PREDICTION OF TURBULENT COAXIAL STREAMS OF CONSTANT AND VARIABLE-DENSITY

The present study investigates the accuracy of well-known turbulence m odels in simulating the mean velocity, turbulence, and concentration f ields for the cases of constant and variable density, turbulent, low M ach number, isothermal, confined coaxial streams of different bulk mea n velocities, or axisymmetric mixing layers. The standard k approximat ely epsilon eddy viscosity model and an anisotropic thin shear algebra ic stress model (ASM) are employed for the constant density case. Resu lts for the k approximately epsilon model are determined to be qualita tively satisfactory and superior to those for the thin shear ASM, thou gh both show excessive radial diffusion of axial momentum. Based on th ese conclusions, the k approximately epsilon model, extended for varia ble density, is used for numerical simulations of a similar flow where the inner stream gas has a density four times that of the outer strea m gas. Simulations for the velocity using the k approximately epsilon model are again found to be qualitatively accurate. Predictions for th e concentration field, however, are in good agreement with the data. T he flow fields studied are idealizations of a particular configuration once proposed for a gas core reactor (GCR) nuclear propulsion engine. Nuclear propulsion for space travel, once considered in the 1960s and early 1970s, is being reconsidered, especially for manned interplanet ary travel.