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

• Passive scalar is examined in the self-similar region of a turbulent jet.
• uv and uθ distributions are shown to satisfy momentum and enthalpy equations.
• νT and αT profiles agree very well with the predictions obtained from the equations.
• PrT profile shows a decrease in the jet centerline region and the external zone.

A slightly heated turbulent round jet at high Reynolds number (ReD = 1.5 × 105) 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‾,vθ‾) and the prediction inferred from both momentum and enthalpy equations. Turbulent viscosity (νT) and diffusivity (αT) 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 (PrT) was obtained. These profiles agree with the literature value of PrT 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, PrT tend also to decrease to a lower value (∼0.6).