Simulation and prediction on fluid-gas circulation characteristics of torque limited hydrodynamic coupling

As the hydraulic transmission components, torque limited hydrodynamic coupling regards fluid as the transmission medium, and its gas-liquid two-phase fluid in the chamber works in a complex circulation spiral motion. With the difference of working condition in different filled ratio and speed ratio, gas-liquid two-phase flow presents the different characteristics of combination and distribution law, and it influences the external output performance parameters of the coupling for this reason. Torque limited hydrodynamic coupling's torque limiting function is mainly through the work of changing gas-liquid two phase flows to split the fluid in the working chamber to the front auxiliary oil chamber while the coupling overloads. It is difficult to establish an accurate mathematical model to describe it due to the complexity of its internal gas-liquid two-phase flow. In engineering it is usually through adjusting the flow channel structure parameters repeatedly in the way of the combination of experience design and performance test to meet certain overload and delay start matching requirements, but it is lack of quantitative basis theoretical guidance in design process. In this paper, the three-dimensional transient gas-liquid two-phase flow of torque limited hydrodynamic coupling can be carried on numerical simulation in the way of CFD, and focused on forecasting and analyzing its characteristics of the gas-liquid two-phase flow and its ability of overloading. The torque limited hydrodynamic coupling with front auxiliary oil chamber can be treated as analysis model and its cycle diameter is 200 mm. The high-quality full flow channel model was built by using hexahedral structured mesh, and the sliding mesh method was established for solving the transient flow field. The volume of fluid (VOF) model was used, along with realizable k-ε model on the turbulence model and second-order upwind scheme for solving the momentum and kinetic energy equation, and PISO algorithm was used for pressure and velocity coupling. Finally the numerical simulation can be calculated to analyzing the gas-liquid circulation at different working conditions such as i=0.96, i=0.6 and i=0 when the filled ratio at q=40%, q=60% and q=80%. The results of the numerical simulation show the process clearly that the distribution of the gas-liquid two-phase flow varies with load increasing. By comparing with flow field test results which were acquired by installing the plane array sensor on the pressure surface and suction surface of pump blades, it verified the effectiveness of the emulation algorithms and the calculation results. The research provides a numerical calculation method to forecast the torque dropping condition and estimate the overload capacity of the torque limited hydrodynamic coupling, and provides a theoretical reference for advising the parameters design of the flow channel structure qualitatively and quantitatively.