Some unexpected effects of wavelength and perturbation strength on heat transfer enhancement by Gortler instability

Convective heat transfer is studied in a laminar boundary layer over a concave wall in the presence of Gortler vortices with constant wall heat flux conditions. Comparison of local Nusselt and Stanton numbers demonstrates that the latter is more accurate in revealing three-dimensional flow development. Analysis of heat transfer with different freestream velocities shows that the Reynolds similarity is not valid in the presence of Gortler centrifugal instability and indicates that the Gortler number based on the Blasius momentum thickness enables one to follow the different steps of Gortler instability development. Analysis of the effects of the Gortler vortex wavelength and of perturbation wire diameter shows that the smaller the vortex wavelength, the faster the apparent transition to turbulence. Moreover, larger wire diameters also cause a faster boundary-layer transition. It has been shown experimentally that in the range of heat loading studied here, the buoyancy force has no effect on Gortler vortex generation and growth. (C) 2004 Elsevier Ltd. All rights reserved