Abstract
The volumetric defocusing particle tracking velocimetry (DPTV) approach is applied to measure the flow in the sub-millimeter gap between the disks of a radially grooved open wet clutch. It is shown that DPTV is capable of determining the in-plane velocities with a spatial resolution of 12;upmu mathrm{m} along the optical axis, which is sufficient to capture the complex and small flow structures in the miniature clutch grooves. A Couette-like velocity profile is identified at sufficient distance from the grooves. Moreover, the evaluation of the volumetric flow information in the rotor-fixed frame of reference uncovers a vortical structure inside the groove, which resembles a cavity roller. This vortex is found to extend well into the gap, such that the gap flow is displaced towards the smooth stator wall. Hence, the wall shear stress at the stator significantly increases in the groove region by up to 15% as compared to the ideal linear velocity profile. Midway between the grooves, the wall shear stress is around 4% lower than the linear reference. Furthermore, significant amounts of positive radial fluxes are identified inside the groove of the rotor; their counterpart are negative fluxes in the smooth part of the gap. The interaction of the roller in the groove and the resulting manipulation of the velocity profile has a strong impact on the wall shear stress and therefore on the drag torque production. In summary, this DPTV study demonstrates the applicability of such particle imaging approaches to achieve new insights into physical mechanisms of sub-millimeter gap flow scenarios in technical applications. These results help to bring the design- and performance-optimization processes of such devices to a new level.Graphic abstract
Highlights
The continuously increasing urge for CO2 savings and the expectation of a constantly increasing range of electric drive concepts lead to the need for new ways of saving energy in the automotive industry
Deriving the spatial particle location from its particle image geometry is a crucial step for the single camera 3D defocusing particle tracking velocimetry (DPTV) velocimetry technique, since the uncertainty of the particle location estimation is directly connected to the accuracy of the particle image geometry determination
The in situ calibrated DPTV approach as used in the present study has proven to be a robust and reliable 3D3C velocimetry technique with only one camera, which allows for a comprehensive analysis of the flow in an open wet clutch
Summary
The continuously increasing urge for CO2 savings and the expectation of a constantly increasing range of electric drive concepts lead to the need for new ways of saving energy in the automotive industry. The speed difference between drive and output, in combination with the presence of oil and the sub-millimeter spacing of the plates, lead to a high wall shear stress and to a significant torque, the so-called drag torque. A reduction of this adverse drag torque motivated a variety of both numerical and experimental investigations of the flow in open wet clutches Influencing parameters on the flow pattern are the volumetric flow rate Q of the supplied flow, the self-adjusting gap height h between the rotor and the stator disk, the inner and the outer radius of the rotating disk, R1 and R2 , the angular velocity Ω , and the drag torque Ts , resulting from the speed difference between drive and output unit that is shearing the oil
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