This study will apply planar laser imaging techniques to perform highly quantitative measurements of velocity and scalar fields in turbulent, axisymmetric jet and swirling jet flows. The data will support the development of subgrid-scale (SGS) modeling approaches for large-eddy simulations (LES) of turbulent mixing. Accurate representation of mixing in LES is crucial to efforts to simulate non-premixed combustion systems, where molecular mixing is a necessary precursor to chemical reaction. Very limited tests of SGS mixing models using planar scalar mixing measurements have been reported. Here, particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) will yield simultaneous measurements of velocity and scalar fields in gas-phase turbulent jets, while simultaneous Rayleigh scattering and PLIF will measure single- and multi-species scalar mixing. Refinements to standard cross-correlation PIV algorithms improve the accuracy and resolution of the velocity and velocity gradient measurements, while strict data reduction ensures high accuracy of the PLIF and Rayleigh scattering results. Working in the gas phase allows the investigation of a range of velocity and scalar field length scales relevant to LES of combustion, from the dissipation scales well into the inertial range. The planar nature of the measurements permits spatial filtering that reflects the filtering implicit in LES. Evaluations of SGS mixing model performance will include a priori tests, as well as appropriate, grid-dependent, a posteriori assessments of LES results. These a posteriori tests will involve, besides standard comparisons of scaling properties and mean profiles, assessment of the ability of LES to capture large-scale flow organization, and true LES grid-scale fluctuations, spatial gradients, and probability distributions. The results will provide a rigorous framework for understanding the performance of SGS scalar models. This work will directly inform efforts to apply LES to realistic combustion systems, including gas turbine and internal combustion (IC) engines. Innovative IC engine technologies, such as direct injection, offer significant gains in fuel economy, and attendant reductions in carbon dioxide production. The ability to perform LES of practical engines will greatly facilitate the optimization of their efficiency and emission control. The work will also find applications in LES efforts in geophysical problems, such as those involving transport and mixing in the atmosphere and oceans.
