| Most of the centrifugal pumps in engineering practice are used to carry out the power conversion of the forward and reverse characteristics,and in the process of power conversion carried out in forward and reverse,there will be a decline in energy recovery performance and unstable operation usually,the phenomenon.In this paper,based on the research of IS80-50-315 series low speed centrifugal pump reversed for hydraulic turbine,the research is focused on adding diameter guide vane in front of impeller inlet.Orthogonal experiment is used to combine geometric parameters of guide vane and expand the base circle of volute correspondingly and match the same impeller to form a new guide vane hydraulic turbine model.The optimal performance of guide vane hydraulic turbine model is obtained by analyzing extreme difference,which is to study the effect of changes in geometric parameters of guide vane on the internal flow properties of a guide vane hydraulic turbine;In addition,with the continuous development of research on gas-liquid two-phase flow,this paper has performed constant and non-constant numerical calculations on the guide vane hydraulic turbine under gas-liquid two-phase flow conditions.The main work is to study and analyze the effect of gas volume fraction variation on the external characteristics,internal flow pattern,impeller blade load distribution and pressure pulsation of the guide vane type hydraulic turbine to explore the operation rules of internal mixing medium of guide vane hydraulic turbine under the condition of gas-liquid two-phase flow,which can provide theoretical support for the stability and safety of the turbine unit during operation.The main research content of the thesis and its summary are as follows:(1)Sixteen sets of guide vane models were designed using orthogonal tests for different geometrical parameters of the guide vane,and a new guide vane hydraulic turbine model was formed by enlarging the base circle of the volute and matching the same impeller accordingly,and constant and non-constant numerical simulations were performed.The magnitudes of the effects of different geometric parameters of the radial guide vane on the hydraulic efficiency and head of the guide vane hydraulic turbine were obtained by extreme difference analysis as follows: number of blades greater than radial height greater than exit angle,Among them,the number of diameter guide vanes has the greatest influence on the hydraulic efficiency and head of the guide vane hydraulic turbine,so the number models that have the highest hydraulic efficiency and the head are selected to do further study,these numbers including number 1(outlet angle of 6 °,the number of blades for 5,radial height of 46 mm),number 5(outlet angle of 7 °,the number of blades for 5,radial height of 48 mm),number 9(outlet angle of 8 °,the number of blades for 5,radial height of 50 mm),number 13(outlet angle of 9 °,the number of blades for 5,radial height of 52 mm).It is found that the main frequency of pressure pulsation inside the worm casing of the guide vane type hydraulic turbine is the leaf frequency,the secondary main frequency is 5 times the leaf frequency,and the main frequency and secondary main frequency of pressure pulsation at the gap between the guide vane and the impeller are 1times the leaf frequency and 2 times the leaf frequency respectively;As the flow rate increases,the axial force coefficient of the guide vane type hydraulic turbine gradually decreased,and the radial force has shown a pattern of gradually moving away from the zero radial force value,and is symmetrically distributed about the coordinate origin.(2)The four groups of guide vane hydraulic turbine models with the highest hydraulic efficiency and head are set at the inlet with gas content rates of 0.05,0.1,0.15 and 0.2respectively for numerical simulation and external characteristics analysis,it was found that under the same flow condition with the increase of gas content head increases,while the efficiency shows a decreasing trend,and the model with the highest hydraulic efficiency number 1 was selected for the study,it is found that the blade load at the impeller inlet increases with the volume fraction of the gas,and the impeller blade does not do work and impedes the fluid in the inlet side area of the impeller at low flow conditions,the value of the blade load is increased with the increase of the gas content in the area from the inlet diameter to the outlet diameter of the impeller in the optimal and high flow conditions,while the value of the blade load is decreased with the increase of the gas content in the area near the outlet of the impeller;both the axial force coefficient and the radial force combined force of the guide vane type hydraulic turbine have shown periodic changes in one rotation cycle,and at the optimal working condition,with the increase of gas content,the fluctuation interval of radial force gradually was reduced,and the maximum value of radial force when the gas content was 0 was 60.97% larger than the maximum value of radial force when the gas content was 0.5.The amplitude of the main frequency of the combined radial force pulsation of the impeller at the optimal working condition of zero gas volume fraction is 2.07 times of that at 5% gas volume fraction.However,the difference between the main frequency amplitude of pressure pulsation at 0 gas volume fraction and at 20% gas volume fraction is less than 1%.(3)Non-constant numerical simulation of model No.1 under gas-liquid two-phase conditions,it is found that the gas-liquid mixture will separate when flowing through the volute and enter the radial guide vane,with the increase of gas content,the gas-liquid separation phenomenon is more obviously,the gas-liquid mixture in the volute is mainly flowing along the wall of the volute under the action of centrifugal force,and the gas is affected by less centrifugal force and gradually flows away from the outer wall of the volute towards the outlet of the volute under the action of liquid displacement;the vibration amplitude of the pressure coefficient at the monitoring points in the circumferential direction inside the volute of the guide vane type hydraulic turbine under the optimal working condition is the highest at the gas content rate of 0.05,while the vibration amplitude of the pressure coefficient decreases significantly at the gas content rates of 0.1 and 0.15;the vibration amplitude of the pressure coefficient at the monitoring points in the circumferential direction inside the vane-guided hydraulic turbine volute under the optimal operating conditions is the highest at the gas content rate of 0.05,while the vibration amplitude of the pressure coefficient decreases significantly at the gas content rates of 0.1 and 0.15;the amplitude of pressure pulsation at the dynamic and static coupling surface of the guide vane impeller and guide vane is greater than that inside the volute under optimal operating conditions.This is mainly attributed to the effect of static and dynamic interference,the main frequency amplitude of pressure pulsation at monitoring points 6,7 and8 of the static and dynamic coupling surface are maximum at the gas content rate of 0.05,while the main frequency amplitude of pressure pulsation at monitoring point 9 is minimum at the gas content rate of 0.05,the main frequency amplitude of the pressure pulsation at monitoring point 6 at a gas content rate of 0.05 is 1.96 times higher than that at a gas content rate of 0.15,the main frequency amplitude of pressure pulsation at monitoring point 9 at gas content rate of0.05 is 19.15% lower than that at gas content rate of 0.15,Therefore,the pressure pulsation amplitude of the guide vane hydraulic turbine is more stable at the gas content rate of 0.15. |
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