Experimental investigation of hydrodynamic damping during bending oscillations of blade profiles in water flow

Abstract

The vibration reliability of hydroturbine blades operating in water flow conditions largely determines their ability to dissipate energy during oscillations. Important factors are hydrodynamic damping, which can exceed the structural damping by several orders of magnitude and the energy dissipation in the blade material. Experimental investigations with wide and independent variations in the dimensionless parameters governing the oscillatory processes were conducted to determine the damping in bending oscillations of blade profiles in water flow. The flow angle of attack and geometrical parameters of the lattice remained unchanged. The experiment was performed on the GD-1 facility at the Academy of Sciences of the Ukrainian SSR. The experimental procedure is described. Results show that the hydrodynamic damping of profile oscillations does depend on the profile solidity. Analysis of the data shows that the variation in hydrodynamic damping due to variation in profile solidity does not depend on the Strouhal number, but is determined only by variation in the relative profile thickness: one reason for reduction in the hydrodynamic damping with increase in profile solidity is that a more solid profile is less sensitive to variation of angle of attack.