Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics
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<strong>Experimental</strong> <strong>and</strong> <strong>Numerical</strong> <strong>Study</strong> <strong>of</strong> <strong>Swirling</strong> Flow in Scavenging Process for 2-Stroke<br />
Marine Diesel Engines<br />
Chapter 4<br />
From the contour plots <strong>of</strong> u <strong>and</strong> v , it can also be observed that the peak<br />
tangential velocity regions are not perfectly aligned with the axis lines <strong>and</strong> in<br />
fact are at an angle to the axis lines in clockwise direction. This is possibly<br />
due to the eccentric location <strong>of</strong> the vortex core from the cylinder axis.<br />
Another effect <strong>of</strong> asymmetric swirling flow can also be understood by<br />
2 2<br />
plotting the contour plot for in-plane velocity ( u v ) (Figure 4.14). In<br />
case <strong>of</strong> axis symmetric swirling flow, the velocity contours will have a<br />
circular ring shape. However, in this case a high velocity quarter-moon<br />
shaped region (indicated by a white arrow) is observed. This is probably due<br />
to the effect <strong>of</strong> wall because the vortex core is radially closer to the wall in the<br />
direction <strong>of</strong> eccentricity from the cylinder axis compared to other direction.<br />
(Alekseenko et al., 2006) has discussed in detail about the changes in the<br />
structure <strong>of</strong> flow in helical vortices with <strong>and</strong> without the presence <strong>of</strong> wall.<br />
The normal Reynolds stress components uu , vv , ww , statistically,<br />
represent variance <strong>of</strong> u , v <strong>and</strong> w components <strong>of</strong> velocity respectively. In<br />
case <strong>of</strong> experimental measurements for swirling flow with precessing vortex<br />
core (PVC), the measured values <strong>of</strong> Reynolds stresses are actually a<br />
combination <strong>of</strong> true velocity variance <strong>and</strong> vortex core oscillation. The<br />
contribution <strong>of</strong> oscillating vortex core depends on its amplitude <strong>and</strong><br />
frequency <strong>and</strong> in some cases can be the major contributor.<br />
The uu<br />
component, at z1, has high values concentrated around the vortex<br />
core <strong>and</strong> in an oval shape region elongated along x-axis (Figure 4.15). This<br />
may possibly be due to a precessing vortex core (PVC). The size <strong>of</strong> this region<br />
with peak velocity variations in the core is smaller at ReA compared to ReB.<br />
The region surrounding the vortex core has very low velocity variations but<br />
these variations gradually increase in radial direction towards the near wall<br />
region.<br />
65<br />
<strong>Swirling</strong> Flow in a Pipe
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