• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2443-2453
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• 1994

The structure of turbulence of fully developed flow through four concentric annuli with the rough outer wall was investigated experimentally for a Reynolds number range Re=15, 000-93, 000. Turbulence intensities were measured in three(u, v, w) directions, and turbulence shear stresses in annuli of radius=0.13, 0.26, 0.4 and 0.56, respectively. Due to the square roughness element attached periodically along the axial direction, the radial velocity fluctuations show similar distribution regardless of the different .alpha.cases. However, the axial and circumferential velocity fluctuation profiles demonstrate the longitudinal turbulence structures are strongly influenced by the .alpha. values. The turbulent eddy viscosity deduced form mean velocity distributions and the measured Reynolds shear stresses are also presented and discussed.

• Journal of Energy Engineering
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• v.11 no.4
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• pp.299-305
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• 2002

The present experimental and numerical investigations are performed on the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully devel-oped flow of water and that of 0.2％ CMC-water solution at a inner cylinder rotational speed of 0∼600 rpm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually decreased for turbulent flow regime.