Corrugated Limiting Tab for Supersonic Jet Mixing

The mixing efficiency of limiting tabs of three geometries with triangular corrugations, in promoting the mixing of a Mach 2 elliptic jet has been studied. Limiting tabs of rectangular, triangular and circular-arc geometries with 5% blockage are placed along major and minor axis at the nozzle exit are tested for nozzle pressure ratio from 4 to 8 in steps of one. All the tabs are found to be efficient mixing promoter at all tested NPRs, when placed along major axis at the nozzle exit. However at NPR 4 and 5 circular-arc tab along minor axis is found to retard the near field jet mixing. But the corrugated rectangular tab along minor axis is found to be the best mixing promoter among tested geometries. It causes a maximum reduction of 89% in core length at NPR 6. The corresponding core length reduction for corrugated triangular and circular-arc tab is 78% and 84% respectively. The maximum reduction in core length obtained for corrugated triangular and circular arc tab is found when placed along major axis at the exit of elliptical nozzle. The shadowgraph pictures of the jet reveal that the waves prevailing in the elliptic jet controlled with corrugated limiting tabs along major axis are significantly weaker than those in uncontrolled and controlled (with tabs along minor axis) elliptic jet.