NASA Technical Reports Server (NTRS) 19950012870: Ice Accretion with Varying Surface Tension

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by  NASA Technical Reports Server (NTRS)

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NASA Technical Memorandum 106826
AIAA-95-0538
Ice Accretion with Varying Surface Tension
Alan J. Bilanin
Continuum Dynamics, Inc.
Princeton, New Jersey
for
NYMA, Inc.
Engineering Services Division
Brook Park, Ohio
David N. Anderson
Lewis Research Center
Cleveland, Ohio
Prepared for the
33rd Aerospace Sciences Meeting and Exhibit
sponsored by the American Institute of Aeronautics and Astronautics
Reno, Nevada, January 9-12, 1995
(NASA-TM-10682o) ICE ACCRETION N95-192_5
WITH VARYING SURFACE TENSIOK
(NASA. Lewis Research Center) 13 P
Unclas
G3103 0035009
NationalAeronauticsand
SpaceAdministration

Ice Accretion withVarying Surf'_ Tension
Alan J.Bilmlin
Continmun I)_aamic_ Inc.
David N.
NASA Lewis Research C_tcr
Cleveland, OH
Abstract 0 Air_ U-msfcrterminenergy equation,K
/9 LaUmibeat of freezing, cal/gm
During anicing encounter of aa sircralt in flight, super-cooled I.ment beatof vaporizaticcea,l/gm
waterdroplasimpinging onanairfoil maysplashbeforefreezing. P Density, dyne/cm3
This paper rtpcm tests performed to determine if this cffect is V'_cosity, gin/eras
sigaificam and uses the rtsults to develop an improvod scaling C_w/a Surface tensionofwater againstair,dyne/era
method for use in icing test facilities. Simple laboratorytests Icin8time,rain
showed thatdropssplashou impact atthe Rqa_lds and Wcb_
numbers typical of icing encounters. Further confimmfion of Subscripts:
droplestplas_hmacficmicintgernpscrfc_acidntl_NASA Lewis Air
a
Icing Research Tunnel 0RT) withasmfactant added tothespray Basedondroplet size
wmr toreduoethesurfsoe tmsion. Thermul_g ice shapeswere
f freez_ point
significantlydifferentfromthose formedwhenno smfactantwas i Ice
_kkd to_c wstcr. TheseresultssuggesUxlthatthedropletWeber
m
number must be kept constant to properly scale icing test R Reference size and conditions
conditions. Finally, the paper presents a Webez-number-basod aurf Surface
scaliagmc_l aad rqxa_ results fromscaling testsintheIRTia S Scalc size md conditicm
which model size was reduced up to afactor of 3. Scale and
Total
tot
refaenoe iceshapes are shown whichconfirmtheeffectiveness of
7 Themefical
thisnew scaling method.
Water
w
Nomenclature
Introduction
Accmnulafion parameter,c_aensionless
A¢ Wnxi tmmd icingtests ofsubscale aerodynamic ccaqxnm_ts have
b Relative heatfactor, dimensionless
been _ fordecades Yet,scaling lawswhich relatetunnel
¢ Characteristicmodel length,cm
datato predict what would be anticipatedduringoperation ofthe
Specific heat, cal/gm K
compomm inthe atmospherehaveyetto be_t .u.lx___Thisis
Convective filmheat-transf_ coe_cient,
evident from reviews of scaling laws by Bilanm m 1988 and
oal/sec m2K
Anderson2in1994. Thereexist abouthalfa dozenmethodologies
k Thermal_tivity, cai/sec mK
whichbare competed over theyears forinternationalaccepmace,
LWC Liquid-watercontent,g/m3
butinspiteofyearsofvalidation testing, todatenomctlg_logy
M Mach number,dimensionless
has shown a clear advantage. One reason is that un61quite
Freezing fraction,dimensionless r_ently, tbe abilityofawindtum_ testmgin_ to set iciagt_
Nu Husselt number,dimensionless
c_mdifionssuch asdropletsize andliquid-wateroontcnth,asbeen
P Ambient static pressure, nt/m2 hk_=_d_th nxsmanenmtioanadcalibratisohnort_ The
Pw vaporpressure ofwater, nt/m2 second, andprobably more impcoant, reason isthat almost
Ra Gasconstant forair, 287.0 ntm/kgK without exception previous scaling methodologies have ignored
Re Reynolds number,dimensionless waterdropletimpactandfilmdynamicsinthescalinganab/sis.
t Ambient statictemperature,°C This observation was brought to the attention of the icing
7 Ambient statictanperature, K community in 1988I. Thispaper reports oathe first attemptto
U Droplet velocity, m/s provideexpefia evidoncethatdropleitmpactandwaterfdm
V Airspcat,m/s dynamicscannotbeneglecteidnthederivatioofnscaling hws,
We Weber number,dime_onlcss especialulnydericincgonditiownhserelowfreezinfgractioanms
amicipateT_heresultpsresentehde_ aresignificnaonttjustfor
8 Dropletmedianvolume diameter,gm scaling butthey also sugg_ that ice accretion codes need to
A Filmthicknesosrice thickness, m implement droplet impact and liquid-film dynamic models to
Droplet-energy transferterminenergyequation, K
improvethe accuracy of predictic_s. Discrepancies between Droplet Spluhing Tests
predicted and ram.tared ice shapes are often blamed on
inaccuracies inmodeling the convective heattransfer coefl]cienL The above discmssion meatiooed the use of slow-moving large
We suspect thatsome of thisdiscrepancy couldbeexplained by waterdropletsimpac_ awaU=f_ todetermineiffilmdymmics
considaingdroplet-surfaceinter_om. end splashingcanbeneglected inthedevelopment of scaling laws
end incomput_ models of the ice accretio_ Inthissectice, we
Evidence thatall isnotwell withpastscaling methodologies was report on simple tests which have bern conducted to examine
presented in refenmce 1 whe_ it was arguedthat if both the droplet impactdynamics relevanttoicing
accumulatkm fac_, A¢, end the freezing fi'ectioo, n, were
_m_ly _ at_.,h _at alo_ maerodym_ccompoee_ Figure3 isasketch ofthedrople-imp_ rig used during testing
the prediction of ice _m_i_ and a compsrisco betwem this A burette is mount_ at_ h(h<5 m) _bow asm_ dish
predictio_ andtest datamust agreefavorably. Itwas tben shown sitingonamilligremscale.Byslowlyallowingthewat_ todrop
us_ testdataalong withthe scaling methodology inthe $IMICE fromtbebereeeendmun_g thenumberofdropsprodeu_ p_
scans code3that seriouslymisund=r_ disc_sncies miililit_, onecen easily _te atypicaldropletdiemet_. From
TheSIMICEcode=_es thefreezingfra_oa a_ding _ _e _oes w_ inv_ _xay d_pe_oe _-ak_r_ vmex wa_e_
__y_'. r_el _om_ 1_d _ow_ f_ wi= dropletsrekasedfromrestintostill air,the velocity ofthe
themeasuredand_ icethickness atthe stagnationpointfor droplet asafunction of release height, h,isknow_ Intbetests
twote_having_ freezingfractions,nr,of.15 end .5. The reported here, the droplet diameter was 4.7 mm end theimpact
stas_on-point icee_ isexa_ propor_on_toA_, and veloc_ fromarelease heightof 1_d4.7 mwas4.2 andS.1 m/s,
thepredictionsinfigure1w_e basedonthis. Theactualmeasured resp_vely.
freezing fractions, nw were .35 and .6, respectively. Ice
thicknesses for the lower freezing fre_ion were greater than Theresultsereplottedonfigure4wheredropsimpac_afilmwhich
predi_ed by afactor of 2.3. Thus, either the freezing fraction is1/3,2/3,3/4 md 4/3 oftbeimpacfingdrop diameter. Plottedon
computation orthe estimate of accumul_on parameterwere in _heverticalaxisisthepcrcm_tofmass gainedat_:rtheimpact. For
example, ff the incoming drop'smass iscompletely addedtothe
error.
film, the percent mass gainwonld be 100%. Eve_ atthe low¢_
The suspidon that something may not be correct with the m_pactvelocities of 4.2 m/s, ontheorder of 25%of thein, rain8
mettxxtologyforcomputationofthe collection fact_ ismotivated mass issplashed away. Atthe highest _ velocities, amore
bythe obmvatim of_ impacting ashallow puddle. The surprising result isobtained in thatit ispossible to lose mare c_
_ ofthis collision isshowninfigure2. Here, forthe sake 1/quidf_m the film. A mass loss of 100% implies thatforeve_
of argungnt mdto good approximationduringthe interactionof incoming droplet,two droplets aresplashedaway. Note thatthe
thedropletwiththefilm, we willneglect theshearforces oftheair results are strc_81y dependent on the film-thickness-to-drop-
outhedroplet.The_thedropletfilmdyn_cs arecontrolledby diameter ratio, end film thicknesses which ere less than the
oulythreenondimen_onal parameters: diamet_ofthe_ dropseemtoexperienctehemostmass
ejec6mfromtbefilm.Notethatew,htesotonditiownasrepeated
A/8 filmthickness/drodpilaemteter aminimumofthreetime_andtberepeatabilityappeantobequite
Pw U8/_ Reynolds number
Figure 4 gives the Weber andReynolds nmnbers for the tests
PwU__lcrw'a Webernumber conducted, lb:se canbe competedtoTableIwhere itcm be sem_
that these values are in fact typicalof those enfcipated during
Also, we know from observations thatraindrops splash upon icing. The aboveresults_ se_nOy mggest t_ drop_e_
impacting a water layer. In Table I, we have computed and splashinganddropletimpactdynamicswith aliquidfilmmaybe
tabulated the typical order of magnitude values of these important in the development of scaling laws and alsomust be
no_limemio_l _ for both rain end icing conditiom. modeled ffice accretio_ computer codes sre to make physically
Quite surprising is the result that in 8eaefal the values of the realisticpredictionsoficeaccretion.
Reynolds snd Weber numbe_ forrainaretypical of the values
dta_ ic_ngrHen_, onecan studythe impa_ of l-ram raindrops
moving at10m/s imping al-ram film insteadof studyingthe Icing Tunnel Experiments
/mpsct ofa20-_m_drople_impactingafilm at500 kt_
Ifdropletsplashinghasaneffect ontheice-accreti_m process, then
Thispaperpresenttsheresultosfsimpleexperimenttso_afirm varyingthesurface tens/on of thespraywaterwill chansethe ice
the_ ofd_pletsplaslfirnagreendWerepresentatoifve shape. Two tests were performed in the NASA Lewis Icing
icingencountersI._ngtestisntheNASA LewisIcing ResearchTtmnel(IRT)to evaluatethe effec_ofsurfacete_n on
Tmmelare_ inwhich thesurfacetension ofthe spraywas iceshape.For the first test, Liqui-Noxa,_mm_er_d cleaning
altered bythe additionof asm'factant. Finally,apractical scaling solutim, wasaddedtothespray-barwate_supplysothattbee_tire
method is described and tested in which the droplet We is IRTsprayhadreducedstufacetension. For thesecond test,Kodak
maintainedthe samebetween scale andreferencecondifons. Photo-Ho 600 was addedtothe sprayof asinglenozzle directed
atthecet_ ofthetest_ while the IRTspraybarsmaintained
2
theirnormal sprayofdemineralized water. thegraytimerwm stmzdatthitsime.When theprescribsepdray
period was completed, the spray was shut off and the tunnel
The results of these tests led to the development of a scaling broaglatoidletopcmit pcrsot_ retry imothe testseotioa. The
methodbased ontherequiremo_ thattheWeber number,We,be iceshapewasrecordedbyfirstmdting athinslice throughtheice
matched between scaleandreference tests. Additional testswere normaltothe qdindu exis. Theshapewas tracede.to acardboard
performed inthe IRTto evaluate thismethod. The surfactant- template; these shapes wm'elater digitized andrecorded on a
addiU'onrests,theoonstsm-Wescalingmethoclandthe scalingtests computer disk Aftertheice shspewas reoxded, the modalwas
andresultswin bedescribed inthissectio_ cleaned andtheprocedurreepeatefdorthenextspraycondition.
NASA LewisIcin_ ResearchTunnel. TheIRTisshown infigure
5. Ithasbem desm_l inrefevmce 6. TheIRThasa testsection Results: Su_ace-Tenaion F.x_riments
width¢_2.74m(9fl) andaheightof 1.83m(6tk) Itiscapable
ofoperafionaltest-section airspeedsupto 160m/s (350mph) A SurfaceTensi_ Measurements The surfacetensionofthe
demineralizeIdRT water,two dilu6om of watcr:Liqui-Nox
refiigm'afionsystem pe_nits accurateconU'olof the test-section
mixturest,wo dflufio_ of water:Plm_Flo200mixturesanda
temperature from 230 to 278 K (-40 to40°F .) A water-spray
water:Photo-Fl6o00mixturewasmeasured.Photo-Fl6o00isa
system7 with 8 spray bars provides the ability to control
more_form ofPhoto-Fl2o00sothata600:1mixof
test-s_tion liquid-water content from .2 to 3 g/m3 anddroplet
medianvolume diamet¢_ from 15to40 ttm water to Photo-Ho 600 is_luivalezR to a200:1 mix of waterto
Photo-Flo200. _ wen:madeoathr_ occasiom using
Two sets of spray nozzles, known as the rood-1 and standard m g_3eralmwhichemployedthering-detachnmatmethod,andthe
nozzles, are used in the IRT to provide different ranges of results are given in Table I. The published values of surface
ten,on f_ water at 20°C is 73 dyne/c_ When the_ are
liquid-water content anddroplet size7. For these tests, onlythe
mod-I nozzles were usecL impuritiespreseat,however, thesurface temic_ will beless
this. Itisnotsurlxising,then,thatthe surfacetension ofwaterwas
Fortests using asinglenozzle toaddsuffactaat,a mod-l nozzle found to be lower than the published value. The addifioa of
wasmouatedouthe spray-barsupp_ andaimedsothatitsspray surfactant in the form of Liqui-Nox or either of the Photo-Flo
str_ tl_ modd atthe _at_li_ ofthctcst s_ti_ Thisnozzle conc,eatratiom reduced the surface tensioe of the IRTwater to
abouthalfitsuntreatedvalue. Fmthe=more, increasing the dilution
wassuppliedwithairfromthespray-bar manifoldwhile itreceived
of the water:surfaotant mixture had virtually no effect on the
wa_ fromatrekindependmtofthe spray-bar supply. Thesingle-
surface temio_
no_e waterpressurewascontrolledtothesamevalue asthewater
pressure forthe spraybars. Whenthe single nozzle was used,
Eff___o_fReduoedSurface Tension onIce Shape Initial tests with
surfactantwas added to its water supply while the main spray
_t additioaweremadewithLiqui-Noxaddedtotheentire
systemuseddemimndizedwaterwithnoadditive. Itwasfoundby
iceshapecomparisonswhen demineralizewdaU:rwithno spraybarwatersupply.Attheconolusioonfthesetestsi,twas
necessaryto flushtheestirespraybarsystemthoroughltyo
surfactantwas sprayed titan the single nozzle, thatof the total
waterreachintghecenteorfthemodel,about10%came fromthe removemy traceosfthesurfactafnotrsubsequenitcingtestwsith
demineralizwzadter.To avoidtheinconvenienocfethipsurging
singlenazzleandtherestlh_a the mainspraybars. Consequently,
forallthesingle-nozzle tests thespray-barpressureswere setfor procedure, a single spray nozzle with its own water supply was
aliquid-watercontentof90%thedesired value. mountedonthe sgray-bar array inasuch aposition thatitsspray
would strike themodel atthe center ofthe testscetioe. Thus,the
The tests of the constant-We scaling method were performed singlenazzk couldbeoperatedwith stafactant-treatedwaterwhile
without surfactant the full spray-barsystem operated with untreateddemineral/zed
wmr. Beomsekeshapeswereonlymeamred attl_cemu ofthe
Test Hardware. Ice accretion was measuredon hollow circular model for this study, this arrangcm_ would be effootive if it
producetdhesinekeslmpesasresultefdi'omaddingsurfactmtto
aluminumoylindcrs. Each cylinderwas mountedverticallyinthe
center of the test section. Cylinders with 15.2-, 7.6-, 5.1- and the f_l spray-basrystem.
2.5-cm(6-, 3-, 2- and 1-in) diameterswo-e used. Figure6 shows
how each cylinder was positioned in the IRTtest sectio_ A Totestthesinglo-naz_ system,KodakPhoto-Flo 600 inamixture
of 600:1 water:Photo-Flo was used in the single-nozzle water
xeUaaableshieldwas positioned infrontofthe cylinder toprotect
itfromspray duringthe spray-bar start-up period when the water supply. A (xm_parisonofcentedine ice shapes using the single-
mzzle and full-spray-barsmfactantadd/tim methodsis shownin
andairpressures were stabili_ng. Theshieldcouldberetracted
f ae 7. Thesotidlinerepreseattsheshapere ng fr n adding
rapidlyinto the tunnel ceiling byremote operationof ahydraulic
Liqui-Noxtothespray-bar watersupply. Thedottedlineindicates
aotnator.
the ice shape accretedwhea the single nozzle operated with the
Test Procedure. Testswereperformedbyfirsetstablishitnhge wat_:Photo-Flo mixture. Theshapes oftl_ iceformed bydtho"
desired velocity and temperature. Watersprayconditions were method of delivering surfactant agree within the normal
thenselec_xain,dwhentunnelconditiohnasdstabiliztehde,water rel_atability of the tunnel. This result verifies that the simpler
spray was initiated. Theshroudprotectingthe testcylinder from single-nozzle method of surfactant addition8ives results atthe
thespraywas liftedwhen the sprayconditions hadstab_ and centerline which areequivalent to the less-desirable method of
addingsuwfactanttothefull spray-bar system. and
ca
Asnoted above, the singk ncgzle c_ntn_outed only abont 10%of
%= %-- (2)
the total water _ the model ccmtedine. Thus, most of the
inmming drops would not have tbe reduzed surface temion when
the =agle mzzle was reed to add surfactant Appmmtly, the_ the
impacting droplet surface tension was of less _ to the Thas, forahalf-=ze model, forexample, both the einpmi ead the
phys/cs of the process than the surface tens/on of the unfrozen s=faoe tmsion oftbe spray need to be ronshly donbled over their
wa_ontbestaface _lhemodel. Because dilmic_ has little effect desired refetmoe values. While it is relatively easy to red=ce
on smCa_ tension, once the treated droplets mixed with water on staface temim byadding stafactant to tbe spray watt, iacreming
the surface, the =uface temion of the surface mixture would be the surface tmsion of the sprey to satisfy equation (2) does not
appeertobepr=ti_. Furthmnorteh,e=_,eedsreq_edby
expected to be about the same for eith_ method of adding
equation (1) for smetl-sude models will 8rectally l_duce
unacceptably hish Mach nmnbe_ It seems, then, that this
To test the effect of surfaotant on ice shape,cond/ticm were rum approach to scsl_ is likely to be unusable f_ most seal/rig
wh_hhadprevio=tbyernusedwith_ deninentized s/a_,_on_ _, apr=t/cai sca_ngm¢_xi canbe _
water. The results are shown in flgure 8. Tbe solid line gives tbe by relaxing the need to match Re between scale end reference
drape= tbe=m=']ine Imxhmedwithdeminera]izedwater,endtbe situations. This is areasonable simplification, forthe Re should
dottedlinerepresents tbeshapewhen surfa_ was addedtothe have liUle effect on the flowlield, provided the flow becomes
spray. Infigure _a) results are given f= tests in which 1pertof turbuleat over =mac part of tbe body. W'ah 81aze ioe shapes, the
Liqui-Nox clean_ was added to 400 per_ (by vohune) of point of seperation ead traasition aredetermined bythe Joeshape
water. The edditi_ of surfa_tant totally changed the ratber thin by tbe Re. _, a suding method was
shapeoftbelxns andreduced thehornangle. developed which is based on maintaining the same We for beth
scale and reference _mffttions and isnodng the Re. Tl_ method
Results for the single-nozzle surfat_mt-addition tests ere given in is discussed in the following seetion_
figureS(b).Again,s=fa:tmt addition hadadramaticeffect ontbe
shspcofe=kc A_egh ck_ptesptl=_nsh=b==shownine=
Constant-Weber-Nmnber _ Themethod isontlinedhere.
beach-toepxperimentdsesaibedprevionstiynthispapertobe
Results from weliminary tests to verify tbe method in the IRT are
s/gnificant, anadditional effect of the surfactant on ice shape may described in the next section.
also result from a reduction in droplet size. When the surface
tension is halved, the droplet s/ze cambe exlzx:ted to decrease by unto=oe_pebm_hs=ed_ngmee_s2t,ins=ee_opd=_tso_y
about 25%9. For the single-nozzle tests only about 10% of the the choice of scale model size, c_. The refcrcnoe model size, cR
droplets have reduced mrface te_ion, howev_, so the median md anreference conditions are, of com_, known. The following
volume dim=_ cfthc total spray should be close to that forwater four equations are first solved simulUmeonslyto 8ive the scale
without s='factanL The freezing _ of the
airspeed, Vs, scalestafictemperat_, Ts,scadestaficprcssta'¢,
water:Photo-Flo mixture was tested and found to be the same as
p_ endsudedropsize, _:
water. Althoush the mixture latent heat was not measured for this
study, it shonld be the same as water because of the exUtanely
small emonnt of surfac_mt used. Thus, the primary reasm for the
O)
diff_ in ice shape with and without suffactant is apparently
thechange inthesurfacetensi_ of unfrozen water on the surface
of the model. This observation reinforces the etmelusion of the
droplet-splashing tests that droplet-surfacientengtion plays a
sign/tainctr,oleintheice-accretipornocess.
TS = :T_ + (4)
2e2o,._f 2¢j.,w,a_
Implications for Sealing
P_t,s
The strong effect of droplet-surface interaction demonstrated by pg --
rs (5)
both thesp_ tests and the ic/ng-Umnel tests suggests that the
Weber numbea"needs to be camsidered in developing sc,alin8 2R,T s
methods. Rigorous scaring would requ/re that the Reynolds and
Weber numbers be matched between scale and reference
conditions ]. To do this it is necessary that, approximately,
(6)
vs= v_ o)
¢$
Equation O) results from matching the scale andreference We, isthe vapo¢pressure ofwater atthe surface ofthe model (i.e., at
andeq. on(4)isobtm dbym hingd oi,l 7at_ mdpwistbevaporpressure ofwater intheatmosphere (i.e.,
tmns(seeequatio(n9),below)intheMessingerenergybalance • Thevapor pressuresfor thisstudy were fromPruppacher
andrOeO.
atthemodelsurfaceT.hereisnofumlameamlnecessittyhatthe
droplemtergytermsbematched;however,enequatioinsneeded
tosolvfeorthe statitcemi_aturea,ndequatio(n4)isconvenient. Thescale andreference convective heattransfercoe_dents, hc_s
Equation(5)simplyrelatetshestatipcressurienthetunnetlothe and he,s, in equation (10) were evaluated using the following
known ambientpressur(etunnetlotaplressurea)ndequatio(n6) empiricalexpression from GelderandLewisl°:
resulftrsommatchitnhgedropltertajectories.
Thefreezingfrection,n,was defined byMessinger4 asthefraction 02)
_( v¢ p,) .era
ofimpingingwaterwhich freezes inthe impingement zone. The
scale LWC isfound by equatingthe scale andreference freezing
fraction. From the Messinger energy equation, the freezing
fractionis
Thcfiml scale_ needed isthe spmytime, r. Itwmfound
f " / bymatchingthescaleandreferencaeccumulatiopnmmneters:
n=_e- ¢+e (7)
AS _ LWC VI3Oc,-.
L_ sVsxs Lm_ _V_xs
(13)
Pies Pic_
Thus,
Table m ax,ws remits_catmdations applying thisscaling method
LWC# =
tofrverefereme conditions. Inrefca'tace 2anumberofpublished
scalinmgethodswereslzzvtnoworksax:cessfiwfiltlhryimeJoebut
vsP°%" LWCO VRRh_Po%"
notforglaze. Forlhis reason,reference conditions werechosen to
testthisnewmethod withthemore-diflionlt-to-scale glaze ice.
Verification of _t-Weber-Number Scaling Method. The
InequationUs) and (8), ¢isthedropleetnergytransfteerrm, proposedscaringmetixxiwm appliedinaseries oftests intheIRT
using the ice-accretion testtechniques dis(rased eadier. Scale
sizes of 1/2aad1/3therefe:ence cytinderdiameterswere used.
V 2
(9) Due toatmmducer c_ibration m'cf, both re_m_ and scale
2 ep.w, droplet_ _ md liquid-w_r o0tsmt, L_, werefoundafterthe
completionofthe testtodifferfromthose pleaned. TableHIgives
thereferm_oomlitio(mfirlsitnoefeachtesct4tsew)hichresulted
whea thetest conditionswere om-reaedto give the truedroplet
Itwasnotedaboveinreferencteoequatio(n4)that_ and_ are size,,,_ LWCforthefive testcases. The scale conditionslisted in
equated in this scaling method. Furthermore, the collection Table Ulthenwere obtained byapplying theconstant-Wescaling
method tothese _ reference conditions. Theactualscale
efficiency, flo, must be the same for scale and refevmce tests.
Thus,equation(8) s_mptifiesto zonditions tested are givea in Table IV. Comparingthe scale
conditiominTableIVwiththose inTableHI,onecansee thatthe
es _ vR scaleairspeedstestedwere asmuchas8%lower and scale droplet
LWC s = LWCR (10)
vs sizeswe_ upto18%lowertitan_e values requked bythisscaling
method. Otherscale test conditions wereclose to those requirecL
The scale Weber nmnberstested were lower thanthe reference
values fc¢thesetests byasmuch as28%.
From theMessingeerquationO,isthe airenergytransfteerrm:
Figure9showsthe iceshapes forthe conditions ofcase AinTable
IV. Thesolid line represonts the ice shapewhich resulted from
testing at the refereace zonditions. The dashed line is the scale
1:2 gmKA Pw,_l- Pl,
0=T_- T- r--+ £93 -- (11) result. Thescaleiceshapecoordinateshavebee_ multiplied bythe
2e_ joule " p
inverse of the scale factor so thatthe shapes can be compared
directly. The scaletestfor case A was performed on a7.6-cm
cylindermdresul_ inhorn-glazeice very similarinoverall shape
whereristhereoav_ factor, taken as .875 inthisanalysis,pw,_ f and quantityofice tothereference conditions tested on a 15.2-cm
cylinder.Figures 10m_! 11arealso for rofercace trots with 15.2- 3. Ruff, G.A.: "Analysis end Verificati(m of the Idn8
an cylimkrsbut withtxmditiom giviagdiffeamtforms ofglaze ice. ScalingFatmfi(ms,"AEDC-TR-85-30, VolI(Rev),Mard,,1986.
Inesch case the scale t_it, using a 7.6-ran cylinder, gave shapes
veryclose tothe _ shapes. 4. Mossinser, B.L., "Equilibrium Temtzxatm'e of ea
UnheatedIdn8 Surface asaFunctkm ofAh'speed," J.Aemn. Sd.
Figures 12 m_d13 present results for testing with a 7.6.ran 20No. l,Jm 1953, pp29-42.
reference cylinder end 5.1-cm and2.5-cm scale cylinders. The
results for the 5.1-¢m cylinders m'eshownindashedlinessmithe 5. BilminA,J.md Te_e,M.E.:"NumericaSltadieosfthe
ice shapes for the 2.5-¢m cylinders arerepreseated with dotted Depositica of Material ReleasedFrmn FixedendRotaryWing
lines. Figure 12shows results forhorn glaze ice, md figure 13is _" NASA CR-3779, March, 1984.
forgi_¢ ice atawarmertempersa_. In eachcase, the two scale
testsfaithfully reproduced therofa_ce ice shape. 6. Soc6=r,Rmald K aad _o, Charles,R., "NASA
LewisIda8 _ TunnelUs="Maaual,"NASA TM 102319,
Agreement between scale and re:ference ice shapes was Jua¢1990.
K_fic, mflybetteru.qmgthe ctmstant-WeseaFmgmethodthan has
beandcmoastrated inpaststudiesusing otherscaliagmctht_ in 7. Ide,RobertF.,"LiquiWd aterCtmtmtandDropletSize
theIRT2. CalibratioofntheNASA LewisI_ngResearh,Tunnel,N"ASA
TM I02447,Jan1990.
Concluding Reauu_ 8. P_pps_her,HansR.sadK1ettJ,ames D.,Microp_ic, s
of Clouds andPrecipitation, Reidel, Bos_ 1980.
Thisstudylu_&:mtmstrm_dthe_ ofdroplet splashtothe
ice-_ou process. Simple tests perRmnedwithRe md Weof 9. In_bo, Rctom'tD., "I_qu_ FuelSpray Processes inFdgh-
masnitudmtypicaldthose inicin8e_c_nters showedthatdroplet Pressm-eGasHow," NASA TM86944, July, 1985.
splash can have as/gnificsnt effect oa suffsce dynamics. Tests
were alaopeffccmed inthe NASA Lewis IcingResearchTunnel 10. Gek_, ThomasF.andLewis, JamesP.: "Compsdsoa of
which demonstratedthatalteringthe su_ce tensica of thespray Heat Traasfer from Airfoil in Natural and Simulated Icing
canhaveadrmmt/ceffectontheiceshape. Theseobservsficm led Coaditio_s," NACA TN 2480, Scpt_ber, 1951.
tothe _ ofanewscaling method inwtfichthescale and
reference Wearethe same. II. Lmgmuir, Irving and Blodgett, Katharine B.: "A
Mathematical Investigatitm of Water Droplet Trajec_xies," Army
Thismetixxi was tested inthe IRTusing cylinders. Because of a Air Forces Tedmic,alReport No. 5418, February,1946.
transducer calibrationerror, the scale We was asmuch as28%
lower than the reference value. Nevertheless, scale ice shapes
closely matched the reference shape when cylinder s_.es were
scaledby asmuch asafsctor ofthree. These preliminaryresults
suggestthatitmaybepossible toscale adequatelyevm when We
isnotheld exactly ctmstant Additioaal tests am_ tovcti_
tlfs scsling nmhodwithawider tense ofcoadificm, withdifferent
geometries andwith greater size ratios.
pred_oa mtxicls cmzgatlyinclude no¢xms_dcratioa
Table L Order-of-Masnitude F_,stima_ ofNtmdimenskmal
of_oplet spl_ _ aady _ that=_=idmaioa of
ParametersCoaa-olliagtheDymma_ ofImpactofaDroplet
drop__ _ m-eimportanttoiceaccretioenndneed
With aFilm
tobe tx,miderednotjustinscalinmgethodsbutinmslytical
models_icesccmkm m well.TheReynoldssndWebermmabers
Rain Icing
needtobeinvestigatedcerefid_ tomorefidb'mgiersta_ theirrole
intheice-accretion process. A/8 Oto® OtolO
PojU2 _/O'w/a 103 103to lO4
Reference=
pmU_/_w 103 103
1. Bilaaia, A. J., "Proposed Modificatiens to the Ice
A¢,crctioa/Iciag Scalia 8 Theory,"AIAA Paper AIAA-88-0203,
January1988.
2. Andersca, David N.: ,'Rime-M,ixed-andGlaze-Ice
Evaluations of Three Scaling Laws," AIAA 94-0718, January,
1994.
Tablc II. Surface Tcmion of Spray Mixtures
a, dyne/cm
Mixture (Conceatr_c_s areby Volume)
9-2-93 12-13-93 12-8-94
Tap Water(20°C) 63.1 59.2
IRT Deminendized Water 48.6 65.1 59.8
400:1 IRT Demimmdized Water :Liqui-Nox 28.7
560:1" IRT_ Water :Liqui-Nox 30.2
200:1 IRT Demineralized Water :Photo-Flo 200 28.4 29.8 **
400:1 IRT _ Watea-:Phot_Flo 200 28.3 28.6 **
600:11RT _ Water :Photo-Fio 600 ** 29.6
"E,_imated Dilmioa "Not Measmed
Table In. Examples of Scaling With _ We
Case Mode Diam, Tt_, V, 8, LWC, t, M Re x 10.5 Wesx 10.3
K K m/s jan g/m3 rain
Ref. 15.2 263.7 265.9 67.0 40.8 1.10 42.9 .206 7.73 2.36
A
Scale 7.6 263.3 267.2 87.6 23.9 1.30 14.0 .269 4.97 2.36
Ref. 15.2 266.5 268.7 67.2 40.8 1.11 42.8 .205 7.62 2.39
B
Scale 7.6 266.1 270.0 88.0 23.9 1.26 14.4 .269 4.90 2.39
Ref. 15.2 260.9 264.9 89.5 40.7 .884 40.3 .276 10.28 4.18
C
Scale 7.6 260.2 267.1 117.4 23.7 .993 13.7 .363 6.54 4.18
Ref. 7.6 263.7 265.9 66.7 61.0 .897 26.6 .205 3.85 3.50
D Scale 1 5.1 263.5 266.6 78.1 44.6 .988 13.8 .240 2.98 3.50
Scale 2 2.5 263.0 268.2 102.3 26.0 1.12 4.6 .315 1.90 3.50
Ref. 7.6 266.5 268.7 67.4 58.0 .887 26.7 .206 3.82 3.41
E Scale 1 5.1 266.3 269.4 78.8 42.4 .963 14.0 .241 2.95 3.41
Scale 2 2.5 265.8 271.1 103.3 24.7 1.05 4.9 .316 1.89 3.41
Table IV. Scaling Test Conditions
Case Mode Di_m., Trot, V, 8, LWC, t, M Rex 10.5 We,_x 10-3
gin K K m/s tun g/m3 min
Ref. 15.2 263.7 265.9 67.0 40.8 1.10 42.9 .206 7.73 2.36
A
Scale 7.6 263.7 267.2 83.9 20.7 1.24 15.4 .258 4.76 1.88
Ref. 15.2 266.5 268.7 67.2 40.8 1.11 42.8 .205 7.62 2.39
B
Scale 7.6 266.3 269.8 83.9 20.8 1.21 15.7 .256 4.68 1.89
Re£ 15.2 260.9 264.9 89.5 40.7 .884 40.3 .276 10.28 4.18
C
Scale 7.6 260.4 266.6 111.8 20.7 .964 14.8 .346 6.27 3.32
Ref. 7.6 263.7 265.9 66.7 61.0 .897 26.6 .205 3.85 3.50
D Scale 1 5.1 263.4 266.3 76.7 38.5 .960 14.4 .236 2.93 2.92
Scale 2 2.5 262.9 267.5 95.6 21.3 1.08 5.1 .294 1.79 2.51
Ref. 7.6 266.5 268.7 67.4 58.0 .887 26.7 .206 3.82 3.41
E Scale 1 5.1 266.2 269.1 76.2 46.4 .967 14.4 .233 2.86 3.49
Scale 2 2.5 265.8 270.3 95.3 21.5 1.05 5.3 .292 1.76 2.52
1.0II-"- "c s/m'
tj,, LFFU, n
_" A n_ 6
. °'81. • 4 1.2 .15 ]
L_-11 .8 .5 //
0.6 • -15 1.2 .5 ////"
_mmsm _/_4-mmC_m
F / nr= .15 DishW_h Wm l_m
,. 0.0
0.0 0.5 1.0 1.5
[I II
AocxnnulatioPnarameter, Ac ////////////////////////
Figure 1. Stagnati_Point IceAccreticalc_a2.5-cm-diameter Fipre & _ SetupforStudyofDroplet-Film-Impact
Cir_ularCy_der. DropletVdocity,60m/z (Ref.l) Dyna_
00 ___
-100 - _" ---- 4.2 1138 9800
WamFam
0 -- 8.1 4234 19000
-150 I I I
0.0 0.5 1.0 1.5
WaterFilm Thickness /Drop Diameter
Figure2. RaindroptmpactingaShaUowPuddle.4-8, uis Figure 4. Mass Gain By Water FilmDue to Droplet lmpa_
much less tlum l_e acoustic speed inwater.
8