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Research Papers

In-Plane Forces Prediction and Analysis in High-Speed Conditions on a Contra-Rotating Open Rotor

[+] Author and Article Information
Benjamin François

Aerodynamic Department,
Airbus Operations S.A.S.,
306 Route de Bayonne,
Toulouse Cedex 9 31000, France
e-mail: benjamin.francois@cerfacs.fr

Martin Laban

Flight Physics and Loads Department,
National Aerospace Laboratory, NLR,
Anthony Fokkerweg 2,
Amsterdam 1059CM, Netherlands
e-mail: martin.laban@nlr.nl

Michel Costes

Onera, The French Aerospace Lab,
8 Rue des Vertugadins,
Meudon F-92190, France
e-mail: michel.costes@onera.fr

Guillaume Dufour

Institut Supérieur de l'Aéronautique
et de l'Espace (ISAE),
Université de Toulouse,
10 avenue Edouard Belin, Toulouse 31400, France
e-mail: guillaume.dufour@isae.fr

Jean-François Boussuge

CFD Department, CERFACS,
42 avenue Gaspard Coriolis,
Toulouse 31000, France
e-mail: boussuge@cerfacs.fr

The expression 1P-forces (1P stands for once-per-revolution) can also be found in literature to define the in-plane forces on a propeller. However, the 1P-forces expression will not be used in this work.

The mesh density ratio is here expressed to the third power to give an average density ratio for each direction.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 17, 2013; final manuscript received December 11, 2013; published online January 31, 2014. Assoc. Editor: Alok Sinha.

J. Turbomach 136(8), 081002 (Jan 31, 2014) (16 pages) Paper No: TURBO-13-1006; doi: 10.1115/1.4026311 History: Received January 17, 2013; Revised December 11, 2013

Due to the growing interest from engine and aircraft manufacturers for contra-rotating open rotors (CROR), much effort is presently devoted to the development of reliable computational fluid dynamics (CFD) methodologies for the prediction of performance, aerodynamic loads, and acoustics. Forces transverse to the rotation axis of the propellers, commonly called in-plane forces (or sometimes 1P forces), are a major concern for the structural sizing of the aircraft and for vibrations. In-plane forces impact strongly the stability and the balancing of the aircraft and, consequently, the horizontal tail plane (HTP) and the vertical tail plane (VTP) sizing. Also, in-plane forces can initiate a flutter phenomenon on the blades or on the whole engine system. Finally, these forces are unsteady and may lead to vibrations on the whole aircraft, which may degrade the comfort of the passengers and lead to structural fatigue. These forces can be predicted by numerical methods and wind tunnel measurements. However, a reliable estimation of in-plane forces requires validated prediction approaches. To reach this objective, comparisons between several numerical methods and wind tunnel data campaigns are necessary. The primary objective of the paper is to provide a physical analysis of the aerodynamics of in-plane forces for a CROR in high speed at nonzero angle of attack using unsteady simulations. Confidence in the numerical results is built through a code-to-code comparison, which is a first step in the verification process of in-plane forces prediction. Thus, two computational processes for unsteady Reynolds-averaged Navier–Stokes (URANS) simulations of an isolated open rotor at nonzero angle of attack are compared: computational strategy, open rotor meshing, aerodynamic results (rotor forces, blades thrust, and pressure distributions). In a second step, the paper focuses on the understanding of the key aerodynamic mechanisms behind the physics of in-plane forces. For the front rotor, two effects are predominant: the first is due to the orientation of the freestream velocity, and the second is due to the distribution of the induced velocity. For the rear rotor, the freestream velocity effect is reduced but is still dominant. The swirl generated by the front rotor also plays a major role in the modulus and the direction of the in-plane force. Finally, aerodynamic interactions are found to have a minor effect.

Copyright © 2014 by ASME
Topics: Rotors , Blades , Thrust
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References

Figures

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Fig. 2

Two different Airbus nacelle designs for AI-PX7 configuration

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Fig. 3

Splitting of the computational domain

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Fig. 4

Blade mesh: (a) front blade and (b) rear blade

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Fig. 5

Blade to blade mesh: (a) elsA and (b) ENSOLV

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Fig. 6

Definition of the azimuthal angle: (a) front rotor and (b) rear rotor

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Fig. 7

Global forces on rotors: (a) thrust coefficient on the front rotor, (b) thrust coefficient on the rear rotor, (c) in-plane force modulus on the front rotor, (d) in-plane force modulus on the rear rotor, (e) in-plane force angle on the front rotor, and (f) in-plane force angle on the rear rotor

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Fig. 8

Fast Fourier transform on CIP signal from elsA computations: (a) front rotor and (b) rear rotor

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Fig. 9

Thrust coefficient CT on a single blade: (a) front blade and (b) rear blade

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Fig. 10

Kp distribution on blade at ξ=0.75

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Fig. 13

Instantaneous induced velocity flow-fields in an X-plane at one chord upstream of the front rotor: (a) normalized axial induced velocity ux/Vx∞ and (b) Δαloc (deg) due to induced velocity field

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Fig. 12

Velocity triangle for propellers at nonzero angle of attack with induced velocities

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Fig. 11

Velocity triangle for propellers at nonzero angle of attack: (a) front view of propellers and (b) advancing blade

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Fig. 19

Impact of the aerodynamic interactions on a rear single blade: (a) filtered thrust coefficient CTHF on a rear single blade and (b) thrust coefficient CT on a front single blade

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Fig. 16

Impact of the increase of the axial velocity due to the front stage: (a) axial velocities on an X-plane at one chord upstream to the rear rotor and at ξ = 0.75 and (b) velocity triangle for the advancing blade

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Fig. 17

Relative flow angles Φr (deg) upstream of the rear rotor: (a) X-cut at one chord upstream of rear rotor (α = 1 deg) and (b) extraction from a line at ξ = 0.75

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Fig. 18

In-plane forces on the rear rotor regarding time step: (a) modulus and (b) angle

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Fig. 15

Impact of the aerodynamic interactions on a front single blade: (a) filtered thrust coefficient CTHF on a front single blade and (b) thrust coefficient CT on a rear single blade

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Fig. 14

In-plane force on the front rotor regarding time step: (a) modulus and (b) angle

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