Frequencies in the Vibration Induced by the Rotor Stator Interaction in a Centrifugal Pump Turbine

Abstract

The highest vibration levels in large pump turbines are, in general, originated in the rotor stator interaction (RSI). This vibration has specific characteristics that can be clearly observed in the frequency domain: harmonics of the moving blade passing frequency and a particular relationship among their amplitudes. It is valuable for the design and condition monitoring to count on these characteristics. A CFD model is an appropriate tool to determine the force and its characteristics. However, it is time consuming and needs highly qualified human resources while usually these results are needed immediately and in situ. Then, it is useful to determine these characteristics in a simple, quick, and accurate method. At present, the most suitable method indicates a large amount of possible harmonics to appear, without indicating the relative importance of them. This paper carries out a theoretical analysis to predict and explain in a qualitative way these frequencies and amplitudes. The theoretical analysis incorporates the number of blades, the number of guide vanes, the RSI nonuniform fluid force, and the sequence of interaction. This analysis is compared with the method currently in use, and both methods are applied to a practical case. The theoretical analysis gives a resulting force over the pump turbine, which corresponds well to the measured behavior of a pump turbine in terms of its frequencies and the relationship between their amplitudes. A corrective action is proposed as a result of the analysis and after it is carried out in one of the units, the vibration levels are reduced. The vibration induced by the RSI is predicted considering the sequence of interaction and different amplitudes in the interactions between the same moving blade and different stationary blades, giving a different and original interpretation about the source of the vibration characteristics. A successful corrective action is proposed as a consequence of this new interpretation.

Failure investigation of a large pump-turbine runner

“…The main excitation force for this type of machine comes from the pressure fluctuation induced by the rotor-stator interaction (RSI) [3][4][5]. The RSI arises from the interference between the rotating blades of the runner and the stationary vanes.…”

Investigation on Vibration Characteristics in a Centrifugal Pump with Special Slope Volute

“…At low flow rates, especially, the separate flow structure may transfer from one blade channel to the adjacent channel forming rotating stall phenomenon [10]. In centrifugal pump, flow out of impeller interacts with volute tongue periodically due to the limited blade number [11]. Rotor-stator interaction between impeller and volute tongue would cause pressure pulsating and nonuniform flow field distribution on periphery of impeller.…”

Numerical Investigation of Periodically Unsteady Pressure Field in a High Power Centrifugal Diffuser Pump

“…The phase-averaged velocity field, turbulence field and the blade orientation effects were quantitatively examined in detail. Some other research works [10][11][12][13][14][15][16][17][18][19][20] can be also found for the study of pressure fluctuation caused by periodical unsteady flow in centrifugal pumps. In reality, especially in some high risk applications in which the stability of centrifugal pump is the most important, the circular casing structure has been adopted to increase the reliability of overall structure of the high power pump.…”