Numerical And Experimental Investigation Of Twin-screw Hydraulic Turbine To High Pressure Surplus Energy Recovery

Hydraulic turbine is a kind of energy recovery device which can recycle the kinetic energy and pressure energy of liquid efficiently.In recent years,with the development of technology and the deepening of the research,hydraulic turbine is gradually applied in industrial process.In general,different types of hydraulic turbine have different application ranges,such as single stage pump as turbine is just applicable to low head,high flow rate conditions.For high head and small flow rate condition,there is not yet a hydraulic turbine with mature technology can take into long-term use,thus we need to study and solve it as quickly as possible.As a kind of positive displacement energy recovery device,twin-screw hydraulic turbine can completely response to high head,small flow operation condition.And it is characterized by smooth medium conveying,low pressure pulsation and noise,being not sensitive to working medium,etc.Based on a single suction twin-screw pump as turbine in this research,the internal flow field,unsteady dynamic characteristics,recovery efficiency of it were studied by using the combining method of structure design,theoretical analysis,numerical simulation and experimental research.In this paper,the main work and creative research results are as follows:1.The research status of turbine at home and abroad are summarized in detail and the existing problems of hydraulic turbine in present study are pointed out in this paper,putting forward the development trend and direction of the hydraulic turbine.Combined with the advantages of twin-screw hydraulic turbine,the effect of energy recovery which it can reach under high head and small flow conditions,social and economic benefits which can be generated are introduced in this paper.2.Comparing the existing screw rotor profiles,type A twin-screw profile is optimal to choose and studied.Then this paper puts forward the basic structure of twin-screw hydraulic turbine,determining the master-slave screw assembly and transmission mode.On the basis of above, the twin-screw hydraulic turbine basic theory of external characteristic,energy recovery mechanism and theory of leakage are analyzed.3.The paper used CFD numerical simulation for the first time to complete the internal flow field research of twin-screw hydraulic turbine,revealing the distribution law of pressure field,velocity field and periodic variation characteristics of radial force,axial force,torque and the flow rate in one revolution.Energy recovery characteristics of twin-screw hydraulic turbine under different inlet pressure and rotation speed are analyzed in numerical simulation in application of CFD technology.It investigated the variation characteristics of external characteristic parameters such as flow rate,efficiency and pressure distribution,clearance leakage flow rate influenced by factors such as inlet pressure,rotation speed.We can obtain the changing rule with inlet pressure of hydraulic turbine under different rotation speed.4.CFD numerical simulation was used for the first time to study the structural parameters' impact on recovery efficiency,leakage,torque,axial force and radial force of screws,including the impact of lead Angle(envelope)to screw torque,force and efficiency as well as the impact of different radial clearance and center distance to the leakage loss and efficiency of the hydraulic turbine,etc.The results of the study can provide reference for the determination of size in lead,radial gap and teeth gap in the process of the hydraulic turbine design.5.Experimental research under different working condition of inlet pressure and rotational speed were completed by using the test system of hydraulic turbine to high pressure surplus energy which was developed independently,revealing the change characteristics of turbine experimental efficiency.Compared experimental data and simulation results,this paper analyzed the possible reasons of their differences and put forward the ways and methods to improve the efficiency of turbine recovery.6.Counting the data of numerical simulation results of monitoring points in radial clearance which have different screw axial position,the paper analyzed the formation process of pressure pulsation in time domain and frequency domain of these monitoring points.Combined the screw surface pressure distribution under the specific time,it pointed out the reasons of the change characteristics.