CAJ | 학술논문

水泵水轮机转轮叶片低压边相比其他部位更具有空蚀的危险性。首先基于低比转速混流式转轮设计程序，设计了3种具有不同厚度的叶片，厚度差异主要在叶片低压边位置；然后采用数值模拟方法对3种翼型转轮分别进行了3个不同出力的水轮机工况以及3个不同流量的水泵工况的全流道定常数值计算，对比分析了各计算工况下具有不同叶片低压边厚度的转轮的空化形态及流动特征；最后采用有限元方法对转轮叶片强度进行了校核。研究表明：3种叶片低压边厚度分布规律的转轮均满足强度要求。空化性能方面，水轮机42%出力工况下，翼型2转轮不发生空化；88%出力工况、100%出力工况和水泵大流量工况下，随着叶片低压边的厚度的增大，空化越剧烈；水泵小流量工况与设计工况下，转轮的空化程度并不因低压边厚度的增大而加剧，而是水泵设计工况下，低压边厚度相对最大的翼型3叶片头部绕流平顺，空化性能相对较好，其他2种翼型由于头部出现脱流和漩涡，出现严重空化。
수빙수륜궤전륜협편저압변상비기타부위경구유공식적위험성。수선기우저비전속혼류식전륜설계정서，설계료3충구유불동후도적협편，후도차이주요재협편저압변위치；연후채용수치모의방법대3충익형전륜분별진행료3개불동출력적수륜궤공황이급3개불동류량적수빙공황적전류도정상수치계산，대비분석료각계산공황하구유불동협편저압변후도적전륜적공화형태급류동특정；최후채용유한원방법대전륜협편강도진행료교핵。연구표명：3충협편저압변후도분포규률적전륜균만족강도요구。공화성능방면，수륜궤42%출력공황하，익형2전륜불발생공화；88%출력공황、100%출력공황화수빙대류량공황하，수착협편저압변적후도적증대，공화월극렬；수빙소류량공황여설계공황하，전륜적공화정도병불인저압변후도적증대이가극，이시수빙설계공황하，저압변후도상대최대적익형3협편두부요류평순，공화성능상대교호，기타2충익형유우두부출현탈류화선와，출현엄중공화。
Because flow separation of blade entrance region and low pressure area are located in the inlet of runner at pump mode, and the low pressure of blade at turbine mode usually occurs in the outlet of runner, the low pressure edges of runner are more risks of cavitation compared with other parts for pump-turbine. In this research, first of all, a two-order polynomial was proposed to describe the blade setting angle distribution law along the meridional streamline in the streamline equation. The runner was designed by the point-to-point integration method with a specific blade setting angle distribution with a consideration of the working condition of turbine and the working condition of pump by adjusting the blade setting angle of heading-edge and trailing-edge. Three blades with different thickness distributions of the low pressure edge were obtained in this method. The main difference was located in the relative chord length 0.8-1.0 position. Secondly, in order to analyze and evaluate the performance of designed runners, structured meshes were adopted to describe the geometries such as scroll case, stay vanes, guide vanes, runner and draft tube. Base on Reynolds Averaged Navier Stokes (RANS) equation, steady state numerical simulations of the Francis pump turbine at three turbine operations with different outputs and at three pump operations with different discharges were completed. The computational boundary conditions were applied at the inlet and outlet surfaces of the computational domain. For the inlet boundary condition, the uniform velocity distribution was assumed. As for the outlet boundary condition, the average pressure was set to constant. For the surface of a wall, the non-slip boundary conditions was prescribed, the velocity components were set to zero. Furthermore, for the interaction of the flow between a stator and rotor passage, Frozen Rotor interfaces were used. Comparisons of cavitation morphology and flow characteristics between runners with different thickness distributions of low pressure edge were analyzed. Finally, the finite element method was employed for checking the strength of runner blades, and the maximum equivalent stress values and positions of runner blades were confirmed. The research results showed that the strengths of three kinds of hydrofoil met the design requirement. For cavitation performance, airfoil 2 cavitation did not occur at 42% output operational condition. However, at 88% output, and 100% output and large discharge pump conditions, cavitation became more intense with the increase of the thickness distribution of low pressure edge of runner. At small discharge and design conditions, cavitation was not more intense with the increase of the thickness of low pressure edge of runner. Under the pump design condition, the airfoil3 with the largest thickness distribution of low pressure edge had the better cavitation performance due to the flow around the head of blade was smoothly compared to the other two airfoil runners which had severe cavitation as result of flow separation and vortices.