Effects of trailing-edge modification of guide vanes on the wake vortices under different inflow conditions

Abstract

Karman vortices forming behind blades or guide vanes may induce severe vibration and noise in hydraulic machinery. To solve these problems, the trailing edge of vanes or blades is usually trimmed as a remedy. However, this type of modification is not always effective. Based on an engineering project, two sides of the tail of an asymmetric guide vane were modified respectively. The influence of the modification on the wake flow under different inflow conditions was studied using numerical simulation. The results show that, for the studied case, a 45°-bevel cut on the side of a vane with larger velocity gradient near the trailing edge can effectively suppress the Karman vortex. However, the effect of trimming on the side with smaller velocity gradient is poor. These two ways of trimming can reduce the amplitude of the vortex-excitation force by 73.6% and 35.4%, respectively. When guide vanes opening or head increases, the trimming effect is weakened. In addition, the inflow angle and velocity magnitude have a significant impact on the wake flow behind a hydrofoil. When the attacking angle decreases from 0° to –5°, the amplitude of the vortex-excitation force doubles. When the attacking angle increases to 5°, the Karman vortex street almost disappears. The strength of the Karman vortex is related to the difference between the velocity gradient on the two sides of a vane. The greater the difference, the more stable the wake flow.