Cavitation is a common phenomenon in pump industries, which leads to severe problems, like vibration and noise. It may degrade the pump performance and even damage the solid surface. So it is significant to give a precise prediction of the pump cavitation performance. The original k-ε model is widely used in the past years. However, it is reported that high viscosity of the original k-ε model dampens cavitation instabilities and hence makes it difficult to capture the detachment of the bubbles. Aiming at improving the predictive capability, the partiallyaveraged Navier-Stokes (PANS) is employed in this paper to predict the pump cavitation performance. Experiments on a centrifulgal pump with twisted blades are carried out to validate the simulations. The results show that, compared with the original k-ε model, the PANS model with lower f k value gives a more accurate prediction and can reduce the eddy viscosity in the cavity region, leading to capturing the unsteady bubble shedding phenomenon. The experimental visualizations are performed and the evolution of the cavitation inception and development are obtained exactly at the impeller inlet. Comparisons with the transient numerical simulations are made, which demonstrates the PANS model can successfully capture the cavitation detachment. Finally, the blade load pressure, the pressure distribution in impeller and the pressure fluctuations are analyzed. Good agreement is noticed between simulations and experiment. So it can be concluded that the PANS model can effectively reduce eddy viscosity in cavitating flow in centrifugal pumps and improve the numerical simulation prediction of pump cavitation performance.
Purpose
– The purpose of this paper is to study the unsteady caivitating flows in centrifugal pump, especially for improving the turbulence model to obtain highly resolution results-capable of predicting the cavitation inception, shedding off and collapse procedures.
Design/methodology/approach
– Both numerical simulations and experimental visualizations were performed in the present paper. An improved RCD turbulence models was proposed by considering three corrected methods: the rotating corrected method, the compressible corrected method and the turbulent viscosity corrected method. Unsteady RANS computations were conducted to compare with the experiments.
Findings
– The comparison of pump cavitation performance showed that the RCD turbulence model obtained better performance both in non-cavitation and cavitation conditions. The visualization of the cavitation evolution was recorded to validate the unsteady simulations. Good agreement was noticed between calculations and visualizations. It is indicated the RCD model can successfully capture the bubbles detachment and collapse at the rear of the cavity region, since it effectively reduces the eddy viscosity in the multiphase region of liquid and vapor. Furthermore, the eddy viscosity, the instantaneous pressure and density distribution were investigated. The effectiveness of the compressibility was found. Meanwhile, the influence of the rotating corrected method on prediction was explored. It is found that the RCD model solved more unsteady flow characteristics.
Originality/value
– The current work presented a turbulence model which was much more suitable for predicting the cavitating flow in centrifugal pump.
In order to save energy by broadening its application range, the influence of impeller trim on the performance of a twostage self-priming centrifugal pump was numerically studied. The hydraulic performance experiments and self-priming experiments were carried out. And the unsteady performance of pressure fluctuation and radial force in the pump was analyzed. The results show that with the increase in impeller trim quantity, the best efficiency point of the pump would move to the small flow rate condition. Under the design flow rate, when both the two stages of the impeller were trimmed by 6%, head of the pump was reduced by 13%, efficiency of the pump was as well decreased by 1.69 percentage points, and self-priming time was increased by 1.7%. Thus, impeller trim can be used to meet the operating requirements in the head range of 94-107 m. With the increase in impellers trim quantity, the pressure fluctuation in the positive channel of the radial guide vane and the volute was smaller, while the radial force on the wall of radial guide vane and volute was also smaller.
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