Turbulent Flow Around Rectangular Cylinders With Different Streamwise Aspect Ratios

Abstract

Turbulent flows around a square cylinder and a rectangular cylinder with a streamwise aspect ratio (length-to-height) of 5 in a uniform flow were investigated using time-resolved particle image velocimetry (TR-PIV). The Reynolds number based on the cylinder height and oncoming flow velocity was 16,200. Similarities and differences in the flow dynamics over the cylinders and in the near-wake region were examined in terms of the mean flow, drag coefficient, Reynolds stresses, and triple velocity correlations. The budget of turbulent kinetic energy (TKE) as well as temporal and spectral analyses was also performed. The results show that the primary, secondary, and wake vortexes are smaller for the square cylinder compared to the large aspect ratio cylinder. There are regions of elevated Reynolds stresses and triple velocity correlations along the mean separating streamlines, and the magnitudes of these statistics are an order of magnitude higher over the square cylinder compared to the large aspect ratio cylinder. The topology of the triple velocity correlations shows low-speed ejection and high-speed sweep events, respectively, transporting instantaneous Reynolds normal stresses away from the mean separating streamline into the freestream and toward the cylinder surface, regardless of aspect ratio. Near the leading and trailing edges of both cylinders, regions of negative turbulence production are observed, and the dominant components contributing to this occurrence are discussed. Temporal autocorrelation coefficients of the streamwise and vertical velocity fluctuations show a periodic trend, with a periodicity that is directly linked to the Kármán shedding frequency and its second harmonic.