Subsonic intake under crosswinds: Flow control using pulsed vortex generator jets

Abstract

Ultra-high bypass ratio engines are soon expected to become the norm in the civil aircraft engine industry due to their superior efficiency and lower emissions compared to traditional turbofan engines. Shorter intakes with slimmer lips employed in such engines are more prone to flow separation under off-design conditions and incur severe performance penalties. This study examines the efficacy of several pulsed vortex generator jet (VGJ) configurations on flow distortion within a subsonic intake under strong crosswinds (approaching at 90°). High-fidelity scale-resolving simulations are carried out to study the effect of different pulsing frequencies and the duration of the duty cycles of the VGJs toward mitigating the inlet distortion. Several VGJs are employed on both the windward (outer jets) and leeward sides (throat and diffuser jets) of the intake distributed along its circumference. Different pulsing strategies including blowing-alone, zero-net-mass-flux (ZNMF) jets (with both blowing and suction), and steady suction are tested. Through a detailed examination of instantaneous and time-averaged flow fields, we uncover the nuanced influence of pulsed jets on flow behavior. When compared to the baseline case without control, all the simulations with pulsed jets showed a ≈ 50%–60% reduction in the radial extent of distortion at the fan face. Increasing the duration of the duty cycle promotes wall-normal mixing due to the increased penetration of the jet shear layers into the crossflow. The VGJ configuration with a 50% duty cycle operating at a frequency of 8 pulses per flow-through is found to be optimal. Of all the flow control strategies, the test case with steady suction resulted in an optimal flow control decreasing the distortion coefficient by 37%. The suction phase in the ZNMF jets is also found to be instrumental in ingesting the separation. The distortion coefficient at the fan face is reduced by ≈20% with ZNMF jets in contrast to ≈12.7% with the optimal blowing-alone strategy.