Analysis Of Flow Characteristics And Dynamics Of Tubular Turbine Based On Fluid-structure Interaction

Bulb tubular unit is widely used in low head and large flow hydropower station.Its flow path is straight,large flow,little hydraulic loss and less investment in construction.The special structure of bulb tubular unit has some influence on the stability of the unit,which makes the influence of the vibration on the running quality of the bulb tubular unit more severe than that of the other type.Due to the limitation of the bulb ratio,the rotary inertia of the tubular turbine is small,so the hydraulic vibration of the hydraulic turbine has a great influence on the stability of the unit.The bulb turbine has a wide range of operation,the internal flow of runner and the dynamic characteristics of runner structure are different in different flow conditions,therefore,it is of guiding significance to study the internal flow of turbine and dynamic characteristics of runner structure under partial working conditions.In this paper,commercial ANSYS software is used to simulate ten different flow conditions of a tubular turbine in a power station.In order to reveal the influence of flow rate on the flow characteristics of the runner,and the influence of flow rate on the dynamic characteristics of the runner based on the one-way fluid solid coupling calculation method.The main content of this paper is divided into the following aspects:First of all,the constant numerical simulation of the single cycle of the flow conditions is carried out,and the flow pattern and the pressure of the runner are studied.The results show that because of the wide running range of the cross flow turbine,the flow of water to the blade head appears outside the bypass except the small flow rate,the overall flow field distribution of the runner is more uniform.Influenced by the flow around the head,the pressure near the inlet of the blade of the small flow condition is greater,the pressure of the blade suction surface is smaller,and the region is located here.The optimum working condition and large flow condition,the pressure in the middle of the blade pressure surface is close to the wheel flange,the suction surface of the blade is in the middle of the blade,and the pressure near the flange hub is lower.Secondly,unsteady numerical simulation of flow conditions is conducted to investigate the characteristics of blade pressure pulsation with variable flow rate.The study shows that the small flow condition of each monitoring point of blade surface pressure fluctuation amplitude is smaller and relatively little difference;the optimal condition and large flow rate condition,blade inlet pressure fluctuation at the monitoring points of the relatively large amplitude.The amplitude of each pressure pulsation is within 2% of the corresponding water head,and the stability of the runner is better.At the same time,the flow rate has a certain influence on the main frequency of the pressure spectrum.Then,the air and water modes of the runner blades are calculated,and the frequencies of the water modes are compared with the frequencies of various hydraulic excitation sources of the water turbine.The results show that the natural frequencies of the runner blades decrease in different degrees after considering the water body,and the vibration modes are basically the same;at the same time,it is concluded that the rotation frequency of the blade,which plays a major role in the vibration of the blade,is much smaller than the first order natural frequency of the runner blade in water,that is,the main influence of the structure on the flow field is the displacement of the structural deformation.Finally,the response of the runner structure is solved based on the one-dimensional fluid structure coupling method.The results show that the average of the maximum equivalent stress and maximum deformation displacement in leaves in the average minimum flow condition of the average maximum displacement is higher than that of other small flow condition,other conditions with the flow rate increasing.The connecting position between the runner blade and the pivot flange is the stress concentration position of the runner blade,and the deformation displacement of the blade near the flange is the largest,but there is a slight difference in the position of the different flow conditions.