Instability and Transition Measurements in the Mach-6 Quiet Tunnel

Abstract

The Boeing/AFOSR Mach-6 Quiet Tunnel achieved quiet flow to a stagnation pressure of 163 psia in Dec. 2008, the highest value observed so far. It remains quiet at pressures above 160 psia. Under noisy conditions, nozzle-wall boundary-layer separation and the associated tunnel shutdown appear to propagate slowly upstream, whereas under quiet conditions, the propagation is very rapid. A new diffuser insert has been designed, fabricated, and installed in the tunnel in order to start larger blunt models and increase run time. A flared cone with a circular-arc geometry was designed to generate large second-mode N factors under quiet flow conditions. When the computed N factor was 13, large instability waves were measured under quiet flow conditions using fast pressure sensors, but the flow remained laminar. Transition was observed only under noisy conditions. A laminar instability was detected in the wake of an isolated roughness element in the boundary layer on the nozzle wall; this appears to be the first such measurement at hypersonic speeds.

Receptivity of Hypersonic Boundary Layers over Straight and Flared Cones

“…For the PSE results in particular, the presented N-Factors were obtained using (!u) max ; however, N-Factors obtained with other variables were not significantly different. The measured wall-pressure fluctuations, to which the present computational results are compared, were obtained in the experiments by Wheaton et al 15 at an axial location of x = 400 mm. From Fig.…”

“…Note that even with these large N-Factors, transition was not observed on the flared-cone model in the experiment. 15 …”

“…This model geometry was tested in the Boeing/AFOSR Mach 6 Quiet Tunnel at the same freestream conditions. [15][16] The second model is a circular flared cone with a spherical blunt nose region (Fig. 3).…”

“…As with the previous model, this geometry was tested in the Boeing/AFOSR Mach 6 Quiet Tunnel at the same freestream conditions. 15 The third model consists of a 5° half-angle sharp-cone region and a circular flared-cone region (Fig. 4).…”

“…Simulations were performed on three axisymmetric geometries for which experimentally measured instability data are available for comparison: 1) a straight cone, 2) a circular flared cone with the flare starting from the nose, and 3) a circular flared cone with an initial straight nose region tangent to a flare downstream. The first two geometries were tested in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University [15][16] and the third geometry was tested in the NASA Langley Mach 6 Quiet Tunnel. [17][18] In each case, we first solved for the mean flow field and then performed linear local and non-local stability analyses for the computed boundary-layer profiles.…”