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TRANSITION INVESTIGATIONS ON A M=5 RAMP

Christian Stemmer
Lehrstuhl fur Aerodynamik, Technische Universitat Munchen Boltzmannstr. 15, D-85748 Garching, Germany

Nikolaus A. Adams
Chair of Aerodynamics and Fluid Mechanics, Department of Mechanical Engineering, Technical University of Munich, 85748 Garching bei München, Germany

Abstrakt

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.