Research on fluid flow stability with baffles of different size in a hydrodynamic coupling during partially liquid-filled operating conditions

The hydrodynamic coupling is a power transmission device dependent on the liquid medium momentum change with the advantage of slow shock, isolation of torsional vibration, start light load and overload protection, which is applied in engineering, mining, construction, lifting the transport machinery, et al[ 1 ]. The hydrodynamic coupling without inner ring usually works in partially liquid-filled operating conditions, when the flow state changes suddenly with the rotating speed ratio changing. This may lead to unstable gas-liquid two-phase flow in a hydrodynamic coupling in a certain ratio range. To improve the stability of two-phase flow, a baffle is set inside the circulatory circle of a hydrodynamic coupling. The baffle blocks part of the flow area between two wheels in the hydrodynamic coupling. The size of baffle plays an important role on the effect for improving the flow stability. To investigate the influence of the baffle to the internal flow stability, the two-phase flow (liquid-filling rate is 80%) in hydrodynamic couplings with baffles in different sizes and without baffles were studied by Computational Fluid Dynamics (CFD) numerical simulation with the rotating speed of pump at constant 2200 r/min and rotating speed of turbine changing from 0 to 2200r/min. The corresponding distributions of streamlines and characteristics curves were obtained. Through the analysis of turbine torque and efficiency, it is verified that the baffle could improve the flow stability, and the different distributions of streamline could explain the reason. In addition, optimal range of baffle size c 30% 40% is obtained by analyzing the simulation results. This will provide a basis for the improvement of design in the hydrodynamic coupling.