LATERAL VELOCITY FLUCTUATIONS AND DISSIPATION TIME-SCALE RATIOS FOR PREDICTION OF MEAN AND FLUCTUATING TEMPERATURE-FIELDS

Further testing of a previously developed diffusivity-based model for predicting mean and fluctuating temperatures in water and liquid sodiu m flows downstream of a multi-bore jet block in which one jet is heate d is performed but using air as the working fluid. The apparatus used enabled geometric similitude with the previous studies. The previous m odel used longitudinal turbulence intensities and longitudinal integra l length scales to estimate values of the eddy diffusivity of heat. Me asurement of lateral velocities in the present work allowed a signific ant improvement to be made in the modelling procedure. It was found th at the lateral turbulence intensity was a more effective velocity scal e to use and a length scale based on lateral velocity fluctuations was more apt. The Prandtl number effect on temperature dissipation rates found previously in water and sodium is extended by the results using air, leading to a simple algebraic relation between the Prandtl number and dissipation time scale ratio. The non-isotropic nature of the flo w is identified and is seen to influence the results.