“On the Reynolds dependence of turbulent flames: the cascade through the lens of power laws, surface density function, and fractal analysis”
By: Dr. Fabrizio Bisetti
Assistant Professor in Aerospace Engineering, The University of Texas at Austin
ABSTRACT: Turbulent burning rates are several times greater than their laminar counterparts, primarily due to the enhancement in flame area brought by flame wrinkling and hydrodynamic straining. Recognizing the central importance of the Reynolds number as a measure of scale separation in turbulent flows, we investigate the Reynolds number scaling of turbulent burning rates, all other dimensionless groups held constant. The study is based on a database of large-scale direct numerical simulations of unsteady spherical turbulent premixed flames. Our data and complementary theoretical analysis identify a clear power-law scaling for the burning rates. The exponent is found to hold instantaneously and is related to the dependence of the Bray-Moss-Libby wrinkling scale from the Reynolds number. Remarkably, we find that the same power law exponent value applies to the fractal inner cutoff scale of the flame surface, i.e. the Minkowski–Bouligand scale below which the flame surface is topologically smooth. Although it remains unclear whether the proposed scaling law extends to other flame configurations such as jet and swirled flames, our findings offer strong support to fractal closures in turbulent combustion and provide the means for improved predictions.
BIO: Fabrizio Bisetti is an Assistant Professor in Aerospace Engineering at the University of Texas at Austin, where he moved in late 2016. Prior, Prof. Bisetti held a faculty appointment at King Abdullah University of Science and Technology (KAUST), where he joined the Clean Combustion Research Center (CCRC) in July 2009 as a founding faculty. Prof. Bisetti holds a Laurea (Politecnico di Milano, 6/2003), MS (UT Austin, 8/2002), and PhD (UC Berkeley, 12/2007) in Mechanical Engineering. Upon graduation, he joined the Center for Turbulence Research at Stanford University as a Postdoctoral Fellow (1/2008-6/2009). Prof. Bisetti’s research interests are in turbulent combustion, soot formation in turbulent flames, turbulent aerosols, turbulent mixing, plasma assisted ignition, and numerical methods for reactive and plasma flows. His research activities combine High Performance Computing (HPC) and theory to understand complex multi-physics/multi-scale processes in turbulent flows, e.g. aerosol/turbulence interaction, turbulent combustion, and plasma-assisted ignition.
Friday, April 23, 3-4pm, Zoom meeting link: https://nmsu.zoom.us/j/99609263954