Effects of added mass and moments of inertia on hydroelectric turbines for dynamic applications using structural acoustic simulation

Abstract

This paper proposes and evaluate coupled structural acoustic simulation, SAS, as the preferred method to predict the added mass and moments of inertia of turbine runners in hydroelectric applications. The method is briefly described and focus is primarily on highlighting the effects and benefits of SAS in comparison with previously published work (Jasper, 1956; Benkö and Holmén, 1966; Hofstad, 2004). These traditional methods scale the mass and moments of inertia of the runner using rule-of-thumb guidelines with different scaling factors. SAS in comparison can directly be applied on the CAD geometry of the runner and calculate the mass and moments of inertia dependent on its direction of motion (or rotation). Added mass is highly dependent on the geometry of the runner and the enclosing waterway. This is apparent from the SAS calculations which shows that the added mass of a Kaplan runner changes due to runner geometry, runner blade angle, and shape of the enclosing waterway. All of which the traditional methods are incapable of. In addition to describe SAS and its benefits the numerically derived added mass and moments of inertia is included in a rotor dynamic analysis of two examples and the results are compared to those obtained using traditional methods. Parameters important for rotor dynamic analysis, such as the polar moment of inertia and the radial added mass, is in the present example increased with about 300% and 60% respectively, when a Kaplan runner is operated between speed-no-load to full load.This paper highlights the differences between SAS and the traditional empirical methods. It is shown that SAS gives more detailed results than the traditional methods while still being computationally effective. Consequently, SAS is the preferred method of choice for deriving the added properties.