Numerical Investigations of Hypersonic Boundary-Layer Stabilization by means of Porous Surfaces

Kurzfassung

Hypersonic laminar flow control for delayed laminar-turbulent transition is of high importance for reentry vehicles since early transition results in an increase of the heat transfer by factors between 3 and 8 resulting in significant cost and weight increases of the thermal protection systems. A lot of different strategies are used to delay or prevent the transition onset. The presentation covers the manipulation of the transition process by means of porous surfaces to influence the growth of second modes in a passive way. The second mode, or so called Mack mode, is the dominant mode for the transition process at hypersonic Mach numbers. The first part of the presentation is focused on numerical analyses using direct numerical simulation (DNS) and linear stability theory (LST). For these numerical investigations a flat plate with equally spaced, cylindrical, blind pores are used. The second geometry is an 7° half-angle cone model, which consists partly of ultrasonically absorptive material with a natural porosity. This cone was investigated experimentally in the DLR High Enthalpy Shock Tunnel Göttingen (HEG) and compared with linear stability calculations.