The contrarotating open rotor is, once again, being considered as an alternative to the advanced turbofan to address the growing pressure to cut aviation fuel consumption and carbon dioxide emissions. One of the key challenges is meeting community noise targets at takeoff. Previous open rotor designs are subject to poor efficiency at takeoff due to the presence of large regions of separated flow on the blades as a result of the high incidence needed to achieve the required thrust. This is a consequence of the fixed rotor rotational speed constraint typical of variable pitch propellers. Within the study described in this paper, an improved operation is proposed to improve performance and reduce rotor-rotor interaction noise at takeoff. Three-dimensional computational fluid dynamics (CFD) calculations have been performed on an open rotor rig at a range of takeoff operating conditions. These have been complemented by analytical tone noise predictions to quantify the noise benefits of the approach. The results presented show that for a given thrust, a combination of reduced rotor pitch and increased rotor rotational speed can be used to reduce the incidence onto the front rotor blades. This is shown to eliminate regions of flow separation, reduce the front rotor tip loss and reduce the downstream stream tube contraction. The wakes from the front rotor are also made wider with lower velocity defect, which is found to lead to reduced interaction tone noise. Unfortunately, the necessary increase in blade speed leads to higher relative Mach numbers, which can increase rotor alone noise. In summary, the combined CFD and aeroacoustic analysis in this paper shows how careful operation of an open rotor at takeoff, with moderate levels of repitch and speed increase, can lead to improved front rotor efficiency as well as appreciably lower overall noise across all directivities.

References

References
1.
Smith
,
L. H.
, Jr.
,
1987
, “
Unducted Fan Aerodynamic Design
,”
ASME J. Turbomach.
,
109
(
3
), pp.
313
324
.10.1115/1.3262108
2.
Hager
,
R. D.
, and
Vrabel
,
D.
,
1988
, “
Advanced Turboprop Project
,” NASA SP-495.
3.
Mitchell
,
G. A.
,
1988
, “
Experimental Aerodynamic Performance of Advanced 40°-Swept, 10-Blade Propeller Model at Mach 0.6 to 0.85
,” NASA TM-88969.
4.
Neumann
,
H. E.
,
Bober
,
L. J.
,
Serafini
,
J. S.
, and
Chang
,
L.-K.
,
1983
, “
An Analytical and Experimental Comparison of the Flow Field of an Advanced Swept Turboprop
,” Paper No. AIAA-1983-189.
5.
Podboy
,
G. G.
, and
Krupar
,
M. J.
,
1989
, “
Laser Velocimeter Measurements of the Flow Field Generated by an Advanced Counter Rotating Propeller
,” Paper No. AIAA-1989-434.
6.
Shin
,
H.-W.
,
Whitfield
,
C. E.
, and
Wisler
,
D. C.
,
1994
, “
Rotor-Rotor Interaction for Counter-Rotating Fans. I—Three-Dimensional Flowfield Measurements
,”
AIAA J.
,
32
(
11
), pp.
2224
2233
.10.2514/3.12281
7.
Celestina
,
M. L.
,
Mulac
,
R. A.
, and
Adamczyk
,
J. J.
,
1986
, “
A Numerical Simulation of the Inviscid Flow Through a Counter-Rotating Propeller
,” ASME Paper 86-GT-138.
8.
Schnell
,
R.
,
Yin
,
Y.
,
Voss1
,
C.
, and
Nicke1
,
E.
,
2010
, “
Assessment and Optimization of the Aerodynamic and Acoustic Characteristics of a Counter Rotating Open Rotor
,”
ASME
Paper GT2010-22076.10.1115/GT2010-22076
9.
Peters
,
A.
, and
Spakovszky
,
Z. S.
,
2010
, “
Rotor Interaction Noise in Counter-Rotating Propfan Propulsion Systems
,”
ASME
Paper GT2010-22554.10.1115/GT2010-22554
10.
Zachariadis
,
A.
, and
Hall
,
C. A.
,
2009
, “
Application of a Navier-Stokes Solver to the Study of Open Rotor Aerodynamics
,”
ASME
Paper GT2009-59332.10.1115/GT2009-59332
11.
Kirker
,
T. J.
,
1990
, “
Procurement and Testing of a 1/5 Scale Advanced Counter Rotating Propfan Model
,” Paper No. AIAA-1990-3975.
12.
Moinier
,
P.
and
Giles
,
M. B.
,
1998
. “
Preconditioned Euler and Navier-Stokes Calculations on Unstructured Grids
,”
6th ICFD Conference on Numerical Methods for Fluid Dynamics
,
Oxford, UK
, March 31–April 3.
13.
Spalart
,
P. R.
, and
Allmaras
,
S. R.
,
1994
A One-Equation Turbulence Model for Aerodynamic Flows
,”
Recherche Aerospatiale
,
1
, pp.
5
21
.
14.
Whitfield
,
C. E.
,
Mani
,
R.
, and
Gliebe
,
P. R.
,
1990
, “
High Speed Turboprop Acoustic Study (Counter Rotation), Volume II, Computer Programs
,” Technical Report, NASA CR-185242.
15.
Whitfield
,
C. E.
,
Mani
,
R.
, and
Gliebe
,
P. R.
,
1990
, “
High Speed Turboprop Acoustic Study (Counter Rotation), Volume I, Model Development
,” Technical Report, NASA CR-185241.
16.
Hanson
,
D. B.
,
1980
, “
Helicoidal Surface Theory for Harmonic Noise of Propellers in the Far Field
,”
AIAA J.
,
18
(
10
), pp
1213
1219
.10.2514/3.50873
17.
Majjigi
,
R. K.
, and
Gliebe
,
P. R.
,
1984
, “
Development of a Rotor Wake/Vortex Model
,” Volume
I
, Final Technical Report, NASA CR-174849.
18.
Majjigi
,
R. K.
,
Uenishi
,
K.
, and
Gliebe
,
P. R.
,
1989
, “
An Investigation of Counter-Rotating Tip Vortex Interaction
,” NASA CR-185135.
19.
Sears
,
W. R.
,
1941
, “
Some Aspects of Non-Stationary Airfoil Theory and Its Practical Application
,”
J. Aeronaut. Sci.
,
8
(
3
), pp
104
108
.10.2514/8.10655
20.
Amiet
,
R. K.
,
1976
, “
High Frequency Thin-Airfoil Theory for Subsonic Flow
,”
AIAA J.
,
14
(
8
), pp
1076
1082
.10.2514/3.7187
21.
Cumpsty
,
N. A.
,
1977
, “
A Critical Review of Turbomachinery Noise
,”
ASME J. Fluids Eng.
,
99
, pp
278
293
.10.1115/1.3448745
22.
Parry
,
A. B.
, and
Crighton
,
D. G.
,
1989
, “
Prediction of Counter-Rotation Propeller Noise
,” AIAA Paper No. 1989-1141.
23.
Parry
,
A. B.
,
1997
, “
Modular Prediction Scheme for Blade Row Interaction Noise
,”
J. Propul. Power
,
13
,
334
341
.10.2514/2.5186
24.
Vaczy
,
C. M.
, and
McCormick
,
D. C.
,
1987
, “
A Study of the Leading Edge Vortex and Tip Vortex on Prop-Fan Blades
,”
ASME J. Turbomach.
,
109
(
3
), pp.
325
331
.10.1115/1.3262109
25.
Sujuki
,
D.
, and
Haimes
,
R.
,
1995
, “
Identification of Swirling Flow in 3-D Vector Fields
,” Paper No. AIAA-1995-1715.
26.
Haimes
,
R.
, and
Kenwright
,
D.
,
1999
, “
On the Velocity Gradient Tensor and Fluid Feature Extraction
,” Paper No. AIAA-1999-3288.
27.
Metzger
,
F. B.
, and
Rohrbach
,
C.
,
1986
, “
Benefits of Blade Sweep for Advanced Turboprops
,”
J. Propul.
,
2
(
6
), pp.
534
540
.10.2514/3.22938
28.
Parry
,
A. B.
, and
Vianello
,
S.
,
2010
A Project Study of Open Rotor Noise
,”
14th CEAS-ASC Workshop (& 5th Scientific Workshop of X3-Noise)
,
Warsaw, Poland
,
October
7–8
.
29.
Maksymiuk
,
C. M.
, and
Watson
,
S. A.
,
1983
A Computer Program for Estimating the Aerodynamic Characteristics of NACA 16-Series Airfoils
,” NASA Tech. Memo 85696.
30.
Parry
,
A. B.
,
Howarth
,
N.
, and
Taylor
,
M. D.
,
2008
, “
Aeroengine
,” International Publication No. WO 2008/096124 A2.
You do not currently have access to this content.