MODELING CONFINED JET FLOW

The prediction of confined jet mixing, which occurs in many processes from jet pumps to furnaces, is studied by testing and improving turbulence models. Numerical simulations of axisymmetric parabolic jet flows, with the two-equation k-epsilon eddy-viscosity model and the second-moment closure in its algebraic form (ASM), are compared with measurements. This leads to the identification of defects that cause high rates of mixing, similar to those shown in earlier work with free jets. Modifications to the dissipation rate equation, proposed for the free jet, are addressed by examining the effects of anisotropy-related proposals and the sensitization to irrotational strains. The involvement of large structures in transport phenomena is also considered via bulk-convection-based models. A combination of 20 percent gradient diffusion and 80 percent bulk convection appears to mimic the transport process for turbulent energy reasonably well. The computations, made with a finite-difference/finite-volume parabolic solver with an efficient forward marching technique, show that there is still room for improvement in the modeling of jet flows, and some suggestions for further work are made.