Heat Transfer on Flat Surface Impinged by an Underexpanded Sonic Jet

Underexpanded impinging jets include complicated flow phenomena such as shock structure, sonic surface, and recirculation zone in a central impingement region, and the local heat transfer on an impinged surface has a different characteristic than a subsonic impinging jet. Studying this can be helpful in understanding the relation between supersonic flow characteristics and heat transfer on a surface. It can also provide a proper design factor for the impingement cooling technique by a high-speed jet. The convective heat transfer coefficients have been measured on a flat surface impinged by an underexpanded sonic jet. In addition, the visualization of shock structures and surface pressure measurements have been conducted to support the heat transfer measurement results. From the results, the distribution of the heat transfer coefficient on the central impingement region due to the interaction between the sonic surface and recirculation flow has been obtained. It has also been observed that the turbulence diffusion from the shear layers around the jet edge and the sonic surface into a jet core induce high heat transfer on a surface.