i- ' iin fiq. i. it can be seen that vent holes area of 55? to 50$ are desired fcr the 3 mm...
TRANSCRIPT
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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/ »
'
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.
u GO O
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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
.00
65
55
5ü0
cm
4.5
4.0
35
3J0
25
2P
15
W
05
0.1 0 -1 1 2 cm
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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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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