This paper deals with the CFD analysis of cavitating flow in the mixed-flow pump with the specific speed of 1.64 which suffers from a high level of noise and vibrations close to the optimal flow coefficient. The ANSYS CFX package has been used to solve URANS equations together with the Rayleigh-Plesset model and the SST-SAS turbulence model has been employed to capture highly unsteady phenomena inside the pump. The CFD analysis has provided a good picture of the cavitation structures inside the pump and their dynamics for a wide range of flow coefficients and NPSH values. Cavitation instabilities were detected at 70% of the optimal flow coefficient close to the NPSH3 value (NPSH3 is the net positive suction head required for the 3% drop of the total head of the pump).

This article presents results of the experimental research and numerical simulations of the flow in a pumping system’s discharge object with the welded siphon. The laboratory simplified model was used in the study. Two stationary flow regimes characterized by different volume flow rates and water level heights have been chosen. The study concentrates mainly on the regions below and behind the siphon outlet. The mathematical modelling using advanced turbulence models has been performed. The free-surface flow has been carried out by means of the volume-of-fluid method. The experimental results obtained by the particle image velocimetry method have been used for the mathematical model validation. The evolution and interactions of main flow structures are analyzed using visualizations and the spectral analysis. The presented results show a good agreement of the measured and calculated complex flow topology and give a deep insight into the flow structures below and behind the siphon outlet. The presented methodology and results can increase the applicability and reliability of the numerical tools used for the design of the pump and turbine stations and their optimization with respect to the efficiency, lifetime and environmental demands.

No abstract

This paper presents the numerical analysis of flow in the pumping station including the influence of free water level in the suction and discharge objects. The suction object is based on a draft tube. Two solutions of the discharge objects (with the overflow walls and with the welded siphon) are compared so as to optimize the efficiency and start-up of the station. All calculations are based on the ANSYS CFX software with the SAS-SST and the DES scale resolving simulations. The numerical solution of the free-surface flow is carried out by means of the Volume-of-Fluid method. Calculations of flow inside one complete pump station passage provide a good picture of the distribution of water velocities and the corresponding heights of water level in front of the suction draft tube, above the overflow wall crown as well as inside and behind the siphon during the start-up. The calculations are verified with some experiments carried out in the hydraulic laboratory of the Centre of Hydraulic Research. Conclusions show the higher overall efficiency of the station with the siphon-based discharge objects but also indicate some special requirements for the start-up of this station.