Effect of Two-phase Flow on Drag Torque in a Wet Clutch
The effect of two-phase flow on drag torque in a wet clutch was investigated through a three-dimensional fluid simulation and an experimental study on aerated oil flow for a single set of wet clutch disks. At the low rotation speed of clutch disk, the flow field was single-phase and the drag torque increased linearly and was proportional to the rotation speed. When the induction of air bubble, that is, aeration was occurred and the flow field was changed to the two-phase flow, the drag torque decreased and reached gradually a negligible small value at the high rotation regime. At the first stage of the transition to two-phase flow, the change of drag torque curve well represented by a two fluid model of simple sphere bubbles. However, the oil-air mixed flow was not numerically modeled by the present model at high rotation speed because of the shape change of induced air bubbles. Additionally, the effect of grooves on fractional material was assessed experimentally, and it was found that radial groove reduced the drag peak value and shifted its peak rotation speed to a lower regime because radial groove enhanced the ejection of oil into the outside of clutch disks.