1. Dirk Rabe, Gunther Wilke
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Parametric Design Studies of the Helicopter Rotor Noise using Variable-Fidelity Methods
Dirk Rabe, Gunther Wilke
DLR Institute of Aerodynamics and Flow Technology
May 17th, 2018
74th AHS Phoenix, Arizona

2. Content Motivation Methodology
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Content
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Design Study
Conclusion and Outlook

3. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Design Study
Conclusion and Outlook

4. 1. Motivation ERATO blade design
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
1. Motivation
ERATO blade design
Multidisciplinary development of rotor blades takes time
ERATO (DLR/ONERA) design process – 8 years
ERATO  Blue Edge® – 17 years
 25 years of design and development for quiet rotor blade
Development tools range from BET+wake models to higher order CFD
Goal:
Find fast and accurate methods for aeroacoustic design studies
Descent flight and BVI
Source:
H160 with Blue Edge® blade

5. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Study
Conclusion and Outlook

6. 2. Methodology Comprehensive Code HOST Flow/Vortex solution
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
2. Methodology
Comprehensive Code
HOST
Flow/Vortex solution
HOST, UPM, FLOWer
FW-H-Aeroacoustic Code
APSIM
Sound
Pressure
Propagation
Fluid-Structural-Numerical process chain

7. 2. Methodology BET + wake models: airfoil tables prescribed/free wake
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
2. Methodology
BET + wake models:
airfoil tables
prescribed/free wake
Panel method:
incompressible (correction factor)
inviscid
CFD:
higher order schemes
40 Mio. grid cells
HOST
P.WAKE
F.WAKE
Radial 39
Chord 1
Azimuth [°] 2
UPM
Oneshot UPM
Coupled UPM 17 49 2
FLOWer4
Euler
RANS 80
144
0.1

8. 2. Methodology BET + wake models: airfoil tables prescribed/free wake
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
2. Methodology
BET + wake models:
airfoil tables
prescribed/free wake
Panel method:
incompressible (correction factor)
inviscid
CFD:
higher order schemes
40 Mio. grid cells
HOST
P.WAKE
Radial 39
Chord 1
Azimuth [°] 2
UPM
Coupled UPM 17 49 2
FLOWer4
RANS 80
144
0.1

9. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Design Study
Conclusion and Outlook

10. 3. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
3. Comparison of Various Methods for selected Rotor Blades
HARTII
NB [-] 4
R [m/ft]
2.0/6.56
Mtip [-]
0.638
μ [-]
0.150
Ct/σ [-]
0.594
7AD 4
2.1/6.89
0.660
0.154
0.533
ERATO 4
2.1/6.89
0.616
0.165
0.631
Wind tunnel tested rotor blades
Different blade tip shapes by aeroacoustic means
Investigation of 6° descent flight
My – advance ratio
Wind tunnel blade:
HARTII
7AD
ERATO

11. 3. Comparison of Various Methods for selected Rotor Blades – HARTII
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
3. Comparison of Various Methods for selected Rotor Blades – HARTII
Experiment
P.WAKE
Coupled UPM
RANS
Assessment:
fair(o)
good(+)
good(+)
HARTII – noise carpets – 8–40 BPF – SPL [dB]

12. 3. Comparison of Various Methods for selected Rotor Blades – 7AD
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
3. Comparison of Various Methods for selected Rotor Blades – 7AD
Experiment
P.WAKE
Coupled UPM
RANS
Assessment:
bad(-)
good(+)
fair(o)
7AD – noise carpets – 8–40 BPF – SPL [dB]

13. 3. Comparison of Various Methods for selected Rotor Blades – ERATO
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
3. Comparison of Various Methods for selected Rotor Blades – ERATO
Experiment
P.WAKE
Coupled UPM
RANS
Assessment:
fair(o)
good(+)
fair(o)
ERATO – noise carpets – 8–40 BPF – SPL [dB]

14. 3. Comparison of Various Methods for selected Rotor Blades – Review
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
3. Comparison of Various Methods for selected Rotor Blades – Review
Methods
HARTII
7AD
ERATO
P.WAKE o -
F.WAKE
Oneshot UPM ++ +
Coupled UPM
Euler
RANS
Assessment of noise carpets
Average simulation resources [cpuh]

15. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Design Study
Conclusion and Outlook

16. 4. Results of the Parametric Design Study – Baseline
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Baseline
7AD baseline:
ERATO flight state
lower Mtip
 2 dB noise reduction
Use of validated methods:
P.WAKE
Coupled UPM
Investigated parameters:
an/dihedral
twist
Rotor blade definition of the 7AD baseline

17. 4. Results of the Parametric Design Study – Anhedral
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Anhedral
Samples
Best sample
P.WAKE
Coupled UPM

18. 4. Results of the Parametric Design Study – Anhedral – P.WAKE
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Anhedral – P.WAKE
Baseline
Best Design
Difference
P.WAKE – anhedral – noise carpets – 8–40 BPF – SPL [dB]

19. 4. Results of the Parametric Design Study – Anhedral – Coupled UPM
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Anhedral – Coupled UPM
Baseline
Best Design
Difference
Coupled UPM – anhedral – noise carpets – 8–40 BPF – SPL [dB]

20. 4. Results of the Parametric Design Study – Anhedral – Coupled UPM
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Anhedral – Coupled UPM
Coupled UPM – anhedral – comparison of vortex fields

21. 4. Results of the Parametric Design Study – Twist
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Twist
P.WAKE
Coupled UPM
Twist distribution
Samples
Best sample

22. 4. Results of the Parametric Design Study – Twist – P.WAKE
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Twist – P.WAKE
Baseline
Best Design
Difference
P.WAKE – twist – noise carpets – 8–40 BPF – SPL [dB]

23. 4. Results of the Parametric Design Study – Twist – Coupled UPM
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Twist – Coupled UPM
Baseline
Best Design
Difference
Coupled UPM – twist – noise carpets – 8–40 BPF – SPL [dB]

24. 4. Results of the Parametric Design Study – Review of noise reduction
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
4. Results of the Parametric Design Study – Review of noise reduction
An/Dihedral
Twist
P.WAKE (max. SPL / largest reduction)
-1 / -10
-3 / -3
Coupled UPM (max. SPL / largest reduction)
-6 / -7
-1 / -7

25. Comparison of Various Methods for selected Rotor Blades
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Motivation
Methodology
Comparison of Various Methods for selected Rotor Blades
Results of the Parametric Design Study
Conclusion and Outlook

26. 5. Conclusion and Outlook
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
5. Conclusion and Outlook
Conclusion:
Investigation of wind tunnel tested rotor blades:
best results were found using free-wake coupled panel method
CFD results roughly 4 dB under estimated for all test cases, higher grid resolution necessary
Performed parametric design study with anhdral and twist:
design trends of wake model and panel method align, prediction discrepancies exist
dihedral showed most promising results
Outlook:
 double check parametric design study results with CFD
optimization study, combination of design parameters
multi-objective investigation (aerodynamics + aeroacoustics)

27. Thank you for your attention. Are there any questions?
> AHS74 > Dirk Rabe • Parametric Design Studies of Helicopter Rotor Noise >
Thank you for your attention.
Are there any questions?