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 Fig gure 4.9: Tan ngential Velocity for f L3=4 4D. and sca ans for the local l minimuum of the inn-plane veloccity magnitudde 2 2 u v (Cartesian coordinates) iin the region cclose to the cyylinder axis. The pro ofile shape re esembles closeely to the moodel of Burgeer vortex i.e. a rotation nal flow core region r with riggid body rotattion (forced vvortex) followeed by an ir rrotational/ po otential flow region also rreferred to as ‘free vortex’ oor ‘annular r’ region. Sinc ce, in this expeeriment, no mmeasurements wwere conducteed close to cylinder wall l, the velocity profile in thee high velocityy gradient ‘waall layer’ re egion cannot be b seen. At posit tions very close to the cylindder inlet, the ssize of the vorttex core is smaall compare ed to outer potential flow/ / free vortex rregion and thee peak value oof non-dim mensional tang gential velocitty in the rotattional region iis higher at loow Reynold ds number Re eB compared too ReA. This diifference dimiinishes with thhe swirl de ecay and grow wth in the foorced vortex rregion downsttream the floow direction at z5. At z6 a small peak in the magnittude of tangential velocity is observed d as a result of f the flow beinng acceleratedd due to small diameter outlet pipe (z6 6 at L3 is comp paratively closser to cylinderr outlet than z9 and z13 at LL2 and L1 respectively). r In I general, thee effect of variiation in Reynnolds number is only ob bserved in the vortex core reegion and thee potential floww region seemms to be insensitive to su uch variation aat all the measuuring positionns. 4.2.3 Axial Vel locity Profi file Chapter 4 The axial velocity V exhibits a ‘wake-like’ profiile (Figure 4.100). The effect of z Reynold ds number see ems to be moore pronounceed compared to V not onnly in term ms of size of inn ner forced vorrtex but also inn the magnituude of Vz at thhe 58 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 Figu ure 4.10: Axial Velocity for L3=4 4D. vortex core. c At ReA, compared to ReB, the valuue of V in thhe vortex core is z less and d very close to o zero but no rreverse flow iss observed at the vortex corre. At z1, in n the potentia al flow regionn, V seems too be nearly thhe same at botth z Reynold ds number an nd steep graddient in the vvalues of V is observed at z larger radial distances s. Downst tream the flow w, at z6, the waake like profille of axial veloocity decays annd become es more flat and a the sensittiveness to Reeynolds numbber can only bbe seen in the region with w peak valuues of V . Thhis is very inteeresting becauuse z contrary y to V , the axial a velocity seems to be mmore responsive to variationns in Reyn nolds number and less to thee downstreamm swirl decay. TThe V velociity z gradien nt in the region n at large radiial distances has decreased aand the cylindder outlet seems s to have e no effect in pronouncingg a regeneratioon of wake-likke profile at z6. 4.2.4 Mean Axial Vorticiity Chapter 4 The flow w at z1 has a core with a largge value of noormalized meaan axial vorticiity (calc culated by firs st normalizingg x, y with cyllinder radius R and u, v witth z bulk flo ow velocity Vb b) (Figure 4.111). The vorticiity distributionn seems to havve a Gauss sian like profi ile. The vortexx core region has high vortticity with steeep gradien nts at lower Re. R Very low vorticity is oobserved only at large radiial distance es from the vortex core. Thhe irregularityy in the profille is due to thhe uncerta ainties in data acquisition annd processing. 59 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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