Oscillating Flow over Bluff Bodies in a U-Shaped Water Tunnel,
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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The studies deal with sinusoidally oscillating separated and unseparated flows over various types of bluff bodies. First, the characteristics of a large U-shaped vertical water tunnel are described and then the numerical and experimental results obtained with circular cylinders are presented. It is shown that for two-dimensional, attached, and laminar-flow conditions the data are, as expected, in good agreement with the Stokes Wang analysis. The oscillatory viscous flow becomes unstable to axially periodic Taylor-Goertler vortices above a critical Keulegan-Carpenter number K K U sub mTD for a given Beta Beta D squpsilon T. For larger values of K the effects of separation and vortex shedding become increasingly important, eventually leading to a very interesting half Karman vortex street in the transverse direction in the range 8 K 13. The discrete vortex model of the separated oscillating flow is shown to provide a reasonably satisfactory explanation of the transverse vortex street. An attempt is also made, through use of an idealized vortex model, to explain the observed flow modes and the cycle-to-cycle variations in forces and pressures in terms of their sensitivity to small stochastic variations in the position of the vortices.
- Fluid Mechanics