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Boundary layer transition over a lifting body of 1.6 m length at 2° angle of attack has been simulated at Mach 6 and a unit Reynolds number 1.0 x 107 m-1. The model geometry is the same as the Hypersonic Transition Research Vehicle designed by the China Aerodynamics Research and Development Center. Four distinct transitional regions are identified, i.e. windward vortex region, shoulder vortex region, windward cross-flow region and shoulder cross-flow region. Multi-dimensional linear stability analyses by solving the two-dimensional eigenvalue problem (spatial BiGlobal approach) and the plane-marching parabolized stability equations (PSE3D approach) are further carried out to uncover the dominant instabilities in the last three regions as well as the shoulder attachment-line region. The shoulder vortex is conducive to both inner and outer modes of shear-layer instability, of which the latter most likely trigger the vortex breakdown. A novel method is presented to substantially reduce the computational cost of BiGlobal and PSE3D in resolving the cross-flow instabilities in cross-flow regions. The peak frequencies of cross-flow modes lie between 15 and 45 kHz. Whereas oblique second Mack modes are marginally unstable in the windward cross-flow region, they could be strong enough to compete with the cross-flow modes in the shoulder cross-flow region. In the shoulder attachment-line region, there exists only one unstable mode of Mack instability, differing from previous studies that show a hierarchy of modes in the context of symmetrical attachment-line flows. Results of the numerical simulation and multi-dimensional stability analyses are compared when possible, showing a fair agreement between the two approaches and highlighting the necessity of considering non-parallel effects. [ABSTRACT FROM AUTHOR]

Tripping of boundary-layers from laminar to turbulent flow, which may be needed in specific practical applications, requires introducing high amplitude disturbances into the boundary layers without large drag penalties. As a possible improvement on fixed trip devices, a technique based on feedback instability is demonstrated in the present contribution for a Mach 1.5 boundary layer. The compressible Navier-Stokes equations are solved directly using a high-order (fifth-order in space and third-order in time) finite difference method. The geometries tested include wall-mounted rectangular blocks and off-surface cylinders. For a particular combination of an upstream cylinder and downstream block, a feedback loop is observed to provide more robust self-amplification of disturbances than a cylinder alone, whereas blocks by themselves only enhance a convective instability. A Fourier analysis and an impulse response simulation are used to confirm the presence of an acoustic feedback loop for the cylinder-block configuration. A parametric study of the size of the cylinder, the height, and the location of the rectangular block is also provided. It is observed that the feedback strength is not monotonically related to the height and location of the rectangular block. [ABSTRACT FROM AUTHOR]