Vortex Shedding from a Circular Cylinder with Spiral Fin

Abstract

The effect of simple spiral fin around a bare tube on Karman vortex shedding was experimentally investigated. We measured the distributions of the mean velocity, the intensity of velocity fluctuation, the spectrum of velocity fluctuation and the coherence distribution of Karman vortex in the spanwise direction. And the flow around a fin tube was visualized by using smoke wire technique. As a result it was made clear that the periodic velocity fluctuation caused by Karman vortex was remarkably observed in the wake of the fin tube although the fin was mounted around a bare tube with a large pitch along the tube axis. The vortices in the near-wake of the fin tube make cells structure with the scale of the pitch length of the fins. The rotation axis of each vortex was inclined against the tube axis. The large scale vortex was formed by the coalescence of the vortex cells. Therefore, the spanwise scale of the vortex in the wake of the fin tube was larger than one pitch of the fins.

Recent advancements toward the understanding and control of turbulent flows (Summary of ICJWSF2013)

“…As for the noise of heat exchanger, the vortex shedding noise generated from a circular cylinder with spiral fin in cross flow is investigated experimentally (Hamakawa, et al, 2013).…”

Air cooling of a finned cylinder with slot jets of different height

“…The effect of the spiral fin around a bare tube on the von Karman vortex shedding has been investigated at Re ¼ 21,000 in [17] by varying the ratio of the fin pitch, p, to the external diameter of the tube without fins, D, with the purpose of avoiding the match with the natural frequency of an heat exchanger cavity and of preventing damages. The conclusions are that the flow is deflected on the surface of the bare tube, similarly to what happens on a smooth tube, with a cell structure of the same scale of the pitch length and with the axis of rotation of each vortex inclined with the tube axis.…”

Wake behind a rough (metal foam-covered) cylinder in cross-flow

“…Moreover, other studies on vortex shedding of finned-cylinders show that the vortex shedding frequency is well correlated with the cylinder effective diameter, which is based on the projected frontal area of the cylinder (Mair et al [142], Hamakawa et al [143]). Unlike the aforementioned studies on the detached structures from the wake of finned and bare cylinders, no specific investigation has been conducted in the literature regarding the foamed cylinder type.…”

“…Zdravkovich [137] indicated the role of the fins as vortex-spoilers as they disturb the shed vortices, making them less coherent and threedimensional. Moreover, other studies on vortex shedding of finned tubes show that the vortex shedding frequency is well correlated with the tube effective diameter, which is based on the projected frontal area of the tube (Mair et al [142], Hamakawa et al [143] and Ligrani et al [139]). Unlike the mentioned studies on the detached structures from the wake of finned and bare tubes, no specific investigation has been conducted in the literature regarding the foam-wrapped tube type.…”

“…In the case of detached structures from the wake, studies show that attaching extra surfaces to a tube affects the shedding process [137,[139][140][141][142][143]. Won et al [140] reported that adding fin causes intense, highly unsteady secondary flows and vortex pairs which increase secondary advection and turbulent transport.…”