FIV2018 Paper Management System, FIV2018 Conference

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Experimental investigation of flow around a rotating rough sphere
Nan Gao, Zhuoyue Li

Last modified: 2018-06-24

Abstract


The spinning motion of a solid particle translating in fluid generates lift force, which is usually referred to as the Magnus effect. Recent investigations (Kim et al. 2015) revealed that the lift and drag forces on the particle undergo significant changes when the status of the boundary layer over the retrieving side of the particle transitioned to a turbulent state (the top and bottom sides are typically referred to as the advancing side and the retrieving side where the near wall velocity becomes faster and slower, respectively, due to rotation). In their case, the transition occurred at a Vs/U (ratio of the surface velocity over the freestream velocity) of 0.75 to 1.0 and a Reynolds number close to the transitional Reynolds number. They found the lift force became negative. The forces on a spinning sphere with a larger Vs/U is not studied. It is expected that as Vs/U increases the boundary layer on the advancing step could also transition to a turbulent state. In this paper, we are going to present a set of detailed measurements of the lift/drag forces of a spinning golf ball in a water tunnel with a Reynolds number of Re_D= 8000 for a range of Vs/U between 0 and 6.0. The flow fields downstream of a spinning sphere were also studied (some parts will be studied) using a time-resolved stereoscopic PIV system. The field-of-view was perpendicular to the incoming flow to capture the three velocity components in the yz plane (x is the streamwise direction). Preliminary measurements found the flow around the spinning golf ball changed significantly, and there appeared to be several critical velocity ratios at Vs/U =1.0, 2.0 and 3.0. The drag of the sphere increased when Vs/U increased from 1.0 to 2.0, and plateaued when Vs/U increased from 2.0 to 3.0; the drag then decreased graduated when Vs/U increased from 3.0 to 6.0. Snapshot Proper Orthogonal Decomposition of the flow field measured downstream of the spinning golf ball suggested a high frequency mode emerged in cases Vs/U>3.0 that may link to the transition of the boundary layer on advancing side. The large scale structures in the turbulent boundary layer were shed downstream in the streamwise direction reducing drag force. More detailed discussion of the changes in the drag and boundary layer state will be presented in the final paper.


Keywords


rorating sphere, lift and drag, separation

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