THE STRATEGY OF CALCULATION METHODS FOR COMPLEX TURBULENT FLOWS

摘要

We distinguish "simple shear layers", in which the turbulence is affected only by a simple shear with the same sign everywhere, from "complex" flows such as interacting shear layers and shear layers with extra strain rates. Nearly all two-dimensional or mildly three-dimensional flows with significant Reynolds stress gradients are "fairly thin shear layers" dominated by the shear-stress gradient. In such flows, the shear stress can be used as a velocity scale for the turbulence, which simplifies closure of the time-mean equations of motion. So-called "invariant modeling" is incompatible with the thin-shear-layer or fairly-thin-shear-layer approximations. A calculation method for complex flows is outlined: it is pointed out that at present such methods are not likely to be applicable to all flows without change in empirical input. Numerical problems are discussed: rules for "cheating the computer" by marching elliptic problems and otherwise treating 'unknown quantities as known are urgently needed.