Development of most amplified wavelength Görtler vortices

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.