Research On The Steady-state And Transient Characteristics Of Hydraulic Dynamometer Using CFD

Hydraulic dynamometer is widely used in the power performance testing of high-speed motors,engines,turbines and other power equipment due to their simple structure,low price,stable and reliable operation.With the continuous development of high-speed performance of power equipment,the transient startup characteristics of power equipment during the startup process have become the focus of attention.Hydraulic dynamometer is used as the load equipment of power equipment,and its transient startup characteristics have been critical for the performance test of power equipment.Early research scholars focused on the overall structure,steady-state characteristics and control system of hydraulic dynamometers.There are relatively few studies on the transient loading characteristics of hydraulic dynamometers.This paper uses three-dimensional computational fluid dynamics(CFD)to systematically study the steady-state and transient flow laws inside the hydraulic dynamometer,and analyze the influence of the stator and rotor structure on the external characteristic curve of the dynamometer.On the basis of it,the factors affecting the transient start-up characteristics of the hydraulic dynamometer are further studied,and the differences between the transient start-up process characteristics and the steady-state characteristics are compared.The specific research contents are as follows:(1)A complete flow model of the hydraulic dynamometer was established.The steady-state operating conditions of the hydraulic dynamometer are numerically simulated,and the steadystate external characteristic curve is compared with the test data.The result shows that the simulation result is highly consistent with the test result,which proves that the simulation result is highly reliable and effective.(2)According to the steady-state working condition of constant speed,the flow law inside the hydraulic dynamometer is deeply studied through the speed cloud diagrams and pressure cloud diagrams at different cross-sections.In addition,the influence of the stator and rotor structure on the flow characteristics of the hydraulic dynamometer is studied from the angle of the blade angle and the number of rotor blades.The results show that when the number of stator blades is 15 and the number of rotor blades is 15,the power machine has a large absorption torque.In addition,the angle between the stator and rotor blades is 45°,and the absorption torque of the hydraulic dynamometer is the largest.(3)On the basis of steady-state simulation,study the transient starting characteristics of hydraulic dynamometer.Comparing the transient startup(loading)process of the hydraulic dynamometer with the steady-state loading process,the results show that the transient startup process of the hydraulic dynamometer will cause the hysteresis of the internal flow field state.In the initial stage of startup,this transient effect of the flow field state hysteresis is more obvious.Further research on the factors affecting the transient start-up characteristics of the hydraulic dynamometer from the perspective of loading law and blade structure is studied and the results show that the absorption torque at the initial stage of transient startup is mainly affected by the startup acceleration.The greater the startup acceleration,the greater the absorption torque at the initial stage of the startup.In the middle and late stages of transient startup,the absorption torque is mainly affected by the state of the flow field.The longer the loading time,the weaker the flow field hysteresis and the greater the absorption torque.At the same time,it was found that the larger the blade angle at the initial stage of startup,the lower the absorption torque;in the middle and late stages,the blade with an angle of 45° absorbs the larger torque.When the number of rotor blades is 17,there is larger absorption torque and smaller oscillation amplitude during transient startup process with good load characteristics.