Flow control of a square cylinder at the most unfavorable angle of attack via bionic shark scales

An experimental study was conducted to investigate the aerodynamic performance and wake flow of a square cylinder at varying wind angles of attack (AoAs). The efficacy of the bionic shark scale has been assessed for suppressing flow separation at the most unfavorable AoA. The Reynolds number was fixed to be 17 100. The root mean square (RMS) values of the pressure coefficient fluctuations on the upper and lower walls for the AoA = 0° were approximately twice those for the non-zero AoAs. To analyze the underlying mechanism, a high-speed particle image velocimetry system was employed to accurately capture the characteristics of the wake flow. The results indicate that the maximum turbulent kinetic energy, the saddle point closest to the surface, the largest fluctuations of the proper orthogonal decomposition mode coefficients, and the vortex-shedding position nearest to the cylinder all occur at AoA set to be 0°. Because of the strong unsteady pressure at 0°, the different spacing of the shark-scale texture and square cylinder was applied for flow stabilization and controlling unsteady pressure. The results show that the mean and RMS of the pressure coefficient are reduced by 17% and 53%, respectively, under the optimal control condition, and that the unsteady flow structure behind the cylinder is alleviated.