Experimental Characterization of Supersonic Single- and Dual-Impinging Jets

Abstract

Supersonic single-impinging jet flows are known to exhibit strong unsteadiness levels and acoustic signatures due to large-scale resonant motions. However, the flowfield characteristics of two such jets operating in tandem, where properties are influenced by jet–jet interaction and coupling, are relatively unknown. The present study reports on the experimental investigation of the flowfield associated with two underexpanded, impinging jets operating at a nozzle pressure ratio of 2.65 and discharged from identical converging nozzles with exit diameters of 25.4 mm. Comparisons with a single-impinging jet operating at the same conditions are provided through flow visualizations, near-field acoustics, and surface pressure measurements. Fountain flow produced by the interaction of wall jets (a unique feature of dual-impinging jets) is found to be relatively strong at short impingement heights and contributes to additional loads on the ground surface. Unsteadiness in dual jets is weaker than that in a single jet at conditions involving resonance, and the fountain upwash plays an important role in the process. Although the feedback mechanism that drives the resonance in both impinging jet configurations is similar and the corresponding instability mode shapes are retained, there are differences in the strengths of the instability modes between the two configurations.