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 4.50: Sketch of Centrebody and turn ning section (Faler et al., 1977). the cyli inder outlet wall w comparedd to z9 and z113 for L2 and L1 respectivelly. There is a small relat tive differencee observed in the overall mmagnitude of thhe data val lues among th he three cylindder lengths duue to human errror involved in reading g the lower me eniscus positioon of water levvel in the U-tuube manometeer. 4.5 Discussi ion The cu urrent experim ment studies a confined swirling floww in a circullar cylinder. The focus has h been to understand not oonly the charaacteristics of thhe confine ed swirling flo ow but also too study the poossible effect. In other words the beh havior of the swirling floww, when the length/ aspeect ratio of thhe cylinder in which the e swirling floww is confined, is changed whhile keeping thhe same in nlet and outlet t conditions. CConducting thhe experiment at two different Reynold ds numbers has h also provided additionnal informatioon on the floow characte eristics. The tur rning section in figure 4. 50 facilitates in transitionn of radial annd tangent tial momenta (from swirl geenerator) to radial and axiaal thus resultinng in very small magnitude of radial vvelocity in thee cylinder as ccan be observeed in Kitoh h (1991). For the t setup deveeloped in this study, in ordeer to keep somme engine cylinder featu ures in the testt model, theree exists is no ceenter body. Thhe flow en nters in the cylinder c with a strong raddial componennt (blade anggle diverge the flow at an average anggle of 26 degreee from the raadius) and theen this rad dial momentu um decreases significantly. . This indicattes that in thhe current setup the rad dial velocity mmagnitude is ppossibly largerr at the cylindder cross se ection very clo ose to the cylinder inlet commpared to thee radial velociity magnitu ude measured d by aforementioned vane tyype swirl geneerator design bby (Kitoh, 1991). A ver ry confined aand small sizze vortex coree, at z1 in thhis experim ment, may be because of stronger radial velocity commponent at thhe cylinder inlet (Okul lov, 2010). HHowever, the details of thhe 3D velociity distribu ution at the cylinder c cross-sections, prioor to z1, wherre the vortex is generat ted was not po ossible to meassure using PIVV due lack of ooptical access to laser an nd cameras. Centrebodyy Chapter 4 100 Swirling Flow in a Pipe
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figur re 4.49: Normal lized mean Axial l Velocity y in different radial directions d at z3. Chapter 4 The ave eraged data re esults from PIV experimenntation have sshown a heliccal vortex flow f inside th he cylinder. HHowever, the LLDA experimeental results ffor mean tangential velo ocity at a meaasuring plane, , prior to the first measurinng plane z1 in case of PI IV measuremeents, have shoown a symmettric profile. Thhis demons strates the tran nsition of an aaxis symmetricc swirl to asymmmetric swirl at cylinder cross-section ns very close tto cylinder innlet. The asymmmetric velociity distribu ution measured in the swirl generator seeems to die out when the floww, after pa assing through h the contractioon section, ennters the test cyylinder. The tan ngential veloci ity profile at zz1 shows a Buurger vortex liike profile i.e. . a rotation nal forced vor rtex core surroounded by ann irrotational annular regioon. Contrar ry to the theo oretical profilee of Burgers vortex and thhe experimenttal results discussed d by Leibovich L (19884), the forcedd vortex is nott surrounded bby an irrot tational regio on. In fact, thhe forced vorttex is surrounnded by a weaak vortical l region follow wed by a smalll region wheree the vorticityy values are veery small ( Figure 4.11). This is possibly due to GGörtler vorticces in the neear cylinder wall region. As the swirrl decays dowwnstream and the vortex size increase es, this weak vortical v regionn almost disapppears. The axial velocity hass a wake-lik ke profile with no reverse fflow at the voortex core. Wiith the decay in the swirl, for the axi ial velocity, thhe local maximmum decreasees and the loccal minimu um, also defi ined as vortexx advection vvelocity (Veltee et al., 20088), increase es. For the cylinder c lengtth of 8D this trend continues until at position ns z11 where the t axial veloocity profile bbecomes nearrly flat. Simillar velocity y profiles and behavior, aloong the cylinnder/ pipe for tangential annd axial co omponents, ha ave been obseerved by Steennbergen et al. . (1998) for thhe experim mental measurements of swiirling flow witth ‘concentrateed vortex’. The distribution of velocity compoonents is not ssymmetric for measured crooss sectiona al planes given in table 4.11. For examplee figure 4.49 shows the axiial velocity y profiles alo ong positive and negativee X and Y axis using thhe approxi imate position n of vortex corre as the origiin. A line plott has been useed for the e experimenta al data to giive a clear ppresentation oof the velociity asymme etry. Due to rectangular sshape of cameera view, the data for largger radial positions p along g Y-axis could not be measured. 101 Swirling Flow in a Pipe
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DTU Mechanical Engineering Section
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Experimental and Numerical Study of Swirling ... - Solid Mechanics

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