AIRFRAME NOISE MODELING APPROPRIATE
FOR MULTIDISCIPLINARY DESIGN AND
OPTIMIZATION
42
nd
AIAA Aerospace Sciences Meeting and Exhibit
Reno, NV, January 7, 2004
AIAA

2004

0689
Serhat Hosder, Joseph A. Schetz, Bernard Grossman
and William H. Mason
Virginia Tech
Work sponsored by NASA Langley Research
Center, Grant NAG 1

02024
2
Introduction
Aircraft noise: an important performance criterion and
constraint in aircraft design
Noise regulations limit growth of air transportation
Reduction in noise needed
To achieve noise reduction
–
Design revolutionary aircraft with innovative configurations
–
Improve conventional aircraft noise performance
–
Optimize flight performance parameters for minimum noise
All these efforts require addressing noise in the
aircraft conceptual design phase
3
Aircraft Noise Components
Airframe
Aircraft Noise
Engine
Engine/airframe interference
Include aircraft noise as an objective function or
constraint in MDO
–
Requires modeling of each noise source
Airframe noise
–
Now comparable to engine noise at approach
–
Our current focus
4
Trailing Edge Noise:
noise mechanism of a clean wing
–
scattering of acoustic waves generated due to the passage of
turbulent boundary layer over the trailing edge of a wing or flap
In our study, we have developed a new Trailing Edge
Noise metric appropriate for MDO
5
Why Do We Model Trailing Edge Noise?
Trailing Edge Noise: a lower bound value of airframe
noise at approach (a measure of merit)
Trailing Edge Noise can be significant contributor to
the airframe noise for a non

conventional configuration
–
traditional high

lift devices not used on approach
–
A Blended

Wing

Body (BWB) Aircraft
•
Large Wing Area and span
–
A conventional aircraft or BWB with distributed propulsion
•
Jet

wing concept for high lift
–
An airplane with a morphing wing
A Trailing Edge Noise Formulation based on proper
physics may be used to model the noise from flap
trailing edges or flap

side edges at high lift conditions
First step towards a general MDO model
6
Outline of the Current Work
Objective: To develop a trailing edge
noise metric
–
construct response surfaces for aerodynamic noise minimization
Noise metric
–
Should be a reliable indicator of noise
–
Not necessarily the magnitude of the absolute noise
–
Should be
relatively
inexpensive to compute
•
Computational Aeroacoustics too expensive to use
•
Still perform 3

D, RANS simulations with the CFD code GASP
Parametric Noise Metric Studies
–
2

D and 3

D cases
–
The effect of different wing design variables on the noise metric
7
The Trailing Edge Noise Metric
dy
y
y
D
y
H
y
Cos
y
l
y
u
a
I
b
NM
)
(
),
(
)
(
)
(
)
(
)
(
2
0
2
3
0
5
0
2
3
ref
NM
I
I
dB
NM
log
10
)
(
)
log(
10
120
)
(
NM
I
dB
NM
wing
TE
z
y
V
receiver
noise source
H
x
u
0
characteristic velocity for turbulence
l
0
characteristic length scale for turbulence
free

stream density
a
free

stream speed of sound
H
distance to the receiver
trailing edge sweep angle
polar directivity angle
azimuthal directivity angle
Sin
Sin
D
2
2
]
,
[
2
Following classical aeroacoustics theories from Goldstein and Lilley, we
derive a noise intensity indicator (
I
NM
)
Noise Metric:
(directivity term)
, with
I
ref
=10

12
(W/m
2
)
8
Modeling of
u
0
and
l
0
)
(
)
(
0
z
TKE
Max
y
u
)
(
)
(
0
z
TKE
Max
y
l
Characteristic turbulence velocity scale at the trailing edge
New characteristic turbulence length scale at the trailing edge
is the turbulence frequency observed at the maximum
TKE
location for each spanwise location
.
TKE
and
obtained from the solutions of
TKE

(
k

)
turbulence model equations used in RANS calculations
Previous semi

empirical trailing edge noise prediction methods
use
d
or
d
*
for the length scale
–
Related to mean flow
–
Do not capture the turbulence structure
9
Unique Features of the Noise Metric
Expected to be an accurate relative noise measure
suitable for MDO studies
Written for any wing configuration
Spanwise variation of the characteristic turbulence
velocity and length scale taken into account
Sensitive to changes in design variables (lift
coefficient, speed, wing geometry
etc
.)
The choice of turbulence length scale (
l
0
) more
soundly based than previous ones used in semi

empirical noise predictions
10
Noise Metric Validation
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1
2
3
4
5
6
7
OASPL
si
NM
si
1.122
2.0
1.497
1.164
0.831
0.499
0.665
1.497
Re
c
x10

6
1.5
0.0
1.5
2.0
0.0
0.0
deg
1.122
2.0
1.497
1.164
0.831
0.499
0.665
1.497
Re
c
x10

6
1.5
0.0
1.5
2.0
0.0
0.0
deg
NM
and
OASPL
results are
scaled with the values
obtained for case 1
Experimental NACA
0012 cases from
NASA
RP 1218
(Brooks
et al.
)
All cases subsonic
Predicted Noise Metric
(
NM
) compared with the
experimental
OASPL
The agreement
between the predictions
and the experiment is
very good
Experimental
11
Parametric Noise Metric Studies
Two

Dimensional Cases
–
Subsonic Airfoils
•
NACA 0012 and NACA 0009
–
Supercritical Airfoils
•
SC(2)

0710 (
t/c
=10%)
SC(2)

0714 (
t/c
=14%)
–
C

grid topology (388
64 cells)
Three

Dimensional Cases
–
Energy Efficient Transport (EET) Wing
•
S
ref
=511 m2,
MAC
=9.54 m
•
AR
=8.16,
L
=30
at
c/4
•
t/c
=14% at the root
t/c
=12% at the break
t/c
=10% at the tip
–
C

O topology, 4 blocks (884,736 cells)
Steady RANS simulations with GASP
–
Menter’s SST
k

turbulence model
0.08
0.04
0.00
0.04
0.08
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
SC(2)

0710
SC(2)

0714
z/c
x/c
X
Y
Z
12
Parametric Noise Metric Studies with
NACA 0012 and NACA 0009
58.00
59.00
60.00
61.00
62.00
63.00
64.00
65.00
0.70
0.80
0.90
1.00
1.10
1
2
3
2.453 dB
1.164 dB
NACA 0012, c=0.3048 m,
C
l
=1.046, lift=1010 N
NACA 0012, c=0.3741 m,
C
l
=0.853, lift=1011 N
NACA 0009,
c=0.3741 m,
C
l
=0.860, lift=1018 N
NM
(dB)
C
l
V
=71.3 m/s,
Mach
=0.2,
Re
c
=1.497
10
6
& 1.837
10
6
Investigated noise reduction by decreasing
C
l
and
t/c
–
Increased chord length to keep lift and speed constant
–
Total noise reduction=3.617 dB
Simplified representation of increasing the wing area and
reducing the overall lift coefficient at constant lift and speed
–
Additional benefit: eliminating or minimizing the use of high lift devices
13
Parametric Noise Metric Studies with
SC(2)

0710 and SC(2)

0714
0.0
0.4
0.8
1.2
1.6
2.0
2.4
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
C
l
SC(2)

0710
SC(2)

0714
0.0
0.4
0.8
1.2
1.6
2.0
2.4
0.00
0.01
0.02
0.03
0.04
0.05
0.06
C
l
C
d
SC(2)

0710
SC(2)

0714
Realistic approach conditions
–
Re
c
=44
10
6
–
V
= 68 m/s,
Mach
=0.2
Corresponds to typical transport
aircraft
–
With
MAC
=9.54 m
–
Flying at
H
=120 m
–
Approximately the point for
the noise certification at the
approach before landing
Directivity terms
–
=90
and
=90
Investigate the effect of the
thickness ratio and the lift
coefficient
14
Noise Metric Values for the Supercritical Airfoils
at different C
l
values
20.0
25.0
30.0
35.0
40.0
45.0
50.0
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
NM
(dB)
C
l
SC(2)

0710
SC(2)

0714
At relatively lower lift coefficients (
C
l
< 1.3)
–
Noise metric almost constant
–
The thicker airfoil has a larger noise metric
At higher lift coefficients (
C
l
>1.3)
–
Sharp increase in the noise metric
–
The thinner airfoil has a larger noise metric
15
3

D Parametric Noise Metric Studies
with the EET Wing
0.00
0.15
0.30
0.45
0.60
0.75
0.90
1.05
1.20
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0
43
86
128
171
214
257
300
343
C
L
W/S (kg/m
2
)
0.00
0.15
0.30
0.45
0.60
0.75
0.90
1.05
1.20
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
C
L
C
D
Realistic approach conditions
–
Re
c
=44
10
6
,
V
= 68 m/s,
M
=0.2
–
Flying at
H
=120 m
Stall observed at the highest
C
L
–
CL
max
=
1.106
W/S
max
=315.7 kg/m
2
(64.8 lb/ft
2
)
–
Less than realistic
C
L
and
W/S (~430 kg/m
2
) values
Investigate the effect of the lift
coefficient on the noise metric
with a realistic geometry
Investigate spanwise variation
of
u
0
and
l
0
16
Section C
l
and Spanload distributions
for the EET Wing
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0
0.2
0.4
0.6
0.8
1.0
Inboard
Outboard
2y/b
C
l
0.836
0.534
0.375
0.970
C
L
= 0.219
0.689
1.084
1.106
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.0
0.2
0.4
0.6
0.8
1.0
Inboard
Outboard
0.836
0.534
0.375
0.970
C
L
= 0.219
0.689
1.084
1.106
C
l
c/c
a
Loss of lift on the
outboard sections at
the highest lift
coefficient
Large region of
separated flow
Shows the need to
increase the wing area
of a clean wing
–
To obtain the required
lift on approach with
lower
C
L
•
Lower noise
17
Skin Friction Contours at the Upper Surface of
the EET Wing for different C
L
values
y
/
b
0
.
2
0
0
.
4
0
0
.
6
0
0
.
8
0
1
.
0
0
C
f
0
.
0
0
9
4
0
.
0
0
8
6
0
.
0
0
7
8
0
.
0
0
7
0
0
.
0
0
6
2
0
.
0
0
5
4
0
.
0
0
4
6
0
.
0
0
3
8
0
.
0
0
3
0
0
.
0
0
2
3
0
.
0
0
1
5
0
.
0
0
0
7

0
.
0
0
0
1

0
.
0
0
0
9

0
.
0
0
1
7
y
/
b
0
.
2
0
0
.
4
0
0
.
6
0
0
.
8
0
1
.
0
0
y
/
b
0
.
2
0
0
.
4
0
0
.
6
0
0
.
8
0
1
.
0
0
y
/
b
0
.
2
0
0
.
4
0
0
.
6
0
0
.
8
0
1
.
0
0
0
0
0
0
2
2
2
2
C
L
=0.375,
㴲
C
L
=0.689,
㴶
C
L
=0.970,
㴱0
C
L
=1.106,
㴱4
18
0.0E+00
1.0E02
2.0E02
3.0E02
4.0E02
5.0E02
6.0E02
7.0E02
0.0
0.2
0.4
0.6
0.8
1.0
Inboard
Outboard
C
L
=0.836
C
L
=0.534
C
L
=1.084
C
L
=1.106
C
L
=0.970
2y/b
TKE
and
l
0
Distributions at the Trailing Edge of
the EET Wing for different C
L
values
0.0
25.0
50.0
75.0
100.0
125.0
150.0
175.0
200.0
225.0
0.0
0.2
0.4
0.6
0.8
1.0
C
L
=0.836
C
L
=0.534
C
L
=1.084
C
L
=1.106
C
L
=0.970
2y/b
Inboard
Outboard
TKE
max
(J/kg)
l
0
(m)
Maximum
TKE
and
l
0
get larger starting from
CL=0.836, especially at
the outboard section
Dramatic increase for
the separated flow case
Maximum
TKE
and
l
0
not constant along the
span at high
C
L
19
Noise Metric Values for the EET Wing at
different C
L
values
15.0
25.0
35.0
45.0
55.0
65.0
75.0
0.2
0.4
0.6
0.8
1.0
1.2
NM
(dB)
C
L
NM
total
NM
upper
NM
lower
At lower lift coefficients
–
Noise metric almost constant
–
Contribution to the total noise from the lower surface significant
At higher lift coefficients
–
Noise metric gets larger
•
Dramatic increase for the separated flow case
–
Upper surface is the dominant contributor to the total noise
20
Conclusions
A new trailing edge noise metric has been developed
–
For response surfaces in MDO
–
For any wing geometry
–
Introduced a length scale directly related to the turbulence structure
–
Spanwise variation of characteristic velocity and length scales considered
Noise metric an accurate
relative
noise measure as shown by
validation studies
Parametric noise metric studies performed
–
Studied the effect of the lift coefficient and the thickness ratio
–
Noise reduction possible with decreasing the lift coefficient and the
thickness ratio while increasing the wing area
–
Noise constant at lower lift coefficients and gets larger at higher lift
coefficients. Sharp increase when there is large separation
–
Characteristic velocity and length scales not constant along the span at
high lift coefficients due to 3

D effects
21
Future Work
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