Study of strong temperature mixing in subsonic grid turbulence

Strong temperature mixing in subsonic air turbulence is studied in an open‐circuit wind tunnel with a 0.5 m cross section. The specially constructed heating grid consumes up to 300 kW of electric power at a mean flow velocity of 11 m/sec. The highest mean absolute temperature $\mathrm{〈T〉}$ reaches 370°K, while the rms temperature fluctuation $\mathrm{\theta \prime }$ at midtunnel is typically 6°K. Basic statistics of the temperature field are measured and discussed. It is found, in particular, that (i) the streamwise decay of the normalized mean‐square temperature fluctuation ${\mathrm{(\theta \prime \hspace{0.17em}/\hspace{0.17em}<\hspace{0.17em}T\hspace{0.17em}>)}}^2$ is not sensitive to the applied heating rates, suggesting that so far buoyancy contributes little to the dynamics of the turbulence; (ii) the observed decay rates are much higher than those reported by others in the literature and are consistent with the higher drag characteristics of the present grid; (iii) the temperature fluctuation spectrum, when normalized by local fluid properties and dissipation rates, retains a universal form and show an inertial‐convection subrange of limited extent; (iv) the one‐dimensional universal scalar inertial Kolmogoroff constant, ${\beta }_1$ , determined from such subrange has a value of 0.60±0.06.