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

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Experi imental and Numerical N Stud dy of Swirling Flow in Scaveenging Processs for 2-Stroke Chapter 5 Marin ne Diesel Engin nes Fig gure 5.19: Norm malized Reynolds ds Norm mal Stress Com mponents @ z and d 6 25% port closure. 124 Effect of Piston Position
Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Chapter 5 At z the overall magnitudes of the normal stress components have decayed 6 approximately by an order of 10 with ww still having the highest values (Figure 5.19). uu and vv have nearly the same magnitude and since they represent the variance in tangential and radial velocity components, the values are higher in the vortex core region. However, ww is very low in the core region and gradually increases in the radial direction towards the cylinder wall. As discussed in section 5.1.1, at z for 25% port closure, the 6 mean axial velocity has a jet-like profile. This indicates that in the center of the jet the axial velocity is comparatively more stable and fluctuates more around the mean value as the radial distance from the vortex core increases. However, for u and v components it is the vortex core region where higher and vv at z has higher values in a large 6 fluctuations are observed. v v region around the cylinder axis and gradually decreases in the radial direction towards the wall. 50% Port Closure Figure 5.20 shows that at z with 50% port closure, the magnitude of all the 1 Reynolds normal stress components have further increased. Compared to 25% port closure, the peak value of ww at z has increased almost twice. 1 The difference in magnitude of in-plane normal components uu and vv at z , as observed in case of 25% port closure in figure 5.18, does not exist and 1 have nearly the same range. The spatial distribution of uu and vv show two distinct regions lying side by side where one has the highest values and the other has the lowest values. This distribution can be understood by looking at the tangential velocity and the three dimensional velocity distribution in figures 5.6 and 5.13 respectively. The mean vortex core location is in the third quadrant at a radial distance of approximately r/R=0.15 and very close to negative Y-axis line. Due to the effect of wall an asymmetric tangential velocity distribution is observed which has higher peak at r/R=0.4 along positive X-axis compared to negative X-axis where small dip in the profile is observed. The contour plots for uu and vv show that if they are added together, a region with high values will be obtained almost very close to the position where the vortex core is located. The adjacent region with low values is possibly, due to wall effect here, a distorted shape of the region observed in (Figure 5.18) in between the wall and vortex core where the minimum values are observed for uu and vv . The ww although having anisotropic spatial distribution still exhibit some features as in case of z with 25% port closure i.e. the minimum values exist in the jet 6 center and increases along the radius towards the wall. However, a different feature is observed that after a radial distance of approximately r/R=0.5 the fluctuations in axial velocity starts decreasing towards the wall. This feature, however, could not be observed for z with 25% port closure possibly due to 6 location of peak value region being outside the PIV measurement area. r r 125 Effect of Piston Position
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