DNS of unsteady heat transfer increase on a curved surface due to wake-induced turbulence

Abstract

From experimental studies it is well established that free-stream and wake-induced turbulence can increase the heat transfer on curved surfaces such as turbine blades or cylinders even if the mean flow matches corresponding laminar velocity profiles. Here, preliminary results of an investigation using (embedded) Direct Numerical Simulation (DNS) are reported that aim at identifying the responsible physical mechanisms for this phenomenon. The setup follows an existing experiment where a heated cylinder is subjected to the turbulent wake of a smaller cylinder placed upstream. The Reynolds number based on the diameter of the heated cylinder is Re = 48, 000. A key parameter identified in an experimental correlation is the characteristic turbulence level Tu_a that includes a dependency on Re and the mean flow acceleration. For the present study, Tu_a is an order of magnitude higher than those reported in any previous DNS. The obtained Nusselt number is in good agreement with the experimental correlation. More and better resolved data is currently produced for further analysis.