JEC COMPOSITES MAGAZINE - Issue #105 - June 2016 - 28

flow simulation

Tab. 3: Comparison of several parameters and results of the simulations conducted with various element sizes

Distance from injection 10 cm
Time of flow front arrival (s)

Mesh size
2 mm

5 mm

10 mm

20 mm

2.49

2.53

2.60

2.71

1.61

4.42

8.84

Error to the 2 mm mesh (%)
Number of elements in the model

2000

800

400

200

Ratio of computation time compared
to the 2 mm mesh calculation

1/1

1/6.5

1/30

1/124

Mesh size sensitivity
of the method

Fig. 2: Fluid fraction after 95 seconds of injection
in single- and dual-scale simulations (top view of
the cavity)

results of both simulations are presented
in figure 2.
Figure 2 presents a mapping of the fluid
fraction after 95 seconds of injection. The
predictions of the single-scale simulation
state that the part is fully filled with the
resin, but in the dual-scale simulation,
it can be observed that the tows are
not saturated at the end of the cavity.
Moreover, the reactive computation
reveales the imminent resin solidification in the tows in this region, making
impossible a further filling even with a
longer injection time. Thus the dual-scale
reactive simulation demonstrates that the
injection parameters determined with a
classical single-scale simulation do not
allow to fill the part properly.

Fig. 3: Evolution of pressure at different locations
in the cavity for different mesh sizes

One of the claims of the developed technique is its ability to treat dual-scale flow
with the same degree of precision for various element sizes. Therefore, isothermal
1D filling simulations with constant inlet
pressure were conducted using meshes
with element sizes ranging from 2 mm
to 20 mm. The characteristics of the
textile and the processing conditions are
described in table 2.
The length of the unsaturated area was
measured in the simulations conducted
with different mesh sizes. It was estimated at 6 mm for the 2-mm mesh and 5.7
mm for the 20-mm mesh. These values
are very close, although, for the 20-mm
mesh, the elements are three times bigger
than the unsaturated area. This highlights
the ability of the model to track the unsaturated area accurately, even with large
elements.
Furthermore, tracking pressure evolution
and macroscopic flow front arrival at specific positions in the cavity makes it possible to determine if the resin is spread
the same way between the macro- and
micro-scale with a small or a large mesh.
Figure 3 shows the evolution of pressure
at different locations in the cavity.
Figure 3 shows that the evolution of
pressure is very similar for mesh sizes
2, 5 and 10 mm. Table 3 presents the
flow front arrival time at 10 cm from the
injection line for the different mesh sizes.
These arrival times are compared to the
one obtained with the 2-mm mesh and
the relative errors are presented.

28 jec composites magazine / No105 June 2016

Table 3 shows that the error on the macroscopic flow front arrival is increasing
with increasing mesh size. However, even
when dividing the number of macroscopic elements in the model by a factor of
10, this error remains under 10%. Furthermore, the method remains accurate
in a range of 10% for elements more than
three times bigger than the unsaturated
area. This demonstrates the flexibility
of the proposed model and its ability to
treat an isothermal injection case accurately for several element sizes. Finally,
the advantages of the new numerical
method in terms of CPU time reduction
can be noticed. In the case of the 10-mm
mesh, the computation time is reduced
by a factor 30 while the error on the time
of flow front arrival stays smaller than 5%
compared to the 2-mm mesh.

Conclusions
Dual-scale numerical injection methods
make it possible to predict manufacturing defects encountered in high-speed
RTM processes as intra-tow porosities.
The developed approach demonstrates
an interesting ability to treat dual-scale
injection cases: the numerical strategy
combined with its weak sensitivity to
mesh size leads to computation times
similar to regular single-scale approaches.
The next step will be to validate the
approach by confronting the numerical
results with experimental results before
industrial implementation in PAM-RTM
from ESI's PAM-COMPOSITES simulation suite. n
More information:
www.esi-group.com/composites

http://www.esi-group.com/composites

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #105 - June 2016