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Direct numerical simulation is used to study a turbulent plane wall-jet including the mixing of a passive scalar. The Reynolds and Mach numbers at the inlet are Re= 2000 and M = 0.5, respectively, and a constant coflow of 10% of the inlet jet velocity is used. The passive scalar is added at the inlet enabling an investigation of the wall-jet mixing. The self-similarity of the inner and outer shear layers is studied by applying inner and outer scaling. The characteristics of the wall-jet are compared to what is reported for other canonical shear flows. In the inner part, the wall-jet is found to closely resemble a zero pressure gradient boundary layer, and the outer layer is found to resemble a free plane jet. The downstream growth rate of the scalar is approximately equal to that of the streamwise velocity in terms of the growth rate of the half-widths. The scalar fluxes in the streamwise and wall-normal direction are found to be of comparable magnitude. The scalar mixing situation is further studied by evaluating the scalar dissipation rate and the mechanical to mixing time scale ratio.

Direct numerical simulations of plane turbulent nonisothermal wall-jets are performed and compared to the isothermal case. Two non-isothermal cases are studied; a cold jet propagating in a warm environment with inlet ambient to jet density ratio of ρ/ρ j = 0.4, and a warm jet in a cold surrounding where ρa/ρ j = 1.7 at the inlet. The ambient and wall temperature are kept equal and constant, and a temperature dependent viscosity is used. Results from the non-isothermal cases are compared to those obtained in a previously studied isothermal wall-jet with the same inlet Reynolds and Mach numbers. A passive scalar is also included in the simulations to study mixing. The influence of the varying temperature on the development and jet growth is studied as well as the influence on turbulence statistics and fluctuation intensities of the temperature and passive scalar. The warm jet contains smaller turbulent structures, and the cold jet larger, than the isothermal one. The change in structure and intensity affect the development and mixing in the jets.

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