Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics
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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 />
Fig gure 4.50:<br />
Insta antaneous positio on <strong>of</strong><br />
vorte ex core at z1.<br />
Chapter 4<br />
The pr resence <strong>of</strong> a precessing vvortex<br />
core ( (PVC) is a vvery<br />
important<br />
characte eristic to be identified i becaause<br />
if presennt,<br />
the value o<strong>of</strong><br />
its frequency<br />
<strong>and</strong> am mplitude will affect the exxperimental<br />
reesults<br />
in diffeerent<br />
ways. Foor<br />
example<br />
in case <strong>of</strong> pr<strong>of</strong>ile p plots foor<br />
velocity commponents<br />
witth<br />
precession <strong>of</strong><br />
vortex core c there will<br />
be a shift inn<br />
the radial poosition<br />
<strong>of</strong> the pr<strong>of</strong>ile lines ffor<br />
each ti ime step/ ins stantaneous ssnapshot<br />
in case <strong>of</strong> PIV.<br />
This shift is<br />
proport tional to the amplitude a <strong>of</strong> the<br />
precession <strong>and</strong> a final teemporal<br />
averagge<br />
<strong>of</strong> all th he instantaneo ous measuremeents<br />
will resullt<br />
for example in a vortex coore<br />
size lar rger than the e actual one. . On the othher<br />
h<strong>and</strong> thee<br />
frequency <strong>of</strong><br />
precessi ion will introd duce a bias in RMS values o<strong>of</strong><br />
velocity commponents<br />
in thhe<br />
vortex precession p reg gion. This means<br />
that the mmeasured<br />
valuues<br />
<strong>of</strong> Reynolds<br />
stress co omponents an nd turbulent kkinetic<br />
energyy<br />
(TKE) includde<br />
a bias in thhe<br />
vortex core c region.<br />
Figure 4.50 4 shows th he instantaneoous<br />
vortex coree<br />
position forr<br />
z1 at ReA usinng<br />
the algo orithm define ed in section 44.3.6.<br />
The alggorithm<br />
is onlly<br />
applicable to<br />
instanta aneous data fo or z1 only becauuse<br />
for the othher<br />
downstreaam<br />
positions thhe<br />
instanta aneous data ca an have more than one vorrtex<br />
in the vorrtex<br />
core regioon.<br />
From figure f 4.51 it i can be seeen<br />
that for most <strong>of</strong> thee<br />
instantaneouus<br />
measure ements the vo ortex core loccation<br />
is not fixed <strong>and</strong> mooves<br />
in an area<br />
between n r/R= ± 0.2. However, H to cconclude<br />
any ffurther<br />
detailss<br />
like precessioon<br />
frequen ncy <strong>and</strong> ampli itude, high sppeed<br />
<strong>and</strong> timee<br />
resolved PIVV<br />
measuremennts<br />
are nec cessary comp pared to currrent<br />
PIV expperimentationn<br />
used in thhis<br />
experim ment. The peri iodicity in thee<br />
vortex core pprecession<br />
cann<br />
be detected bby<br />
well-def fined peaks in n the frequenncy<br />
spectra annd<br />
in case thhere<br />
is no peaak<br />
observe ed then the vo ortex precessioon<br />
is considereed<br />
to be r<strong>and</strong>oom<br />
(Escudier et<br />
al., 2006 6).<br />
In orde er to find ou ut the existennce<br />
<strong>of</strong> a preecessing<br />
vorteex<br />
core <strong>and</strong> iits<br />
consequ uent frequency y, LDA measuurements<br />
are cconducted<br />
at a radial distance<br />
102<br />
<strong>Swirling</strong> Flow in a Pipe