Experimental investigation of geometric and inlet condition effects on hub riblets for corner separation suppression

Herringbone riblets generate an upflow motion above the convergent line and a downflow motion along the divergent line. This peculiar flow phenomenon provides a potential for flow control in a compressor. This study employs experimental wind tunnel measurements to investigate the application of hub-mounted herringbone riblets to mitigate corner separation in a compressor cascade. The riblets were placed on the hub upward of the blade leading edge, with the cascade operating at low Reynolds numbers ranging from 1.0 × 105 to 2.0 × 105. First, the flow control mechanism of these hub riblets was revealed. The results show that in the spanwise direction, these riblets can enhance the downward motion of the fluid near the leading edge, which enhanced velocity profile and weakens the horseshoe vortex. In the pitchwise direction, hub riblets lead the suction leg of the horseshoe vortex away from the wall, delaying the onset of corner separation and reducing its size. The direction of rotation of the blade separation vortex was reversed after application of the riblets, and all of them resulted in a reduction of losses to about 9.5%. Further investigation into riblets geometry showed that increasing riblets height narrowed the pitchwidth of corner separation while increasing losses near the 0.1 span, whereas width and length had minimal impact on loss contours. Finally, performance evaluations under varying inlet Reynolds numbers and incidence angles indicated sensitivity to incidence angle but less influence from Reynolds number. These findings provide valuable insights into the industrial implementation of hub-mounted riblets for reducing corner separation losses.