Hydraulic Optimization Design Of Two-way Counter-rotating Axial Flow Pump Turbine For Tidal Power Station

As a renewable energy source,tidal energy is efficient and clean.It can be developed and applied on a large scale.The two-way operation mode of the tidal unit can provide relatively continuous power,with strong grid adaptability and adjustable peak operation.However,the efficiency of the tidal unit is particularly low when it is pumped in reverse operation.The counter-rotating unit has higher efficiency,more compact structure,more stable performance curve and better cavitation resistance.If the counter-rotating technology is applied to the tidal power station,it is expected to be able to more effectively improve the performance of the unit's pumping conditions on the basis of giving full play to the advantages of power generation,and provide more potential energy for the next generation.Counter-rotating technology is widely used in wind turbines,and is still rare in the field of pumps and turbines.Its hydrodynamic design and structural design are still immature.The counter-rotating mechanism has a strong interference and the internal flow is complicated.Applying it to the tidal unit,under the premise of realizing the forward and reverse power generation and the basic functions of forward and reverse pumping,it has important engineering significance and academic value to improve the performance of the various working conditions.In this paper,the hydraulic optimization design of the two-way counter-rotating axial flow pump turbine of the tidal power station is carried out.The performance of the twoway counter-rotating axial-flow pump-turbine is studied by the combination of theoretical analysis and hydraulic optimization design and calculation.The variable speed and stability of the counter-rotating impeller are summarized and analyzed.The performance variation law of counter-rotating axial flow tidal unit under variable speed is explored,which provides theoretical support for the subsequent development of tidal power station unit power generation mode.The main research contents and conclusions are as follows:1.Two common counter-rotating unit structures for tidal power stations were constructed,and the hydraulic design of two-way counter-rotating axial-flow pump turbines with "S" shaped blades was constructed.Through the calculation and analysis of the influence of the gap between different impeller stages on the performance of the unit,the variation of the head and efficiency of the unit under different interstage clearances is obtained.From the vorticity distribution and the axial section pressure cloud diagram analysis,the influence of the interstage gap on the unit is summarized,and the range of the interstage gap is determined.2.The airfoil placement angle and interstage clearance are used as optimization parameters,and the quadratic regression orthogonal combination test design method is used to optimize.A significant test was performed on the optimized regression model,and single factor effect analysis and two-factor effect analysis were performed.The method of improving the performance of the unit from the aspects of changing single factor and double factor is summarized.3.Through the variable conversion direct optimization method to find the optimal solution for each working condition;With the critical value of each working condition as the condition,the value of each working condition factor is determined in the region where the frequency is high by frequency analysis and statistical optimization.A statistical screening of all the listed optimization schemes is carried out,and a set of optimization schemes in which the comprehensive performance of each working condition is optimized is obtained.4.By analyzing the performance changes of the two-wheels under the conditions of the first-stage impeller and the secondary impeller,the power of the first-stage impeller and the secondary impeller under the same speed are revealed.The first stage impeller variable speed and the secondary impeller variable speed are analyzed respectively for the pump working condition and the turbine working condition,and the radial force changes of the first stage impeller and the secondary impeller are analyzed.The matching speed of the two-stage impeller power operation is obtained,and the variation law of the radial force of the first stage impeller and the secondary impeller under variable speed is revealed.