Investigation of passive scalar mixing in a turbulent free jet using simultaneous LDV and cold wire measurements

摘要

A slightly heated turbulent round jet at high Reynolds number (Re_D = 1.5 × 10~5) was studied using simultaneous Laser Doppler Velocimetry and cold wire thermometry measurements. Seeding material deposit on the cold wire was controlled in order to prevent any contamination of the temperature measurements. Turbulent momentum and heat fluxes were measured in the self-similar region of the jet. Compared to what was published in previous studies, a remarkable agreement was obtained between the experimental data (uv, uθ) and the prediction inferred from both momentum and enthalpy equations. Turbulent viscosity (v_T) and diffusivity (α_γ) were also determined and they agreed very well with the calculated distributions. From these quantities, a good estimation of the radial distribution of the turbulent Prandtl number (Pr_T) was obtained. These profiles agree with the literature value of Pr_T in the bulk of the jet region where it can be considered constant and equal to 0.81. However, a tendency to decrease to ~0.6 near the jet centerline was observed and corroborated with other authors. In the external region, Pr_T tend also to decrease to a lower value (～0.6).