水車吸出し管内に発生する渦心の挙動について

Abstract

The vibration in the draft tube of a water turbine becomes most severe when the turbine is running near one-half of its normal load. This is caused principally by the eccentric vortex core rotating around the center of the draft tube. This paper describes the results of a theoretical investigation of frequency and force of the periodic vibration caused by the eccentric vortex core. The vortex core can be stable and is concentric with the draft tube when the radius ratio of the core to the draft tube is less than 0.577. When the ratio grows beyond 0.577,the vortex core becomes unstable and takes an eccentric position about the tube axis. The eccentricity of the vortex core can not be determined theoretically and its magnitude is estimated on the basis of the experimental results obtained from a model draft tube. The vortex core is seen to rotate about the tube axis and to move along the boundary layer of the draft tube wall.