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

Abstract

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 × × 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. NomenclatureC D = drag coefficient of square cylinder based on D as the reference length C DR = drag coefficient of rod C DT = total drag coefficient, = C D + C DR (d/D) C L = lift coefficient of square cylinder based on D as the reference length C p = pressure coefficient, = (P − P st )/ 1 2 ρU 2 D = length of side of square cylinder D = projected cross-stream dimension of the square cylinder in incidence d = diameter of rod f = vortex-shedding frequency L = distance between the axes of square cylinder and rod P = surface pressure P st = static pressure in the test section Re = Reynolds number based on D, U D/ν Sr = Strouhal number based on D Sr = Strouhal number based on D U = freestream velocity x, y = streamwise and lateral coordinates α = circumferential angle measured from the front stagnation point of the rod θ = angle of incidence ν = kinematic viscosity of fluid ρ = density of air

Time-averaged topological flow patterns and their influence on vortex shedding of a square cylinder in crossflow at incidence

“…Other investigators, e.g. , Dutta et al (2003), and Sarioglu et al (2005), reported similar trends for the behavior of the aerodynamic forces and vortex shedding.…”

Bi̇r Kanat Profi̇li̇ Ve Bi̇r Dai̇resel Si̇li̇ndi̇r Etrafindaki̇ Akişin Aerodi̇nami̇k Karakteri̇skti̇kleri̇

“…Flow control around the cylinder with the help of control rod [1][2][3][4], splitter plate [5][6][7] can be given as literature examples. Especially, flow around a circular cylinder has encountered in many engineering applications, for example, in the cooling tower, chimney and so forth.…”

“…Especially, flow around a circular cylinder has encountered in many engineering applications, for example, in the cooling tower, chimney and so forth. Sarioglu et al [3] and Igarashi [8] investigated experimentally the effects of a thin rod having circular cross section, placed before a square cylinder in different distances, on the flow. They showed that there are two different flow structures depending upon the gap ratio between the two objects.…”

Large Eddy simulation of cross-flow around a square rod at incidence with application to tonal noise prediction

“…If a circular rod is positioned upstream of the square one a second non-shedding mode is possible [54] depending on the distance between the rods. Smoke visualisation of the shedding and not-shedding modes is shown in figures 2.5a and 2.5b.…”

“…(a) Vortex shedding [26], Re D = 11000 (b) Non-shedding controlled by an upstream circular rod [54], Re D = 34000 Figure 2.5: Smoke visualisation of the wake of a square rod from Igarashi [26] and Sarioglu [54].…”