Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figu ure 2.9: Vorte ex Breakdown Ty ypes: (a) Bubble (b) Spiral. (Alek kseenko et al., 2007). The vortex breakdow wn is often nnot only asym dependent in nature e (Lucca-Negrro et al., 2000 high sp peed camera, conducted viisualization o Reynold ds number in the range of 110 of singl le and double e spiral breakd Sarpkay ya et al. (1995 5) to be a co speed camera. c This conical c shape high ro otational spee eds of 1000 re (2000) show s that at high h Reynolds at the center c line nev ver becomes n show th hat for high Reynolds numb celled bubble b form an nd bursts into 5 mmetric but al 0). Novak et a f vortex brea . The observvations reveal kdowns whichh previously w onical shape uusing a comp is observed ddue to rotatio ev/s. The measurements b s number of 3 x 10 negative/ rever bers the spiral o turbulence. 5 lso highly timme al. (2000) usinng kdown at higgh ed the existence was observed bby paratively lowwer ons of spirals at by Novak et aal. the meaan axial velociity rsed. Additionnally, the resullts breakdown bbypasses the twwo At high h Reynolds numbers, n a llarge three ddimensional tiime dependent instability is develope ed called as ‘PPrecessing vorttex core (PVC)’ (Yazdabadi et al., 1994 4). This is the result of the forced vortex region of the flow becominng unstable and displace ed from the ax axis of symmettry and start tto precess about the axis s (Lucca-Negr ro et al., 20000). The PVC has a regular frequency annd amplitu ude and in som me cases can caause many prooblems by locking onto othher system instabilities and a resonatingg with them (Yazdabadi eet al., 1994). AAt high Re eynolds numb bers, the vorteex breakdown is also observved to dart bacck and fort th along the axis a (Novak et al., 2000). 2.3.6 (a) (b) Helical Vortex V Structures Chapter 2 In swirl flows with filament f type vortices, the vvortex filamennt almost nevver has a straight/ rectilinear axis ddue to differrent instabilitties and wavves 24 Swirling Flows
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figure F 2.10: Vortex Vo Filament in n a ch hamber with rota ating bo ottom (Alekseenk ko et al l., 2007). Figure 2.11 1: Streamlines (Proj ojections) in a cross-section nal plane for f a helical vort tex Filament in a tu ube (Alekseenko et al., 1999). Chapter 2 propaga ating along it (Alekseenko et al., 2007). IInstead the voortex filament is radially y displaced fro om the axis off the containerr (pipe/ cylindder in this casse) and tak kes the shape of a helix wrrapped aroundd the cylinderr axis along thhe flow. Sw wirl/ vortex flo ows exhibitingg this characteeristic are calleed ‘helical swirrl/ vortex flows’ f (Figure 2.10) (Alekseeenko et al., 20007). Helical swirl flows, like axis-symmmetric and nnon-helical asyymmetric swiirl flows, involves i the characteristicss e.g. wave ppropagation oon vortex corre, vortex breakdown and a PVC etc., that have been discusseed in previouus sections s. However, the t helical sttructure of thhe vortex corre brings moore complexity to the ov verall flow strructure and iits consequent behavior. For example in case of a helical h swirl fllow confined iin a device likke pipe/ cylindder etc., Fi igure 2.11 shows the streammlines (projecttions) when thhe vortex core is radially y displaced (fo or further posssible structurees see Alekseennko et al., 19999 & 2007 7). The conseq quent effect off cylinder walll is like a ‘miirror vortex’ i. .e. the actu ual vortex feel ls that there iis another vorrtex of identiccal properties at the sam me radial dista ance from the wall but rootating in oppposite directioon (Figure 2.12). 25 Swirling Flows
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Experi imental <strong>and</strong> <strong>Numerical</strong> N Stud dy <strong>of</strong> <strong>Swirling</strong> g Flow in Scaveenging<br />
Processs<br />
for 2-Stroke<br />
Marin ne Diesel Engin nes<br />
Figure F 2.10:<br />
Vortex Vo Filament in n a<br />
ch hamber with rota ating<br />
bo ottom (Alekseenk ko et<br />
al l., 2007).<br />
Figure 2.11 1:<br />
Streamlines (Proj ojections)<br />
in a cross-section nal plane<br />
for f a helical vort tex<br />
Filament in a tu ube<br />
(Alekseenko et al.,<br />
1999).<br />
Chapter 2<br />
propaga ating along it (Alekseenko et al., 2007). IInstead<br />
the voortex<br />
filament is<br />
radially y displaced fro om the axis <strong>of</strong>f<br />
the containerr<br />
(pipe/ cylindder<br />
in this casse)<br />
<strong>and</strong> tak kes the shape <strong>of</strong> a helix wrrapped<br />
aroundd<br />
the cylinderr<br />
axis along thhe<br />
flow. Sw wirl/ vortex flo ows exhibitingg<br />
this characteeristic<br />
are calleed<br />
‘helical swirrl/<br />
vortex flows’ f (Figure 2.10) (Alekseeenko<br />
et al., 20007).<br />
Helical swirl flows, like axis-symmmetric<br />
<strong>and</strong> nnon-helical<br />
asyymmetric<br />
swiirl<br />
flows, involves i the characteristicss<br />
e.g. wave ppropagation<br />
oon<br />
vortex corre,<br />
vortex breakdown <strong>and</strong> a PVC etc.,<br />
that have been discusseed<br />
in previouus<br />
sections s. However, the t helical sttructure<br />
<strong>of</strong> thhe<br />
vortex corre<br />
brings moore<br />
complexity<br />
to the ov verall flow strructure<br />
<strong>and</strong> iits<br />
consequent<br />
behavior. For<br />
example<br />
in case <strong>of</strong> a helical h swirl fllow<br />
confined iin<br />
a device likke<br />
pipe/ cylindder<br />
etc., Fi igure 2.11 shows<br />
the streammlines<br />
(projecttions)<br />
when thhe<br />
vortex core is<br />
radially y displaced (fo or further posssible<br />
structurees<br />
see Alekseennko<br />
et al., 19999<br />
& 2007 7). The conseq quent effect <strong>of</strong>f<br />
cylinder walll<br />
is like a ‘miirror<br />
vortex’ i. .e.<br />
the actu ual vortex feel ls that there iis<br />
another vorrtex<br />
<strong>of</strong> identiccal<br />
properties at<br />
the sam me radial dista ance from the<br />
wall but rootating<br />
in oppposite<br />
directioon<br />
(Figure 2.12).<br />
25<br />
<strong>Swirling</strong> Flows
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