Experimental and Numerical Study of Swirling ... - Solid Mechanics

Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke
Marine Diesel Engines
Chapter 6
However, the RNG k model with T.I 10% predicts the existence of the
separation to a comparatively shorter distance downstream.
The vortex core seem to get instantaneously instable in case of RNG k
model with T.I 1% and with RSM the vortex core seems to be stable in the
cross-sections very close to the piston surface and then gets unstable further
downstream. One of the possible reasons may be the effect of the
aforementioned flow separation at the wall. For RNG k model with T.I
10%, the vortex core is comparatively stable and also predicts a smooth
growth in the vortex core size along the flow.
The flow in the outlet pipe has been predicted different by RNG k
model and RSM. For all cases the flow in the outlet pipe initially has a jet
like velocity profile but cases with RNG k model show that after nearly
half of the outlet pipe length, this jet-like velocity profile becomes unstable
and then develops a nearly uniform velocity profile. RSM predicts a jet-like
velocity profile throughout the outlet pipe.
6.2.4 Normalized Reynolds Normal Stresses
The Reynolds normal stress components at z 1 and z 5 are shown in figures 6.16
and 6.17) respectively. As mentioned earlier, these contour plots show a
temporal snapshot of normal components of Reynolds stresses from RSM
simulation case and do not include the contribution from unsteady flow
simulation. Therefore, an exact comparison may not be possible here with
the experimental data. Compared to the experimental results shown in
Chapter 4, the results to some extent give reasonable qualitative agreement.
At z , higher values of the normal stress components are observed in the
1
region near the axis of the cylinder and the wall region and the region in
between has low values. In case of ww ,
the model also give a half circle arc-
like shape region with peak
ww values. The magnitude of peak values for
all the normal stress components are close to the experimental values
(Figures 4.15, 18 and 21).
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Numerical Modeling