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region. All three turbulence models show separation bubbles in the recirculation
region. The size of the bubbles in the recirculating regions are larger for k-
ε
and
SST k-
as compared to RSM. It could also be observed that the prehydraulic jump
angles are different for all the three different models
ˉ
'
cases. The RSM has the
highest angle of 54
°
compared to that of the SST k-
ˉ
41
°
and k-
ε
31
°
, and it is
signi
cantly different with the computation by the RSM compared to the other two
models. This phenomenon is attributed to the feature of the RSM, which accounts
for anisotropic turbulence in simulation predictions. Comparing the numerical
prehydraulic jump angle results to the experimental angle of 56
, it is clear that
RSM in this sense gives a more accurate representation than the other models for
complex
°
flow prediction.
RSM is more accurate at solving complex
fl
ˉ
in 2D turbulence models since RSM solves transport equations for all components
of the speci
fl
ow
fields than the k-
ε
and SST k-
c Reynolds stress tensors directly. Therefore, RSM can more accu-
rately simulate rapid changes in strain rate or anisotropic effects due to swirling
motion off the ramp
'
s trailing edge. Since RSM can more accurately predict the
irregular unsteady
flow details, this explains the longer boundary length and higher
standard deviation result from Fig.
18
. RSM
fl
'
s prediction of the prehydraulic jump
angle more accurately represents the experimental angle as compared to the k-
ε
and
ˉ
SST k-
model predictions.
8 Conclusions
The following conclusion are presented below as preliminary to using geometric
nozzle modi
cation and CFD for improving SRM ef
ciency in SRM design
8.1 Experimental Study
Induced breakup due to modi
ed geometry is predictable to some degree of
precision by numerical simulation.
Breakup initiation and intensity can be represented by a geometric-speci
c
Reynolds and Weber numbers.
The migration of water into the air stream increases with increase in speci
c
Reynolds and Weber numbers. Signi
cant increase in breakup was seen at
Speci
c Reynolds and Weber numbers values of 243 and 80, respectively. This
serves as an approximate threshold for the onset of water breakup.
The slope of the distribution concentration is shallow corresponding to the
drastic breakup behavior.
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