Flow field characterization of a rotating cylinder

Direct numerical simulation is used to study the flow field around an infinitely long circular cylinder rotating in fluid with no outer boundary. Wall shear stresses and normal pressure fluctuations are considered with reference to flat, non-rotating geometries to help identify any flow field differences introduced by Coriolis forces. In the present case, Coriolis forces are experienced only by the turbulence field. The dominant effect is to decrease the streamwise turbulent velocity level relative to the other two components. A consequential effect is that the two components of wall shear stress fluctuations become almost equal and spectra for streamwise and spanwise wall shear stress fluctuations become almost identical. This is a distinctly different behaviour from that of non-rotating flat plate and straight pipe flows. Instantaneous wall shear stress fluctuations indicate a near wall flow structure similar to that of other boundary layers with sweeps and ejections. No flow reversals of wall shear stress are indicated. A good correlation of the wall shear stresses and the turbulent kinetic energy exists for y(+) < 10. Budgets of Reynolds normal stress components illustrate the role played by Coriolis forces in the production and redistribution of turbulence energies. Wall pressure fluctuations are found to be of much larger spatial extent than velocity fluctuation scales while the probability density distribution of pressure fluctuations is almost Gaussian but does display a Reynolds number effect for skewness and Kurtosis. The ratio of rms pressure fluctuations to mean streamwise wall shear stress follows closely that for flat plate boundary layer and channel flows. (C) 2008 Elsevier Inc. All rights reserved