Experimental investigation of the nonlinear pressure fluctuations in a residual heat removal pump

Residual Heat Removal Pumps have very strict requirements to maintain nuclear power plant safety and therefore unsteady pump operations are very critical in determining system reliability. The operational stability has however been affected by pressure pulsations that are induced by rotor-stator interactions. A pressure measurement test was undertaken to investigate the nonlinear pressure fluctuation characteristics at angular and axial positions within the annular volute wall. Diametric mode and bispectrum analysis were subsequently applied to reveal the dominant frequencies of the pressure pulsations induced at the stationary parts, and also to analyze the nonlinear frequencies in the frequency domain due to the impeller-diffuser and diffuser-volute interactions. The pressure pulsations on the volute wall were significantly affected not only by the flow rate, but also by the sensors’ position. The highest amplitude was observed at a frequency that was four-fold the blade-passing frequency at a diameter mode of 1. When the flow rate increased, the amplitude of the high harmonics of the blade-passing frequency increased, whereas the amplitudes of the blade-passing and shaft rotating frequencies decreased. In the axial direction, flow rate greatly influenced the propagation of pressure fluctuations whose dominant frequency are blade-passing frequency, vane-passing frequency and their high harmonics. The spectral domain was dominated by high harmonics of the blade-passing frequency (3St and 4St). Conversely, the circumferential pressure fluctuation was significantly affected by rotor-stator interaction and was independent of flow rate. The study provided sufficient information for further work to reduce pressure pulsations in the residual heat removal pump.