The mechanism about the flow characteristics of dimples on the highly loaded compressor blade induced by their geometry and flow conditions

To clarify the flow control mechanism of the dimple surface and its influencing factors, this paper arranged cavity structures on the suction surface of a highly loaded compressor cascade. The Reynolds-averaged Navier-Stokes equations were utilized to calculate the impact of the geometric structure and inlet conditions of a dimple on the flow characteristics and flow control effect on the dimple surface. Additionally, the stress-blended eddy simulation was employed to compute the unsteady characteristics of the dimple vortex. By using the Liutex vortex determination criterion, flow regimes (diffuser-confuser, horseshoe vortex, and tornado-like vortex) and vortex axis morphologies (I-axis, C-axis, and V-axis) were identified. The flow regime diagram based on the Reynolds number and depth-to-diameter ratio was drawn, and boundary formulas for each flow pattern were provided. The vortex shedding frequency (1900-2300 Hz) and the main stream impingement frequency (5400-8154 Hz) for the cavity with a relative depth of 0.0625 were detected. By quantifying the vortex intensity coefficient and the increments of the inlet and outlet parameters of the cavity, the vortex and flow control capabilities were assessed. The results revealed that the peak vortex intensity occurred in the depth-to-diameter ratio range of 0.2-0.5, and the increase in dimple depth can improve the vortex intensity and delay the depth-diameter ratio corresponding to the peak value. The increment of turbulent kinetic energy and flow velocity at the outlet of the dimple to the flow field was proportional to the depth and inversely proportional to the depth-diameter ratio.