Reynolds number effects on the flow over a twisted cylinder

We investigated the Reynolds number (Re) effects on the flow statics over a helically twisted elliptical (HTE) cylinder in the range of 3 x 10(3) <= Re <= 1 x 10(4) using large eddy simulation. For comparison, a smooth cylinder was also considered. The present flow statistics for the smooth cylinder are quite consistent with previous findings at Reynolds numbers of Re = 3900/4000 and 10 000 that were obtained by combining particle image velocimetry measurements and direct numerical simulations [Dong et al., "A combined direct numerical simulation-particle image velocity study of the turbulent near wake," J. Fluid Mech. 569, 185-207 (2006)]. The mean drag and root mean square (RMS) lift coefficients had almost linear relations with Re. The HTE geometry showed more effective performance for the reduction of the drag and the RMS lift coefficients with increasing Re. The RMS streamwise velocity for the HTE cylinder appeared different from that of the smooth cylinder. The HTE cylinder lacked RMS streamwise velocity behind the cylinder base, indicating small magnitudes of the fluctuations. In general, the tip of the mean vorticity layer for the HTE cylinder is thinner than that for the smooth cylinder. The thickness of mean vorticity layer depends on the spanwise direction rather than Re. Also, the tips of contours of the Reynolds stress are much sharper with increasing Re and approach the separation position of the cylinder surface. The elongated vortex formation length decreases almost linearly with Re. Published under license by AIP Publishing.