Study On Characteristics Of The Blade Tip Leakage Of The Bulb Tubular Turbine

Tubular turbine is an important hydraulic machinery and equipment for the development of ocean tidal energy.With the development of clean and renewable energy in China,people pay more and more attention to the performance optimization of tubular turbine,so that it can operate efficiently in a wider range of working conditions.In tubular turbines,the tip leakage at the tip of the blade has always been an important factor affecting the flow pattern inside the runner.The tip leakage vortex formed from the tip leakage will cause flow instability on the suction surface of the blade,and the resulting cavitation will cause blade vibration.Therefore,it is necessary to study the influence of tip leakage on the internal flow field and the performance of tubular turbine.In this paper,through numerical simulation methods,many flow characteristics of tip leakage and tip leakage vortex are studied.At the same time,its influence on the internal flow of the tubular turbine is analyzed.Related work is as follows:(1)In the tubular turbine,affected by the wake of the water guide mechanism and the rotation of the blade,the tip leakage and tip leakage vortex at the tip of the blade are complicated and variable.In order to improve the accuracy of numerical simulation,this paper uses a rotation and curvature correction based on the eddy viscosity model firstly numerically simulated the gap flow field of a single foil to verify the accuracy of the eddy viscosity model.The study found that the increase in the angle of attack will have an impact on the location,shape,tip leakage,load near the blade tip,and airfoil lift resistance of the tip leakage vortex and tip separation vortex.Aiming at the special situation of the tip leakage flow field at high angle of attack,this paper analyzes in detail the variation rule of the tip leakage at a large angle of attack of 12°.The velocity and pressure distribution near the gap are obtained.The results show that at 12° angle of attack,the axial velocity and vorticity of the vortex core will decrease significantly as the gap decreases.In the case of small gap,the flow field near the gap shows strong instability along the flow direction.(2)The numerical simulation of the foil tip leakage vortex verifies the accuracy of the vortex-viscosity model based on the rotation and curvature correction.At the same time,the relevant conclusions can provide a reference for the research of the tip leakage of the tubular turbine.In the study of the tip leakage vortex at the tip clearance of a tubular turbine,the blade placement angle was fixed,and the influence of different guide vane openings on the tip leakage was analyzed.The results show that as the guide vane opening increases,the water inlet angle of the runner continuously decreases.Under this influence,the tip leakage vortex generation position moves from the head of the blade to the middle position of the blade tip.The low-pressure area on the suction surface is also moved backwards due to the tip leakage vortex.At the same time,the study also compared the difference between the tip leakage vortex,tip separation vortex and the load near the blade tip under the gap of 0.5mm and 2mm.Similar to the result of the foil,the increase in the gap makes the tip leakage vortex closer to the suction surface.The analysis of the pressure pulsation near the blade tip shows that the amplitude of the pressure pulsation in the area affected by the tip leakage vortex will increase.The amplitude of the main frequency of pressure pulsation on the shroud of the runner increases and then decreases along the axial direction.The energy loss in the runner is mainly concentrated near the tip leakage vortex,and the closer to the vortex core,the greater the loss intensity.(3)The influence of tip leakage on the internal flow of the draft tube was analyzed.Two situations were selected:the optimal working condition and the partial working condition,and the pressure and velocity distribution of the draft tube inlet section and the variation of the draft tube vortex band were analyzed and compared.At the same time,the vortex zone of the draft tube changes from cylindrical to spiral along the axial direction.This change reduces the main frequency of pressure pulsation near the draft tube axis from 3 times the axial frequency to less than 1 time the axial frequency.Affected by the tip leakage,the amplitude of the pressure pulsation near the wall surface of the draft tube inlet increases significantly.The amplitude of pressure pulsation on the draft tube wall gradually weakens from the inlet along the axial direction.Under partial operating conditions,the amplitude of pressure pulsation is larger than that under optimal operating conditions.