Numerical Investigation and Validation of Jet Temperature Effects on Nozzle-Afterbody Drag

Abstract

In this study, jet temperature effects on afterbody drag in subsonic, transonic and supersonic flow conditions have been investigated for a wide range of nozzle throat total pressure to free-stream static pressure ratio (NPR) at Mach numbers 0.6, 0.9 and 1.2 using CFD. Preliminary CFD simulations are conducted for cold air flow with constant specific heat. Experimental data available in NASA Technical Paper 1766 is utilized for validation purposes thus, the CFD simulations are carried out for the identical geometry and boundary conditions reported in the technical paper. Depending on the Mach number, either pressure-based solver with coupled algebraic multigrid scheme or implicit density-based flow solver with Roe-FDS are used for the simulation of compressible flows to maintain convergence and obtain accurate solutions. Second order upwind schemes are preferred for all simulations and it is shown that convergence problems could be prevented when density based solvers are used at relatively high Mach numbers. For all simulations SST k-ω turbulence model proposed by Menter is selected. Based on a robust and verified CFD approach for cold jet analysis, the average drag coefficients Cd at various NPR values between 1.5 and 7 have been successfully estimated at all Ma with relative errors ranging from 5 to 15 % compared to experimental data. Then, the same numerical approach is adopted to the hot jet analysis. Further comparisons to empirical relations revealed a satisfactory agreement only at Ma = 1.2, but no acceptable match at Ma = 0.6 and 0.9.