Stability Analysis of Hypersonic Boundary Layer Flow over Microporous Surfaces

Abstract

Hypersonic boundary-layer-transition is dominated by so-called Mack modes, second mode instabilities that can be damped passively by acoustic absorptive coatings. Those coatings are realised in practise by porous walls. In the present paper a second mode stability analysis is performed for a boundary layer flow at Mach 6 over a smooth wall and various porous walls. The influence of the porosity, the radius and the thickness of the pores is investigated. For this study three different codes are used: The linear stability code SLST of the University of Southampton in comparison with the DLR linear stability code NOLOT and finally direct numerical simulations including the modelling of the pores through the wall. Good agreement for a smooth wall as well as for different porous wall cases is demonstrated.