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

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Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figur re 5.11: Average ed 3D Velocity Field at t z 25% port 1 closure (Color Contour represen nt the Normalize ed out of the t plane velocity y compon nent Vz / V . b 5.1.2 Mean Vel locity Fieldd The me ean three dim mensional veloocity field dataa is presentedd for fully opeen intake port p are alrea ady discussed in Chapter 4 and thereforre not discusseed here. Fo or the remain ning piston poositions, the rresults are discussed only fo for few specific positions s. The results aare presented ffor ReA only. FFor ReB and thhe remaini ing positions, the results aree given in Apppendix B. 25% Por rt Closure Chapter 5 At z th he vortex core e has enlargedd and still surrounded by a high velociity 1 region (Figure ( 5.11). The core is sttill eccentric frrom the cylindder axis and hhas less steep gradients. The radial thickness of tthe high velocity region hhas reduced d compared to fully open port. The velocity gradually decreases at larger radial r distance es from the higgh velocity region. The in-pplane swirl is in clockwi ise direction. Flow at t z results in axial velocity to be large nnear and around the cylindder 6 axis (Figure 5.12). Th he direction oof in-plane swwirl velocity iss clockwise annd the arro ow vectors indicate that thhe core regionn behaves likee a sink i.e. thhe fluid particles from large radial distances movves towards tthe vortex coore while following f a cu urved path. TThis is possiblly due to the cylinder outllet contrac ction as z is clo ose to the cylinnder outlet. 6 118 Effect of Piston Position
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figure e 5.12: Averaged d 3D Velocity Field at z 25% port 6 closure (C Color Contour represent t the Normalized d out of the e plane velocity compone ent Vz / V . b Fig gure 5.13: Averaged 3D Velocit ty Fiel ld at z 50% port 1 closu ure (Color Conto our repr resent the Norma alized out of the plane velo ocity com mponent Vz / V . b 50% Por rt Closure Chapter 5 For 50% % port closure, the three dimmensional veloocity distributtion is discusseed only for r positions z and a z . 1 5 At z th he axial velocit ty has a jet-likee profile. The peak of the prrofile is broadder 1 and the e gradients are e spatially moore smooth annd distinct (Fiigure 5.13). Thhe in-plane e velocity vectors indicate tthat the tangeential velocityy at one side of the vort tex is higher than the otherr due to the efffect of wall. Itt must be noteed that in figure 5.13, the peak in aaxial velocity does not coiincide with thhe vortex core. Repeate ed measuremeents and alsoo variation inn time betweeen pulses for f PIV measu urement resultted in the simmilar behaviorr. The reason of this non n-coincidence for being stattistical or somme fluid characcteristic is could not be found f out by the t author. The axial velocity has s almost a uniiform distribuution at cylindder cross-sectioon at z (F Figure 5.14). The T regions wwith maximumm and minimmum values aare 5 119 Effect of Piston Position
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Manuscript J Mar Sci Technol manus
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DTU Mechanical Engineering Section
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