Conditional analysis of turbulent heat transport in a quasi two-dimensional wake interacting with a boundary layer

A conditional averaging technique has been used for the analysis of experimental data obtained from heat flux measurements in the region of interaction of a cylinder wake with a. boundary layer. The circular cylinder was placed normal to the flow and parallel to a flat plate, just outside of the boundary layer. The surface of the cylinder was intentionally rough, following our observation that in this way the velocity power spectrum in the intermediate wake could be forced to acquire some quasi two-dimensional turbulence characteristics, namely to display a scaling region deviation from the -5/3 power law which is characteristic of homogeneous, three-dimensional turbulence. The streamwise and the normal (to the plate) velocity components, as well as the temperature at the same position, have been recorded simultaneously, using hot wire anemometry. Time variations of the relevant Reynolds shear stress and heat fluxes were evaluated directly from the experimental data. These results were then conditionally averaged according to the quadrant splitting analysis technique. It was found that in the boundary layer region, a particular fluid motion ('ejections', in the quadrant splitting analysis terminology) dominate the flow. That motion is the main carrier of hot fluid from the boundary layer to the wake. (C) 1999 Elsevier Science Ltd. All rights reserved.