AIRFRAME NOISE MODELING APPROPRIATE

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Feb 22, 2014 (3 years and 5 months ago)

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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,




C
L
=0.689,




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