Experimental Study on the Unsteadiness of an Axisymmetric Shock-Wave/Turbulent-Boundary-Layer Interaction with Separation

An axisymmetric shock-wave/turbulent-boundary-layer interaction (STBLI) induced by a step is studied experimentally at M∞ = 3.93. A detailed discussion of the unsteady flow field developed along the upstream and downstream separation regions – ahead and behind the step – is presented in terms of the time-dependent pressure data and its spectral analysis. The separation shock exhibits low-frequency motions at a dominant frequency of 391 Hz, and evidence suggests the dominance of downstream flow effects (in the recirculation region) on the large-scale low-frequency pulsations of the separation bubble. The dominant instabilities at the inception of the shear layer are found to be two orders of magnitude higher than the shock unsteadiness and decrease progressively along the interaction as shear layer eddies grow in size.