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

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Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Chapter 6 However, the RNG k model with T.I 10% predicts the existence of the separation to a comparatively shorter distance downstream. The vortex core seem to get instantaneously instable in case of RNG k model with T.I 1% and with RSM the vortex core seems to be stable in the cross-sections very close to the piston surface and then gets unstable further downstream. One of the possible reasons may be the effect of the aforementioned flow separation at the wall. For RNG k model with T.I 10%, the vortex core is comparatively stable and also predicts a smooth growth in the vortex core size along the flow. The flow in the outlet pipe has been predicted different by RNG k model and RSM. For all cases the flow in the outlet pipe initially has a jet like velocity profile but cases with RNG k model show that after nearly half of the outlet pipe length, this jet-like velocity profile becomes unstable and then develops a nearly uniform velocity profile. RSM predicts a jet-like velocity profile throughout the outlet pipe. 6.2.4 Normalized Reynolds Normal Stresses The Reynolds normal stress components at z 1 and z 5 are shown in figures 6.16 and 6.17) respectively. As mentioned earlier, these contour plots show a temporal snapshot of normal components of Reynolds stresses from RSM simulation case and do not include the contribution from unsteady flow simulation. Therefore, an exact comparison may not be possible here with the experimental data. Compared to the experimental results shown in Chapter 4, the results to some extent give reasonable qualitative agreement. At z , higher values of the normal stress components are observed in the 1 region near the axis of the cylinder and the wall region and the region in between has low values. In case of ww , the model also give a half circle arc- like shape region with peak ww values. The magnitude of peak values for all the normal stress components are close to the experimental values (Figures 4.15, 18 and 21). 158 Numerical Modeling
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figure e 6.14: Normali ized Reynolds Normal Stress Compon nents at z . 1 Figure e 6.15: Normali ized Reynolds Normal Stress Compon nents at z . 5 ( uu ) m ( uu ) m ( vv ) m ( vv ) m ( ww ) m Chapter 6 ( ww ) m At z , for fo uu and vv the moddel also prediccts an elongatted oval-shapeed 5 region. Remarkably, it also showss that this ovval shaped reggion is tilted at some an ngle with X an nd Y axes linees respectivelyy. However, thhe magnitude of peak va alues for uu , vv and w ww are a bit t lower than thhe experimenttal results in Figures 4.1 17, 4.20 & 4.223) respectivelly. For ww also the moddel gives sim milar features as the experimmental data. 159 Numerical Modeling
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DTU Mechanical Engineering Section
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