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

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Experi imental and Numerical N Stud dy of Swirling Flow in Scaveenging Process for 2-Stroke Chapter 5 Marin ne Diesel Engin nes Fig gure 5.26: Norm malized Reynold ds Shea ar Stress Compon nents @ z6 6 and 25% port closu ure. 134 Effect of Piston Position
Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines 50% Port Closure Chapter 5 At position z , the contour plots for shear stresses are given in figure 5.27. For 1 component uv the distribution profile is following nearly the same pattern as in case of 25% port closure i.e. large values are observed at larger radial distances and decrease towards the vortex core region. This shows that the covariance between u and v components of velocity is high at larger radial distance and low near the vortex center. For uw along X-axis, the peak value is observed in a region at a radial distance of r/R=0.6 from the cylinder axis. Decrease gradually on both sides of this peak region i.e. both towards cylinder axis and near wall region. Similar pattern is observed for vw but along Y-axis. This distribution gets very clear by looking at this from the perspective of cylindrical coordinates. Considering contour plots for both uw and vw components, it becomes clear that vv is the dominant component and v v z is very small at this cross-section plane. At z , the magnitude of shear stress components has reduced by an order of 5 10 (Figure 5.28). For all the uv , uw and vw components, the distribution in the center part of the cylinder exhibit very low values. uw and vw have large values observed in the near wall region. The main reason is that the axial velocity is nearly constant in most of the central portion of the cylinder and fluctuates mostly at the near wall region. 75% Port Closure At position z , the uv is very weak compared to uw and vw (Figure 1 5.29). The distribution pattern of the regions with high uv is still the same. For uw and vw the orientations of the regions with peak values are at an angle to X and Y axes respectively. The radial location of these regions has moved to comparatively lower radial distance from the cylinder axis. Regarding the shear stress components vrv z and v v z , it still seems that the vrv z is stronger than the v v z . The possible vortex breakdown between positions z and z has, in general, 1 2 no significant effect on the distribution pattern of Reynolds shear stress components. For uv the magnitude has reduced to a small extent compared to uw and vw . The covariance between the radial and axial velocity component is still large compared to the covariance between the tangential and axial components. This means that for any disturbance in axial velocity the radial velocity is more sensitive than the tangential velocity. Such axial disturbances are low in the jet center and high in the outer region. r z 135 Effect of Piston Position
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Experimental and Numerical Study of Swirling ... - Solid Mechanics

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