The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine

Abstract

Over the last years, several breakdowns in hydropower plants with low specific speed Francis runners have been reported. One of the main excitation forces in such runners is the pressure fluctuations originating from the rotor stator interaction. In this paper, the rotor-stator interaction has been analyzed utilizing pressure sensors onboard the runner. The pressure sensors were flush mounted in the hub of the runner and the signals were transmitted through a slip-ring system. The measurements have been analyzed relative to the runner angular position by utilizing an angular position sensor mounted to the shaft end. Measurements with different guide vane angle have been compared in order to study the potential flow interaction and the viscous wake effects for the pressure inside the runner. The results from the onboard pressure measurements found that the phase of the guide vane passing pressure seen by the onboard pressure sensors was independent of the guide vane opening. Hence, the potential flow interaction was found to be the dominant effect and no evidence from the viscous wake effect was found on the onboard pressure.

An Analytical quasi 2D steady-state Francis turbine model using first principles

“…𝑉𝑉 𝑚𝑚 = 𝑑𝑑 𝑠𝑠𝑠𝑠𝑠𝑠 𝛽𝛽 (10) Finding the relative velocity W is key to unlocking the velocity component necessary for completing the outlet integral from the AME equation, and as we have seen this has been found using the differential Eq. 3, which used information regarding the angle β.…”

“…For the inlet CS, which is a cylindrical shell at constant radii, the rotor stator interaction and the potential flow effect of the guide vanes will give a periodicity of the magnitude of the Vθ component [10]. However, let us for simplicity assume that the Vθ is constant everywhere.…”

Calculation of Pressure Pulsations in the Flow Part of the First Stage of an Axial Turbine in the Rotor-Stator Interaction Zone

“…An unsteady flow, pressure pulsations and dynamic loads in a radial-axial turbine [6,7] and in an autonomous turbine with a partial supply [8] are investigated. In recent years, considerable attention has been paid to unsteady structural loads due to pressure pulsations arising in the rotor-stator zone, which can be responsible for the destruction of rotor blades [9,10]. CFD-CAA methods are used to analyse the effect of the clearance between the blades of a lowpressure turbine on noise generated as a result of the rotor-stator interaction [11].…”