| The development of low head and ultra-low head hydraulic resources in inland and coastal areas makes low head and large flow tubular turbine widely used.Due to the short diversion pipe of tubular turbine,it is affected by different forms of wave flow in reservoir area.When water flows through the tubular turbine from the reservoir,the wave force brought by wave flow fluctuation and the unstable flow in the turbine superimpose on each other,which has a severe influence on the safe and stable operation of the unit.Based on this,in the case of free liquid level and water gravity,this research adopts the inlet wave generation method to numerically generate second-order Stokes and micro-amplitude waves respectively in reservoir area,and carries out the unsteady numerical study on the real machine of tubular turbine under the dynamic change of liquid level.The transient flow characteristics and frequency amplitude characteristics of water pressure pulsation in tubular turbine under the combined effect of different liquid level fluctuations and water gravity are studied,and the propagation law of liquid level fluctuation characteristics in turbine and its influence on the inherent transient flow and water pressure pulsation in unit are discussed.(1)Firstly,the prototype performance of tubular turbine is studied when the reservoir level is static and fluctuating,respectively.By comparing the internal flow characteristics of the turbine with or without liquid level fluctuation,it can be seen that:wave flow acting on the tubular turbine causes the complicated fluid flow in the turbinet,and the radial component of absolute velocity increases while the axial component decreases.Compared with condition without fluctuation,the pressure increases to a greater extent,the low-pressure area in the center of the tailpipe increases,the stepped pressure distribution shows different curve distribution,and the cavitation erosion is more obvious.(2)According to the velocity inlet wave generation method,the evolution law of the internal flow characteristics of tubular turbine under two wave forms of second-order Stokes wave and micro-amplitude wave is studied.The research results show that:under different guide vane openings and flow rates,the pressure imposed on each flow component of the unit increases obviously due to different wave flows and decreases gradually along the fluid moving direction.The influence of second-order Stokes wave is greater than that of micro-amplitude wave.(3)Finally,the pressure pulsation characteristics of the unit under two wave currents are compared and analyzed.The analysis shows that the top and bottom pressures on different flow components are basically the same.Under the joint action of wave current and runner,each flow component is subject to two pressure pulsation periodic changes,the wave current gradually decreases with the passage of the position,and the trend of pressure pulsation periodic change decreases.At the same time,different wave currents cause different pressure pulsation of main flow components under different working conditions,which leads to unstable operation of tubular units,increased unsafe factors,shorter maintenance cycle,and higher operating costs. |
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