BOUNDARY-LAYER TURBULENCE AS A KANGAROO PROCESS

A nonlocal mixing-length theory of turbulence transport by finite size eddies is developed by means of a novel evaluation of the Reynolds st ress. The analysis involves the contruct of a sample path space and a stochastic closure hypothesis. The simplifying property of exhange (st rong eddies) is satisfied by an analytical sampling rate model. A nonl inear scaling relation maps the path space onto the semi-infinite boun dary layer. The underlying near-wall behavior of fluctuating velocitie s perfectly agrees with recent direct numerical simulations. The resul ting integro-differential equation for the mixing of scalar densities represents fully developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type of stochastic process. The model inv olves a scaling exponent epsilon (with epsilon-->infinity a, in the di ffusion limit). For the (partly analytical) solution for the mean velo city profile, excellent agreement with the experimental data yields ep silon approximate to 0.58.