Research On Cavitating Flow In Axial-Flow Pump

The cavitation phenomenon exists widely in many domains with liquid transporting process. The occurrence of cavitation will decrease the performance of conveying machinery and cause cavitation erosion, lead to additional vibration. The uncontrollable cavitation will cause serious or even disastrous consequences. The study of cavitating flow belongs to categories of multidiscipline crossing. Revealing the mechanism of cavitation and then controlling the degree of cavitation effectively are the urgent need for academy and engineering. At present, researches on the cavitation two-phase flow theory are still on exploration road, especially in the internal field of hydraulic machinery. Under the support of National Natural Science Fund (No.50776040), the self-designed model axial-flow pump is adopted as the study object. Systematic study on cavitation evolution and cavitating flow mechanism in model pump has been done. The major works and achievements are as following.1. Based on the basic theories of cavitating flow in hydraulic machinery, detailed descriptions about influencing factors of cavitation and methods of cavitation monitoring and positioning were given. The idea of using Thomas-coefficient and combination research methods of vibration and photograph to study the cavitating flow in axial-flow pump was put forward.2. Combined with the analysis of flow mechanism in axial-flow pump, the nature of variable circulation design was discussed. The formula of distribution coefficient about outlet circulation meeting pump energy performance was derived. The axial-flow pump was designed with above method. The validity of design was verified by pump performance tests.3. According to comparative analysis of calculation results of four turbulence models, the adaptive simulation model of cavitating flow in axial-flow pump was determined. Based on conformed method, the three-dimensional steady turbulent cavitating flow in the pump was simulated. The preliminary study on location and evolution law of cavitation was carried out. The influence of cavitation on pump performance and erosion was alos given. The structure and features of cavitating flow through blade tip clearance was revealed.4. The details of unsteady cavitating flow under different cavitation coefficient were captured and measured by using high speed imaging and image processing technology. The time and space characteristics of cavitating flow in different stages were obtained. A judging basis for detecting pump’s cirtical cavitation point was proposed form perspective of cavitation shape. The lifecycle of incipient cavitation, distributation of vortex cavitation, occurrence region of cavitation were obtained. The variation characteristic of cavitating flow in the pump was basically grasped.5. The suitable measurement and analysis methods of vibration signal were proposed. The vibration induced by hydraulic factors was measured by using LMS sound&vibration measurement. The vibration characteristics of model pump under different situations were analysised and the relationship between vibration and pump running condition was approximately masted. The judging methods of best efficiency point and cavitation degrees of the pump were proposed. The research results provide an effective reference for safe operation of pump.Research achievements and methods form this paper can be extended and applied on study of cavitating flow in other types of hydraulic machinery.