Schlieren Visualization of Dual Injection in Supersonic Cross Flow

In order to minimize the length of supersonic-combustion ramjets (scramjets), injected fuel should mix rapidly with the supersonic crossflow. Tandem dual jet injection shows improved mixing performance over single jet injection. However, experiments on mixing by tandem dual jet injection have not yet addressed the jet shear layer, in which the mixing occurs. The paper reports on investigation of the jet shear layer, in a continuous air-indraft supersonic wind tunnel, at a Mach number around 1.6. A Schlieren set-up has been realised for recording images of 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 function of two parameters (i)
𝐽, the ratio of the momentum of the jet and that of the crossflow and (ii) the nondimensionalized distance 𝑆 between the dual jets. An empirical similarity relation has been established for the timeaveraged location of the jet upper shear layer as function of 𝐽 and 𝑆 covering the investigated conditions (𝐽 = 2.8, 3.8 and 4.8 while 𝑆 = ∈ [0: 9.87]). The found empirical relationship has been validated for lower and for higher values of 𝐽. The empirical similarity relation provides 𝑆𝑜𝑝𝑡, the spacing for maximal penetration of the jets, as function of 𝐽.