Influence of Mach Number on Tornado Corner Flow Dynamics

Abstract

Since maximum Mach numbers in an F5 tornado are expected to, at least, reach ?0.4, a study was undertaken to determine the major potential compressibility effects in such flows. Results from compressible large-eddy simulations of tornado corner flow dynamics are summarized. Comparison with previous incompressible simulations indicates that Mach number effects tend to be modest and may be estimated by an isentropic approximation. As the average maximum Mach number M within the tornado increases above one-half, the largest changes occur for ?low-swirl? corner flows, those exhibiting a central vertical jet off the surface capped by a vortex breakdown, with the vortex breakdown found to occur at significantly greater heights as M increases. It also appears that the highest Mach numbers are most likely to occur during rapid transients in near-surface intensification that can sometimes occur during a tornado's evolution.