Detached eddy simulations of a Mach 3, turbulent flow over a blunt fin were performed. Past experiments have shown that this configuration generates a large, three-dimensional, unsteady, separated region. Our previously published detached eddy simulations exhibited large-scale unsteadiness even in the absence of fluctuations in the incoming flow. The introduction of synthetic turbulence at the inflow boundary altered that separation motion. With the previous simulations as a reference baseline, a parametric study was carried out of the response of the flow to time-periodic forcing of the incoming boundary layer. The disturbances were introduced into the boundary layer through momentum and energy source terms. The spatial form of the source terms was based on averages of the baseline flow, conditioned on the motion of the separation shock. The response of the separation shock motion to the imposed perturbations was found to be dependent on the frequency of forcing. With a forcing frequency representative of the characteristic large-scale separation unsteadiness in the baseline flow, the separation shock motion was phase locked to the applied force, and a larger forcing amplitude led to greater separation motion. The separation region did not, however, respond strongly to disturbances in a higher frequency range. These results show that, in a flow that oscillates in the absence of upstream disturbances, separation motion can be modulated by upstream forcing of a particular form. Similar results have been obtained in the past for flows where separation unsteadiness is directly driven by incoming turbulence, but the modulation of self-excited oscillations in the present class of flow is a different behavior. It suggests opportunities for flow control of strong shock-wave–boundary-layer interactions.

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• Aerodynamics
• Boundary layers
• Flow instability
• Instability control
• Shock waves