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Published unde licence by IOP Publishing L d
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CFD analysis o wing-p opelle in e ac ion on he NASA X-57
Maxwell ai c a wing
A. Pa il1 and J. Na á il2
1 S uden , Mas e s in Ae ospace Enginee ing, Fachhochschule Wiene Neus ad ,
Aus ia, exchange s uden a B no Uni e si y o Technology, B no, Czech Republic
2 Assis an P o esso , Ae onau ics and Space Technology G oup, Ins i u e o
Ae ospace Enginee ing, Facul y o Mechanical Enginee ing, B no, Uni e si y o
Technology, B no, Czech Republic
Co esponding au ho email: an i a.pa [email protected]
Abs ac . Due o global wa ming conce ns, he A ia ion indus y is ying o educe i s ca bon
oo p in . Elec ic p opulsion (EP) is one way o doing his, whe e he powe is ob ained om
elec ical sou ces. The concep o dis ibu ed elec ic p opulsion (DEP) is in he ocus now.
NASA’s X-57 Maxwell, a high winged, all-elec ic expe imen al ai c a , uses his concep .
The p esen wo k aims a de eloping a CFD model (ANSYS Fluen ) o e alua e ae odynamic
pe o mance o wo con igu a ions o NASA’s X-57 ai c a wing; (i) wing and nacelle (clean
wing) and (ii) wing, nacelle and one elec ic p opelle unde c uise condi ion; and compa e i
wi h he esul s o wind unnel expe imen pe o med by NASA/A ms ong X-57 esea ch
p og am. Pa ame e s like li , d ag and p essu e coe icien s (CL, CD, CP) a e compa ed o
bo h cases. A good ma ch is obse ed o CL, CD and CP, hus alida ing he model. The
uns eady RANS sol e is e y e icien in cap u ing he e ec s o p opelle slips eam on he
wing. A e alida ion, his model is u he used o simula e ae odynamic pe o mance o a
wing wi h mul i-p opelle (DEP) con igu a ion.
Keywo ds: Dis ibu ed P opulsion, NASA X-57, elec ic ai c a , p opelle , ae odynamic
e iciency, ae odynamic pe o mance, p opelle slips eam, CFD, wing geome y, meshing,
ANSYS Fluen , wind unnel expe imen , u bulence model, li , d ag, p essu e coe icien ,
angle o a ack.
1. In oduc ion
The ai anspo indus y has been ad ancing, inc easing i s size wo old e e y wen y yea s. This led
o high consump ion o uel, which in u n led o an inc ease in g eenhouse gas emissions as well as
noise. To limi i s con ibu ion o global wa ming, he a ia ion indus y aims o educe CO2 emissions
in hal by 2050, compa ed o 2005 le els [AIAA, 2021]. This can be achie ed by pu ing in o p ac ice
inno a i e ways o p opulsion, namely hyb id p opulsion o all-elec ic p opulsion. In hyb id
p opulsion, a combina ion o in e nal combus ion engines and elec ic mo o s is used, while in all-
elec ic p opulsion, ba e ies a e used as he main sou ce o powe . Con en ional p opulsion sys ems
a e complica ed, equi e high empe a u e ma e ials and special echniques o p oduc ion, hus
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p o ing o be qui e expensi e. Shi ing he ocus o uncon en ional p opulsion sys ems has he
po en ial o educe uel usage and oxic emissions, and also conside ably educe cos o p oduc ion.
Elec ic p opulsion could qui e possibly help in educing uel consump ion by 90%, make he equi ed
powe independen o ligh condi ions, and p o ide be e eliabili y compa ed o con en ional ICE
p opulsion sys em [Pa e son e al., 2016].
Hyb id p opulsion can be applied using 4 con igu a ions: se ies, pa allel, se ies/pa allel, and u bo-
elec ic hyb idiza ion. I can be applied sui ably o bo h la ge comme cial ai c a s and smalle
egional ai c a s. Howe e , conside ing he weigh o elec ical equipmen as well as uel anks, he
ope a ing emp y weigh o he ai c a could be highe . This could equi e a comp omise be ween
ligh ange and uel sa ing.
All-elec ic p opulsion has an imp essi e scope o de elopmen . I is a scalable echnology ha
can easily be implemen ed in small as well as la ge scale ai c a s. The powe densi y o ba e ies and
ene gy e iciency o elec ic mo o s a e de eloped and imp o ed con inuously, making his echnology
mo e iable. All-elec ic p opulsion is es ima ed o educe main enance and uel cos s by 50%
[Manuel Randon e al., 2021].
In con en ional p opulsion sys ems, he u bine needs o be coupled wi h he engine, which b ings
limi a ions in e ms o ope a ion. In elec ic p opulsion, he p opelle s a e decoupled om he EMs,
which allows each p opelle o be ope a ed a op imal condi ions. E en hough EMs p oduce less
h us as compa ed o ICEs, due o hei ligh weigh and smalle size, se e al EMs can be u ilized o
p oduce he equi ed h us and imp o e pe o mance. This concep o i ing se e al EMs on he
ai c a is known as dis ibu ed elec ic p opulsion (DEP).
DEP consis s o a p opulsion sys em ha is closely in eg a ed wi h he ai c a s uc u e. I is a
mul i-p opelle con igu a ion whe e he p opelle s, d i en by EMs, a e dis ibu ed along he wing
and/o uselage (p opulsi e uselage concep ) [Ke in R Moo e al., 2018]. This con igu a ion is
capable o p oducing high li in a sho ime, which can educe he dis ance equi ed o akeo .
Nume ous DEP ai c a s a e unde de elopmen o STOL and VTOL ea u es. The NASA X-57
Maxwell, Au o a Fligh Sciences XV-24 Ligh ning S ike, Joby A ia ion S2, Lilium Je , Ai bus
Vahan VTOL ai c a s a e some examples [Kim Hyun e al., 2018].
Pa el Hospodář e al. (2019) applied DEP con igu a ion o a modi ied wing o a gene al a ia ion
10-sea e ai c a . The modi ica ion was ha he wing a ea was educed by hal . They applied CFD
analysis using a RANS OpenFoam sol e and applied Spala -Allma as u bulence model o sol e o
comp essible s eady low. Fo he clean hal wing, he li coe icien dec eased; howe e , when DEP
was applied, he hal wing p o ided he same li as he o iginal wing.
The NASA X-57 Maxwell all elec ic expe imen al ai c a is being de eloped by NASA o employ
he DEP con igu a ion. I is a modi ica ion o he Tecnam P2006T ai c a , whe e he win engines a e
eplaced by wo elec ic mo o s on he wing ips, and 6 smalle mo o s along he leading edge o each
wing, and he wing a ea is educed om 145 sq. . o 55.1 sq. . The wing- ip mo o s a e c uise
mo o s ha help o educe d ag om wing ip o ices, while he six smalle mo o s p o ide high li
du ing akeo and landing. The smalle p opelle s a e oldable once in c uise condi ion, o u he
d ag educ ion and op imized ene gy consump ion. This concep p o ides highe li , dynamic p essu e
a low speeds, p opulsi e e iciency, and lowe d ag [NASA 2022].
NASA conduc ed wind unnel es s o he X-57 Maxwell using he Lockheed Ma in Low Speed
Wind unnel (LSWT), as pa o he NASA/A ms ong X-57 Resea ch p og amme. They conduc ed
es s o a clean wing case and a wing- ip p opelle moun ed wing case. A scaled down model was
used o he es s, and pa ame e s like eloci y wake, li , d ag, and p essu e coe icien s we e
obse ed. In June 2019, NASA conduc ed he AIAA Wo kshop o In eg a ed P opelle P edic ion,
wi h he goal o making a ailable a da abase ha can be used by o he esea che s o alida ing hei
CFD models. The alida ed CFD models can be used o accu a e p edic ion o wing-p opelle
in e ac ions, and can possibly educe cos o de elopmen . This p omo es he use o CFD analysis o
he NASA X-57 Maxwell, hus accele a ing he de elopmen o he ai c a p o o ype [NASA, 2019].
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The da abase consis s o esul s om es s ca ied ou o Mach 0.04, 0.08, 0.11, angles o a ack
om -10o o +20o, o CT 0.0 (p opelle o ) and 0.04 o 0.4 (p opelle on), and aile on de lec ion om
-45o o +45o. The wing model was digi ally scanned o p o ide a 3D CAD model, and some meshes
we e also made a ailable o CFD use.
The aim o he p esen wo k is o de elop a RANS based CFD model o assess he pe o mance o
he NASA X-57 Maxwell ai c a wing, by e e ing he da a om WIPP wo kshop o alida ion o
wo cases: (i) clean wing and (ii) wing- ip moun ed p opelle wing. This alida ed model is hen used
o analyze he ae odynamic pe o mance o a DEP con igu a ion on he wing. The o iginal wing- ip
p opelle geome y, ha was ob ained om he wo kshop, is modi ied o ha e 6 smalle p opelle s
dis ibu ed along he leading edge o he wing. The emphasis on de eloping a RANS sol e o his
wo k is o educe compu a ional ime ha is usually qui e high o sol e s like LES and DES, while
main aining he accu acy o esul s, and making a humble con ibu ion o he de elopmen o he
NASA X-57 Maxwell ai c a .
2. Me hodology
2.1. Clean wing case
The geome y and mesh we e ob ained om WIPP. A s eady s a e, p essu e-based RANS (Reynolds-
A e aged Na ie S okes) sol e was se up using ANSYS Fluen . The k-ω SST u bulence model wi h
ai as ideal gas, coupled scheme and second o de disc e iza ion was used. Bounda y condi ions we e
based on pa ame e s om he wind unnel expe imen : Inle eloci y 27.2 m/s (Mach 0.08), 15o
empe a u e, no slip wall and p essu e inle . Re e ence alues o wing su ace a ea and mean
ae odynamic cho d we e aken as 0.43587 m2 and 0.25781 m espec i ely. Residuals we e se o 10-6,
and calcula ions we e un o AOA 0, 5, 7, 15 and 17 deg ees, un il con e gence.
2.2. Wing- ip moun ed p opelle case
The geome y a ailable om WIPP was modi ied using CATIA o include a o a ing domain a ound
he p opelle . Ini ially, calcula ions we e un o only he isola ed p opelle , o alida ion o he
equi ed o a ional speed o p oduce h us speci ied by WIPP. Fig. 1 shows he plo o h us s
o a ional speed. The o a ional speed o 640 ad/s was conside ed o u he calcula ions, as i
p o ided a h us o 80 N, which co esponded wi h he expe imen al esul s.
Fig. 1: Plo o Th us VS Ro a ional Speed
Fig. 2: Plo o CD VS Mesh Size
A hyb id, uns uc u ed mesh was c ea ed using ANSYS Meshing, mainly consis ing o e ahed ons
wi h p isma ic in la ion laye s nea he wing and p opelle blades’ su ace. A mesh dependence s udy
ha was done o meshes wi h 1.5, 6, 12 and 24 million elemen s. Fig. 2 shows he plo o d ag
coe icien alues o hese meshes. A di e ence o less han 5% was obse ed be ween he 12 and 24
million elemen s meshes. Thus, he 12 M elemen s mesh was op imized and used o u he
29.6653
74.2
80.9796
131.9386
202.686
0
50
100
150
200
250
400 600 800 1000
T (N)
ω ( ad/s)
0.034473
0.031965
0.029184 0.028872
0.028
0.029
0.03
0.031
0.032
0.033
0.034
0.035
010 20 30
CD
To al Elemen s (M)
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calcula ions. The sol e se up in ANSYS Fluen was he same as he clean wing case, wi h addi ional
se ings o he p opelle : ame mo ion in cell zone condi ion, whe e speed and axis o o a ion we e
speci ied.
2.3. Mul i-p opelle (DEP) case
The wing- ip moun ed p opelle geome y was modi ied in CATIA by adding 6 smalle p opelle s
along he leading edge o he wing, as obse ed in Fig. 3. I was necessa y o de ine ligh condi ions
be o e se ing up he calcula ions. Using he same me hod as o he wing- ip p opelle , isola ed
p opelle calcula ions we e ca ied ou o he smalle p opelle . A h us s o a ional speed plo was
ob ained, as shown in Fig. 4. Equal powe dis ibu ion among all p opelle s was assumed. The h us
a io was assumed as co esponding o he powe a io o he p opelle s. The NASA X-57 Maxwell
da ashee was e e ed o powe alues o he p opelle s, while he h us alues we e aken om he
isola ed p opelle calcula ions. The h us a io was closes o he powe a io when he o a ional
speed o he smalle p opelle was conside ed o be 1680 ad/s. The e we e conce ns ega ding he
a ailabili y o an elec ic mo o ha p o ides his kind o speed; howe e , he model used o analysis
is a 40.5% scaled down e sion. When he model is scaled up, he equi ed o a ional speed is no as
high, and inding an app op ia e elec ic mo o is manageable.
Fig. 3: Mul i-P opelle Wing Geome y
Fig. 4: Plo o Th us VS Ro a ional Speed
F om he da ashee , he powe o c uise mo o is 60 kW and ha o he smalle p opelle is 10.5 kW.
The powe a io was aken as:
𝑃𝑜𝑤𝑒𝑟 𝑅𝑎𝑡𝑖𝑜 = 𝑃𝑜𝑤𝑒𝑟 𝑓𝑜𝑟 𝑠𝑚𝑎𝑙𝑙𝑒𝑟 𝑝𝑟𝑜𝑝𝑒𝑙𝑙𝑒𝑟𝑠
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 =6 ∗ 10.5
60 + 6 ∗ 10.5 = 0.5122
The h us o he c uise mo o is 74.2 N o 620 ad/s. F om Fig. 3.10, i he h us o smalle
p opelle is conside ed o be 11.5481 N, he h us a io is:
𝑇ℎ𝑟𝑢𝑠𝑡 𝑅𝑎𝑡𝑖𝑜 = 𝑇ℎ𝑟𝑢𝑠𝑡 𝑓𝑜𝑟 𝑠𝑚𝑎𝑙𝑙𝑒𝑟 𝑝𝑟𝑜𝑝𝑒𝑙𝑙𝑒𝑟𝑠
𝑇𝑜𝑡𝑎𝑙 𝑇ℎ𝑟𝑢𝑠𝑡 =6 ∗ 11.5481
74.2 + 6 ∗ 11.5481 = 0.4829
Once he ligh condi ions we e de ined, a mesh was c ea ed based on he mesh speci ica ions om he
wing- ip moun ed p opelle case, and s eady s a e calcula ions we e pe o med.
3. Resul s and discussion
3.1. Clean wing case
Li , d ag and p essu e coe icien s om he CFD calcula ions we e compa ed wi h expe imen al da a.
Fig. 5 shows he plo o compa ison o li cu es. As obse ed, he e is a good ma ch in he alues. A
sligh di e ence is obse ed o highe AOA, which is expec ed due o o e -p edic ion o low
1.1432
3.9253
7.4062
11.5481
0
2
4
6
8
10
12
14
800 1300 1800
T (N)
ω ( ad/s)
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sepa a ion by he u bulence model. Fig. 6 shows a schema ic o he wing, wi h loca ions a which
p essu e coe icien s we e measu ed o he wind unnel es s. Figu es 7 and 8 show he plo o
compa ison o p essu e coe icien s o CFD calcula ions wi h expe imen al da a, a loca ions 44.386
and 60.955 inches.
Fig. 5: Compa ison O Li Cu es
Fig. 6: Loca ions o CP Along he Wing
Fig. 7: Compa ison o Cp Plo a Loca ion 44.386” on
Wing, C =0, AOA 15o
Fig. 8: Compa ison o Cp Plo a Loca ion 60.955”
on Wing, C =0, AOA 15o
As obse ed, he e is good ag eemen o he alues, and hus he clean wing case is conside ed o be
alida ed.
3.2. Wing- ip moun ed p opelle case
Fig. 9 shows he compa ison o d ag pola s alues ob ained om CFD calcula ions o hose om he
expe imen al da a. The e was a misma ch o alues a highe AOA. Also, he e was a misma ch o
p essu e coe icien alues a 60.955 in, a he leading edge; i.e., in he wake o he p opelle . A e
ying ou di e en u bulence models and se ings (GEKO model, cu a u e co ec ion, e c.), i was
obse ed ha s eady s a e calcula ions we e no su icien o p o ide accu a e esul s. Thus, a ansien
(uns eady, ime-dependen ) sol e was se up, wi h k-ω SST u bulence model. The se ings om
s eady s a e sol e we e applied, wi h he only di e ence being Mesh Mo ion ins ead o F ame Mo ion
o he p opelle . Calcula ions we e un o 5000 imes eps, wi h a imes ep size o 10-4 s, and 40
i e a ions pe imes ep, ha ing an angula inc emen o he p opelle posi ion o 0.036o pe imes ep.
Ini ially, a imes ep size o 10-3 was aken; howe e , i p o ed o be qui e la ge, as he esul s we e
simila o he s eady s a e sol e . A imes ep sensi i i y s udy was no pe o med. The ansien sol e
p o ed o be success ul in p o iding accu a e esul s, o he d ag pola s as well as he p essu e
coe icien plo s. Fig. 10 shows p essu e coe icien plo s a 60.955 in.
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-20 -10 010 20 30
CL
AOA
WT EXPT
CFD CALC
-5
-4
-3
-2
-1
0
1
2
-0.5 00.5 11.5
CP
x/c
CFD CALC
WT EXPT
-4
-3
-2
-1
0
1
2
-0.5 00.5 11.5
CP
x/c
CFD CALC
WT EXPT

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Fig. 9: Compa ison o D ag Pola s
Fig. 10: Plo o CP Compa ison
As obse ed, he e is an imp o emen in esul s o ansien calcula ions om s eady s a e
calcula ions. This alida es he wing- ip moun ed p opelle case, and he model is now calib a ed o
DEP con igu a ion analysis.
3.3. Mul i-p opelle (DEP) case
As he e was no expe imen al da a a ailable om WIPP o his case, he esul s we e compa ed wi h
s eady s a e esul s o he wing- ip moun ed p opelle case. Figu es 11 and 12 show he compa ison o
d ag pola s, including and excluding he p opelle espec i ely. Fo he p opelle included case, he e
is signi ican educ ion in d ag, which was as expec ed. Fo he p opelle excluded case, he e is a
sligh inc ease in li , and also an inc ease in d ag. This is due o he addi ion o nacelles on he wing
which educe he smoo hness o he wing su ace.
Fig. 11: D ag Pola s Compa ison including p opelle
Fig. 12: D ag Pola s Compa ison excluding p opelle
Fig. 13: Li Cu es o Dep Wing (CFD Resul s)
Fig. 14: Li Cu es o Di e en Wing Con igu a ions –
[Pa el Hospodář, 2019]
-0.5
0
0.5
1
1.5
2
-0.6 -0.4 -0.2 00.2 0.4
CL
CD
WT-PROP
INCL
WT-PROP
EXCL
STEADY
PROP EXCL
STEADY
PROP INCL
TRANSIENT
PROP INCL
TRANSIENT
PROP EXCL
-5
-4
-3
-2
-1
0
1
2
3
4
-0.5 00.5 11.5
CP
x/c
WT EXP
CFD STEADY
CFD TRANSIENT
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-0.8 -0.6 -0.4 -0.2 0
CL
C
D
WING-TIP PROPELLER
MULTI-PROPELLER
0
0.5
1
1.5
2
00.1 0.2 0.3 0.4 0.5
CL
C
D
WING-TIP PROPELLER
MULTI-PROPELLER
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15 20
CL
AOA
WING-TIP PROP EXCL
MULTI-PROP EXCL
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The esul s om CFD calcula ions o he mul i-p opelle wing case also show ag eemen wi h he
indings o Pa el Hospodář. Fig. 13 shows he compa ison o li cu es o mul i-p opelle case wi h
wing- ip moun ed p opelle case. The e is de ini ely an imp o emen in ae odynamic pe o mance due
o he applica ion o DEP o he wing. Fig. 14 shows a compa ison o li cu es o a no mal wing, a
wing wi h hal wing a ea and DEP on he hal wing, om he esea ch done by Pa el Hospodář. I is
obse ed ha he li dec eases o he hal wing, howe e , when DEP is applied, i shows
pe o mance simila o he o iginal wing. Thus, he p elimina y esul s a e sa is ac o y.
The smalle p opelle blades in his geome y we e scaled down om he la ge p opelle s. Howe e ,
hose we e no he op imal blades used in he NASA X-57 Maxwell. A new p opelle geome y was
aken om he VSP3 model a ailable on he NASA X-57 websi e, and he geome y was modi ied.
Fig. 15 shows he new geome y.
Fig. 15: Modi ied DEP Wing Geome y
Fu he wo k will be ca ied ou using he modi ied geome y.
4. Conclusion
The p esen wo k was dedica ed owa ds applying he RANS based CFD sol e o ANSYS Fluen o
analyze wing-p opelle in e ac ions o he NASA X-57 Maxwell ai c a . Clean wing and wing- ip
moun ed p opelle cases we e alida ed using da a om wind unnel es s p o ided by WIPP. The
indings showed ha he s eady RANS solu ion was unable o cap u e he wing-p opelle in e ac ion.
Howe e , he uns eady RANS sol e was able o cap u e i accu a ely, and showed good ag eemen
wi h he expe imen al esul s, especially o he CP plo s. This sol e was hen used o simula e he
ae odynamic pe o mance o he DEP con igu a ion o he wing. P elimina y calcula ions showed
good ag eemen wi h indings om o he esea che s. In his way, his s udy is able o con ibu e o he
de elopmen o he ai c a . I also shows ha a RANS based sol e is capable o p o iding good
esul s and can sa e a lo o compu a ional ime o esea che s, compa ed o LES, DES based sol e s.
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Acknowledgemen s
This wo k has been suppo ed by he p ojec No. FSI-S-23-8163 unded by The Minis y o Educa ion,
You h and Spo (MEYS, MŠMT in Czech) ins i u ional suppo and by he esea ch he p ojec RCI
( eg. no. CZ.02.1.01/0.0/0.0/16_019/0000765) suppo ed by EU.
Re e ences
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