Investigation of Drag Coefficient at Subcritical and Critical Reynolds Number Region for Circular Cylinder with Helical Grooves

Abstract

Drag reduction of an object is the major concern in many engineering applications. Experimental studies have been carried out on circular cylinder with helical grooves in a subsonic wind tunnel. Different cases of helical grooves with different pitches, helical groove angles and number of starts of helical groove on circular cylinder are tested. Experimental results show the drag coefficient is sensitive with Reynolds number and decreases at critical Reynolds number and at subcritical and supercritical or transcritical Reynolds number the drag coefficient increases as compared with smooth cylinder. The longitudinal grooves over the cylinder surface are tested and showed that drag coefficient much decreases at the subcritical and critical Reynolds number region. The experimental results are validated with available literature and obtained good agreement.

Experimental and numerical investigation of flow over spiral grooved cylinders

“…A number of uncertainties could have influenced the measured values of drag coefficient C D , such as the level of incoming flow turbulence, 37 blockage, and the aspect ratio of the cylinder. 13 All of these could have yielded different ranges of flow of the critical Re, where the separation angle measured from the front stagnation point changed from about 80° to 100°. 17…”

“…A number of uncertainties could have influenced the measured values of drag coefficient C D , such as the level of incoming flow turbulence, 37 blockage, and the aspect ratio of the cylinder. 13 All of these could have yielded different ranges of flow of the critical Re, where the separation angle measured from the front stagnation point changed from about 80°to 100°. 17 The experimental results of the spiral grooved cylinder exhibited a similar trend on the curve of C D as a function of Re as was noted by Eguchi et al 2 In addition, they fell in the same critical flow region of Re.…”

“…This experimental setup is different from that of experiments where the instruments used for measurement are connected directly to the cylinder. 13,36 Additionally, in their experiment, to mitigate the effect of the end wall of the cylinder on C D , the ends were set very close to the wall of the wind tunnel. In present experiment, the wind tunnel was wide enough and a very long cylinder was used, and thus the effect of the wire ends was insignificant.…”

“…The helical angle β (shown in Figure 2(a)), groove angle θ, pitch distance h p , and the number of grooves in the circumferential direction of a grooved cylinder are experimentally examined through wind tunnel tests. 13 According to their findings, the drag coefficients are sensitive to Re, and decrease only in the flow range of the critical Re compared to a cylinder with smooth walls. Cactus-like surface pattern has been applied to a cylindrical cylinder and longitudinal grooves of varying depths have been tested in a wind tunnel.…”