Conluding Remarks

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w/o mean v ind C L

C L ~ 0

Figure 6.9: Example of two-dimensional airfoil dataand theosillation ofangle of

attak dueto theinidene alongablade yle. Comparisonbetween theasewith

and the asewithout meanindued veloities.

angleofattakofasinglepropellerinduedbyitswake;itsminimumvalueisfound

in the downward moving blade zone, beause there the wake has more vortiity.

Seond, the dash-dotted urve represents the angle of attak indued by the front

rotor wake; its minimum value is plaed around

270

, where the front rotor wake

hasmorevortiity. Finally,thesolidurveshowstheadditionofbothontributions,

asin the ase of a CROR. It presents a redutionof the amplitude of the

∆α

and

an inreaseinits phasewithrespetto thesinglepropellerase.

Finally, the ontribution of the BPF modes in HOST simulations is negligible

(bars 4and 7). However, ananalysisof thesensitivity of1P phaselag totimestep

presented by François et al. [François2013b℄, puts forward that the BPF modes

have animpat ofaround

3.5

for the front rotor (

−17%

) and

3

for therearrotor

(

−7%

). Theseosets an be a onsequene of thethree reasonsexposedin setion

6.2: usingdierent timesteps,negletingvisouseetsinHOST,andreduingthe

bladeto its quarter-hord line inHOST.

6.4 Conluding Remarks

A detailed ode-to-ode assessment between elsA CFD solver and HOST

lifting-line ode, has been performed on a generi ontra-rotating open rotor geometry

(AI-PX7) at high-speed onditions and at

1

of inidene. Three dierent types

of HOSTsimulations have been performedin order to assess theimpat of naelle

eetsand unsteadyorretions onaerodynami performaneand 1Ploads.

Azimuth [ ]

[ ]

0 90 180 270 360

-1.5 -1 -0.5 0 0.5 1 1.5

Auto Mutual r/R=0.75

FR wake amplitude and lag

Figure 6.10: Angle of attak evolution during a revolution for a rear rotor blade

setion. Auto-induedandmutually-indued

∆α

areplottedtogetherwiththetotal

∆α

for agivenblade setion

simulations within reasonable pith angles modiations, i.e.

∼ 1.36

. Onthe one

hand, osets obtained in 1P loads modulus have been redued when adding the

eet ofthe naelle. Onthe otherhand,theunsteadyairfoilmodelimplementedin

HOST allows reduing mismatheson the rearrotor 1P loadsphase lag.

Fairresultshavebeenobtainedforglobal bladethrust,eventhoughtheomparison

has also highlighted some shortomings of the present method inthepredition of

the rear potential eet on the front rotor. This phenomenon has been explained

by the fat that hord eets are not onsidered in lifting-line methods, and they

beome important forrotors thatarelose one to eahother.

In the omparisons of thrust distribution along the blade, the shape predited by

elsA wasalso obtained in HOST, but with some minor osets. Theywerenotied

near the blade root due to the wall eet. Moreover, aeptable dierenes in

maximummeanloadswerealsoobserved(

−8%

)andtheirpositionwasslightlyloser

to the bladetip than inelsA simulations. The rstharmoni waswell aptured by

all HOSTsimulations, thoughinstallationeetsoverestimate itsamplitude onthe

front blade. Unsteadyorretionsredued thephaselagoftherstmode,and thus

results getloser toelsA ones.

Induedveloityeldshaveshown,ononeside,theimpatofnegletinghordeets

inHOSTand,ontheotherside,theapaitytoaptureorretlythepotentialeet

of thetipvorties and the global eet ofthe front wake on therearrotor.

A method to identify the mehanisms governing thrust and 1P loads has been

presented. Thoughsomenon-lineareetsappearinsomeoftheresults,themethod

enables to determine the quantitative impat of eah mehanism on global

perfor-The front rotor behavior predited by HOST is very lose to the one of a

single-rotatingpropeller,astherearrotorhasaverysmallontributiononitsperformane

and1P loads(

< 10%

). Theseresultshaveto beanalyzedtakinginto aount what

has been exposed in setion 6.2, i.e. that HOSTsimulations neglet hord eets,

leading to an underestimation of the potential eet of therear rotor on the front

rotor.

On the ontrary, the most important mehanism on the rear rotor response is the

front rotor wake eet. Indeed, more than

50%

of its thrust is due to the

ombi-nation ofpositiveaxial andnegative irumferential

~v ind

fromthefront rotorwake.

Moreover,this wakedereasesthe1Ploadnorm(

−41%

)and inreasesitsphaselag

signiantly (

+18%

).

Finally, while installation eets play an important role in the predition of 1P

loads for both rotors, the unsteadyorretions have shown to be important for the

1Pphaselag, mainlyintheaseofthefrontrotor,where moreimportantinidene

variations our.

The next hapters will be devoted to the implementation and rst validation

tests of a oupling strategy between a HOST simulation and an elsA near-wall

meshinordertoobtainamoderate-ostmethodologythattakesintoaount

three-dimensional,hord,ompressibility,andvisosityeetsinpropellerandopenrotor

ases.

Code Coupling

Development of a Coupling

Strategy between HOST-MINT

and elsA Codes

Contents

7.1 CurrentCoupling between HOST/MESIRand elsA . . . . 154

7.1.1 HOST/MESIR-elsACouplingStrategy. . . .154

7.1.2 MainAdvantagesandShortomings oftheStrategy . . . 155

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