Experimental investigation on the effect off near walls on the eigen frequency of a low specific speed francis runner

• Published in: Mechanical systems and signal processing Vol. 118; pp. 757 - 766
• Main Authors: Østby, Petter T.K., Sivertsen, Kjell, Billdal, Jan Tore, Haugen, Bjørn
• Format: Journal Article
• Language: English
• Published: Berlin Elsevier Ltd 01-03-2019; Elsevier BV
• Subjects: Added mass; Eigenvalues; Fluid dynamics; Fluid-structure interaction; Francis runner; Housing; Microelectromechanical systems; Modal testing; Nearby walls; Number theory; Resonant frequencies; Turbines; Walls; Water tanks; Modal testing; Added mass; Francis runner; Nearby walls; Fluid-structure interaction
• ISSN: 0888-3270; 1096-1216
• DOI: 10.1016/j.ymssp.2018.08.060

•Modal test of low specific speed Francis Runner.•Three different environments; air, water and water filled turbine housing.•Traveling wave excitation to differentiate mode shapes and nodal diameters.•40% frequency reduction of main modes in water.•Installed into turbine housing changes damping more than eigen frequencies.
The importance to correctly predict the natural frequency of a turbine runner have been demonstrated several times. It is now common practice to include the added mass effect of the surrounding water when calculating the natural frequencies. In this paper the added mass effect of water on a simplified low specific speed francis turbine runner is experimentally investigated. Three cases are investigated. 1: The runner hanging in air. 2: The runner hanging in a tank of water. 3: The runner installed into the turbine housing. The measurements reveal a frequency reduction of about 40% when the runner is hanging in water. Installing the runner into the turbine housing does not significantly change the natural frequency of the main blade modes. Modes which vibrate heavily on the outside of the runner are visible in the water tank but becomes dampened when installed into the turbine housing.