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
At z 5 in figure 5.21 the fluctuations in u and v velocity components are
higher in the region around cylinder axis and lower at large radial positions
near cylinder wall. Due to increase in the size of the vortex core this region
with higher values is large. However, the relative difference between the
minimum and maximum values is small. Fluctuations in the axial velocity
component w is still dominant. The cylinder center region has minimum
ww values and the near wall region has the highest values. For all the
normal Reynolds stress components, the decrease in magnitude from z to z 1 5
is by an order of 10. Compared to fully open port, the magnitude of all the
normal Reynolds stress components are nearly twice the value at z . 5
The effect of wall at z has changed the distribution of Reynolds stress
1
components v v and vrv r in the cross-sectional plane. The region around
the vortex core location still has higher values but the region with low
magnitude of v v and vrv r ,as in case of 25% closure, is distorted.
However, at z a more clear picture can be seen where their values increase
5
from large radial positions in the direction of cylinder axis region where the
vortex core is resided.
75% Port Closure
When the intake port is 75% closed, the variance in the axial velocity is very
large at z 1 compared to u and v velocity components (Figure 5.23). The
spatial distribution is also very anisotropic for ww . For all aforementioned
cases where the axial velocity has a jet-like profile, the fluctuations in axial
velocity are comparatively low at the center of the jet. The gradual increase in
the outward radial direction decreases again towards the wall, after attaining
a high value. The radial location of this peak ww region seems to exist at
the outer periphery of the jet where a mixing occurs with the fluid near the
wall region. In the current case, this peak region is at a smaller distance from
the jet center than previous cases possibly because the wall recirculation zone
has comparatively grown in case of 75% port closure at z . uu and vv
1
components have lowest values at large radial positions from the vortex core.
There is radially large region around the cylinder axis where patches of high
and low values are observed. The peak values of uu and vv are nearly
half the value of ww .
A resultant of the uu and vv components given in figure 5.23 with the
same color scale as figure 5.22 shows that the in-plane Reynolds normal
stresses are higher in the central region around cylinder axis and decreases
towards the wall region.
128
Effect of Piston Position