Volume of Fluid vs. Cavitation CFD-Models to Calculate Drag Torque in Multi-Plate Clutches

Wet-running multi-plate clutches and brakes are important components of modern powershift gearboxes and industrial powertrains. In the open stage, drag losses occur due to fluid shear. The identification of drag losses is possible by experiment or CFD-simulation. For the calculation of the complex fluid flow of an open clutch, CFD-approaches such as the volume of fluid (vof) method or the Singhal cavitation model are applicable. Every method has its own specific characteristics. This contribution sets up CFD-calculation models for different clutches with diverse groove designs. We present results of calculations in various operating conditions obtained from the Singhal cavitation model and the vof method. The usage of modern commercial CFD-Tools (Simerics MP+) results in short calculation times. The developed CFD-models consider the geometry of a complete clearance consisting of a friction plate and a separator plate, the gap between the plates and the flow conditions arising from the design of the plate carriers. The full 360-degree modeling makes it possible to take arbitrary groove designs on the friction and separator plate into account in contrast to frequently used circumferential symmetry. We carried out a high number of calculations with various influencing factors such as operating conditions, groove design, speed ratio and feeding oil temperature. We proof the numerical solutions with results from experiments. The basis of a broad validation of the models are characteristic values obtained from experimental investigations on the drag loss test rig LK-4. The usage of serial production parts from automobile and industrial applications ensures a data basis that is reliable and relevant for practical work. The contribution characterizes the examined CFD-approaches with respect to computing effort and the validity of the results. Furthermore, it shows the pros and cons of the specific CFD-approaches (vof and cavitation) to calculate the drag losses of wet multi-plate clutches.