Research On The Transient Flow Characteristics Of High-power Hydrodynamic Coupling Under Dynamic Speed Regulation

The high-power hydrodynamic coupling driving device is an important speed control and energy saving equipment for thermal power station and nuclear power station by virtue of its superior speed regulation,energy saving effect and good transmission performance,and its applications gradually expands to metallurgy,petrochemical and many other fields.With the increasing capacity of generator set,the input speed and power of the hydrodynamic coupling greatly increase,and the internal flow is in an extremely complex transient state of gas-liquid two phase flow.The transient effect caused by the internal flow leads to the capacity reduction,instability of the external characteristics,the serious heat and so on,which seriously affects the safe and stable operation of the generator set.Currently,the research on the transient flow field of hydrodynamic coupling in China is limited to velocity,pressure distribution and gas-liquid two-phase distribution of flow under steady conditions,and the analysis objects are mainly moderate or small power hydrodynamic couplings.The phenomenon makes it hard to accurately grasp the flow characteristics of high-power hydrodynamic couplings in transient conditions,which limits the application and development of hydraulic speed regulation in the high-power transmission field.In this paper,YOCQ510 high-power hydrodynamic coupling is chosen as the research object,gas-liquid two-phase transient flow characteristics of high-power hydrodynamic coupling under the dynamic speed conditions are calculated with CFD numerical method,and the validity of the calculation was verified by the internal and external characteristics of synchronous test.The work of this paper provides the necessary theoretical basis for the development of the independent products of high-power hydrodynamic coupling.The main research works and conclusions are as follows:1.Numerical method for gas-liquid two phase transient flow of high-powerhydrodynamic couplingBased on the characteristics of internal flow,certain regions of the channel are encrypted properly,and the thickness of boundary layer is determined through the calculation.Meanwhile,considering the accuracy and economy of the calculation,several grid models are divided and the effects of the quality/quantity of different grids on the numerical results are analyzed;The hybrid RANS/LES method and VOF two-phase flow model are selected to simulate the flow,and results show that the simulation method can better predict the circulation law of high-power hydrodynamic coupling,and have higher numerical accuracy;By writing the UDF program,the motion law of the gas-liquid two phase flow during the dynamic process of the output speed of high-power hydrodynamic coupling is simulated.2.The influence of Reynolds number on the characteristics of turbulent transient flowTaking the pump input speed as the breakthrough point,which is the key parameter affecting Reynolds number,the influence of Reynolds number on the transient flow of a hydrodynamic coupling under dynamic speed regulation is studied.With the increase of Reynolds number,the flow structure of hydrodynamic coupling changes significantly,and the turbulence intensity of internal flow of pump wheel is obviously higher than that of the turbine.Because of the influence of gas phase,the flow near two-phase junction fluctuate greatly.Meanwhile,combined with dynamic cyclic flow process of gas-liquid two phase fluid under dynamic speed regulation with high pump input speed,the flow law of the high-power hydrodynamic coupling can be better grasped.3.Analysis of transient flow characteristics of high-power hydrodynamic couplingWhen the Reynolds number is high,according to the gas-liquid two-phase distribution and the circulation state of the coupling,taking the inlet and outlet of the pump/turbine and the suction surface/pressure surface as the main analysis area,the transient characteristics of the flow of high-power hydrodynamic coupling under dynamic speed regulation are studied.The results show that the distribution ofturbulent kinetic energy and turbulent energy dissipation tends to be consistent in the mainstream of the hydrodynamic coupling,and the suction surface at the inlet of the pump blades is the most intense turbulent dissipation area;Friction loss near the blades is more serious than that of the wall,and there is a regional extreme value near the turbine inlet,especially when the slip ratio is large.4.Research on synchronous test of internal/external characteristics of hydrodynamic couplingThe synchronous test rig for internal/external characteristics is built,and test schemes are established accordingly.The torque characteristics of the pump and turbine of four groups liquid filled rates(q=60%,q=70%,q=80%,q=90%)under different speed ratio conditions are collected,and through comparison,the experimental results and the numerical results are in good agreement.Meanwhile,through the visualization test of PIV,the flow images under dynamic speed regulation conditions are processed,and compared with the numerical results,the validity of numerical calculation of the flow under dynamic speed regulation process is verified.