Study On Transient Flow Characteristics Of Tubular Turbine

With the development of medium and high head hydraulic resources tending to be saturated,the development of low head hydraulic resources is imminent.Bulb tubular turbine is widely used because of its superior hydraulic performance and economy.With the development of tubular turbine units to high parameters and large capacity,how to ensure their safe and stable operation has always been a hot research topic.In particular,the study of improving the dynamic quality of tubular turbine in the transition process is the most important.In this paper,several types of transient process of tubular turbine are studied in-depth.The main work is as follows:According to the movement characteristics of the runaway process of tubular turbine,combined with the three-dimensional N-S equation describing the internal flow of the turbine,a numerical calculation method of the runaway process of turbine based on macro continuous model is established by using the secondary development of User Fortran program and CFX software.Three-dimensional transient numerical simulation was carried out on the runaway process of tubular turbine under different combined working conditions.The unit runaway speed characteristic curves obtained under different blade angles were in good agreement with the experimental results.At the same time,the transient law of the working parameters and the dynamic characteristics of the internal flow field of the tubular turbine are studied,and the pressure fluctuation inside the turbine is predicted,and the reason of the abnormal vibration of the unit during the runaway process is revealed.The cavitation model based on Rayleigh-Plesset equation is introduced to study the cavitation characteristics of the tubular turbine during the runaway process.The influence of cavitation on the runaway process is discussed in detail,and the cavitation position of the tubular turbine during the runaway process is captured.In view of the limitations of this method in simulating the dynamic process of tubular turbine including the moving boundary,a lattice Boltzmann method based on particles is introduced and verified by relevant examples.Firstly,the two-dimensional flow around a cylinder at two Reynolds numbers is simulated,and the variation law of the relevant characteristic parameters calculated is in good agreement with the experimental results.Secondly,the energy characteristics and pressure fluctuation characteristics of tubular turbine under steady conditions are predicted,and the comparison with the test results is satisfactory.Finally,the transient simulation of the runaway process of the tubular turbine is completed,and the results of the calculation are in good agreement with those of CFX,which proves the feasibility of the method applied to the three-dimensional flow simulation of the turbine.Based on lattice Boltzmann method,a rigid body dynamic model is introduced to simulate the full shutdown process of tubular turbine during accident load rejection.In the simulation,User Defined Functions is used to control the closing of guide vanes.The variation laws of macro parameters such as turbine speed,water torque and axial force under different guide vane closing modes are compared in detail,and the water pressure variation inside the turbine is quantitatively analyzed,thus obtaining the best closing mode for improving the dynamic quality of load rejection process.In addition,the force characteristics of the guide vane and runner and the transient flow field inside the turbine were studied in detail,revealing the causes of the lateral oscillation of the unit and vortex in the draft tube.A three-dimensional transient numerical simulation method for double regulation load increase and decrease process of tubular turbine is proposed,and the load decrease process of tubular turbine from rated condition to partial load condition is numerically simulated.The variation rules of external characteristic parameters and the variation characteristics of internal pressure of turbine in the load reduction process under three different linkage modes are analyzed and compared.The research shows that the combined closure of guide vanes and blades is beneficial to the operation stability of turbine during the condition conversion process.In addition,the force characteristics of the blades and internal pressure pulsation characteristics during the load increase process are analyzed and discussed.It is found that the amplitude of pressure pulsation in front of and behind the guide vane is larger than that in the process of load reduction,which increases the instability of the turbine operation.