NUMERICAL PREDICTION OF THE STRUCTURE OF HIGH-TEMPERATURE AXISYMMETRICAL TURBULENT JETS

Turbulent axisymmetric jets at high temperature are studied numericall y by using first and second order turbulence models. Regarding the tem perature fields, on which we concentrate in this work, predictions wit h both types of models do not show large differences. In general, pred ictions agree well with the measurements; the existing differences are usually favorable for the second order model. The effect of solving a transport equation for the scalar dissipation rate on the prediction of the mechanical to scalar time scale ratio and on the prediction of the scalar fluctuations is studied. The influence of varying the densi ty ratio on parameters such as the axial decay rates of the temperatur e and velocity and the turbulence intensity are studied. Two definitio ns of the mixing efficiency are introduced. According to both definiti ons, the mixing efficiency decreases with increasing effects of buoyan cy.