AIRFRAME NOISE MODELING APPROPRIATE

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
1.0E-02
2.0E-02
3.0E-02
4.0E-02
5.0E-02
6.0E-02
7.0E-02
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