Variable Viscosity Jets: Entrainment and Mixing Process

Abstract

Turbulent jets with viscosity stratification are very important from both fundamental and practical viewpoints. In this study, we carry out a comparison between Constant Viscosity Flows and Variable Viscosity Flows, in a round jet, on the basis of the same initial conditions (same jet momentum and/or the same initial Reynolds number). The two fluids are density-matched. A propane jet issues into a slight nitrogen coflow for which the kinematic viscosity ratio is \(R_{v} \equiv \nu _{N_{2}}/\nu _{\mathrm{propane}} = 3.5\). The Reynolds number of the jet (based on the diameter, the initial velocity and the propane viscosity) is of 8000. The direct interactions between the velocity and the scalar fields reflect the need to perform simultaneous measurements of these two physical quantities. The stereo-Particle Image Velocimetry (stereo-PIV) and the Planar Laser Induced Fluorescence have been chosen for the velocity and the concentration measurements, respectively. Experimental results are discussed, for both velocity and scalar fields, in the axial plane of the turbulent axisymmetric jet. It is shown that the presence of a strong viscosity discontinuity across the jet edge results in an increase in both the scalar spread rate and the turbulent fluctuations.