7/27/2019 Ex181 Automotive Clutch[1]

1/2

Copyright 2002 Fluent Inc. EX181 Page 1of 2

A P P L I C A T I O N B R I E F S F R O M F L U E N T

Understanding the flow patterninside a clutch is necessary for

designers who are trying tooptimize the cooling of the parts,

which are subjected to frictional

heating. In this example,FLUENT is used to predict the

amount of air passing through the

holes of the clutch cover duringoperation. This air flow is the

primary source of cooling. The

clutch rotates at a high speed

inside a stationary gearbox bell

housing. To simulate this motion,

the multiple reference frames(MRF) model is used to obtain a

steady state solution of the flow

field.

The MRF model has been heavily

used with widespread success formodeling rotating parts in a

variety of equipment. The flow in

the region surrounding the

rotating components is modeled in

a rotating frame, in which these

components are at rest, while theflow adjacent to the stationary

components is modeled in the lab

frame. An interior surface

separates the two frames, and

information is continually passed

across this surface as the solutionproceeds. The model is more

economical than the time-

EX181

dependent sliding mesh model, inwhich the flow is tracked by a

continually rotating grid. For thecase of the clutch, the rotation

speed is high and only the time-

averaged flow is of interest, sothe MRF model is the most

suitable choice for the simulation.

The rotating assembly of the

clutch was imported from ProE

into GAMBIT and inserted into

the bell housing, which was

created in GAMBIT. A hybrid

volume mesh was built thatcontained 700,000 tetrahedral and

prism cells, split between the

rotating and stationary regions.

The rotating reference frame was

given a rotation speed of 2000

rpm, to match that of the clutch.A flat plane parallel to the

flywheel, positioned between the

clutch cover and the top of the

bell housing, was used as the

interior surface between the

frames. Above this surface, thewalls of the housing are at rest.

Below the surface, the housing

walls are also at rest, and this is

accomplished by assigning the

walls a rotational speed of 0 in

the absolute frame. Turbulencewas treated with the RNG k-

model with the Swirl Dominated

Automotive ClutchIn this example, FLUENT 5 is used to simulate the flow inside a clutch housing. The clutch has

complex geometry and rotates at a high speed in the stationary housing. A steady-state treatment for

the flow simulation, involving multiple reference frames, is used. The results can be used as an

indicator of how well the air flow can cool the frictional heating that is generated by the clutch during

operation.

Figure 1: The geometry of the rotatingassembly, including the pressure plate (blue),the diaphragm spring (magenta), and thecover (green and red)

7/27/2019 Ex181 Automotive Clutch[1]

2/2

Copyright 2002 Fluent Inc. EX181 Page 2of 2

Flow option, and standard wall

functions were used for the near

wall treatment. Only isothermal

flow was considered, since thepurpose of the simulation was to

focus on the airflow inside thecover.

Figure 1 shows the clutch

assembly, including the pressureplate (blue), the diaphragm spring

(magenta), and the cover (greenand red). This entire assembly

rotates inside the bell housing. A

close-up view of the surface mesh

on the clutch cover is shown inFigure 2. The six holes on the top

of the clutch cover were meshedwith prism shaped elements, as

can be seen from the triangular

faces on top of the cover and

quadrilateral faces on the sides of

these openings.

Figure 3 shows contours of static

pressure on the rotating clutchassembly. The pressure is fairly

uniform on the clutch cover, but

variations are in evidence on the

edges of the flow passages,suggesting that the flow does

indeed penetrate into theopenings, as desired. This finding

is further supported by path lines

colored by velocity magnitude,

shown in Figures 4 and 5. Inthese figures, strong flow is in

evidence both inside the clutchcomponents (Figure 4) and inside

the bell housing (Figure 5).

In summary, this example

demonstrates that FLUENT can

successfully compute the flow

inside a clutch using the MRFmodel. More geometry details

could be added to future modelsin order to improve the accuracy

of the predictions. In addition, a

thermal calculation could provide

useful information on maximumtemperatures reached in the clutch

to check whether they areacceptable or not. Using this

information, the CFD results

could help engineers design and

dimension components in order tooptimize the cooling.

Courtesy of Automotive Products UK

Ltd.

Figure 3: Contours of staticpressure on the rotating assembly

Figure 2: Local detail of the surface mesh

Figure 4: Path lines illustrate the flow in the vicinity of the cover Figure 5: Path lines illustrate the flow inside the bell housing