Experimental investigation on clocking effect of vaned diffuser on performance characteristics and pressure pulsations in a centrifugal pump

Clocking effects can generally have a great influence on the operational state of centrifugal pumps. In order to analyze the effects of the positions of the vaned diffuser relative to the annular volute on the performance characteristics and the pressure pulsations of a centrifugal pump, experimental tests were carried out at three different relative positions. Frequency domain and time-frequency domain of the pressure pulsations were obtained using the Welch's power spectral density estimate and the short-time Fourier transform (STFT) methods, respectively. The diameter mode analysis was applied to explain the dominant frequency induced by rotor-stator interaction. The results showed that the centrifugal pump can obtain the highest efficiency when the diffuser was fixed at position A, where the diffuser was rotated 90 degrees in counterclockwise direction from position B. The maximum difference in the efficiency between 0.9Q(d) and 1.1Q(d) was 1.5% under three different diffuser positions. The pressure pulsations in the volute were determined not only by the impeller-diffuser interaction but also by the diffuser-volute interaction. Furthermore, nonlinear frequency existed in the frequency domain of the pressure pulsations at the volute outlet. The relative positions of the diffuser had great effect on the dominant frequency and the amplitudes of the decomposed frequencies of the pressure pulsations. A comparison of the amplitudes of the main frequencies of the pressure pulsations showed that the transient pressure on the volute had the lowest pulsations when the trailing edge of the diffuser reached the left corner of the volute outlet (position B).