Control of Flow Around Square Cylinders at Incidence by Using a Rod

摘要

Aerodynamic characteristics of a square cylinder at incidence were investigated experimentally in the wake of a small rod at a Reynolds number of 3.4 x 10~4. The dimensionless gap L/D was varied from 1.71 to 8.00. Depending on the spacing L/D, two flow patterns with and without vortex shedding from the rod were observed. Pressure measurements on the rod and square cylinder and hot-film measurements in the wake of the cylinder were carried out. The combined influences of the rod and angle of incidence on the pressure distributions and vortex-shedding phenomenon were investigated. Without the rod, as the incidence increases from 0 deg, the reattachment on the lower side surface of the square cylinder occurs at the vicinity of 13 deg, and this corresponds to a jump in the Strouhal number. However, when the rod was set upstream of the square cylinder, the reattachment occurs at smaller angles of incidence depending on L/D. At zero angle of incidence, the minimum value of drag on the square cylinder is obtained for L/D = 2.0 and produces a drag that is 30% that of the square cylinder without rod. For L/D = 1.71, with increasing the angle of incidence C_D values approximate to those of the square cylinder without rod. In the case of L/D ≥ 2.7, there is a considerable decrease in C_D in the region θ ≤ 10 deg; however, the effect of the rod on C_D decreases beyond θ= 10 deg.