Numerical investigation of the added mass effect of submerged blade disk structures: From simplified models to Francis turbine runners

Abstract

In daily operations, there are lots of blade disk structures operating in water, e.g., hydraulic turbines and pumps, whose dynamic behavior may be severely affected by the added mass effect. Their mode shape change problem from vacuum to water due to the added mass effect has been studied in this paper. The added mass effect of simplified blade disk structures submerged in still water has been studied numerically first in this paper. Acoustic fluid–structure interaction technology has been used to simulate the fluid and structure coupling effect. Through comparing the strain energy percentage of the disk part in water with those in air under different disk material densities, it showed that different parts of the submerged blade disk structures can suffer from different average added mass factors, which makes the modal shapes of some modes with strong blade disk interactions change a lot from vacuum to water, thus produces a large influence on the optimal design of submerged blade disk structures. Based on the conclusions of the simplified model, the situation of a Francis turbine runner model was investigated, and the results fit the conclusions on the simplified model very well.

Keywords

• Added mass effect
• Blade disk structures
• Acoustic fluid-structure interaction
• Natural frequency
• Mode shape
• Francis turbine