Study On The Flow Characteristics Of Tubular Turbine With The Anti-cavitation Edge Of Blade

Tubular turbine is an important hydraulic equipment for the development of ocean tidal energy.As my country attaches great importance to the development of clean and renewable energy,people are paying more and more attention to the performance optimization of tubular turbines to enable them to operate efficiently under a wider range of working conditions.The gap leakage flow at the tip of the blade is an important factor that affects the internal flow of the tubular turbine runner.The gap leakage vortex formed by it will cause flow instability on the suction surface of the blade.Cavitation caused by the gap leakage vortex can also cause blade wear.In this paper,numerical simulation methods are used to study the influence of anti-cavitation edges with different thicknesses under different working conditions on the internal flow of the tubular turbine and the flow characteristics of the gap leakage vortex.The related work content is as follows:(1)Numerical calculation method is used to calculate the flow field of the tubular turbine model before and after the skirt is added.The results show that:the existence of the anti-cavitation edge has little effect on the pressure of the blade head section,but the gap pressure on the other cross-sections all increase.At the same time,the anti-cavitation edge can reduce the pressure difference between the two sides of the gap,which is beneficial to reduce the leakage of the gap and reduce the strength of the leakage vortex.The anti-cavitation edge has a certain diversion effect to reduce the high pressure area caused by fluid accumulation on the pressure surface of the blade.The addition of anti-cavitation edges can improve the flow separation phenomenon on the suction surface of the blade.The water inlet side of the blade is easily affected by the leakage vortex.After installing the anti-cavitation edge,the streamlines of the water inlet edge are evenly distributed,especially the 3mm thickness anti-cavitation edge model has the most significant improvement.The leakage vortex is pushed away from the suction surface by the anti-cavitation edge.After installing the anti-cavitation edge,the high-speed jet flow and the gap separation vortex overflow in the gap on the middle section of the runner are significantly improved.the runner are significantly improved.Affected by leakage vortex,small vortex bundles appear on the inner side of the anti-cavitation edge,and the track length of the small vortex bundles gradually becomes longer as the thickness of the anti-cavitation edge increases.The influence range of the leakage vortex formed on the blade head is reduced after the anti-cavitation edge is installed.The axial velocity in the gap from the starting point of the anti-cavitation edge to the end point is smaller with the anti-cavitation edge model,and the leakage phenomenon is improved most obviously near the starting point of the anti-cavitation edge.The addition of anti-cavitation edges reduces the peak volume of cavitation and improves the cavitation performance of the runner.The regions are concentrated near the gap leakage vortex and gap separation vortex,and the closer to the vortex core,the higher the loss.The improvement effect of the anti-cavitation edge on the leakage vortex continues to the draft tube,and the leakage vortex in the draft tube is significantly reduced after the anti-cavitation edge is installed.(2)Under partial conditions,the flow separation phenomenon of the model without anti-cavitation edge still exists.When the thickness of the anti-cavitation edge increases to 3mm and 4mm,the flow separation phenomenon almost disappears,and the area near the water inlet edge of the blade that is affected by the leakage vortex is also significantly improved.Compared with the optimal working conditions,the effect of anti-cavitation and reducing leakage is more significant.As the opening of the guide vane increases,the phenomenon of high-speed jet overflow in the gap is improved,resulting in a decrease in jet driving force,which in turn makes the leakage vortex gradually approach the gap separation vortex in the non-cavitation-resistant edge model,and finally merge,increasing the tip flow field.After installing the anti-cavitation edge,the leakage vortex is difficult to approach the separation vortex due to the physical push of the anti-cavitation edge;the clearance separation vortex becomes more serious as the opening of the guide vane increases;the effect of anti-cavitation edge to reduce leakage also becomes stable with the increase of guide vane opening.The increase of the guide vane opening limits the development of leakage vortex.The fusion phenomenon of the gap separation vortex and the leakage vortex is significantly reduced after the anti-cavitation edge is installed.The loss coefficient of the runner decreases with the increase of the guide vane opening,and the loss coefficient of the anti-cavitation edge model is reduced,and the loss coefficient of the 4mm thickness skirt model is always the smallest.