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 5.1.4 Reynolds Shear Stresses 25% Port Closure Chapter 5 The shear stress components of Reynolds stresses are given in figure 5.25 for z 1 . It can be seen that the covariance of in-plane velocity components u and v is small compared to uw and vw components. Shear stress component uv is weak in the region around cylinder axis and large values are observed in two pairs of distinct regions/ zones. These regions lie adjacent to each other and have opposite signs, however, with almost same absolute value of their magnitude. Shear stresses uw and vw are high in the cylinder axis and near wall region. In the cylinder axis region, uw and vw have high values in two small adjacent zones with opposite signs. The zones in the near wall region also exhibit opposite signs for two ends of X-axis and Y-axis for uw and vw respectively. At z , the Reynolds shear stresses are reduced by a factor of 10 (Figure 5.26). 6 The spatial distribution of uv component still has the zone pairs as discussed for z . However, their shape is more distorted showing small 1 gradients of uv in the cross-sectional plane. For uw and vw the two adjacent zones around the cylinder axis have grown in size and cover large portion of the cross-sectional plane. The zones in the near wall region have high values but seem to have radially shrunk toward cylinder wall. In general it can be said that with the decay in the swirl along the cylinder, the magnitude of Reynolds shear stresses decreases and their spatial distribution increase. For z , the region in between the cylinder axis and the near wall 6 exhibits large covariance values among the velocity components. For 25% port closure, the covariance between v and v r is large at larger radial distances. The Reynolds stress component v v r at z decreases slowly 1 towards the cylinder axis and increase again to a small extent in the vortex core region. v v z is low in the near wall region and increases to its peak value at a radial distance of r/R=0.15 and then decreases again in the vortex center. vrv z has largest values in the near wall region and decreases towards the vortex core region. At z , the distribution of vv 6 z and vrv z spread to distances around the cylinder axis. Both the components attain high values at a comparatively larger radial distance from the cylinder axis and decreases in the vortex center. 132 Effect of Piston Position
Experi imental and Numerical N Stud dy of Swirling Flow in Scaveenging Processs for 2-Stroke Chapter 5 Marin ne Diesel Engin nes Figure F 5.25 5: Normalized N Reyn nolds Shear S Stress Com mponents @ z1 and 25% po ort closure. c 133 Effect of Piston Position
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Experimental and Numerical Study of Swirling ... - Solid Mechanics

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