CFD Analysis of the Nozzle Jet Plume Effects on Sonic Boom Signature

Abstract

An axisymmetric full Navier-Stokes computational fluid dynamics study is conducted to examine nozzle exhaust jet plume effects on the sonic boom signature of a supersonic aircraft. A simplified axisymmetric nozzle geometry, representative of the nozzle on the NASA Dryden NF-15B Lift and Nozzle Change Effects on Tail Shock research airplane, is considered. The computational fluid dynamics code is validated using available wind-tunnel sonic boom experimental data. The effects of grid size, spatial order of accuracy, grid type, and flow viscosity on the accuracy of the predicted sonic boom pressure signature are quantified. Grid lines parallel to the Mach wave direction are found to give the best results. Second-order accurate upwind methods are required as a minimum for accurate sonic boom simulations. The highly underexpanded nozzle flow is found to provide significantly more reduction in the tail shock strength in the sonic boom N-wave pressure signature than perfectly expanded and overexpanded nozzle flows. A tail shock train in the sonic boom signature is observed for the highly underexpanded nozzle flow. Axisymmetric computational fluid dynamics simulations show the flow physics inside the F-15 nozzle to be nonisentropic and complex. Although the one-dimensional isentropic nozzle plume results look reasonable, they fail to capture the sonic boom shock train in the highly underexpanded nozzle flow. Nomenclature

Analysis of Exhaust Plume Effects on Sonic Boom for a 59-Degree Wing Body Model

“…Under-expanded exhaust nozzle flow had a favorable result on near field pressure signatures, suggesting that the nozzle plume shock location could be controlled through control of nozzle pressure or nozzle divergent section geometry. This work was confirmed by Bui 6 for much higher pressure ratios. The effects of the exhaust plume need to be integrated onto a supersonic vehicle in order to validate the effect on overall sonic boom signature.…”

Free underexpanded jets in a quiescent medium: A review

“…The authors tested several exit diameters, ranging from 0.026 to 0.119 in, for a contoured and a conical nozzle. [137,138,112,117,118,84,14] thereon. To summarize, it is common to describe both the diameter of the jet and its maximum value for which it appears that both increase with the pressure ratio [30,68,69,65,43,85,129,53] until a priori an asymptotic value [30,43];…”

“…The earlier works start to deal with simplified computations, such as the parabolized Navier-Stokes equations [27,148,175,112,37,215,222] or the thin-layer approximation [223]. Then, one may find some papers dealing with the Euler equations [138,111,147,75,36,214,17,81,115,82,20,119,219,14,120,23,[262][263][264][265][266]177]. Most often, they are based on finite difference schemes [147,36,214,115,82,14,264,265,177] even if now new ones used the finite volume method [138,75,81,20,263,120,23] or even the finite element method [111].…”

“…Since the first numerical studies, and even now, the easiest way and the less expensive from a computational point of view is to consider the Reynolds Averaged Navier-Stokes equations (if obviously the flow is turbulent). Logically, this approach has been largely tested [110,31,132,63,138,243,34,216,218,116,45,220,84,21,22,55,[267][268][269][270][271]122,249], with the k ε − model in an overwhelming majority of papers (be it its incompressible formulation or some of the proposed compressibility corrections of the k CC ε − − class model). Even if this approach is acceptable to obtain the mean behavior of the flow, there are still some discrepancies between the results obtained with the various turbulence models (k ε…”

“…Diameter of the intercepting shock: More studies have been dedicated to this feature, both experimentally [56,[69][70][71]123], theoretically [69,70,72,99,76,139,100,102,140,105,128,107] and numerically [141,137,138,112,117,118,84]. Surprisingly enough, the available data are quite poor and one may only say that it seems to be also dependent on the square root of the pressure ratio [69,70,123]; may sometimes depend on the convergence angle [68,70,117] even if it is not the case for some configurations [56,70].…”