Wake flow evolution behind a circular cylinder with two perpendicular slits at various angles of attack

A wind tunnel experiment was performed to study the wake vortex dynamic behind a circular cylinder with two perpendicular slits (TPS) using time-resolved particle image velocimetry. The experimental studies were conducted at a Reynolds number of 1767 based on the incoming airflow and the diameter of the circular cylinder. The slit was built in the circular cylinder with a width of 0.08D (D is the diameter of the circular cylinder). The angles of attack were set from 0° to 45° from the incoming airflow direction. The time-average result, such as turbulence kinetic energy, streamline, and normalized Reynolds shear stress, were investigated to illustrate the influence of the angles of attack on the wake flow. The evolution of wake vortex shedding at one period was divided into four phases based on proper orthogonal decomposition analysis. This suggests that the wake vortex shedding behind the circular cylinder with TPS at various angles of attack exhibits notable modifications compared to the uncontrolled case. The mean velocity at the point of the wake slit hole revealed a jet flow blowing out from the slit and interacting with the wake flow. Moreover, the effect of drag coefficient reduction was estimated owing to TPS. Graphical abstract