Dual Injection in Supersonic Crossflow: Analysis Jet Shear Layer from Schlieren Images

Abstract

In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the supersonic crossflow to minimize the length of the scramjet. Tandem dual-jet injection has shown improved mixing performance over single-jet injection. However, experiments on tandem dual-jet injection have not addressed the jet shear layer, in which the mixing occurs, yet. The present study investigates the jet shear layer, as well as the bow shocks in front of the jets, in a continuous air-indraft supersonic wind tunnel at Mach number 1.55. A schlieren setup has been used for visualizing the flow features. A largely automated algorithm for processing schlieren images has been developed to determine the location of the upper boundary of the jet shear layer. The penetration of the jet is studied as a function of 1) J, the ratio of the momentum of the jet and that of the crossflow, and 2) the dimensionless distance S between the dual-jets. An empirical similarity relation has been established for the time-averaged location of the jet upper shear layer as function of J and S, covering the investigated conditions (J ∈ 2.8;3.8;4.8, S ∈ 0∶9.87). This empirical similarity relation provides S opt , the spacing for maximal penetration of the jets as function of J.