Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet

Abstract

Solid surfaces located in the vicinity of a supersonic jet may affect its flow dynamics and greatly change its aeroacoustic characteristics. Large-eddy simulations (LES) are performed to investigate the effects of a plate on a highly-heated rectangular supersonic jet. The rectangular nozzle has an aspect ratio of 2.0 and is operated at overexpanded conditions with a nozzle pressure ratio of 3.0 and a nozzle temperature ratio of 7.0. Four cases with a plate-to-nozzle distance ranging from 0 to 3 times of the jet equivalent nozzle diameter are investigated. The large-scale implicit LES computations are performed by a well-validated in-house finite-volume based CFD code, which uses an artificial dissipation mechanism to represent the effects of small-scale turbulence structures and to damp the numerical oscillations near shocks. The temperature-dependent thermal properties of air in the highly-heated jets are considered by the chemical equilibrium assumption. Numerical results show that among the four jets, the case with the plate directly attached at the nozzle lip shows significant different flow and acoustic fields from the others. It exhibits a longer jet potential core length but without forming a series of well-structured shock diamonds. The other cases show similar shock/expansion wave structures as observed in the free jet but their jet plumes bend towards the plate. This bending leads to one jet to scrub over the plate in the downstream. The scrubbing effect, together with the unaffected shock-shear layer interactions and high plate pressure loading, leads to a stronger acoustic power in the near acoustic fields for this jet as compared to the others. The spectrum analysis in the nozzle upstream direction shows that the plate removes or mitigates the screech tone observed in the free jet and slightly amplifies the acoustic amplitudes in the low-frequency range.