Aerodynamic and heat transfer analysis of a impinging jet on a concave surface

Impinging jets are often used in applications requiring important localized cooling. For example, this technique is commonly used to reduce blade temperatures inside gas turbines. When the jet impacts the inner surface of the leading edge of a gas turbine blade, this geometrical configuration is similar to a jet impinging a concave surface inside a cavity. Previous studies have shown that for a certain range of geometrical and dynamic parameters, a jet injected in a cavity may sometime become unstable which is characterized by an oscillatory or flapping movement of the flow within the cavity. The objectives of this study are to investigate some features of this behaviour from velocity fields inside the cavity, pressure coefficients and Nusselt number distributions on the concave surface. This was accomplished using unsteady numerical simulations of a laminar flow at different Reynolds numbers for six different cavity configurations. Furthermore, PIV measurements were realized for some of the configurations in order to validate the numerical results. The results show that for four geometrical configurations, the flow entered in an oscillatory movement inside the cavity. This behaviour can be related to the difference in pressure between the output channels and the main vortex structure present inside the cavity. However, no clear link has been established between the frequency of the oscillatory flow and the geometrical parameters used.