Control of flow around a circular cylinder using a patterned surface

Abstract

Controlling the flow around a circular cylinder by the use of patterned surface roughness is investigated. In this study, experimental work to reduce drag coefficient of a circular cylinder was carried out with particular attention to change in the distribution of surface roughness. Drag coefficient of a circular cylinder having discretely patterned surface was compared with uniformly roughened surface. When the circular concave and convex patterns with relative surface roughness of about 1% of the diameter were added discretely to the surface, drag coefficient of a cylinder of the patterned roughness is lower than a cylinder with uniform surface roughness of the same degree, and remains approximately constant beyond the critical Reynolds number. Measurement of the pressure distribution indicated that circular cylinders with a lumped patterned roughness made it possible to reproduce a supercritical state in lower Reynolds number range. It was considered that the lumped patterned roughness changed the flow around the circular cylinder, causing a combining of the laminar separation and the turbulent separation. The drag force characteristics of the circular cylinders were well explained by the results of the pressure distribution measurement. In conclusion, it was found that density and arrangement of lumped roughness was the key factors in controlling the drag characteristics of a circular cylinder. It seems to be possible to adjust those two factors to optimize the drag coefficientReynolds number relationship. Methods in this study to control the drag characteristics in the vicinity of the critical Reynolds number can be applied to all of cylindrical structures in various fields.

Along-Wind Aerodynamic Damping of Wind Turbine Towers: Determination by Wind Tunnel Tests and Impact on Tower Lifetime

“…As a result, the Reynolds number in wind tunnel tests does not match that in the full-scale prototype. However, the resulting scale-effects can be reduced to some extent by an increase in the model's surface roughness [24][25][26][27][28][29] or through the modification of the experiment flow, either increasing flow turbulence [30] or using pressurized wind tunnels [31]. Many of these studies are summarized elsewhere [32][33][34][35][36].…”

“…The dimpled pattern is roughly based on the patterns shown by Bearman [26] and Hojo [28] and is described in detail for its potential use in Reynolds scale effects reduction in wind tunnel measurements. The dimpled pattern was defined through milling dimple spheres of diameter D DI MPLE equal to one-eighth of the model diameter, a depth of 0.025 times the corresponding model diameter, which results in a dimple width D CUT equal to 10% of the model diameter.…”

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…In contrast, for large velocities the drag coefficient is smaller but the drag force assumes larger values and is significant for the motion of the aerostat. It is worth mentioning that the exact value of the drag coefficient in relation to the Reynolds number can be estimated experimentally after building the aerostat, so on this stage of investigations, approximation of the c x value is based on literature data concerning objects of quite similar shapes [32].…”