Wavelet analysis of the turbulent wake generated by an inclined circular cylinder

Abstract

Three-dimensional velocity and vorticity characteristics in the near wake of a stationary circular cylinder at an inclination angle α in the range of 0°–45° are analysed using the wavelet multiresolution technique, where α = 0° represents the case of the cylinder in a cross-flow. This study aims to examine the dependence of the velocity and vorticity characteristics at different wavelet levels on α as compared with that obtained at α = 0°. The validity of the independence principle (IP) for vortex shedding was also examined. It was found that the IP is only applicable for α < 45°. The energy spectra for the intermediate and large-scale structures decrease in terms of their maximum energy and disperse extensively over an enlarged frequency band with the increase of α. At α = 45°, the large-scale vortex dislocations may occur because of the increase of the three-dimensionality in the wake region. The consequences of vortex dislocations in the wake region can also be seen from the results of the velocity and vorticity variances and velocity autocorrelation coefficients at wavelet level 7. Although the large-scale structures are the dominant contributors to the Reynolds stresses at all inclination angles and followed by the intermediate-scale structures, the wake vorticity is mostly dominated by the small- and intermediate-scale structures and has the smallest values at large-scale structures.

Keywords:

• inclined cylinder wake
• vortex shedding
• turbulent structures
• turbulent wakes