HEAT TRANSFER DUE TO THE IMPINGEMENT OF AN AXISYMMETRIC SYNTHETIC JET EMANATING FROM A CIRCULAR ORIFICE: A NUMERICAL INVESTIGATION OF A CANONICAL GEOMETRY

Synthetic jets are produced by periodically injecting and ejecting fluid from an orifice. The mass flow rate is conserved in such a jet but net momentum flux is created due to the difference in the fluid dynamics at the orifice between the ejection and suction parts of each cycle. When pointed towards a heated surface, the synthetic jet can be used for cooling using the well-known advantages of jet impingement. In the, present work, we have created a "canonical" jet in order to investigate the flow and heat transfer of a purely periodic synthetic jet which is not influenced by the manner in which it is generated. As such the "canonical" jet and the resulting heat transfer, can be considered to be dependent solely on the driving suction/ejection mechanisms at the orifice and thus can be examined independently of the actuator. The unsteady Navier-Stokes equations and the convection-diffusion equation were solved using a fully unsteady, laminar, three-dimensional axisymmetric finite volume approach in order to capture the complex time-dependent flow field created by different frequencies. The influence of jet-to-surface distance, Reynolds number, and driving frequency on heat transfer were investigated. Both stagnation and averaged Nusselt numbers were observed to be less dependent on frequency. Heat transfer was found to be higher at high Re numbers and low jet-to-surface distance. Results were compared with the steady continuous jet, experimental data of previous studies and the canonical slot synthetic jet at the same Reynolds number. A circular jet was found to be less efficient in removing heat over the heated wall than a slot synthetic jet.