Study On The Influence Of The Shaft Inclination Angle Of The Guide Vane On The Performance Of Tidal Bidirectional Tubular Turbine

As a kind of abundant clean and renewable energy,tidal energy has been paid more and more attention.The bidirectional tubular turbine is the first choice for tidal energy exploitation.At present,most of the research on bidirectional tubular turbine is focused on the runner,while the research on the movable guide vane is relatively few,and the research on the shaft inclination angle of the guide vane is very scarce.The shaft inclination angle of the guide vane is the included angle between the center axis of guide vane and the center line of the main shaft of hydraulic turbine.This paper adopts the method of numerical simulation to study the influence of the shaft inclination angle of the guide vane on the performance of tidal bidirectional tubular turbine,and compares and analyzes the positive and reverse energy performance,internal flow field structure and pressure pulsation characteristics of the turbine under different shaft inclination angle in the guide vane.The main research contents and results are as follows:(1)The positive and reverse operating conditions of the tubular turbine under different shaft inclination angle in the guide vane were simulated under the optimal operating conditions and low flow conditions(0.8Q110),and the variation rule of external characteristic parameters and the distribution of internal flow field characteristics of the tubular turbine were obtained.From the external characteristic parameters,it can be seen that the turbine efficiency under the optimal positive and reverse conditions increases first and then decreases with the increase of the shaft inclination angle in the guide vane.The change of internal flow field characteristics is analyzed emphatically,including blade surface pressure,axial force,radial force and inlet and outlet axial surface velocity,etc.In addition,the flow line and vortex structure distribution of the draft tube in the positive working condition and intake in the reverse working condition were analyzed.(2)In order to better measure the influence of the shaft inclination angle of the guide vane on the hydraulic loss of each flow component,the entropy generation theory was used to analyze the location,magnitude and type of entropy generation of each flow components under different working conditions.By comparing the entropy generation loss with the traditional hydraulic loss,it is found that the entropy generation loss is in good agreement with the traditional hydraulic loss,and the overall trend of change is consistent.The calculation results show that the shaft inclination angle of the guide vane has the greatest influence on the entropy production of the draft tube in the positive working condition and the intake in the reverse working condition.The energy loss in the whole flow passage is the least when the shaft inclination angle of the guide vane is 85 degrees.With the increase of the shaft inclination angle of the guide vane,the local entropy production rate on the back of the runner blade and each section of the draft tube decreases gradually in the positive working condition,and the local entropy production rate on each section of the intake also decreases gradually in the reverse working condition.(3)In order to explore the influence of the shaft inclination angle of the guide vane on the internal pressure pulsation in the flow field,pressure monitoring points were set in each flow component to obtain the pressure pulsation of each flow component under different shaft inclination angle of the guide.According to the calculation results,the pressure at each monitoring point in the reverse working condition and the positive low flow working condition(0.8Q110)is low-frequency pressure pulsation.In the positive optimal working condition,more complex low-frequency pressure pulsation is likely to occur when the shaft inclination angle of the guide vane is 65 degrees.At 85 degrees,the amplitude of pressure pulsation of each flow component under different working conditions is generally low.