Hypersonic boundary-layer transition experiments are performed at the von Karman Institute for Fluid Dynamics in the low-enthalpy Longshot wind tunnel. Freestream Mach numbers are within the range , and freestream unit Reynolds numbers vary within the range . The model is a 7 deg half-angle cone, which is 800 mm long, with exchangeable nose tips for which the radii vary between 0.05 and 10 mm. The natural transition process is investigated using flush-mounted thermocouples, fast-response pressure sensors, and a laser-based schlieren flow visualization technique. The most amplified frequencies retrieved experimentally from wavelet analysis techniques compare excellently with linear stability theory results and confirm the inviscid nature of the instabilities observed along geometries with a small amount of nose-tip bluntness. The corresponding factors at the transition onset are inferred from the experimental location where transition is initiated. Schlieren images exhibit the typical rope shape of second-mode instabilities for the sharpest nose tips, but not along blunter geometries where instabilities peak outward of the boundary-layer edge. The different measurement techniques used show that the maximum amplitude of the second-mode waves is reached shortly after the location with the minimum wall heat flux. Schlieren images show that wave packets break down to turbulence near the middle of the transition region.
Influence of Nose-Tip Bluntness on Conical Boundary-Layer Instabilities at Mach 10
AIAA Journal ; 57 , 9 ; 3859-3873
01.09.2019
Aufsatz (Konferenz) , Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch