Inlet distortion is typically encountered during off-design conditions on civil aircraft and in S-ducts in military aircraft. It is known to cause severe deterioration to the performance of a gas-turbine engine. As intakes become shorter, there is an increased interaction between the inlet distortion and the downstream fan. Previous studies in the literature use Reynolds-averaged Navier–Stokes or unsteady Reynolds-averaged Navier–Stokes to model this unsteady interaction, due to the substantial

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... computational cost associated with high-fidelity methods such as large-eddy simulation/direct numerical simulation. On the other hand, it is well known that turbulence models have limitations in terms of predicting distorted flows. In this paper, a mixed-fidelity approach is proposed and employed to study the intake–fan interaction at an affordable computational cost. The results demonstrate that there are two mechanisms via which the fan affects the separated flow. First, the suction effect of the fan (effective up to almost half of the chord length upstream of the fan) alleviates the undesired distortion by "directly" changing the streamline curvature, intensifying the turbulence transport and closing the recirculation bubble much earlier. Second, the enhanced turbulence in the vicinity of the fan feeds back into the initial growth of the shear layer by means of the recirculating flow. This "indirect" feedback is found to increase turbulence production during the initial stages of formation of the shear layer. Both the direct and indirect effects of the fan significantly suppress the inlet distortion.