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Chapter 7: Basic Vibration Control: Reduction at source (Part – III)
Noise and vibration generated by fluid flow
In fluid mechanics, turbulence refers to disturbance in a flow, which under other
circumstances would be ordered, and as such would be laminar. These disturbances
exert an effect on the flow itself, as well as on the elements it contains, or which are
submerged in it. Flowing gases or liquids can generate high sound pressure levels
when they interact with a solid structure or as a free stream jet. In addition the
machines generating the flow, as for instance compressors pumps and IC-engines
usually give high pressure pulsations in the connected pipes. The pressure pulsations
can however also excite the structure and generate structural vibrations which produce
sound. Figure 2-17 shows an example of a circulation pump producing pressure
pulsations in the water in a heating system. The sound waves are transmitted through
the pipes to the radiators, where the large metal surfaces vibrate and radiate sound.
This is similar to how the vibrations of the strings in a musical instrument are
transmitted through the bridge to the sound box. When the sound box vibrates, sound
is transmitted to the air.
Interest in flow induced vibrations (FIV) lies in the fact that the source of vibration is
dissipated energy caused by turbulence, or in other cases, by eddies that produce
oscillating lift forces that impregnate objects immersed in the fluid with a vibratory
movement.
There are two basic FIV mechanisms:
a self-induced vibrating mechanism
a forced vibration mechanism.
Turbulent fluid flow in pipes also produces sound which can be radiated from the
pipes and transmitted to the building structure. This noise and vibration can be
controlled by reducing the turbulence in the pipe or covering the pipe with sound
absorbing material. The vibrations can be isolated from the wall or ceiling with
flexible connecting mechanisms.
Turbu
mean
densi
There
Two
two s
ulence colla
ns of the turb
ity. The form
e are many
particularly
situations in
Fig
aterally gen
bulent stress
mer cause the
practical ap
curious, alb
question are
. 2.17 Vibra
erates press
tensor the tu
e noise, and
pplications o
beit useful on
e:
ation mechan
sure and de
urbulence pr
as such, are
of the analys
nes, have so
nism [2]
ensity variat
roduces vari
deemed to b
sis of turbule
olved some s
tion in the
ations in pre
be sound sou
ence genera
serious prob
fluid. By
essure and
urces.
ated noise.
lems. The
Determination of leaks through the seat of safety relief valves from the outside
by means of non-intrusive techniques.
Element breakage due to resonance frequencies.
The first of the above situations has been used to detect safety relief valve leaks in
BWR nuclear plants. The theoretical principle employed is that the seat leak flow
produces turbulence which in turn generates a characteristic sound. Turbulence, which
in general, manifests itself as vortices or eddies, will in the Von Karman sense, give
off a determined frequency. Moreover, the lower scale turbulence will have its own
frequency in accordance with the Lighthill model. Thus, the pressure waves that are
generated with a defined frequency will constitute an external dryer load that
increases its total dynamic load.
The fluid instabilities, though more specifically with that which makes the flow
bistable, given that this represents a transition within the turbulent system. Not-
withstanding, what follows is a brief description of other instabilities about which
references and studies abound. Turbulent flow, as has been above, is a generalised
process, whereas instability is different. This is an unexpected situation, and one
which, in principle, should not be happening. Quite often it is associated with the
local formation of turbulence in a laminar, ordered flow. The most widely known
instabilities model and study turbulence of this type of situation, but there are other
instabilities in a turbulent flow that cause changes to the flow pattern. As with
turbulent flow and its transition, instabilities possess factors that give rise to same
instability. One of the most absurd process features is that the white noise can induce
order in a system that is non linear and non stationary, is not in equilibrium. That is, a
chaotic system can be ordered by itself.
Figur
gener
Claes
When
tone,
direct
Figur
circul
re 0-18 Exa
rated vibrati
s Folkesson.
n air passes
can be pro
tion of flow,
re 2-19 Sou
lar cross sec
ample of no
ions in pip
) [1]
an object a
oduced. This
, such as wit
und generatio
ction bar a lo
oise and vi
es. (Picture
at certain spe
s can be pre
th a "tail," or
on by air fl
oud Strohal
ibration con
: Asf, Bull
eeds, a stron
evented by
r by making
low past an
tone is prod
ntrol by red
erbekämpnin
ng pure tone
making the
the object's
object in a
duced. Noise
duction of t
ng, 1977, I
e, known as
object long
shape irregu
an air stream
and vibratio
turbulence
Illustrator:
a Strohal
ger in the
ular.
m. For the
on control
meas
Bulle
This
certai
chimn
wind
gener
sound
chopp
filling
and t
the ed
chara
Figur
rubbe
[1]
When
the du
rapid
flow
ures includ
erbekämpnin
type of soun
in wind spe
ney in a spi
direction, i
ration can be
d can arise
ped, creating
g the empty
the noise and
dge interacti
acter of the s
re 0-20 Nois
er material. (
n a gas or liq
duct walls. T
dly change d
are close tog
de disturbin
ng, 1977, Illu
nd generatio
eeds. A poss
iral. The pit
it encounters
e found in a
from the tra
g a siren (pu
y space in th
d vibration.
ing with the
sound becom
se and vibrat
(Picture: As
quid flows in
The noise and
direction, if t
gether.
ng the regu
ustrator: Cla
on can be of
sible solutio
tch of the sp
s an irregula
a cutter whee
ack for hold
ure tone) no
he track with
A strong to
e cavity at ce
mes broad ba
tion control
f, Bullerbek
n ducts or p
d vibration f
the flow mo
ular product
es Folkesson
f importance
on is to mou
piral must no
ar object. A
el revolving
ding the plan
ise and vibr
h a rubber p
onal sound is
ertain freque
nd.
of a cutter w
kämpning, 19
ipes there is
from turbule
oves at a fast
tion of vor
n.) [1]
e for instanc
unt a strip o
ot be consta
An example
g under no-lo
ne blade. A
ration. Minim
plate reduce
s generated b
encies. After
wheel by fil
977, Illustrat
s always som
ence is incre
t rate, and if
rtices. (Pict
e around ch
of sheet met
ant. Regardl
of this type
oad conditio
An air stream
mizing the c
es the pumpi
by vortices
r filling the
lling the cav
tor: Claes Fo
me turbulenc
eased if the f
f objects blo
ture: Asf,
himneys at
tal on the
ess of the
of sound
ons, where
m is being
cavities by
ing action
formed at
cavity the
vity with a
olkesson.)
ce exciting
flow must
ocking the
Figur
duct
Claes
Figur
shriek
and v
bends
befor
re 0-21 Smo
wall vibrati
s Folkesson.
re 2-22 show
king sound.
vibration. To
s. Tubing pi
re the stream
ooth pipe w
ions and sou
) [1]
ws a branch o
The branch
o control the
eces were p
m reaches the
walls without
und. (Pictur
of a steam li
h has two sh
noise and v
laced betwe
e next valve.
t discontinui
re: Asf, Bull
ine having th
harp bends w
vibration a ne
en the valve
ities give les
lerbekämpni
hree valves
which also p
ew branch w
es, so that tu
ss turbulenc
ing, 1977, I
which produ
produce a lo
was created w
urbulence wa
e exciting
Illustrator:
uce a loud
ot of noise
with softer
as reduced
Figur
and i
incid
Folke
When
will b
speed
propo
will t
re 0-23 Noi
increasing th
ent on the
esson.) [1]
n a flowing
be generated
d will produc
ortional to th
therefore me
ise and vibra
he distance
valve. (Pic
gas mixes w
d. This has
ce a lower so
he flow spee
ean that the s
ation control
between va
cture: Asf,
with a non-m
already bee
ound level. F
d to the pow
sound will be
l of a steam
alves. Both
Bullerbekäm
moving gas
en discussed
For speeds b
wer of 8 (U8)
e reduced by
m line by intr
measures r
mpning, 197
so called je
d in chapter
below 200 m
). A reductio
y about 24 dB
roducing sof
reduce the t
77, Illustrat
et noise and
10. A lowe
m/s the sound
on of the spe
B.
fter bends
turbulence
tor: Claes
d vibration
er outflow
d power is
ed by half
Figur
gener
Bulle
Since
relati
greatl
Figur
air st
betwe
1977
This
parts
tubul
noise
mout
In th
centra
re 0-24 Jet n
ration is
erbekämpnin
e, the jet noi
on to the sp
ly reduced b
re 0-25 Princ
tream aroun
een the jet
, Illustrator:
principle can
with comp
lar mouthpie
e and vibrat
thpieces whi
is mouthpie
al stream.
noise and vi
increased
ng, 1977, Illu
ise and vibra
peed of the
by using an a
ciple for jet
nd the core j
stream and
Claes Folke
n be used to
ressed air a
eces. Very h
tion develop
ich produce
ece, part of
bration gene
by distur
ustrator: Cla
ation level is
surrounding
air stream wi
noise and vi
jet exhaust
d the surroun
esson.) [1]
o reduce the n
after process
igh exit spee
ps. The simp
less noise an
the compres
erating by fr
rbances in
es Folkesson
s determined
g air, noise
ith a lower s
ibration redu
to reduce th
nding air. (
noise and vi
sing which
eds are requ
mple tubular
nd vibration
ssed air mov
ree stream tu
the strea
n.) [1]
d by the spee
and vibratio
speed outside
uction by int
he relative f
(Picture: As
ibration from
is often car
uired, and a s
mouthpiece
, such as a d
ves at a low
urbulence. T
am. (Pictu
ed of the jet
on productio
e the jet stre
troducing a s
flow speed d
f, Bullerbek
m cleaning o
rried out wi
strong high
e can be rep
dual flow mo
wer speed ou
The sound
ure: Asf,
stream in
on can be
am.
secondary
difference
kämpning,
f machine
ith simple
frequency
placed by
outhpiece.
utside the
Figur
aroun
Bulle
If the
frequ
The l
sever
vibra
re 0-26 Noi
nd the core
erbekämpnin
e diameter o
uency. If the
low frequenc
ral small on
ation, but this
ise and vibr
jet exhaust
ng, 1977, Illu
of a gas outl
diameter is
cy noise and
es. To some
s is more eas
ration reduc
in the form
ustrator: Cla
let is large,
small the no
d vibration ca
e extent this
sily controlle
ction by intr
m of a dual
es Folkesson
the noise an
oise and vibr
an be reduce
s will increa
ed.
roducing a
flow mouth
n.) [1]
nd vibration
ration will pe
ed by replaci
ase the high
secondary a
hpiece. (Pic
n will peak a
eak at high f
ing a large o
h frequency
air stream
cture: Asf,
at the low
frequency.
outlet with
noise and
Figur
stream
noise
Claes
Steam
steam
vibra
jet st
stream
Figur
core
1977
The
distur
princ
re 0-27 Prin
m into sever
e and vibrat
s Folkesson.
m safety val
m escape can
ation a diffus
treams and h
m pack.
re 0-28 Jet n
jet stream
, Illustrator:
inflow to fa
rbance givin
iple applies,
nciple for jet
ral smaller je
tion generati
)
lves may dis
n produce hi
ser was form
high frequen
noise and vib
into several
Claes Folke
fans is very
ng a lot of
, for example
t noise and
et streams. T
ion. (Picture
scharge man
igh level, low
med as a per
ncy noise an
bration redu
l smaller jet
esson) [1]
important
turbulence
e, to propell
vibration re
This reduces
e: Asf, Bull
ny times eac
w frequency
rforated cone
nd vibration
uction in a st
t streams. (
for sound g
the sound w
ers in water.
eduction by
the turbulen
lerbekämpni
ch day. Sou
y sound. To
e. The holes
which is ab
team safety
(Picture: As
generation. I
will be mor
.
dividing th
nt mixing are
ing, 1977, I
und producti
control the
s produce m
bsorbed in t
valve by div
f, Bullerbek
If there is a
re intense. T
he core jet
ea and the
Illustrator:
on during
noise and
many small
the down-
viding the
kämpning,
an inflow
The same
Figur
gener
Asf, B
Fans
30 ex
close
increa
from
can b
be us
Figur
disco
Folke
re 0-29 Pri
rating inflow
Bullerbekäm
should there
xamples are
to a sharp b
ased. To con
the fan so t
be made smo
sed to give a
re 0-30 Fan
ontinuities an
esson.) [1]
inciple fan
w turbulence
mpning, 1977
efore not be
shown whe
bend. The flo
ntrol the noi
that the turb
oother, and t
smoother fl
noise and v
nd the fan. (
and propel
e increases t
7, Illustrator
placed close
ere the fan is
ow is disturb
ise and vibr
bulence has t
the fan move
ow through
vibration con
(Picture: Asf
ller sound
the noise an
r: Claes Folk
e to any disc
s placed too
bed and the n
ation the co
time to die d
ed away from
the bend.
ntrol by incr
f, Bullerbek
generation.
nd vibration
kesson.) [1]
continuities i
o close to co
noise and vib
ntrol vanes
down. In the
m the bend.
reasing the d
kämpning, 19
Inflow dis
n generation.
in a duct. In
ontrol vanes
bration at th
can be mov
e other case,
Guide vane
distance betw
977, Illustra
sturbances
. (Picture:
n Figure 2-
, and too
he outlet is
ved farther
, the bend
s can also
ween duct
ator: Claes
Turbu
in the
can b
by a s
Figur
smoo
forme
Rota
Unba
is a v
wher
preve
usefu
cause
unbal
togeth
rotate
will
exper
impro
uncom
Dyna
unbal
ulence will f
e form of bu
be produced
slow change
re 0-312 Pri
oth duct tran
ed. (Picture:
ating Balan
alance is the
very importa
e high spee
ents excessiv
ul life. Unbal
es the rotor
lanced mass
her generate
es and tries t
be transmit
rience this f
ove the mas
mpensated c
amic Unbal
lances and i
form if the p
ubbles and p
by a large,
e in volume.
inciple for n
sitions. Beca
Asf, Bullerb
nce & Unba
most comm
ant factor to
d and reliab
ve loading o
lance in a ro
r to vibrate
s componen
e a centrifuga
to move the
tted to the
force once p
ss distributio
centrifugal fo
lance, illustr
is the most
pressure in a
produces a ro
rapid chang
noise and vib
ause a rapid
bekämpning
alance
mon source o
be consider
bility are sig
of bearings a
otor is the re
. The vibra
nt with the
al force. Sin
rotor along
rotor's bea
per revolutio
on of a roto
orces.
rated in Fig.
common ty
a liquid syst
oaring noise
ge in volume
bration redu
pressure dro
g, 1977, Illus
of vibration
red in the m
gnificant con
and avoids fa
esult of an un
ation is pro
radial acce
nce the mass
g the line of
arings, and
on. Balancin
or, so that i
. 2.27, is a
ype of unbal
em drops ra
and vibratio
e. Noise and
uction in a li
op is avoide
strator: Claes
in machine
modern mach
nsiderations
fatigue failur
neven distrib
oduced by t
eleration du
component
action of the
any point
ng is the pro
it rotates in
combination
lance found
apidly. Gas i
on. The pres
d vibration i
quid filled p
d less gas bu
s Folkesson.
with rotatin
hine design,
s. Balancing
re, thus incre
bution of ma
the interacti
ue to rotatio
rotates, the
e force. The
on the bea
ocess of atte
n its bearing
n of static an
in rotors. T
s released
ssure drop
is avoided
pipe using
ubbles are
.)[1]
ng parts. It
especially
of rotors
easing the
ass, which
ion of an
on, which
force also
e vibration
aring will
mpting to
gs without
nd couple
To correct
dynam
mach
A rot
count
must
tempo
to me
these
to be
to the
of th
frequ
accel
a filte
vibra
vibra
direct
“FununderFluid
mic unbalan
hine is runnin
tor is balance
teracts the u
be determin
orary) altera
easure the r
trial correct
determined
e unbalance,
he vibration
uency of rota
lerometer mo
er tuned to th
ation at the r
ation meter,
tly proportio
damentals or IITR-KTH
d Instabilities
nce, it is n
ng and to ad
F
ed by placin
unbalance in
ned. The pri
ations to the
resulting ph
tions enable
. Any fixed p
, once per re
signal, unb
ation. The vi
ounted on th
he rotational
rotational fr
which disp
onal to the fo
of Sound anH MOU for s, Practical A
necessary to
dd balancing
Fig 2.32: Dy
ng a correctio
n the rotor. T
inciple of pe
mass distrib
ase and ma
e the amount
point on the
evolution of
balance is s
ibration due
he bearing ho
l frequency o
requency is
plays the m
orce produce
nd Vibrationcourse deve
Approach by
o make vib
masses in tw
ynamic unba
on mass of a
The size and
erforming fie
bution of the
gnitude of b
t and positio
bearing exp
f the rotor. T
seen as an
to the unbal
ousing. The
of the rotor,
measured. T
magnitude. T
ed by the unb
ns” by KTHelopment. Tuy Carlos Gav
bration mea
wo planes.
alance
a certain size
d position o
eld balancin
rotor, by ad
bearing vibr
on of the req
periences the
Therefore in
increase in
lance is mea
vibration sig
so that only
The filtered
The indicate
balanced ma
H Sweden [urbulence, V
vilán Moreno
asurements w
e in a position
of the correc
ng is to mak
dding trial m
ration. The
quired correc
e centrifugal
a frequency
the vibrati
asured by me
gnal is passe
y the compon
signal is pa
ed vibration
ass.
1], this booVibrations, No [2]
while the
n where it
ction mass
e (usually
asses, and
effects of
ction mass
force due
y spectrum
on at the
eans of an
ed through
nent of the
assed to a
n level is
ok is used Noise and