Abstract
To survive in a complex environment, nature has produced efficient and versatile resource-rich structures. One of the novel drag reduction designs comes from the efficient movement of sharks through microscope riblets aligned along the flow direction. In this paper, the effectiveness of sharkskin-inspired riblets in reducing the aerodynamic loss of compressor cascade flow was investigated using the high-fidelity numerical simulation method. Two key normalized parameters, i.e., s+ and h+, were selected to parameterize various riblet designs, and the corresponding relative change in cascade performance was first investigated based on the unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations with/without a transition model. Then, the large eddy simulations in conjunction with the wall-adapted local eddy viscosity model were conducted to investigate the cascade flow with the selected riblet design cases. By comparing the flow resistance, transition positions, vortex formations, and turbulence fluctuations of the boundary flow, the flow control mechanisms of the riblets were finally studied. Simulation results show that compared with the prototype case, the total pressure loss can be reduced by up to 20.5% in the fully turbulent environment. This is because the spanwise fluctuation of the turbulent vortices is impeded inside the boundary layer, and the turbulent vortices are lifted above the riblet tip. Low-speed streaks inside the riblet valleys generate relatively low shear stresses, while the high-shear stresses occur only at the riblet tips. However, when considering the transition from laminar to turbulent boundary flow, the aerodynamic performance of compressor cascade strongly depends on the riblet position relative to the transition region on cascade suction side (SS). The total pressure loss can only be reduced by up to 8.1%, and even most riblet designs degrade the cascade performance. The major reason is that the riblets are located upstream of the transition zone, especially at the small incidence angles. Due to the installation of riblets, the contact area between the laminar flow and the wall surface is increased, and the downstream laminar-to-turbulent transition is promoted.
