An Annular Impinging Jet Alternated by Pulse-Modulated Synthetic Jets

The present experimental study focuses on a generation and control of annular impinging jets. The used working fluid is air. An active flow control system is designed with six radial synthetic jets, which are generated by a common actuator located in the central body of the annular nozzle. The synthetic jets are pulse-modulated. Flow visualization and measurements of the wall pressure and wall heat transfer have been performed. Two flowfield steady patterns A and B (small or large recirculation bubbles, respectively) are recognized. The pattern B exists without the actuation, the unmodulated actuation causes the flowfield switching into the pattern A, and the pulse-modulated actuation generates an alternating flowfield. The present results indicate that the area of higher heat transfer can be slightly spread by means of flow alternation. However, the penalty for this slight gain is a substantial reduction of the heat transfer in the central area.