VORTEX SHEDDING FROM A RING IN TURBULENT-FLOW

Vortex shedding from a bluff ring in turbulent flow has been investigated experimentally. The shedding frequency, measured using a hot wire placed within the near wake of the ring, was found to be only weakly dependent on the characteristics of the upstream turbulence. For turbulent length scales of the same order as the cross-stream width of the annular section of the ring, the shedding frequency increases monotonically with turbulence intensity (u'/U) to a value, at u'/U=0.14, some 5% greater than in uniform flow. In contrast, for much larger length scales, the increase in shedding frequency is much smaller, although the circumferential coherence of the shedding process is very much weaker than in smooth flow or in turbulence with much smaller length scales. The implication of these results is that vortex flowmeters constructed using a ring as the shedding body, rather than the more usual body shapes which span the pipe diameter, may be relatively unaffected by changes in the turbulence structure of the upstream flow.