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 5
outward. As discussed before, the presence of piston will make major portion
of the flow to enter in to the cylinder at an angle to the piston top surface
(Figure 5.3). This angle makes the fluid jet coming from intake port along
the cylinder circumferential periphery to meet at some axial distance from
the piston surface facing the cylinder axis. The fluid after meeting at that
axial distance will then move outward to other regions of a given (near
cylinder inlet) cross section. The solid body rotation and low pressure near
the cylinder wall (near the cylinder intake port) provides favorable condition
for transporting the fluid to other regions.
5.1.3 Reynolds Normal Stresses
The distribution of Reynolds normal stress components are expressed in
Cartesian coordinates. For a given cross-sectional position all the three
normal components are presented under a single figure and scaled to same
color values so as to get a comparison of the relative magnitude of each
component. Each Reynolds stress component is normalized by square of the
bulk velocity and the symbols represent normalized stress components. The
results are also discussed from the perspective of polar coordinates as
discussed earlier in Chapter 4.
25% Port Closure
At z , figure 5.18 shows that all the Reynolds normal stress components are
1
higher compared to fully open port (see Section 4.2.5). This indicates an
increase in the variance/ fluctuations of corresponding velocity components.
It can be seen that ww attains the highest and vv has the lowest values.
For all the three components, the vortex core and the near wall region has
higher fluctuations. The region in between the vortex core and the wall has
fewer fluctuations. In the near wall region ww is the dominant component
and has comparatively large values. The spatial distributions of all the
components show increased anisotropy of the normal components. Thus
vortex core and near wall regions have most of turbulent kinetic energy for
and
the given cross-sectional plane. Considering polar coordinates, vv vrv r at z are higher in the vortex core and near wall regions and the
1
annular region has smaller values.
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Effect of Piston Position