Numerical Study of Jet Plume Instability from an Overexpanded Nozzle

The compressible jet plume from a planar overexpanded nozzle is investigated by solving the Reynolds-Averaged Navier-Stokes equations with several turbulence models. Computations are conducted for a series of exit-to-throat area ratios (Ae/At) from 1.0 to 1.8 and a range of nozzle pressure ratios (NPR) from 1.2 to 1.8. The results are compared with available experimental data in a nozzle of the same geometry. The asymmetric jet plume is well predicted by the simulation and is consistent with the experiments. Among the different turbulence models tested, the two-equation Shear Stress Model (SST) is found to agree closest to the experiments. The simulations are able to predict the velocity profiles, total pressure decay, and axial jet thickness distribution in the jet plume reasonably well. Jet mixing is governed by Ae/At and to a lesser extent by NPR. Increasing Ae/At results in a significant increase of mixing rate. Computations of turbulent kinetic energy (TKE) show that, with increasing Ae/At, the peak TKE in the plume rises and moves towards the nozzle exit. Significant increase of TKE inside the nozzle results from the asymmetric flow separation. Nomenclature Ae = nozzle exit area At = nozzle throat area F = thrust Ht = throat height M = Mach number m = mass flux me = mass flux at nozzle exit NPR = nozzle pressure ratio = pres / pa pa = ambient pressure pres = reservoir pressure pt = local total pressure Ta = ambient temperature Tres = reservoir temperature x = axial coordinate y = transverse coordinate δ = jet thickness I