbarotropic equation of state describing the thermodynamic properties of the mixture is used. However, in pure barotropic fluid regions, the isentropic version of Euler equations is employed. In addition, the third-order Piecewise Parabolic Method is employed to solve the model equations. The governing equations are first evolved in the Lagrangian coordinate system and then the computed results are mapped onto the fixed Eulerian grid in the following remapping step. As compared with other methods, a remarkable feature of our approach is that the scheme is third-order accurate in smooth regions of the solution and is able to give a steeper representation of discontinuities. Numerical results demonstrate satisfactory performances of this approach. © World Scientific Publishing Company.
Thu, 01 Mar 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/547092007-03-01T00:00:00Z
- 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
- A high-resolution method for compressible two-fluid flows and simulation of three-dimensional shock-bubble interactionshttps://scholarbank.nus.edu.sg/handle/10635/54251Title: A high-resolution method for compressible two-fluid flows and simulation of three-dimensional shock-bubble interactions
Authors: Zheng, J.G.; Lee, T.S.
Abstract: A high-resolution method is developed to capture the material interfaces of compressible two-fluid flows in multiple dimensions. A fluid mixture model system with single velocity and pressure is used, and viscous effect can also be taken into account. A consistent thermodynamic law based on the assumption of pressure equilibrium is employed to describe the thermodynamic behaviors of the pure fluids and mixture of two components. The splitting and unsplit Eulerian formulations of piecewise parabolic method are extended to numerically integrate the hyperbolic part of the model system, whereas the system of diffusion equations is solved using an explicit, central difference scheme. The block-structured adaptive mesh refinement (AMR) capability is built in the hydrodynamic code to locally improve grid resolution. The resulting method is verified to be at least second-order accurate in space. Numerical results show that the discontinuities, particularly contact discontinuities, can be resolved sharply. The use of AMR allows flow features at disparate scales to be resolved sufficiently. In addition, three-dimensional shock-bubble interactions are simulated to investigate effects of Mach number on bubble evolution. The flow structures including those peculiar to three-dimensional bubble are resolved correctly, and some physical phenomena with increasing Mach number are reported. Copyright © 2012 John Wiley & Sons, Ltd. A high-resolution diffuse interface method is developed to capture the material interfaces arising from the compressible multi-fluid flows. The various flow features at disparate spatial scales can be resolved sufficiently by using the block-structured adaptive mesh refinement algorithm. Our method is proved to be accurate, stable and robust. In addition, the interactions of the spherical helium and krypton bubbles with shock wave are investigated numerically, and the effect of shock strength on bubble evolution is examined. © 2012 John Wiley & Sons, Ltd.
Mon, 20 May 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/542512013-05-20T00:00:00Z
- 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
- Study of shock and induced flow dynamics by nanosecond dielectric-barrier-discharge plasma actuatorshttps://scholarbank.nus.edu.sg/handle/10635/127692Title: Study of shock and induced flow dynamics by nanosecond dielectric-barrier-discharge plasma actuators
Authors: Zhao, Z; Li J.-M; Zheng, J; Cui, Y.D.; Khoo B.C.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1276922015-01-01T00:00:00Z