Abstract
The internal unsteady flow in the variable capacity type fluid coupling is analyzed by CFD, considering the movement of free-surface. The torque curve of CFD shows very good agreement of experimental one. In the area of instability of the fluid coupling, where the torque and rotational speed varies very much in the experiment, the numerical result shows that there are two different flow patterns in this area. In a pattern, most of working fluid is rotating in the rotor area, and it transfers small torque only. In anther pattern, the working fluid rotates around the air area, that is concentrated at the center of fluid coupling, and it can translates large torque. When the flow go around between these two flow pattern, the torque will be varied widely.
