Numerical investigations of the effects of hub-mounted herringbone riblets on corner separation in a linear compressor cascade

Corner separation can degrade the aerodynamic performance of a compressor, and even lead to stall or surge conditions, while the vortex details for lightly loaded compressor cascade at low-Reynold-number condition are not clear. In the present study, the relationship between the vortex structures and losses for the lightly loaded baseline cascade at a Reynolds number of 150 000 was investigated. Then, herringbone riblets are placed on the hub, upstream of the blade leading edge to mitigate the adverse effects of corner separation and reduce the overall pressure losses of the cascade. Based on experimental results, numerical simulations were carried out to gain an insight into their effect on the characteristics of the flow field. Our results show that introducing herringbone riblets in front of the blade leading edge can reduce total pressure loss by up to approximately 5.5%, depending on the angle of attack and the distance between the blade and the riblet strip. The results indicate that the vortices induced by the riblets enhance momentum transfer near the blade leading edge, while the riblet channels guide the fluid in the designed direction, thereby suppressing crossflow on the hub. In the baseline cascade, the interaction among the hub separation vortex, trailing edge vortex, and concentrated shedding vortex develops a distinct n-shaped vortex structure within the corner region, which causes a total pressure drop. In contrast, the hub-mounted herringbone riblets can redirect the suction part of the horseshoe vortex away from the blade, delaying and constraining the development of the hub separation vortex, and ultimately suppressing corner separation.