Passive suction jet control of flow regime around a rectangular column with a low side ratio

A passive jet method was experimentally investigated to manipulate the unsteady vortex shedding around a rectangular column. This method employed a circuit channel connecting the windward and leeward sides of the column to implement the windward passive suction and leeward passive blowing synchronously to modify the flow regime around the column. A bare column model with a side ratio of SR = 1.3 was utilized as a baseline case and the same column models covered with passive suction/jet rings served as controlled cases. Based on different angles of attack (AoAs) of the column models, the Reynolds number varied from 29,300 to 48,200 at an oncoming wind velocity of 10 m/s. At different intervals of suction/jet rings, the surface pressure distributions, aerodynamic forces, and flow structures of the column models were measured to evaluate the control effectiveness of the passive jet method. The results indicated that a notable reduction in the fluctuations of both the surface pressures and aerodynamic forces was achieved. Meanwhile, the mean values of drag forces were also evidently decreased. The flow regime was modified in the vicinity of passive jet holes. The main separation vortices were stretched by the small-scale reverse vortices induced by the jet flow. In addition, the TKE level in the wake flow was considerably decreased in the controlled cases. By extracting eigenvalues and mode coefficients, the POD analysis revealed that the descent of the low-order mode energy corresponded to the suppression of the vortex shedding. The series of phase reconstruction and POD-filtered flow fields demonstrated that the passive jet flow could interact with the shedding vortices and weaken the strength of the vortex shedding process.