NUMERICAL-ANALYSIS OF TURBULENT CROSS STRESSES AND PRESSURE IN THE DEVELOPING REGION OF AN AXISYMMETRICAL JET

A numerical study was conducted of the transition region of an axisymm etric isothermal jet, fi-om 10 to 44 diameters downstream of the nozzl e exit. The transition region is of particular interest because if off ers an opportunity to examine the relationship among physical quantiti es in a developing now. A model for the Reynolds cross-stress terms wa s developed from empirical correlations of mean velocity. It was then used, along with correlations for RMS velocities, to numerically predi ct pressure in the developing region This turbulence model is more acc urate than experimental measurements in high Reynolds number, transiti onal flows because the scales of turbulence in these conditions are to o small to resolve experimentally. Numerical results show that close c oupling exists between the mean axial velocity and the Reynolds cross- stresses. Similarly, a close relationship exists between the axial and radial RMS velocity fluctuations and the developing pressure gradient s in the axial and radial direction Therefore, when the mean velocitie s reach fully similar form, similarity of Reynolds cross stresses is a lso required. The axial and radial fluctuations continue to develop, a nd asymptotically approach similar forms at rates closely matching the decay of the mean pressure gradients. The information presented here can be used to test turbulence models applied to developing flows.