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14th International Symposium on Particle Image Velocimetry – ISPIV 2021
August 1–5, 2021

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

Robin Leister1∗, Jochen Kriegseis1

1 Institute of Fluids Mechanics (ISTM), Karlsruhe Institute of Technology (KIT), Germany
∗ robin.leister@kit.edu

Extended Abstract
The trend to lower energy consumption in the automotive industry still offers potential in various fields of
application. One powerful saving strategy is described by the idling behavior of wet clutches, where the
speed difference between drive and output, and the cooling oil in combination with a sub-millimeter spacing
leads to significant amounts of wall shear stress (WSS) and accordingly drag torque. Minimization of this
adverse effect has been found to be possible by means of grooved clutch-disk geometries, which have been
demonstrated to correlate with the drag torque (see e.g. Neupert et al., 2018). The main interplay between
torque and fluid flow in open wet clutches has been analyzed by Leister et al. (2020) in a dimensionless
way. Today, a detailed investigation of a clutch flow, however, is missing for a larger variety of groove
patterns and the cause-effect relations remain yet to be fully understood. Especially, the clear identification
of the so-called foot print of a particular groove geometry in the flow field and corresponding WSS – thus
drag-torque predictions – still requires further research efforts.

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. Particularly,
the achieved spatial resolution of 12 µm provides reasonably well resolved 3D3C flow information in the
rotor-stator gap and, moreover, inside the grooves under investigation.

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

R2

R1

µ,
ρ

Ω

h

(a) test rig with rele-
vant parameters

h

W

H

(b) camera setup (left) and open clutch test rig with
groove parameters (right)

lens

focus layer

glass plate

grooved disk

(c) Sketch of the DPTV working principle in
the rotor-stator gap

Figure 1: Detailed sketches of (a) the test rig, (b) the set-up and typical groove geometries, (c) the measure-
ment principle.

mailto:robin.leister@kit.edu


(a) Defocused diameter distribution and corresponding in-
tensity of one particle averaged in circumferential direc-
tion. The data is acquired with a back-illuminated 10 µm
pinhole, which mimics a particle.

(b) Cavity roller in the rotor-fixed frame of reference. Contours of
radial velocity ur are superimposed by Γ1-isolines (–) and vectors
of uϕ −ΩRm and uz. (•) indicates the Γ1 vortex-center location.

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. Both used detection methods are evaluated according their suitability and robustness
for this scenario of application. The acquisition related interplay between magnification and defocusing
sensibility, where the trade off between aperture and object distance must be considered, is analyzed both
theoretically and explicitly for this scenario and recommendations regarding further choice of equipment are
given. Figure 2(a) shows the diameter of the defocused image and the corresponding intensity. The particle
image ranges from a Gaussian shape at z∗ = 0 to a defocused ring with low intensity 2 mm apart the focus
layer.

To complement the study, 3D3C velocity information from the measurements are discussed accord-
ing to both their respective measurement accuracy and corresponding insights for a deeper fluid mechanic
understanding of the flow. Figure 2(b) shows all three velocity components for a radial groove, where a
cavity roller manipulates the wall-shear stress in the vicinity of the groove. The Γ1-criterion indicates the
vortex-center location, which coincidences with the maximum outflow velocity ur. The derived insights are
foreseen to provide a valuable contribution to the drag-torque predictions and accordingly design optimiza-
tion strategies for future clutch optimization efforts.

References
Fuchs T, Hain R, and Kähler C (2016) In situ calibrated defocusing PTV for wall-bounded measurement

volumes. Measurement Science and Technology 27:084005

Leister R, Fuchs T, Mattern P, and Kriegseis J (2021) Flow-structure identification in a radially grooved
open wet clutch by means of defocusing particle tracking velocimetry. Experiments in Fluids 62:29

Leister R, Najafi AF, Gatti D, Kriegseis J, and Frohnapfel B (2020) Non-dimensional characteristics of open
wet clutches for advanced drag torque and aeration predictions. Tribology International 152:106442

Neupert T, Benke E, and Bartel D (2018) Parameter study on the influence of a radial groove design on the
drag torque of wet clutch discs in comparison with analytical models. Tribology International 119:809 –
821