Effect of acoustic excitation on flow over a partially grooved circular cylinder

Abstract

An experimental investigation was carried out on the flow over a partially grooved circular cylinder over a Reynolds number range of 3 x 104 to 1.22 x 105 with and without acoustic excitation. Without excitation the flow over the smooth half of the cylinder was observed to shift to higher subcritical regime. The flow over the groove half, however, is shifted to supercritical or transcritical flow regime. With excitation, on the smooth half it is the separated laminar shear layer which locks in with the excitation frequency, resulting in the shift from subcritical to supercritical or transcritical regimes. On the groove half excitation is not effective for the flow within the transcritical regime. With excitation, the lift is found to reverse its direction while the drag is nearly the same.

Drag on a Cylinder with an Apple-Shaped Cross Section

“…A 7.6% drag reduction by the U-shaped groove, as shown in Figure 10, is similar to the results numerically obtained by Ladjedel et al [6].Their reduction was 9%, but 0.8% by the experiment. The flow in the U-shaped groove, as seen in Figure 13(h), is similar to the open shallow cavity flow [22].…”

“…Thus, when the laminar boundary layer on a circular cylinder separates, the drag must be larger than that in the case of a turbulent boundary layer. For passive drag reduction, the laminar boundary can be promoted to a turbulent one by placing a small rod in front of the circular cylinder [1]; placing small rods [2], tripping wires [3], bumps [4], lateral [5] or longitudinal V-grooves [6] [7] or longitudinal U-grooves on the cylinder's surface [8]- [10]; adding longitudinal grooves like those of a cactus [11] [12]; increasing surface roughness [13] or porousness [14]; or adding patterns [15] like the dimples of a golf ball.…”

Vortex interaction in the formation region of a grooved circular cylinder

“…With additional results and those of Lo and Ko (1995), due to the e ect of the presence of grooves on the other half, the ow on the smooth half of the present partially grooved cylinder is within the subcritical regime and is divided into the lower and upper subcritical subregimes at Re d = 1:0 × 10 4 (Kourta et al, 1987).…”

“…The range of Reynolds numbers was 7:7 × 10 3 6Re d ¡1:3 × 10 5 and was within the subcritical regime of a smooth cylinder. At this Reynolds number range, Lo and Ko (1995) have found that the minimum static pressure coe cient C pmin on the groove half gradually increases, while that on the smooth half remains constant. This means that within this Reynolds number range, the ow on the groove half shifts from subcritical to upper subcritical, critical, supercritical and transcritical regimes, while that on the smooth half to the lower and upper subcritical regime.…”

“…Recently, based on the ow over a partially grooved cylinder and conditional sampling technique, Lo and Ko (1997) observed the existence of these secondary vortices in the transcritical regime of a smooth cylinder, in which a turbulent near wake is found. The adoption of a partially grooved circular cylinder resulted in ow shifting to higher regimes (Ko et al, 1987;Lo and Ko, 1995). This allowed the study of the ow in higher regimes at low Reynolds number.…”