The picture shows the concentration of a passive scalar in isotropic turbulence from a 512x512x1024 grid point DNS of a reacting scalar (unsheared) mixing layer with Schmidt number order one. The image shows the wide range of length scales involved in the turbulent mixing. The simulation was run to generate a data set for studying a canonical flow in non-premixed turbulent combustion research, a reacting scalar mixing layer with a passive reaction (minimal heat generation). To help ensure the simulation was realistic, it was carefully matched to specific laboratory experiments of an analagous flow in which two streams of air at different temperatures mix in grid turbulence. The laboratory experiments simulated were those of Ma and Warhaft. In addition to revealing important aspects of both the reacting and thermal mixing layers, the simulations provide another important demonstration that it is now possible to simulate actual laboratory experiments. The result is data sets that are highly credible, since all of the detailed statistics from the simulation match those from the laboratory experiment; in addition, the simulations provide information about the flow which cannot currently be obtained in the laboratory. Furthermore, flows that can be difficult to explore in the laboratory (e.g., a reacting scalar mixing layer) can be studied by simulating a comparatively easier flow to measure in the laboratory (e.g, a thermal mixing layer) and adding additional physical phenomena (e.g., passive reactions) as needed. The simulations were run at the Arctic Region Supercomputing Center and were sponsored by the National Science Foundation and the Air Force Office of Scientific Research.

References:

S. M. de Bruyn Kops and J. J. Riley (2000). Re-examining the thermal mixing layer with numerical simulations. Physics of Fluids, 12(1) pp. 185-192.

S. M. de Bruyn Kops and J. J. Riley (2001). Direct numerical simulation of reacting scalar mixing layers. Physics of Fluids, 13(5) pp. 1450-1465.

B-K. Ma and Z. Warhaft. (1986). Some aspects of the thermal mixing layer in grid turbulence. Physics of Fluids, 29(10) pp. 3114-3120.