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 4
Based on the average angle of 28.6° at the radial position of 200 mm, using
the conservation of angular momentum, the design swirl parameter for
current experimental setup is 0.34 (Equation 2.8).
4.2 PIV Experimental Results (L3)
The PIV experimental results are discussed here by describing the mean data
for each flow characteristic. In order to present the results in a
comprehensive and more understandable manner, at first, the results for the
base case of cylinder length L3 are discussed and then the effect of change in
cylinder length is discussed by comparing the results for L1, L2 and L3 at
selected positions. The results for the remaining positions are presented in
appendix A.
4.2.1 Mean Velocity Field
The mean velocity field at z1 is presented for both the Reynolds numbers in
figure 4.6. Each velocity component is non-dimensionalized with bulk flow
velocity Vb.
It can be seen that the resulting in-cylinder swirling flow is comprised of a
concentrated vortex with a small core surrounded by a high velocity region.
The velocity magnitude in the vortex core is very low compared to its
surroundings and mean position of the vortex core is slightly eccentric to the
geometric center of the cylinder. A low velocity region exists at larger radial
positions close to the cylinder wall. Moreover, it can be observed that the
core size, in case of ReB is relatively smaller than the velocity field at ReA.
The flow decays downstream and the size of vortex core region increases
indicating smaller localized velocity gradients compared to upstream
positions (Figure 4.7). Moreover, the high velocity region exists at larger
radial distances from the vortex core and the thickness of the high velocity
region is also not uniform at all circumferential positions at the given radial
distance from the core. This demonstrates the flow having three dimensional
features. The size of the vortex core has further increased and the relative
difference in the core size at two Reynolds numbers still exists.
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Swirling Flow in a Pipe