Analysis And Control Of Tip Clearance Flow Characteristics Of Three-dimensional Hydrofoil

Because of the clearance between impeller rotor and outer edge wall,clearance leakage inevitably occurs in axial flow hydraulic machinery,which will reduce the efficiency and stability of the unit,and cause press.ure fluctuation and cavitation.Because of the complexity of the flow field structure of the axial-flow h,ydraulic machinery,the numerical simulation of tip clearance flow characteristics and cleararnce leakage control is carried out from a simple three-dimensional hydrofoil.The main contents include:(1)The numerical results of tip clearance leakage flow under different turbulence models are compared with the experimental results.It is found that the curvature-modified SST-CC model has some advantages in predicting the length of tip clearance leakage vortices and is in good agreement with the experimental results.The position and three-dimensional structure of the vortex core under different vorticity identification criteria are discussed.The Q criterion is consistent with the lambda2 criterion,which can captur’e the vortices of the gap flow better.(2)By analyzing the leakage flow field in different geometries and working conditions,it is found that there are mainly leakage vortices,separation vortices and induced vortices,and there are some differences in different clearance flow fields.The right-angle airfoil has more distinct separated vortex structure than the round-angle airfoil,especially in the case of large clearance,the blocking effect is stronger and the leakage is lower.Similarly,the structure of clearance vortices varies with different clearance widths.The existence of clearance widths makes the strength of leakage vortices maximum and the possibility of cavitation maximum.In addition,the angle of attack of airfoil is an importan.t factor that causes the pressure difference change on the front and back surfaces of airfoil.The trajectory and intensity of leakage vortices change with it,and there exists a suitable angle of attack to maximize lift-drag ratio.At different flow velocities,the gap leakage and the inlet flow basically keep the same proportion,and the development of leakage vortices is faster when the velocity is small.(3)Discussions on gap leakage control are carried out based on groove shape,groove position and trailing edge inclination angle,groove depth and width.Compared with the C-groove,the rectangular groove can significantly reduce the leakage volume and the strength of leakage vortices under the condition of small clearance,and the suppression effect is stronger.Taking rectangular groove as an example,the optimal grooving scheme is obtained.