Measurement of the intensity of acoustic radiation in water flow during cavitation

TCCICH

L U2t\J% NThU?V1 VOOR DE K1J(MACHT

e'd. ripp ten -cstr.ie

st t. tatuty

st

.owtie iati

in

ter fl

&tag owvitti

(Issledo'ranie intensivnoti

kuticheskik

ii.achenii y

potoke voJ.y pri

kavitatsii)

L. 8. UY&f

ENek&OMASIINOSTRONIE, 1958, (9), 23-27

The psr de.cx1bss the ..riasnta1 method. ed aM the result.

taime4 ing the tnvestipti

_of

ultr..sio re4iati

tres a

sptø-.triaties oesillat in hy1ro'iiic th.la

_aM

med.l

uitii.

resulta iMiost. the pesMblUty of uaia,g the aheracteriatic ultrsaesio spectres to inve.tijst. o.vitaties in _{drsulio thstaflati.,}

C&vitatios in _{t.r flow i. '-fNI.)asisd by aoouatio radistios (mois.)}

a wide range

of

hi

aM low trsqei.s

ii i.s to th.

ribratiosa

of

_{bl.. awing their powth, c.ri.saios}

_aM

_Maqçesramoe

in th, liquid flø..

_{All the.. sa are fairly Intan.. aM}

_b.

det.ct.4 with the obj.ot

of

_{ob..rvin.g the mas cC oevitattow}

dees]it.

?requsn smeljsia

of

the noise spectres aseociat.d with oswitaties

in

liqaids he. bees oriod sut at th

_{V.1. T4i Polytis Imetitut. at}

t.v. The.. .xpsrimest. _{. merri.d ut is the diffuser}

_of

_a

o-dynaiic sl

of

r.cts*gelar orces .sti

with 41

4jj

_of

31 z 31 .ltng e enge. tostrioties esciUster

aM in

droturbtn.s. &coua tic radiatice pidred by pissoal.otri.

d.tectors aM overt.d into electric osoilltiess 'ii after suitabl

1ifiosties, . tod to an lMiostimg iaatzest to a .athoi. ray

osciuloçsp.

koohelle salt, qes.rta aM bailes tit.nate _{e used sa} piszoslsctric eles.nta in different e xpuri..ata.

P4sUtI11a7

Esr1rrt.

Pr..li.ienry .srita ver carried sut im the diffuser itthe

dro4uio thm] Sn

dar to thtsin tntentiom cosoerniag the

of

th. total cevitat tow ... iectr Saj a rsa r.usuiier, with a wide

beM alifter

_eM

a special

_3y.sr.

Us ix a het erodyn resuiver aystes

with rrow beM intermediate

fr.qu.

lifiosties

_it

_{pathl. t.}

.t.ct rr.qi.aci.s fro. th. vary lat

to hi# fr.quies of

of 5

s.

noise 1.101 dt the o.tire fr.qosnay .p.etr

a

al..

assaur.d ovar

s specific short

ti

interval.

The peli4".'y

..rits pv, the

foflo'u'ing

r..u]ts:-Osvitat io. ast.. pos...' practiosily a lias .p.otra

with

a

vary vUe

fr.quo.cy rang. fros 1

fr.quo.oies t1w

altmso.ic fr.qusnat.s up

to

pcyoL..

Tb. inteasity d.or.sses with increase in fr-.qus,

tI"(

prsotioslly to isro at o.. megacycle.

In the ultr.so.io ro. it i. possibis to isolst a r.gto.

fro. 100 to 300 ko. fros ,hith with suitable a1ificstio.

it

in

po.

sib], to s]w). noise dus te nearby

o.ohiary.

It thervf'.

appeared ri.iug

to carry cat futher

iav.stigatioa of the ultrsso.io osvitatica noi... s. .ip.z1ta indioat.d that a oevitat io. noIse analyser

iat possess

the f oUing properties:

Ability to asae the

intensity of the

.otic

rediatica over a vil. oo.tiaa ap.otrus tro.

1.. fr.qu.ncl*. up

to ultraso.io fr.quenoi.s

dt the oeder dt

megacycle.

Ability to isolat. a sufficiently asrrca

fr.-qnoncy

bsai

doca to 1000 ayo].. aM

to asarw

th. nois l.v.l of the.. bszidi

Ability to bift this

narro.

froqusaqy baai

alcag the ol.t.

.p.etrus within

the liait.

of

ioh noia, lavai as...

ts are required.

£ special an..lya.r as.

ostriat.d to ast the..

requizassnts.

(1)

'Tb. noise .nmly.sr ass

eo.atrted by L 3. Lso.er

sai

V.V 3j

-'r

s dtz.ctio. oC LV. P.d.rav.

lois. Iatity Ks.arnts

Tb. socuatie siVkt.

r piok.d

by a special probe nuing s pissoslectric

crystal

to ov.rt the

n1osl vibratia into electric

ctUatis.

Thia o.ist.d of s. quarts pitt. cut p.rsll.l to the a9tiosl axis in suob a wy that its wide planes wer. cut psrp.diau1sr to

the electrical

axis. In arder to slji,ist. resnc. .tf.ata, tb. thi*ns.s of the quarta plat. was auth that its natural frequency lay far

abo,. the

observed

oavitat iou frequencies.

Fig.re i sh. the ostruotten

of the probe.

It oiats of a dsltuin rod

ioh is screwed, into the wall

of

the krodynio

tb.wi.l

ioâ.l tuxtne end the probe bo otsinisg the qnarts piste whith ta f ir.iy pressed agei-t the rod

by

of a spring. £ rod tr.'-4 t. the sooa.ttc vibratiasi to the qeerts crystal and

the

resultant .l.otrio oscillstime are fed directly

to

the vaiwe otained is the probe houin.g 'ioh sots e.0 a vid, bend a1ifisr

er the rang. fras 20 zyel.s to 1

.5 los.

object

of

placing the first lifi*r directly inside the probe housing was to el

44n*t.

oapscitative .ff.t. du. to the saurizg syst

and the oeoting osbiss,

analyser desiM

as

the basis

of

the s,bo, .entios.d requi&uits

is sho .htis.li,y tu Ptiire 2. The electrical o.eillsti. tras the prob. are fed to a niser 'ubith also reasive. a voltage frs. the hi

frequ.r

b.t.r.n. asoillat (Q884).

The

xsr

ztput is ted t.

the

first

11fi.r

ted to s freqiasney .1 2.83 $ sad t to s. uusd

amar stag. r. it is .mad with the output tras a eo het.r.aie

oscillator tas.d to 2,3 loe.

Tb. vutyut of the

.so niar is f.4 to

th. ..o narras! bead

.pl4fisr

td to 100 ko.

Th. 100 kas sigeal is

t fed to s detectar stag.

sad f

4ly to the indicator inatzent.

The ssieotias

of

a hiwi int.ra.diat. fr,qiaenr for

the

first liti.r osans that asly s narras freqeenay bend

is

passed whith,

as -4 'ing with

the h.t.ri&dyse fr.qusn by ei or differenc. gives s freqasnay

of

2.83

.

The ]yasr i. fed tras a voltage

stabilised

rectifier,

The arr.'''t described p.rndtt.d the osyitat

tos nadee intity to

b. esasur.d

o'er the frequos rang. fros 50 kas to I Mos.

A pointer eioro.tar was used to

ssur'. the

cavitaticm nois. intensity. Sinos the

aoc.tic r..d.isti

&e

to ca'vitati is wstab1s at all frequencies the thstrent pointer was subject to f uatti sad

in order

to

ol44v&t. the.. fluotuatics

the

inatrsnt was

ahtmtsd by a

ocmdanser so as to increase the 1nstrent

ties

oc*st&nt to &

value

of

fras 8 to 10 s.oda.

As a

result the assswes.nt value obtsinsd was

the asan valus &

the inteosity .t th.

obsrwed

frequency.

The r.oarding of the

o1ete notas sp.otrta for a gives

oavitatim

regles took aroztte1y 4. t. 5 ainitea.

This sppsratua was uasd to

inreltipt. as'vitatie. noise in this

aboye. ( djffusqr

in esêel

droturbias.

the

oavitati stand.

In the ens.

of

the diffuser the probe was betted

alose

to the

ns.rrst oro.s .ecties. When invest ipting node]. turbinas the probe

was boated inside the turbins, sonsuhat

diaplaas4

relative

to the axis

of rotatioe of the

blade.

in

the dir.etton of f1ø and was therefore situated f

au-by

close

to

the

r.gins uhoes the o.,itatiet spp.sr.d to b.

nest jutasse. The

veriaties in

the intensity

of

oavttatic estas I.e

t.ise

1 rdr.tw%iess was investigated by this esano.

The osvitatien noia.s speCtres thtained in

the diffa.r is h

in

gure 3.

The noia, intensity was ala.

.s.s.r.d foe' eodela

with type LP

sed I

iars in the

I kydrodynios isboestory

for type 1%8

-IL. 63 rs in

the

kydruturbtee laboratory at the L.siagrad

tl

Wora,

The araatoriatioe

of the noise

spestra tsiest with ditterest

oavltatis regine., possessing different values ef the avitaties

ooettteient Q" , ars

ta Pipw. ., ièsre

the tzeqummr is plotted

sleng the abseissa. asia end the Intemsity alesg the oedinets s1i.

ob oureu gives the noise

intsity

at different frequencies foe t

gives esvitati

r. Tb. rss.lta obtained lend t. the tollawI.ag

_- noise spectra obtained both in th. diffuser and in the model

tmbinss imdioa.t. the pr..o.

of

herp r4-

_and

i sners1 w

s14 .

e

t. the .p.atrsl oeryse obta.tn.d in the pr.l

44 iiry

.psrinta.

The

sr

of

r4 obtained .iiff.r. with diff.rwnt flos oiti both in

the oas of the diffuser and of the models. ¿. 'rl-. say b. due to the ertti

of

transient acoustic radiation by the oa'vitatlon babb1.s w*ic'z was partteu]ar int.m. at the time & r.00rding.

t

8is the bubbles diff sr in au, their fr.qu. spectra and

iat.nsttiss ist also b. ditfsrent, transient pulses result in a lin'

a-Tb.

ri

oavltaticn noise intensity was obser,d over

t

relativ.:1.y

nsrros frequency baal extending approximately f roe 100 to 250 kns. Th noise intensity dec:rss.sM with inca-ease in f requena,,

b..4ng practically

¡ero at a fr.qiy of I cs.

The resulta obtained represented the nean values over a given tim.

int.ri*l sal the .p.ctr oharacterised the acoustic r.Aiatien for a given regimi during a given finit, bui mot very large tim. later,'.].. Sino. the vibrational charact.r of the otyitation proc... is wiatab1., it

b.00nes

necessary to obtain these spectra

for instantaneous fis eiti (

at l...t during the .ht..t possible tine) taza permitting

t

"e sconTate and dstailsd investigation of their struotn-e end rslati.h1p with the

cavitation pa-coses.

Por this reason the seriaental sathod vea verted and a .ç*cial ultrasonic noia. analyser developed which enabled the mois. spectra to be recorded practically instantaneously ca the sca-sen of a oat

rey tub., The spectra ware permineat].y recorded by pbotogrs.

method of investigating the intensity

of

ultrasonic radiation by sp.ctron

photography.

The aoous tic raitiatico was detected by the semi type

of

probe (see Figure i).

The noise intensity -. sgsred by feeding a voltage proportional to the intensity to the vertical aveop plates of a cathode ray tubs, Thu

wee grat.d by & b.ri

titanate piesoeleotria ele.ent with a

n&ttntl freqoy

of

the ord.r

_of

1.5 io.. Lt the same tise a voltage

prcçortiwal to

the frequency of the seaaured radiatien sea fed to th. borisental eseep plat.. of the cathod.

rey

tube.

A beterodyn. sy.tes

with hi

speed vs.riati of the heterodyns frequency was ilay.d in order to obtain the cclete sp.ctr in a very short period

of ti...

By aean.a at this rrangseent narr re.diati

bends were auoo.ssively passed througi the analyser,

over

the entire rsn of the ultrenanic r.4iati over any desired r.gi of the

ultra-sic epectr, during e. very aht time interval

of

th. order of e or a

few hzmdredths of a seccsd. spectrum 'sea photographed tiring the .e short ti.. interval. ¶ oorreapoeding frequency spec tr was then abose

o.

the s cathode ray s'.sn ath ses photographed. The two nega t ive s war. then superposed and the frequency saale sea transferred to tb_s intensity speotr which enabled the intensity to be determined for sr given frequency. In this respect it should be noted that the

frequency seal. within the li.it.

of

0 and 250 ko. i. practically linear. Th. analyser cyst is chose schematically in Figure 5. The pulses Cros the probe are fed to & sixer valve which also reoeivee a betero4n. voltage so that a certain frequency e is fed to an lifier tuned to

1,.65 kos. After detecticai, the aigeal i. fed to the vertical sweep plates

of

the cathode ray tube The heterodyne frequency is capacitativel.y tuned aver

the range Cran

5J45 to 765 ko. during a period

of

fran 0.1 to 0.01 secid by seams

of

& special relay. Thus th, intensity sp.ctrum between the lits Cros 70 to 300 ko. can be recorded

an

the cathe

ray

screen during the s time int.rval. The spindle of the heterone

variable condenser is rigidly oo.nected to the spindle of a potentiose ter the voltage Cran 'which is fed to the boriztai sweep pistes of the cathode ray tube which are thus .ynábronia.d with the vert io.] sweep frequency. The harisontal sweep length is oantrolled by a special rheostat.

The schene provided for the possibility of switching in & frequency

marking generator in place

of

the prob. using for this purpose a st.'i.rd eisal generator. In addition provision was aleo sede for

6.

contro1liJ1 the amplificati of the _{applied to the vertical sweep} plates and tar regulating the ti _{reqtdr.d for analysis.}

The ayste we.a supplied fran an electrc*i and i stabilised rectifier with a high frequency input filter.

The spectra appearing _an the cathode ray screen were photographed

with a 'Zen1t" oara.

In

order to utilisa the full trame diiiena ians,

the focal length could be adjusted by aeans of a special ring. During photograpby the camera was located at a distance of 200 tras the cathode ray screen.

The appe.ratus described was used to inestigae the acoustic r.4isti of cavitatiou generated by a aaetostriction oscillator at a frequency of

7 kas in

the diffuser at a bydroc'namic channel and with a 250 diaiter .odel of a type

_PL.577

kydroturbine. Tb. .xperi.enta

were carried out in the hyth-cxtynmzatca laboratory of the _{The typ.} of spectrogram obtain.d is shown in Figure

6.

A rauher of spectrograms were obtained with different elitudes of vibraticai of the aaseto-strictios oscillator, thus COrrespOEldin.g to different intensities of

cavi tat tas.

The piotograpb.

obtained

_{establish the following propertie, of} ultraaasic cavitation noise as produced by magnetastriotirsi.

(i) A typical characteristic of all the .pectrogra obtained is

their line structure and the relatively narrow frequen' bend in the region of 100 to 130 kas where the ultrasonic radiation possesses aaiirau intensity for all te magnet astriction vibration amplitudes investigated.

(2) _{ith increase in the mgnetostriction vibration anplitude, i.e.}

with increase in the cavi tat ion intensity, the ultrasonic radiation intensity increases over a narrow frequency _range;

in

..iitiou the intensity also increases at other frequencies up to values of the order of 175 kas; it ebould be noted

however that the intensity within the abcre-ent toned limita always greater than at other frequencies.

(3)

The spectra obtained are fairly twifcrm in character thus indicating the unit ority of the veri ous cavitation procesase in all the case. investigated. Figure 7 shows a spectrogre.e which indicates the intensity and frequency of the radiation produced in the diffuser of a hydrodynamic channel during the early stages of oavitatica developsent.

!xamina tion of the speotrogree of the radia t ion in the diffuser lead

to

th. f ollowin ccneluai:

(i) In the absence of cavitation, the intensity of the ultras onlo radiation is very low. achines in operation produce no

isarked rtd tion

end do not

affect the igr4tude of the cavitat ion radiation.

With the &rrangenent used, line apeotra re obtained. The a&xi radiation intensity was observed at a narrow frec,uency band in the re gicm of 150 kcs.

Le the cavitation oontthues to develop, the axi.a intensity

rin at the sa

frequency region but & general increase in intensity also oocurs at other frequencies, chiefly at lower frequenci.s.

By way of exarple Figuree 8 aM 9 show spectrograi reccuded at the cavitation te et s taM during the invee t

igati on

of a 250 Ma.ieter od.1

PL. 577 runner far the eanc operating

conditions but

different cavitation

r. glees. These tes t e lead to the following conclusions:

-(i) High frequency noise i. practically absent during operation

_of

a aodal turbine without cavitation. Noise

of

u4.partant

intensity is recorded at only a few isolated frequencies. This fully agrees with

spectrogra

of diffuser noise

_recardd in the absence of cavitation. This confirms that the

noise

due to zeachine operation possesses

_no

noticeable hi frequency

(

) L.. the ariginat ion

end

develoçnt of the cavitation proceeds,

the

nois,

intensity also inases. Th. nois spectra extend 8.

9

P.T.S. No. 10g2

still further both into the low.r

and jsr fr.qucy regi.

Tb. frequency r.gic in which the hiest intensities are located

lie betw.sa 80 sM 300 kos. Tb.

1

intensity is located

in th. rs gton

fr

150 to 250 kas.

(3)

The critical cavitation regias orespondln.g to

T,

is a.rks4 by considerable intensity at a wber

of

frequencies and althou no specific indications are .vident in

the

cavitation noise spectra, two or three frequencies in their oun region af the speotrta iniioate oonaid.reble alitudei.

11th

further

dav,loent of

cavitation

the

intity increases in as regions of the .pectrogre*. Tb.a. characteristics war. evident ta sil the experisents pert ord.

The frequency s ctrt of the ul traseaio cavitation noise in a

nodal k'droturbine was oosidarably wider than that obtained by maetostriotion or in the diffuser

of

a ydrodynenlo

Ñutrl.

This ii prssueably due to the fact that

the flou

conditions it the cavitation stand e less honoen.ous.

(5) The experinonts ahowad

that

it was possible to use a nsrros band

noise aenauring

syiton

for th.

investigation of

cavitation. A

1. _{Probe with preamplifier. I - screcne4 cable; 2 - MIS}

amplifier valve; 3 - iean; 4 - *obe hoizJ..g; 5 - IIINlItII.g

150

buik. 6 - uxu ay*al. 7 - plug; 8 - bydxoChke chug.

.vsaaa..aa. s

100

ssa'i ..sus.

50

ka

100 200 300 400 500 600 70G1

fi

40 30 20 10

mi:

_s....

s....

.t

_.4.

lnLenhityga*ge (graduated scale) 200 _Profile 100 20 300 400 500 U) 70

Fil. 4. Radiadca thxe1ty .perwIn le w fer cav'tt*tkes by

a model PL. 634 rez: a - PL. 634 r:

410°; $

lO

80; Qj - 770.

I

9.165; fo

1.192; fl1

.0.145.

b-PL.634rer:p = *2; a10; nj1O0; Q1360.

fVir

0.574; Vv -

0.998.

10

Fi. 2.

Itock diagram of the a(x,ic

radia-tioe analysa.

i - k. f. au11fla: 2

ist m1

3- ist I.!. amplJlIa; 4- 2nd mIxer; 5-2M

t. f. amplifier; I - 4ctec; 7 - 2nd betaodyne;

8 - 1* heterodyne.

s

I

a....,

asasi

s.... i,

u...)

si... s

_{u.... s}

u...,. i'

a...'

u.u. 61

.s..au aaaaauaua

Saul. sauau...s.a

sar am. usassi....

4I1 uuisau..iU

U

'iiuaus.aa.a

f

ayas. i

_sa.aaua

va'au usasuus

'iaflas aasau

I 5Û ₂₀₀ Probe location 300

FIl. 3.

RadIation lnrealry spcftnmle water

fr cavitation ti the differ.ez of a hyo4yiamlc

ckane1.

400 f

ka

Fil. 5.

Slack diagram of u1tras.nc r4titkii

anaiya with high spoed radtng.

i - h. f.

gcnera

_{sad ampU; ta - mixer; Zb - t.f.}

amp1Lf; 2c dettr; 3

-4 - *sply

ix; Sa - and 5

- e.f. amplifier;

6 - htetal swap generaerr; 7

- frtquancy

base gencza; $ - czt

ray tóe.

R.T.5. No. 1002 40 30 20 10 o b)

10i

e.

.1,'-lic

?O k

,

.te4,1, I I

liC 150

Flj. 8,

Spectrogram of r4Iaiban bi wa from a mo1 type

PL5TT nmner 0' 0.213.

e

t

I

100 _{200 250ka}

Fit. 9. SpecVokm of rid1a biw froni a model type

PL. 577 rmaa - 0.230.

li

200 k

1.

R.T.S. No. l0O

FIj. i

Spcctrogra.m of magncuisuctk rl41.' _{P1g. 7. Spscuovn of radiiUa ttizelty la walrz diar}

to the dll.rr vibraban dwing the developmz of