Pressure Fluctuations Produced by a Jet impinging on a Wall at Normal Incidence

Abstract

Impingement jets have crucial role in multi engineering applications, such as cooling, heating and hovercrafts, in addition to understand some meteorological phenomenon such downburst. There were many studies considering heat transfer from the impingement surface, however, there were few studies on the pressure fluctuations over the impingement surface. The current study investigates the unsteady pressure measurement from normal impingement jet, using microphone array. The investigation was implemented at a jet Reynolds number 13,500 based on the jet exit velocity and jet diameter, while the nozzle-to-plate distances were ranging from two to eight jet diameters. Spectral analysis showed that the pressure fluctuations over the impingement surface induce higher frequencies when nozzle-to-plate distances were smaller. The flow structure that develops pressure fluctuations at these frequencies can be inferred depending on literature. At wall-jet region, where the maximum pressure fluctuation was observed, the pressure fluctuations were basically affected by jet vortices and their interaction with the plate after impingement. These vortices merge while they flow over the impingement surface producing high pressure fluctuations.