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Fifth International Symposium on Turbulence and Shear Flow Phenomena
August, 27-29, 2007, Technische Universität München, Munich, Germany

DOI: 10.1615/TSFP5

TRANSITION INVESTIGATIONS ON A M=5 RAMP

pages 843-847
DOI: 10.1615/TSFP5.1320
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ABSTRACT

Direct Numerical Simulations (DNS) have been used to investigate transitional shock wave/boundary-layer interaction for high-speed ramp flow at M=5 and a ramp angle of β = 15°.
The flow separates very early from the flat plate ahead of the ramp in a laminar environment. The flow within the separation bubble is complex as the reverse flow down the ramp separates as well and enables for positive velocities below the separated reverse flow. The reverse flow meanders and 'hits' the high-shear layer from below. This is the cause for weak oblique shock waves (shocklets) emanating from the upper surface of the high-shear layer into the free stream. This flow topology is very stable to boundary-layer instabilities. The most unstable first and second-mode instabilities for the unseparated case have been introduced at the inflow boundary. They reach moderate amplitudes (1%> u' >10%) and lead to turbulent reattachment of the shear layer. The nature of the separation bubble is nevertheless not affected by the instabilities. The separation bubble moves with a frequency not associated with the disturbance frequencies. The reattachment line is distorted in spanwise direction through a longitudinal vortex.

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