Effects of wall transpiration on the supersonic boundary-layer oblique-type transition

Abstract

Abstract The study of transpiration cooling is vital for the development of high-speed aircraft. In the current work, direct numerical simulation (DNS) is performed to investigate the impacts of wall transpiration on the boundary-layer oblique breakdown over a Mach 2 flat plate. The porous injection model is used to mimic the transpiration from the equally spaced circular pores. It has been observed from the numerical results that wall transpiration leads to the amplified growth rate of the imposed oblique mode waves, steady vortex waves, and other higher-harmonic waves. As a result, the occurrence of boundary-layer transition shifts upstream. Due to the presence of transpiration, the normal gradients of both streamwise velocity and temperature are decreased at the wall, which causes reduced skin friction and heat flux in the transpiration region. In addition, when upstream transpiration is present, reductions in skin friction and heat flux can also be observed within turbulent regions. This study provides insights into the DNS investigation on compressible boundary-layer natural transitions coupled with wall transpiration, and the results indicate that more systematic investigations addressing this problem are needed.