The Role of Nozzle Contour on Supersonic Jet Thrust and Acoustics

This work is an experimental and computational investigation of acoustics and performance of a biconical and splined supersonic nozzle to identify the dependencies of noise components on the nozzle design. The convergent section and throat of a biconical supersonic nozzle were optimized with a Reynolds-averaged Navier-Stokes solver to optimize thrust and minimize internal losses. Far-field acoustics and the jet flowfield were measured and studied using large-eddy simulations at design, overexpanded, and underexpanded conditions. The biconical and splined nozzles are designed to be thrust matched at fully expanded conditions. The convergent section and throat contour do not significantly affect the turbulent mixing noise or shock-associated noise at most conditions. Analysis of the jet flowfield shows differences in shock structure, although the "global" shock strength remains relatively unchanged. A comparison of measurements and computations of mean velocity and turbulence shows minor differences in the shear-layer region and near strong shocks. Momentum thrust and pressure thrust were measured and compared with computational results. The contoured throat nozzle provides equivalent thrust with a 4% lower nozzle pressure ratio at the design condition with no acoustic penalty. At equivalent nozzle pressure ratios, the contoured nozzle provides 10% higher thrust with no increase in mixing noise or shock noise.