Simultaneous planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) yield measurements of two-dimensional jet fluid concentration and velocity fields in turbulent crossflowing jets. The jet-to-crossflow velocity ratio is $r = 5.7$ and the jet exit Reynolds number is approximately 5000. The measurements are focused on the developing region of the flow. Two flow configurations are studied, one in which the jet nozzle is flush with the tunnel wall and the other where the nozzle protrudes into the uniform region of the tunnel flow. The jet nozzle in both cases is a simple pipe. The averaged scalar and velocity fields show a strong similarity in growth rates and centreline decay rates between the two nozzle configurations when using the centreline downstream coordinate $s$. This suggests that the flow geometry is less important than, for example, jet exit conditions in determining the initial flow development. The velocity fields show indications of jet-like scaling in the near field, and a possible approach to wake-like scaling in the far field. These canonical scalings are less evident in the scalar fields. Results are presented for the averaged scalar variance, $\langle C^{'2}\rangle$, the scalar flux components, $\langle u_{i}'C'\rangle$, the turbulent normal stresses, $\langle u^{\prime 2}\rangle$ and $\langle v^{\prime 2}\rangle$, and the turbulent shear stress, $\langle u'v'\rangle$. We also discuss the resolution issues bearing on the determination of small-scale fluctuations.

Fine-scale scalar mixing in gas-phase planar turbulent jets is studied using measurements of three-component scalar gradient and scalar energy dissipation rate fields. Simultaneous planar Rayleigh scattering and planar laser-induced fluorescence, applied in parallel planes, yield the three-dimensional scalar field measurements. The spatial resolution is sufficient to permit differentiation in all three spatial directions. The data span a range of outer-scale Reynolds numbers from 3290 to 8330. Direct measurement of the thicknesses of scalar dissipation structures (layers) shows that the thicknesses scale with outer-scale Reynolds number as $\hbox{\it Re}_\delta^{-3/4}$, consistent with Kolmogorov/Batchelor scaling. Average layer thicknesses are described by the relation $\lambda_D=14.5\,\delta\, \hbox{\it Re}_\delta^{-3/4}\hbox{\it Sc}^{-1/2}$. There is no evidence here that Taylor scaling ($\lambda_D\propto\delta\, \hbox{\it Re}_\delta^{-1/2}$) plays a significant role in the scalar dissipation process. The present data resolve a range of length scales from the dissipation scales up to nearly the jet full width, and thus can be used in a priori testing of subgrid models for scalar mixing in large-eddy simulations (LES). Comparison of two models for subgrid scalar variance, a scale-similarity model and a gradient-based model, indicates that the scale-similarity model is more accurate at larger LES filter sizes.

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Scalar imaging velocimetry is here applied to experimental turbulent flow scalar field data to yield the first fully resolved, non-intrusive laboratory measurements of the spatio-temporal structure and dynamics of the full nine-component velocity gradient tensor field ٌu(x,t), as well as the pressure gradient field ٌp(x,t), in a turbulent flow. Results are from turbulent flows at outer scale Reynolds numbers in the range 3,000рRe ␦ р4,200, with Taylor scale Reynolds numbers Re Ϸ45. These give a previously inaccessible level of detailed experimental access to the spatial structure in the velocity gradient tensor field at the small scales of turbulent flows, and through the much longer temporal dimension of these four-dimensional data spaces allow access to the inertial range of scales as well. Sample spatio-temporal data planes and probability distributions spanning more than 75 advection time scales (/U) are presented for various dynamical fields of interest, including the three components of the velocity field u(x,t), the nine components of the velocity gradient tensor field ٌu(x,t) through the full vector vorticity field i (x,t) and tensor strain rate field i j (x,t), the kinetic energy dissipation rate field ⌽(x,t) ϵ 2:(x,t), the enstrophy field 1 2 •(x,t), the enstrophy production rate field ••(x,t), and the pressure gradient field ٌp(x,t). Continuity tests show agreement with the zero divergence requirement that exceeds the highest values reported from single-point, invasive, multi-probe measurements. Distributions of strain rate eigenvalues as well as alignments of the strain rate eigenvectors with both the vorticity and scalar gradient vectors are in agreement with DNS results, as are distributions of the measured helicity density fields u•(x,t). Results obtained for the true kinetic energy dissipation rate field show good agreement, up to 14th-order, with previous inertial range structure function exponents measured by Anselmet et al. ͓J. Fluid Mech. 140, 63 ͑1984͔͒ at much higher Reynolds numbers. In addition, probability distributions scaled on inner variables show good agreement among buoyant and non-buoyant turbulent flow cases, further suggesting that these results are largely indicative of the high Reynolds number state of the inner scales of fully developed turbulent flows.