Experimental and numerical study of jet mixing from a shock-containing nozzle

The compressible jet plume emerging from a planar convergent-divergent nozzle containing a separation shock is investigated experimentally and numerically. The investigation encompasses exit-to-throat area ratios (Ae=At) from 1.0 to 1.8 and nozzle pressure ratios from 1.2 to 1.8. Experiments were conducted in a variable-geometry nozzle facility, and computations solved the Reynolds-averaged Navier-Stokes equations with several turbulence models. The computed mean velocity field outside the nozzle compares reasonably well with the experimental data. Among the different turbulence models tested, the two-equation shear stress transport model is found to provide the best agreement with the experiments. Jet mixing is governed by Ae=At and, to a lesser extent, by nozzle pressure ratios. Increasing Ae=At results in an increased growth rate and faster axial decay of the peak velocity. The experimental trends of jet mixing versus Ae=At and nozzle pressure ratios are captured well by the computations. Computations of turbulent kinetic energy show that, with increasing Ae=At , the peak turbulent kinetic energy in the plume rises and moves toward the nozzle exit. The significant increase of turbulent kinetic energy inside the nozzle is associated with asymmetric flow separation.