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 〈T〉 reaches 370°K, while the rms temperature fluctuation θ′ 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 (θ′ / < T >)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, β1, determined from such subrange has a value of 0.60±0.06.

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The space–time variations of aberrated optical images formed by propagating an incoherent light source through a nearly homogeneous, isotropic, strongly heated air turbulence generated in the laboratory have been studied using high speed cinematography and one-dimensional sampling of the exposed film transparency. The relative amplitude of image intensity fluctuations at high spatial frequencies is found to increase with decreasing exposure time and also with increasing amplitude of the refractive index fluctuations at a fixed turbulence velocity and spectral distribution. In the range of refractive index fluctuation amplitude accessible to the wind tunnel, the photographic correlation time is barely resolvable at the highest framing rate. The observed time scale is found to be of the same order of magnitude as, but noticeable shorter than, the convective dephasing time deducible from wave propagation theories using previously measured properties of the turbulence field and an extended application of Taylor’s hypothesis.