Flow Around a Rotatable Circular Cylinder-Plate Body at Subcritical Reynolds Numbers

Abstract

The behavior of a stationary circular cylinder with an attached plate, under conditions where the entire cylinderplate body rotates about the cylinder axis, has been investigated experimentally for Reynolds numbers between 8 × × 10 3 and 6 × × 10 4 . To see the effect of the plate inclination on the pressure distributions and vortex shedding, the cylinder-plate body was rotated from 0 to 180 deg, unlike freely rotatable cases in previous studies. The plate was located at the center plane of the cylinder, upstream of the cylinder, at the beginning. The diameter of the cylinder and the width of the plate were both chosen to be 35 mm. Measurements of shedding frequency and pressures on the surface of the cylinder were obtained. The results indicate that the shedding frequency was nearly constant in the range of 50-120 deg and, by further increasing the angle from 120 to 160 deg, it strikingly increases and then again decreases at angles larger than 160 deg. The plate also causes important changes in pressures on the surface of the cylinder with increasing inclination angle. For different plate angles, five different types of pressure distributions have been observed. Characteristics of the vortex formation region and location of flow attachments, reattachments, and separations were observed by means of the flow visualizations. The drag coefficient of the cylinder has a maximum value at approximately θ = 75 deg, whereas it has a minimum value at θ = 15 deg. The lift coefficient has two maximums, at θ = 15 and 165 deg, depending on the plate position. The values of C L at about θ = 45 and 160 deg are zero as in the case of the cylinder without a plate. Nomenclature C D = drag coefficient 1 2 2π 0 C p · cos α dα C L = lift coefficient − 1 2 2π 0 C p · sin α dα C p = pressure coefficient, (P − P st )/ 1 2 ρU 2 D = diameter of circular cylinder D = projected cross-stream dimension of the cylinder-plate body f = vortex-shedding frequency L = width of the plate P = surface pressure P st = static pressure in the test section Re = Reynolds number based on D, U D/ν Sr = Strouhal number, f D/U Sr = Strouhal number, f D /U U = freestream velocity x, y = streamwise and lateral coordinates α = circumferential angle measured from the stagnation point of the cylinder θ = plate angle ν = kinematic viscosity of fluid ρ = density of air

Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder

“…Drag coefficients were found at maximum and minimum values at 75 and 15 degree, respectively. While lift coefficient was observed to have two maximum values at the 15 and 165 degrees and minimum values were 0, 45, 158 and 180 degree [4].…”

“…Apelt et al reported that they examined splitter plate behind circular cylinder in range of L/D2 at Reynolds numbers between 10 4 and 5x10 4 . They depicted that using a splitter plate reduces drag and produces narrower wake than that of bare cylinder.…”

“…This means approximately 31% reduction in drag when L/D=1 [1]. Cimbala and Garg investigated plain circular cylinder, fixed/free rotatable splitter plate behind circular cylinder models in range of L/D=5 at 5x10 3 <Re<2x10 4 . They reported that wake of free rotatable cylinder/splitter plate model is nearly same with plain cylinder.…”

“…They also compared cylinder/rigid splitter plate with cylinder/free splitter plate in near wake about vortex formation length and Karman vortex street shedding frequency [2]. At 2x10 4 <Re<8x10 4 Cimbala and Leon exhibited that the change of drag coefficient of plain cylinder, cylinder/rigid splitter plate and cylinder/free splitter plate depending on L/D ratio. The change in drag was observed nearly the same in both splitter plate cases.…”

“…However, when the splitter plate length was increased then drag was reduced [3]. Akansu et al experimented the effect of the circular cylinder with splitter plate from 0 to 180 degree to observe pressure distribution, vortex shedding, drag and lift coefficient at 8x10 3 <Re<6x10 4 . Drag coefficients were found at maximum and minimum values at 75 and 15 degree, respectively.…”