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

Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke
Marine Diesel Engines
50% Port Closure
Chapter 5
At position z , the contour plots for shear stresses are given in figure 5.27. For
1
component uv the distribution profile is following nearly the same pattern
as in case of 25% port closure i.e. large values are observed at larger radial
distances and decrease towards the vortex core region. This shows that the
covariance between u and v components of velocity is high at larger radial
distance and low near the vortex center. For uw along X-axis, the peak
value is observed in a region at a radial distance of r/R=0.6 from the cylinder
axis. Decrease gradually on both sides of this peak region i.e. both towards
cylinder axis and near wall region. Similar pattern is observed for vw but
along Y-axis. This distribution gets very clear by looking at this from the
perspective of cylindrical coordinates. Considering contour plots for both
uw and vw components, it becomes clear that vv is the dominant
component and v v z is very small at this cross-section plane.
At z , the magnitude of shear stress components has reduced by an order of
5
10 (Figure 5.28). For all the uv , uw and vw components, the
distribution in the center part of the cylinder exhibit very low values. uw
and vw have large values observed in the near wall region. The main
reason is that the axial velocity is nearly constant in most of the central
portion of the cylinder and fluctuates mostly at the near wall region.
75% Port Closure
At position z , the uv is very weak compared to uw and vw (Figure
1
5.29). The distribution pattern of the regions with high uv is still the same.
For uw and vw the orientations of the regions with peak values are at an
angle to X and Y axes respectively. The radial location of these regions has
moved to comparatively lower radial distance from the cylinder axis.
Regarding the shear stress components vrv z and v v z , it still seems that
the vrv z is stronger than the v v z .
The possible vortex breakdown between positions z and z has, in general,
1 2
no significant effect on the distribution pattern of Reynolds shear stress
components. For uv the magnitude has reduced to a small extent
compared to uw and vw . The covariance between the radial and axial
velocity component is still large compared to the covariance between the
tangential and axial components. This means that for any disturbance in
axial velocity the radial velocity is more sensitive than the tangential velocity.
Such axial disturbances are low in the jet center and high in the outer region.
r z
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Effect of Piston Position