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

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tor is balance

teracts the u

be determin

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trial correct

determined

e unbalance,

he vibration

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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

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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