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Fifth International Symposium on Turbulence and Shear Flow Phenomena
August, 27-29, 2007, Technische Universität München, Munich, Germany

DOI: 10.1615/TSFP5

DNS AND PIV STUDY OF THE 3D WAKE BEHIND TAPERED CIRCULAR CYLINDERS

pages 667-672
DOI: 10.1615/TSFP5.1040
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Краткое описание

Three-dimensional wake behind a tapered circular cylinder has been studied at low-Reynolds number (transition in the wake regime) by performing Direct Numerical Simulation (DNS) and at higher Reynolds numbers (transition in the shear-layer regime) by Particle Image Velocimetry (PIV). The taper ratio (75) was constant in both the studies. In the PIV study it was found that increase in aspect ratio increases the number of shedding cells along the span, an effect also reported by Piccirillo and Van Atta (J. Fluid Mech., 1993). Both mode A and mode B were found to coexist in the same geometry (DNS) but only in a small span of the cylinder. Flow-visualization revealed that the mode A appeared around Re ~ 200 and mode B around Re ~ 250. Cross-sectional views of mode B in the DNS results revealed the smaller-scale 'mushroom' vortex pair structures, which is remarkably similar to those found by Williamson (J. Fluid Mech., 1996). The wavelength of mode B was found to be λZ/D ~ 1, which is surprisingly close to the experimental value λZ/D = 0.98 found by Williamson (J. Fluid Mech., 1996) in the uniform circular cylinder wake. In the present DNS study it was found that streamwise vorticity ωx becomes large as vortex dislocation occurs, an effect also observed by Piccirillo and Van Atta (J. Fluid Mech., 1993).

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