Flow-structure identification in a radially grooved open wet clutch by means of defocusing particle tracking velocimetry

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 $$12\;\upmu \mathrm{m}$$ 12 μ 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 $$15\%$$ 15 % as compared to the ideal linear velocity profile. Midway between the grooves, the wall shear stress is around $$4\%$$ 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

Analytical simulation of influential parameters affecting grooved wet clutches performance underdisengagement condition

“…This phenomenon in general can cause the deviation simulation results from the experiments. In addition, the assumption of non-slip condition may be violated in some areas at high rotational speeds 23 .…”

Analytical modeling and dimensionless characteristics of open wet clutches in consideration of gravity

“…An analytical model cannot describe complex flow phenomena, like e.g. the vortical system found in the cavity of a radial groove [8]. However, the model can lead to basic findings that clarify the effect of grooves for an initial understanding.…”

“…The experimental approach typically relies on the acquisition of one integral value only, which renders the elaboration of a detailed cause-effect relation as well as a geometrical scaling difficult. Lately an extraction of volumetric (3D) three-component (3C) velocity information out of a two-disk open clutch model was done by the use of defocusing particle tracking velocimetry (DPTV) [8].…”

DPTV-based analysis of the flow-structure/wall-shear interplay in open wet clutches

“…In continuation of the earlier study by Leister et al (2021), which focuses on the fluid mechanic insights, the present study now additionally explicitly addresses the capabilities and limitations of the used DPTV Figure 2: Example results for a radial groove of width W = 1.35 mm and height H = 0.97 mm approach as well as the conducted post-processing steps and the resulting changes upon their variation. Since for this scale of application, where the magnification is relatively moderate, compared to microscopic scenarios, the use of a normal PIV set-up, instead of a microscope, offers a large variety of possibilities and adjustment options.…”

“…To advance beyond the level of drag-torque measurements (at most) in combination with qualitative flow visualization, the method of defocusing particle tracking velocimetry (DPTV) in combination with an in-situ calibration approach (Fuchs et al, 2016) has been successfully adapted to open wet clutches by Leister et al (2021). The chosen experimental setup and DPTV working principle are sketched in Figure 1.…”