Rotational Speed Fluctuation and Internal Flow in a Variable-filling Fluid Coupling

Abstract

The distribution of rotational speed fluctuation rates on the performance map is investigated by a model test. The random fluctuation is small in the range of high speed ratios 0.90∼1.0, and lower speed ratios under the small charging quantity of the working fluid. The domain of large random fluctuation exists in the intermediate range. The periodic fluctuations occur in a narrow region where the output torque rises with an increase of speed ratio. Flow-visualizations with stroboscope, oil-film method and tuft method are performed to study the relation between the internal flow and the rotational speed fluctuation. A vortex perpendicular to the pressure side surface of turbine blade is observed, and the flow from the vortex is found to be unstable when the random fluctuation is large. Furthermore, the state of free surface and air-bubble flow is examined.