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.
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
asin the ase of a CROR. It presents a redutionof the amplitude of the
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 (
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
∆αfor 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.
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
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.
of thetipvorties and the global eet ofthe front wake on therearrotor.
A method to identify the mehanisms governing thrust and 1P loads has been
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
< 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
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 indfromthefront rotorwake.
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
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
Development of a Coupling
Strategy between HOST-MINT
and elsA Codes
7.1 CurrentCoupling between HOST/MESIRand elsA . . . . 154
7.1.1 HOST/MESIR-elsACouplingStrategy. . . .154
7.1.2 MainAdvantagesandShortomings oftheStrategy . . . 155