Effect of forcing by a plasma actuator on impinging-jet heat transfer*

Impinging jets have many engineering applications, such as heating, cooling and drying. This work is part of a larger study focused on using different active flow control strategies for enhancement of the cooling effectiveness of impinging jet arrays. Here, we examine the influence of steady forcing, using a circular Single Dielectric Barrier Discharge plasma actuator, on the Nusselt number (Nu) distribution of an axisymmetric jet impinging on a heated flat surface. In the experiments, the plasma actuator was mounted as close as possible to the sharp edge of the jet exit and was actuated sinusoidally at a frequency much higher than that of the jet’s initial instability. The Nu distribution was measured using temperature sensitive paint applied to a heated stretched stainless steel foil. Data were obtained for jet  Reynolds number based on jet diameter in the range 5,000 to 20,000, jet-exit-to-plate distance range of 2 to 6 diameters, and different forcing amplitudes. The results illustrate the influence of the control on the jet’s cooling effectiveness, and the dependence of this influence on the flow and the forcing parameters. Time-resolved flow visualization is used to examine associated changes in the flow structure.