FLOW PATTERN EVOLUTION AND ENERGY DECOMPOSITION OF FLOWS AT DIFFERENT OPERATING CONDITIONS IN A HYDRODYNAMIC TORQUE CONVERTER

摘要

Power loss and flow blockage in turbomachinery such as hydrodynamic torque converter are usually caused by jet flow, second flow and flow separation. In this paper, the velocity vector and the pressure distribution of the internal flow field in hydrodynamic torque converter were reduced by the method of the Proper Orthogonal Decomposition (POD) to find the main flow structures and the energy decomposition in the passages of pump, turbine and stator. In order to find their evolutionary processes and energy decompositions, oil flow visualizations were conducted at different speed ratios from 0 to 0.8, including stall condition and design operating condition. The results showed that the first few modes containing the majority of energy could provide enough accuracy to predict flow behavior and flow structure in flow passages. Especially when the energy percentage of the first mode was majority, its vortex structures could be recognized easily. But the flow patterns of other modes were different from each other and they made the flow more turbulent and complex, which increases the energy loss in the process of power transmission. Besides that, the change of pressure gradient had a direct influence to velocity vector. The results also indicated that the observed fluid pattern of vortex structure became extensive while the influence of secondary flow decreased in the flow passage of pump with the increase of speed ratio. But the situation is just reversed in turbine, that is, the vortex disappeared gradually and the irregular turbulent flow appeared as the increase of speed ratio. In stator, the vortex structure emerged gradually when the speed ratio increased. So the method of snapshots is a very useful way to analyze the complex flow flied in depth and to predict the trend of development.