Three-dimensional characteristics and axial flow pattern in the wake flow of an oblique circular cylinder

Abstract

Many circular cylindrical engineering structures submerged in fluid are not always orthogonal to flow direction. Oblique circular cylinder is a more general model to study the flow around circular cylindrical engineering structures. Comparing with a normal circular cylinder, there are more three-dimensional effects reflected in the wake flow and aerodynamic forces of an oblique circular cylinder. Moreover, axial flow is a unique and important flow phenomenon in the oblique circular cylinder wake flow. This study introduces a numerical study based on an oblique circular cylinder model and unsteady Reynolds-Averaged Navier-Stokes equations (URANS) to reveal the three-dimensional external flow and axial flow. Effects of the yaw angles take the most attentions. The analyzed flow features include aerodynamic force coefficients, wake flow velocities, correlations between aerodynamic forces and wake flow structures, three-dimensional vortex structures and three-dimensional axial flow. Spectrum signatures of wake flow fluctuation and time-average axial flow pattern are verified by a visualized wind tunnel experiment. Numerical results prove that there are obvious three-dimensional effects in wake flow velocities and aerodynamic forces. Yaw angle, as a crucial parameter, determines the configuration of vortices. Furthermore, yaw angle affects the spectrum signatures of wake flow fluctuation and aerodynamic force fluctuation, and change the spanwise correlation of wake flow. A novel time-average axial flow velocity-distribution pattern is observed in the numerical results and experiment results. Its mechanism is analyzed based on the wake vortex structures.