Mean Flow Development in Dual-Stream Compressible Jets

We present experimental results on the mean e ow development and potential core lengths of single- and dualstream compressible air jets. The research is relevant to noise emission, thermal signature, and combustion in high-speed turbulent jets. The primary e ow was set at Mach number 1.5, and the secondary stream was supplied atfoursubsonicMachnumbersfromnozzlesofvariableareaandshape.Coaxialandeccentricnozzlecone gurations were investigated. In the coaxial arrangements, the secondary e ow reduces the growth rate of the primary shear layer and elongates the primary potential core. As a result, the mass entrainment rate of the coaxial jet is less than that of the singlejet. Thepotentialcoreisstretched by 68%when a secondary stream with area ratio 2.9 issupplied at Mach number 0.9. The eccentric cone guration shows substantial improvement in mixing over the coaxial case and achieves an entrainment rate roughly equal to that of the single jet when the exit areas of the primary and secondary streams are approximately equal. On an equal mass e ow rate basis, the eccentric dual-stream jet with area ratio 0.9 actually mixes faster than the single jet. The potential core and the supersonic region of the jet are elongated much less than in the coaxial case. A semi-empirical model, based on thepresentdata and classical shear layer relations, is proposed for the primary and secondary core lengths of coaxial jets.