Experimental Study of Flight Effects on Slightly Underexpanded Supersonic Jets

The flight effects on the properties of the mixing layer and the shock-cell system of slightly underexpanded supersonic jets are studied experimentally. Particle image velocimetry, schlieren visualizations, and pressure measurements are used in a dual-stream geometry whose outer flow simulates flight up to a Mach number of 0.4. The study of the mixing layer includes the evolution under simulated flight of the turbulence levels, the momentum thickness, and of integral length and time scales of turbulence. The turbulence levels are found constant in flight when defined as the ratio between peak velocity fluctuations and velocity difference across the mixing layer. The analysis of the shock-cell structure comprises an evaluation of flight effects on the length of the entire pattern, and on the length and strength of the individual shock cells. The shock-cell structure is stretched in flight, as well as each shock cell. This comes from the reduced mixing-layer growth occurring under flight conditions. The str...