The effects of turbulence and unsteadiness on vortex shedding from sharp-edged bluff bodies
- Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering
Motivated by a desire to evaluate vortex shedding flow meters for measuring velocity in unsteady turbulent flow applications, the objective of the work was to study the effects of flow disturbances on vortex shedding from sharp-edged bluff bodies. In particular, the combined effects of turbulence and unsteadiness were examined, as well as their separate effects using controlled wind tunnel tests. After causing an initial and sudden decrease in the Strouhal number, increasing turbulence intensity from 2.5 to 10% resulted in only a 2.4% increase in the Strouhal number, for turbulence with a length scale of 0.5 bluff body diameters. Turbulence integral length scale had a significant influence on the Strouhal number, with the greatest effect exhibited for length scales near 3 bluff body diameters. Turbulence of this length scale caused a 26% decrease in the Strouhal number, as compared to a low-turbulence base case. Fluctuating pressure amplitude and signal-to-noise ratio were also affected by turbulence, and decreased significantly when the integral length scale was increased from 0.25 to 0.75 bluff body diameters for a turbulence intensity of 10%. Unsteadiness caused lock-on for forcing at the Strouhal frequency, twice and four times the Strouhal frequency, while no lock-on was observed for forcing at half the Strouhal frequency. The range of lock-on increased with increasing perturbation amplitude and was asymmetric about the resonant frequency. For the cases investigated, the effects of combined turbulence and unsteadiness were additive, with the turbulence shifting the Strouhal frequency, and the unsteadiness causing lock-on about the shifted Strouhal frequency. The results of this study suggest that vortex shedding flow meters should be calibrated in turbulent flows and turbulence length scale must be controlled at the bluff body.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 215411
- Journal Information:
- Journal of Fluids Engineering, Vol. 118, Issue 1; Other Information: PBD: Mar 1996
- Country of Publication:
- United States
- Language:
- English
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