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TECHNION- ISRAEL INSTITUTE OF TECHNOLOGY

DEPAVMENT OF AERONAUTICAL ENOlNEERiNO

N.A.IPA. ItlAlt

..' t CLEARINGHOUSE

Mi i,i V , .. IM ^1/ »

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F61052 67 C 0033

SR 6

Oec:elllber 196 7.

SCIENTIFIC INTFIW~ Rf.roRT No. 6.

SM~ll StHEUlEO THERMOCOUPLF TOT~l T£'."'R~TIIRf. f'ROAES

by

JOSEF RON and Ylt;AL KRrHZnN

Tectmlon - Israel Institute of Technology Departwlent of Aeronautical Enqlneerlng •

Hal fa. Israel.

The research repo,.,ed In thIs docUIIIeflt hess heon sponsored In part by the Aerospace

Re~oa rch laboratories, under r~tract F61052 67 C 0033, throuqh the European Office

ot Aerospace Research (OAR) l~lted State5 Air Force. This res .. rch Is part of the

Separated Flow Research Proqr•, of the ARL, The~hanlcs Olvlslon.

This docUMent has ::een approved for public release and sale: Its distribution Is

unl hnl ted.

ABSTRACT

The design and the calibration of ? mm and 3 mm O.D. shielded thermo-

couple total temperature probes are described.

Thr ? mm O.D. probe recovery factor Is O.Qfl'j « 0.005 and the 2 mm

0.0, one is 0.975 « 0,005 up to flow Mach number of 5.5. The probe response

Is only sllqhtly dependent of Reynolds number. By positioninq of the thermo-

couple junction at the vent holes position its output becomes sensitive to

disturbances, such as shock waves in the flow. This characteristic of the

probe can bo useful In mapping of discontinuities In complicated flow fields.

k.

TAPLF or rrmrNTS

PAGE No.

ARSTRACT I

TABLE OF CONTENTS I I

LIST OF SYMflOLS I I I

LIST OF FIGURES IV

•• INTRODUCTION I

2- THE 2 mm AND 5 mm O.D. SHIFLDEO THERMOCOUPLE PPORE DESIGN 2

3- THE SHIELDED THERMOCOUPLE PPOnES CHARACTERISTICS 2-5

REFERENCES 6

r

11

LIST OF SYMRDLS

M Mack number

r Recovery factor

Re Reynolds Number

T Static temperature

TT Stagnation Temperature

T Recovery Temperature

- IV

LIST OF nnuRrs

Figure No.

1. The 2 mm n.n. shielded tfiermocoup le probe.

2. Errors duo to conduction and radiation losses as a function of

heat transfer rate to the airstream.

3. Recovery factor as a function of Mach number for the 2 mm and

3 mm O.D, probes,

4. Recovery factor as a function of Reynolds number for the 2 mm

and 3 mm O.D. probes.

5. Recovery factor dependence on the ratio of vent holes area to

frontal hole area.

6. Typical response of the 2 mm O.D. probe to the flow structure In

the supersonic wake behind a blunt base.

7. Sensitivity of the probe to flow disturbances as a function of

thermocouple position in relation to the vent holes position.

- I

INTRODUCTIDN

In principle the tempf-raturo inside n pi tot tuho, where the flow is hrounht

to rest at equilibrium, should ho the starjn.ition tompernturo, and could hr; measured

by a temperature trinsducer placed inside the tuhe. The difficulty i <; that in

practice equilibrium doos not exist, since heat is lo^t ^y conduction, convection

and by radiation from the transducer and the prohe walls. Thus the transducer

responds to a temperature T (recovery temperature) which is lower than the

stagnation tompornture. This recovery temperature depends on the probe confiquration,

conductivity and reflectivity of the probes walls, flow conditions about the probe

walls, construction materials etc. It will be shown that such a probe, can bo

specially designed to respond as well to various disturbances in the flow field such

as shock waves, shear or entropy discontinuities etc. In the present investiqation

total temperature probes are developed for studies of the flow field in the supersonic

near waKo. These probes should have recovery factor, r close to unity which Is

also almost independent of Mach and Reynolds number variation, The probes must be

of small dimensions so that a qood resolution can be obtained with minimum disturbance

to the wake flow. A successful total temperature-shielded thermocouple probe was

designed and built at MOL by E. Winkeler (Raf. I). This probe had qood characteristics

hut its dimensions, 6 mm 0,0,, are larq'i for most near wake measurements. In the

present i nvest i qr>t ion probes of 3 mm and 2 mm 0,1), were built and studied. It will be

shown thai those 7 mm and 5 mm 0.0. probes have almost comparable characteristics to

the 6 mm one of Ref. I. The smaller probes ran be made sensitive to flow discontinuities,

so that these can bo also used for flow field mappinq (Rof. 2),

?, TMf 1 mm 'IN'1 'xnn n.n. ,,m!l'1fn TM! ^'»^rniiPi f tifjoff pf.irfj

The drawing .in'l .1 phntrvir iph of fho ? mrri n.r\ prob«.' ir'1 .hown in riqures I r) a.'id

lb respprt i vo I v. Thi; d imonr, i on', nf th(; prnt'rjs .iro n i vcn in T.itiio I.

TA'M I I.

Probe P) mm d mn Vunt Mol(> Aroa

T wd' /4

x, mm x . mm 4

7 mm ;'.()

3 mm 5.0

I.3

2.0

.60

, 40

r'.3 I0

I0

The qlas'j shield is coated with shintnr) pi itnuim n.iint (M.movia paint type XX) baked

at 760 C. The thermocnup le is made of V3 qa'ie iron-constant thermocouple wires

packed in a stainless steel tube filled with inserted thro'jqh a teflon pluq.

The thermocouple junction is obtained hv spot weldiiif) in a mercury bath, The junction

diameter is about I.I times larqer than the wire diameters. The probe's head is qlued

by epoxy rosin to the stainless steel probe holder. The stainless stell tube on which

the probe head is mounted is l.cnt, knee shape (sec; fir). I), so that the probe holder

and support are kept outside the wake region.

5. TMF SHIEU-'m THFRMnrODI'l f PI'QI'rS niARACTimSTir"-,

The recovery factor of the shielded thermocouple probe is defined as

rr - T

where Tj - Recovery Temparature Inside the Probe r

T - Staqnrttion Temperature

T - Static Temperature

The recovery factor is determined hy the bnlanc« of tho losses due to con-

duction and radiation and the ra+o of heat addition from the free stream to the

probe. Trie losses can be evaluated approximately from the known properties of the

probes' materials and rate of heatinq as shown in Fiq. 2. It is seen that for

moderata heat transfer rates to the probe external surfaces total temperature

deficiencies of the order (y—) + (-=■) = 2% to 5!? can T convection radiation

be expected. The recovery factor values depend in qenerjl on the Mach number and

Reynolds number, (or convenience in use particularly In non-uniform flow reqions

(such as In the wake reqlon) it is desirable to have a probe with a calibrated

recovery factor which will be insensitive to the variatiori of these flow paramelers.

The present probes were desiqned to minimize the effects of Reynolds number variation

on the recovery factor and only a small effect of Mach and Reynolds numbers is

detected. The measured recovery factors are 0.^85 » 0.005 and O.^ » 0.005 for the

5 mm O.D. and ? mm 0.0. probes respectively. The variation of the probes output is

shown In Fiqs. 3 and 4 as a function of Mach number and Reynolds numbers. The recovery

factor dependence on the ratio of the vent holes area and frontal hole area is shown

in Fiq. i. It can be seen that vent holes area of 55? to 50$ are desired fcr the

3 mm probe while 50$ to 80$ are needed for the 2 mm probe, while the 6 mm probe required

only 20$ open vent area (Ref. I).

The response time of the proho is important for tmnsient me.isunments and also

for measurements of temperature distribution usinq n traversinq mechanism. The time

response constant T for the 3 mm proho is esfimatod to hn ahout 0.^7 sec, while for

the 2 mr. one, the value is about 0.? sec. These rnsponse timos are reasonable and

enable recordinq of larqe number of temperature points durinq a traverse of few

minutes durinq the wind tunnel test.

An additional feature of the shiloded thermocouple probe is its sensitivity to

disturbances in the flow. When the probe crosses a disturbance (such as .1 shock wave

or a thin shear layer) its recovery factor chanqos abrutly by the cevere chanqos In

the heat transfer rates due to the disturbed flow confiquration in and about the probe.

This characteristic of the probe can be used for detection of disturbances in a flow

field. It was found that the chanqe in the recovery factor may be made positive

(indicating "hlqher" temperature) or negative ("tower" temperature) or even neutral

depending on the position of the thermocouple junction in ratation to the vent holes

position. The maqnitudo of the response of the probe to the disturbances is determined

In the presonf investigation at the jump of the probe's response as it traverses the

trailinq shock and entropy layer at a fixed station in the wake of a wedqe-flat plate

model. A typical probe's response at this position is shown in Fiq, 6, Probes with

varying thermocouple junction position are tested at tde same wako stat'on and th«

probe sensitivity to the wake disturbances is meisured. The results of this measure-

ment for the 3 mm probe is shown in Fiq, 7. It is seen that when the junction Is

positioned near the probe's entrance the probe's output is reduced as the probe crosses

the disturbance while beyond about 1/3 distance towards the vent holes this output be-

comes neutral and then becomes positive as the thermocoup'a junction is moved towards

5 -

the vent holes. The maximum sonsititvitv Is ohtalnor) when the junction Is at the

vent hole position. Similar results are ohtalnf?c) also in the case of the 2mm O.D.

probe. The use of these probes for wike flow mnpplnq Is shown In Reference ?.

Further miniaturization of the probe itesiqn can bo obtained by usinq new

technique for manufacturInq such as by use of new tools for drillinq holes in

qlass etc. These miniature probes can be used for boundary layer studies and

can be useful as additional tools to the qenerally used hot wire techniques.

-

- 6 -

REFERENCES

I. Winkler, M. Eva:"Oesiqn and Calibration of Stagnfttion Temperature Probes

for Use at Hiqh Supersonic Speeds and Elevated

Temper-atures", Journal of Applied Physics, Vol. 25,

No. 2, Feb. 1954, pp. 231-7.32.

2. RoM J., Kronzon, Y. and Seqlner A., : "The Velocity, Pressure and

Temperature Oistrlbutlon in the Turhulent Supersonic

Near Wake Aehind a Two-ntmenslonal Wedrt.;.-Fic:t Plate

Modei",Contract AF 61 0'>7 67 C 1Yl33, Interim Sci.,ntlflc

Report No. 4, TAE Report No. 00 Oec. 1967.

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FIG. 2 ESTIMATES OF TOTAL TEMPERATURE ERROR DUE TO CONDUCTION AND RADiATION

LOSSES

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FIG. 5 RECOVERY FACTOR DEPENDENCE ON THE RATIO OF VENT HOLES AREA

TO FRONTAL HOLE AREA

rui—AA^ji •1.05

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FIG.6 RECOVERY TEMPERATURE PROFILES IN THE TURBULENT NEAR WAKE BEHIND A BLUNT TWO DMENSIONAL BASE AT

M=2.25

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UNr.LASSIFIEO S.C•ntr a..aftceu.,.

ooa.IMT CONTIOL DATA· I&D ,...... ............... ., ......... ., .............................. _. ................ --· ................. t . OltlftiNATIMG ACTIVI~'t fCe..-e ....._, ••· "•~•"" ••cu"'"" c ~••••~•c•"•••

TECHNION RESEAP.CH ANn OEYf LO~,tf.NT FC'UNOA Tl ON Unclassified

AERONAUTICAL EU{;INEERING LAOO~ATORY, ItA I FA,I S~AEL. •• .... u~ I M~OitT TIT'-11

s·-~ALL SHIElnEO TEr~HOCOtJPlf: TOT/\l TP~PEP.A.TURf PP.O~f:S

• DIIIC-~TIV. MDTIII f1',._ e1 ....... _. ...... , ...... , Scientific Interim P.eport No. 6.

I AUTMDIIfiJ f&.a.t- ... , -· ,.,....,

~ Josnf Kr"onzon Ylg<"l .... "'" ... ,.. , .. ····~ .... -~ ~···· l , .. NO. OP2"·~·

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••· c•••acT •• ••-• .... le. ....... A"" ..... ~ .. ,. NUM··•IIfi.J

F 6105?. 67 r. 0033 TAE Pf:Pf'PT rJo • 7(). .. ~"•"•c• .... 7063 .. 61445(')14 ... 11:•:.~~··· .... , ...............................

4 . ()013()7 tl. AVA 1'- AOI'-ITYI'--TAT ... IIDTICU

This document has been ap~r-oved for public r"9lease ~nd sale: It dlstrlhutlon I s un I I m I t"d

tl . IU~L.II .. MTAIIY NOTIII tl. ~-·-·· ... ITAIIY ACTIVITY

TEr.H, OT! IFR l'.er"osrace tlcsallrch lahor"ator I es (I\~) \·!r lght-Pattor"son, ArP, Ohio, 45433.

u A.STIIACT

The design and thA calibration of?. mm and 3 '""" n.n. shielded thenno-courle total ten'f'*"r~~tture prohns i'tre descrl h~d. I

The 3 mm n.n. prd~e recover"y factor lc; o.cms * C'.ons and thP. 2 mm 0.(). OnA I c; o. C)7~ ~ n. 005 up to f I ow .,.,c., nUf"'•ler o.f 3.'i. ThP. prohe response Is .only sl ightlv d~rE'ndent of Pevnolc!-; nurnhrtr. ~Y posltl~nln~ of thP. Thenmo-couple junction at the vent hoiP.s position Its output tlecomes sensitive to d I sturbi'tncns., such ~s shock waveo; In thP. flow. This char~ctP.rlst lc of the p co be c.,,, he u!'ie f u I In maprlnq of dlscontlnultl9o; In complicated flow fields.

\ ,, v

DD .~:::. 1473 ~CLASSIFIF:O

ltiCLASS I~ I ElL_ ____ _ S.Curily Cl•uahc~etiun

••

Small Shielded Thenmocou~le Probes

Total Tel"'f)erature Prohas

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