Excitation and evolution of compressible Görtler vortices induced by free-stream vortical disturbances

We study the nonlinear development of compressible Görtler vortices (GV) excited by free-stream vortical disturbances (FSVD) in a compressible boundary layer over a concave wall. The free-stream Mach number is assumed to be of O(1) and the FSVD are strong enough so that compressibility and nonlinearity are both relevant. The focus is on low-frequency (long-wavelength) components of FSVD, which excite and drive the GV efficiently. The dynamics of the GV are governed by the compressible nonlinear boundary-region equations, supplemented by appropriate initial and boundary conditions, which characterise the impact of FSVD on the boundary layer. The numerical results are compared with experimental measurements in a hypersonic boundary layer at Mach number 6.5. The predicted mean flow distortion and the wall temperature are in good agreement with the experimental results. As the frequency increases, the nonlinearly generated harmonic component with zero frequency and a spanwise wavenumber double that of the FSVD becomes dominant downstream. As a result, the GV become predominantly steady.