Effects of wall curvature on the dynamics of an impinging jet and resulting heat transfer

The effects of wall curvature on the dynamics of a round subsonic jet impinging on a concave surface are investigated for the first time by direct numerical solution of the compressible Navier-Stokes equations. Impinging jets on curved surfaces are of interest in several applications, such as the impingement cooling of gas turbine blades. The simulation is performed at Reynolds and Mach numbers respectively equal to 3, 300 and 0.8. The impingement wall is kept at a constant temperature, 80 K higher than that of the jet at the inlet. The nozzle-to-plate distance (measured along the jet axis) is set to 5D, with D the nozzle diameter. In order to highlight the curvature effects, the present results are compared to a previous study of jet impinging on a flat plate. The specific influence of wall curvature is investigated through a frequency analysis based on discrete Fourier transform and dynamic mode decomposition. We found that the peak frequencies of the heat transfer also dominate the dynamics of primary vortices in the free jet region and secondary vortices produced by the interaction of primary vortices and the target plate. These frequencies are approximately 30% lower than those found in the reference study of impinging jet on a flat plate. Imperceptible differences were instead found in the time-averaged integral heat transfer.