Turbulence structure in the viscous layer of strongly heated gas flows

For dominant forced convection with significant gas property variation, even in low Mach number flow through a circular tube, apparently the only published profile data available to guide (or test) the development of predictive turbulence models are K. R. Perkins` measurements of mean temperature structure. The work here takes the next step: the first mean velocity distributions for this situation are presented. In order to dissect the anatomy of the viscous layer in gaseous, turbulent, tube flow with strong heating, it has been probed via thermal anemometry coupled with diagnostic application of simple computational thermal fluid dynamics. Experiments for air flowing upward in a vertical circular tube were conducted for heating rates causing significant property variation. An unheated entry of fifty diameters preceded the heating. Examination emphasizes the wall region which would conventionally be expected to contain the viscous layer, if the flow were unheated. In the flow called turbulent, after being disturbed in the first few diameters by the heating profiles representing the turbulence quantities appear to recover to approximately self-preserving conditions. In the other two runs with higher heating rates, the turbulence quantities decrease after the immediate thermal entrance until they are small relative to molecular effects.