Experimental investigation of boundary layer instabilities and transition on sharp and blunt cones in Oxford’s High-Density Tunnel

Andrew P. Ceruzzi , andrew.ceruzzi@eng.ox.ac.uk
corresponding author,

Laurent M. Le Page, laurent.lepage@eng.ox.ac.uk

Philipp Kerth, philipp.kerth@balliol.ox.ac.uk

Benjamin A.O. Williams, ben.williams@eng.ox.ac.uk

Matthew McGilvray, matthew.mcgilvray@eng.ox.ac.uk

Affiliation (All):

University of Oxford,
Southwell Building
Osney Mead
Oxford
OX2 0ES

 

Keywords: Hypersonic, Transition, Cone, Instability, Ludwieg Tube, Schlieren, FLDI, laser diagnostics, blunt cone, freestream disturbances

 

Abstract:

Boundary layer instabilities and transition to turbulence on a 7-degree half-angle, 600mm long axisymmetric cone in Mach 6 flow are investigated using a combination of surface pressure measurements, high speed schlieren, multi-point focused laser differential interferometry (FLDI), thin-film gauges, and IR thermography.

The experiments are performed at unit-Reynolds numbers ranging from  in the University of Oxford’s High-Density Tunnel (HDT).

The free stream disturbance environment is characterised with pitot pressure measurements and multi-point FLDI. Nose tip radii will be varied to study the effect of bluntness on the instabilities and transition location.

For sharp nose tips where second-mode waves are the dominant instability, emphasis is placed on interrogating the upstream region of the cone’s boundary layer where the second Mack mode first begins to amplify, for example, those illustrated in Figure 1.

For blunt nose tips, instabilities in the boundary layer as well above the boundary layer, but inside the entropy layer, are simultaneously probed with schlieren and multi-point FLDI.

These measurement techniques are also employed further downstream, with the addition of thin-film gauges and IR thermography, to characterise the breakdown of the boundary layer and the start of transition.

In all cases, the effect of high frequency (>100kHz) free stream disturbances on the transition process is examined through FLDI measurements. The FLDI, which offers greater sensitivity, spatial, and temporal resolution compared to Schlieren, is a key advancement over previous studies.

Overall, the combination of high Reynolds number, large model size, and advanced diagnostic techniques demonstrate the world class capability of Oxford’s HDT as a hypersonic boundary layer transition test facility.