The Prediction of Swirl and Inlet Turbulence Kinetic Energy Effects on Confined Jet Mixing

Abstract

Mixing of a turbulent jet with a coaxial slower-moving secondary stream in a constant diameter tube was investigated. Of special interests were the effects of swirling the jet and initial turbulence kinetic energy. The analysis involved a numerical solution of the governing flow equations which were simplified by the Prandtl boundary layer assumptions. The two unknown turbulent stresses in the flow equations were modeled by defining an isotropic effective viscosity. The effective viscosity was calculated from a two-equation model of turbulence. The turbulence model was modified for swirling flows. Predicted results were compared with experimental results of several investigators. Good agreement was obtained when calculated results were compared with mean velocity and wall pressure data. The addition of swirl to the jet increased the rate of spread of the jet and resulted in decreasing the axial length required for mixing. The initial turbulence levels of the streams were found to have a significant effect on the distribution of mean velocity and pressure. This dependence has not been considered by most investigators and makes it imperative that experimentalists include turbulence information in their presentation of results.