Active Flow Control of Single and Dual Supersonic Impinging Jets using Microjets

摘要

An impinging jet produces a highly unsteady flowfield which produces high noise levels in the near-field, harmful structural vibrations, and significant lift-loss in applications such as Short Take-Off and Vertical Landing (STOVL) aircraft. Furthermore, the presence of multiple impinging jets leads to the generation of a fountain How which further adds complexity to the flowfield. An understanding of the flowfield and implementation of an effective flow control technique is necessary to reduce these adverse effects for better design of STOVL aircraft. In the present study, flowfields of single supersonic round jet (Mach 1.5) and dual impinging jets are explored. The dual impinging jets consist of the supersonic jet and a sonic jet. A microjet flow control technique is applied to mitigate flow unsteadiness, in part by effecting the shear layer instability of the jet issuing from the supersonic nozzle. The effectiveness of the microjet flow control method is investigated with the help of schlieren visualization technique, near-field acoustic measurements, and unsteady surface pressure measurements. Proper Orthogonal Decomposition (POD) technique is applied to the time-resolved schlieren data sets in order to capture dominant modes of shear layer instabilities and acoustic waves. The passive and active influence of the microjet hardware is examined over a range of impingement distances (2.25D - 10D) with a fine resolution (D/16) to obtain detailed resonance characteristics. For single and dual impinging jets, relative to their respective baselines, the microjet control on dual impinging jets shows better near-field noise attenuation of over-all sound pressure level within short impingement distances (H/D < 4.5).