Research On Multi-condition Flow Mechanism In Hydraulic Turbine Based On Gas-liquid Two-phase

With the depletion of fossil energy sources,in addition to the development of new energy sources,the existing energy sources must be used effectively.The main measure is to increase the utilization of existing energy sources.The pressure energy carried by the high-temperature and high-pressure fluids produced in the petrochemical and other production fields is often decompressed by a pressure reducing valve or directly discharged into the environment.This not only causes waste of energy,increases production costs,but also inconsistent with the sustainable development strategy proposed by the country.The use of hydraulic turbines can be very good recovery of this part of the energy,improve energy efficiency,reduce production costs and improve the competitiveness of enterprises.In practice,high-pressure liquids in the petrochemical and synthetic ammonia industries that are recovered by hydraulic turbines often contain a certain amount of gas.The presence of gas will lead to a reduction in the energy recovery rate of hydraulic turbines,and the stability of the unit is deteriorating,vibration and noise often occur,and even affect the life of the turbine.However,there are few reports on the research of hydraulic turbines in gas-bearing conditions.At present,the main problems in the study of hydraulic turbines under gas-liquid two-phase conditions are as follows: First,the basic equations of the hydraulic turbine under the existing gas-liquid two-phase conditions have not been considered about the compressibility of the gas.Second,it is not mature to grasp the internal flow mechanism of hydraulic turbine under gas-liquid two-phase condition.Thirdly,the hydraulic performance of the hydraulic turbine is poor under gas-liquid two-phase conditions.Based on this,this paper will first improve the basic equations of the hydraulic turbine under gas-liquid two-phase conditions,and then use the method of flow field calculation and theoretical analysis to study the flow mechanism inside the hydraulic turbine under the conditions of gas-liquid two-phase.At the same time,the influence of the guide vanes on the internal flow mechanism of the hydraulic turbine is analyzed.Through the above research results,it provides a theoretical basis for the theoretical basis of engineering practice and the research of the hydraulic turbine under the following multi-phase conditions.The main research contents and achievements of this article are as follows:(1)Improvement of the basic equations for hydraulic turbines under gas-liquid two-phase conditionsThere are two-phase velocity separation and gas compressibility under the gas-liquid two-phase condition.The basic equations of the hydraulic turbine under the existing gas-liquid two-phase condition do not consider the compressibility of the gas.In this paper,based on the basic equations of the hydraulic turbine under pure liquid conditions,the basic principle of energy conversion and conservation is taken into account by considering the compressibility of gas,and using Euler's equation and impeller's inlet and outlet speed triangles,the basic equations of hydraulic turbine are further improved.It is found that in the large flow area,the efficiency decreases as the gas content increases,and the gas content has the greatest impact on the hydraulic loss in the impeller.(2)Research on internal flow mechanism of hydraulic turbine under gas-liquid two-phase conditionsUsing a numerical calculation method,a centrifugal pump reverse-rotating hydraulic turbine with a 55.7 specific speed was studied under different flow rates and different gas-bearing ratios,and the gas-bearing rate was analyzed for the external characteristics of the hydraulic turbine and the internal flow field of each flow-through component.The law of influence,through the study obtained in the gas-liquid two-phase conditions of the external characteristics of the hydraulic turbine,the flow characteristics of the two-phase media in the flow components,the flow rate in different gas rates(speed,pressure)Distribution law and hydraulic loss characteristics.As the gas content increases,the flow in the impeller becomes unstable and vortices appear,and the gas volume distribution in the impeller changes faster.(3)The effect of guide vanes on the internal flow mechanism of hydraulic turbines under gas-liquid two-phase conditionsA hydraulic model with guide vanes was designed by adding a set of vanes at the inlet of the hydraulic turbine impeller.To study the effect of guide vanes on the external characteristics of hydraulic turbines and the flow field in each flow-through part under conditions of gas-bearing conditions,and compare them with the external characteristics of hydraulic turbines without guide vanes,internal flow field,and hydraulic losses.The results show that the pressure distribution and gas distribution in the spiral casing before the addition of guide vanes are not uniform,and the higher the gas content is,the worse the homogeneity is.The internal flow is more turbulent and some vortex areas has formed.With the addition of guide vanes,the pressure distribution in the impeller is also very uniform under higher gas-bearing conditions.The uneven distribution of gas and the flow of the mixed medium are all improved,the hydraulic loss is reduced,and the efficiency of the optimal efficiency point is improved.It is obviously higher than the efficiency value of the optimal efficiency point of the non-added vane.However,with the increase of gas-bearing rate,the efficiency of hydraulic turbines with guide vanes is faster than that of turbine turbines with no vanes added.It shows that adding guide vanes can not only improve the internal flow of hydraulic turbine under the conditions of gas-liquid two-phase,reduce hydraulic loss,but also improve the efficiency of hydraulic turbine and the stability during operation.