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

Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke
Marine Diesel Engines
the components in general remains the same but spreads to surrounding
regions. At 50% port closure, the magnitude of Reynolds shear stresses
increases approximately twice the value at 25% port closure. At z , vv 1 r and
vrv z have almost similar distribution as in case of 25% port closure but for
v v z the region near the cylinder axis with peak value disappears indicating
a very small value at large radial distance and almost zero value in the
remaining central portion of the cylinder. As the swirl decays downstream,
for all the shear stress components the magnitude decays and high values are
observed in the larger radial distances from the cylinder axis and central
region of the cylinder has very low values. At 75% port closure, the peak
values of shear stresses is almost twice the value at 50% port closure. For
individual components the distribution pattern at z is nearly the same as
1
previous piston position. An important aspect is observed that the vortex
breakdown between positions z and z has no significant effect on the
1 2
distribution pattern of Reynolds shear stress components.
The closure of cylinder intake port closure has a significant effect on the
mean axial vorticity distribution for a given cross-sectional position and also
along the flow downstream. With the increase in the closure of the intake
port, at initial position z 1 , the Gaussian like profile of mean axial vorticity
starts to deteriorate until 75% port closure where it no longer exists. Also, the
port closure enhances the vorticity transfer from strong localized vortical
zones (vortex core) to other weak vortical region as the swirl decays
downstream the flow direction. Thus, in general, the in-cylinder axial
vorticity distribution is comparatively more uniform at higher cylinder
intake port closures.
1.2 CFD Simulations
The numerical simulations are conducted using RANS based modeling
Approach. The models used are high Reynolds number RNG k and
Reynolds stress model (RSM) with quadratic formulation for the rapid part
of the pressure strain term. The inlet to the computational domain is defined
at a radial distance of 200 mm from the axis of rotation and does not include
the guide vanes. This is carried out to study the possibility of achieving good
results by neglecting the guide vanes region in the computational mesh and
defining the magnitude of radial and tangential velocity components using
the LDA data. The RNG k models are used with an inlet turbulence
intensity of 1% and 10% whereas with the Reynolds stress model (RSM)
turbulence intensity of 10% is defined.
The comparison of normalized tangential velocity profiles show that for all
the positions the results of both RNG k model and RSM are not
predicting the (free vortex type) tangential velocity profile in the annular
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Summary & Conclusions