The Effects of the Downstream Vane on the Torsional Vibration of the Upstream Vane

Some hydraulic turbines sometimes have severe flow-induced vibrations on their vanes. One is the torsional vibration of the stay vane. This vibration occurred despite the stay vane profile was selected to avoid generating large Karman vortex. This vibration was influenced by the guide vane. In this paper, the effects of the attack angle of the downstream vane on the torsional vibration of the upstream vane were examined by about 1/20 scale stay vane experimental equipment. First, the relationships between the attack angle of vanes and the limit of the reduced flow velocity inducing the torsional vibration of the upstream vane were examined. The large torsional vibration of the upstream vane did not occurred without downstream vane. But, the large torsional vibration occurred when the reduced flow velocity exceeds a critical value with the downstream vane. It was substantiated the limit of the reduced flow velocities were 1.5 and 3.0. The large vibration was only generated under a specific velocity range. The dominant torsional vibration frequency slightly increased from 35Hz to 45Hz with the reduced flow velocity. When the attack angle of the upstream vane and the downstream vane were series along streamline, the vibration became large. Next, the torque coefficient and Strouhal number of the upstream vane were evaluated. The torque coefficient for the upstream vane attack angle with the downstream vane was positive. This result showed the upstream vane will occur. And, Strouhal number was 0.35 at the reduced flow velocity 3.0. Strouhal number is near to 0.3 which is result of the previous study of stay vane. There is a possible of the generating vortex.