Search

Intense pressure pulsation, resulted from the flow structure shedding from the blade trailing edge and its interaction with the volute tongue and the casing, is detrimental to the stable operation of centrifugal pumps. In the present study, unsteady pressure pulsation signals at different positions of the volute casing are extracted using high response pressure transducers at flow rate of 0–1.55ΦN. Emphasis is laid upon the influence of measuring position and operating condition on pressure pulsation characteristics, and components at the blade passing frequency fBPF and root-mean-square (RMS) values in 0–20.66fn frequency band are mainly analyzed. Results clearly show that the predominant components in pressure spectra always locate at fBPF. The varying trends versus flow rate of components at fBPF differ significantly for different points, and it is considered to be associated with the corresponding flow structures at particular positions of the volute casing. At the near-tongue region, high pressure amplitudes occur at the position of θ = 36 deg, namely the point at the after tongue region. For different measuring points, angular distributions of amplitudes at fBPF and RMS values in 0–20.66fn frequency band are not consistent and affected significantly by the pump operating conditions.

Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.

The three-dimensional turbulent flow around plate cascades in staggered is an important factor to induce hydro-mechanical vibration. Taking the upstream three plates in side-by-side configuration and the downstream single plate in tandem configuration to form the overall staggered layout of the cascades as the subject of investigation. Based on the Large-Eddy-Simulations (LES), the forces experienced by the plates, velocity distributions and three-dimensional vortex structures around the plates are analysed in detail. Some experiments were also carried out to validate the accuracy of the numerical results by LDA measurement. The mean velocity distributions from LES results agree fairly well with the experimental results. Results show that the existence of the downstream plate hinders the development of the upstream wake and has a significant inhibitory effect on the forces experienced by the upstream plates; When the gap spacing is smaller, the stream-wise length of the reverse flow region between the upstream and downstream plate becomes larger, and the minimum velocity in this region is lower than other reverse flow regions; The flow around the plate cascades exhibits high three-dimensional characteristics, and the amplitude of the fluctuation of the forces on the downstream plate under the interference of the upstream wakes is increased obviously. The downstream plate is located in the wake of the upstream cascade, and has a steady flow to the upstream wake. Analysis on the flow can provide theoretical support for the flow control in hydraulic machinery.