Simulation And Analysis Of The Cavitation Characteristics About The Internal Flow Of The Centrifugal Pump

Centrifugal pump is one of the mostly frequently used fluid machineries. It has been widely used in various important sectors of national economy, such as energy, traffic,agriculture, and even our daily life. With the development of the technology of centrifugal pumps, its impact becomes larger and larger. Cavitation is a phenomenon of unsteady compressible turbulent flow, and a mass exchange between gas phase and liquid phase. It is the main factor affecting the performance and efficiency of pumps. Therefore, the efficiency improvement of centrifugal pumps will definitely reduce the pressure of demand for energies.For this reason, the numerical simulation and analysis of cavitation characteristics for internal flow of centrifugal pumps have a significant meaning in improving their performance and efficiency and saving energy.On the basis of the commonly used 3D modeling software UG NX and flow simulation software ANSYS CFX, the following works were done and the following conclusions were obtained through centrifugal pump modeling and numerical simulation of cavitation:1. The impeller of the centrifugal pump was three-dimensionally modeled, and the tetrahedral unstructured grids of the whole flow passage was divided and generated.2. On the basis of ANSYS-CFX, the cavitation characteristics of internal gas-liquid two-phase flow were numerically simulated under different flow conditions(0.8Q, 1.0Q, and1.2Q). The influence of turbulent flow was considered by using the RNG k-ε turbulence model. The influence of air bubbles was considered by adopting the homogeneous multiphase model and the Rayleigh-Plesset equation. Furthermore, the development of cavitation and the distribution of bubble volume fraction distribution on the blade surface with different NPSHa were analyzed. The results indicate that the location of cavitation development on the blade surface and the volume distribution of cavitation bubbles can qualitatively reflect the generation and development of cavitation flow in centrifugal pumps. Cavitation firstly appears at the inlet near the back of the blade. As the pressure reduces, cavitation develops toward the middle part, and the volume distribution of bubbles continually expands. When the cavitation is severe, air bubbles almost occupy the whole blade surface, block the passage,and break the continuity of flow. Finally, the performance of the pump decreases, the head decreases and cavitation happens.3. The locations of cavitation are corresponding to the low pressure area, but the highest volume fraction of bubbles is slightly behind the lowest pressure spot at the blade inlet.4. With the help of CFX-POST, the head, torque, efficiency, and other characteristic parameters of the pump were calculated, and the cavitation characteristic curve, and the head,efficiency-output pressure curve were made. The results were compared with the experimental results(under the design condition), to verify the accuracy of CFX.