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Derivation of Preliminary Ascent Vibro-Acoustic Environments for the Crew Exploration Vehicle
Presented by:Mike Yang / ATA Engineering
Nancy Tengler / Lockheed Martin Corporation
atSpacecraft and Launch Vehicle Dynamic Environments Workshop
June 27-29, 2006
2
Presentation Outline
• Description of CEV• Development of aeronoise model for different flow regimes
– Attached turbulent boundary layer– Compression corner– Expansion corner
• Comparison to existing empirical data– Titan IV flight data– Apollo/Saturn wind tunnel data
• Prediction of Launch Abort System (LAS) motor noise• Prediction of internal responses using SEA/FEA
– Comparison of SEA and FEA responses• Summary and Conclusions
3
CEV is Comprised of Several Modular Parts
Crew Module Service Module
Spacecraft Adapter
Launch Abort System
4
Objectives
Part 1• Predict external acoustic environment for CEV during the liftoff,
nominal ascent, and abort events– Aeronoise– LAS Abort Motor
Part 2• Use derived external environments to predict internal responses
– Acoustic cavities– Panel responses
• Use predicted responses to aid in design evaluation and refinement
5
Cp Contour Plots Reveal Different Flow Regimes
Attached TBL
Compression Plateau Compression Peak
Expansion Peak Expansion Plateau Attached TBL
q
PPC staticp
tCoefficien Pressure Static
6
Aeronoise Models are Comprised of Three Components
RMS Cross-spectraAutospectra
Increasing Uncertainty
Derived loads are dependent on:
• Dynamic Pressure (q)• Mach (M)• Atmospheric Properties (altitude)
• Density ()• Speed of sound (c)• Ratio of specific heats ()• Kinematic viscosity ()
Flight Parameters Spacecraft Geometry• Determines flow regime• Affects RMS Pressure for
some flow regimes
7
RMS Pressure is Typically Expressed as a Fluctuating Pressure Coefficient
• K, A = Constants determined from experimental data• F = A function of Mach number• P2/P1 = Pressure ratio across shock wave (Function of mach, ratio of
specific heats, shock wave angle)
q
PC RMSp
Cp Equations
Plateau Peak
Attached TBL
Compression Regime
Transonic
Supersonic
Expansion Regime
F
KTBL
2
,
1 M
K pltrncomp
F
K
P
P comp sup,
1
2
F
K
P
PA
P
PAA comp sup,
2
1
23
1
221
2
exp
1 M
K pl
exp42
exp
1A
M
K pk
2
,
1 M
K pktrncomp
8
Fluctuating Pressure Coefficient as a Function of Mach(ISS Trajectory Used for Atmospheric Properties)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00
Mach
Del
ta C
p
Turbulent Boundary Layer Compression Shock - Plateau Compression Shock - Peak
Expansion Shock - Plateau Expansion Shock - Peak
Peak Expansion and Compression Shock Regimes have Highest Cp Values
Peak Expansion Shock
Peak Compression Shock
9
Noise Spectrum Due to Compression Corner
135.0
140.0
145.0
150.0
155.0
1 10 100 1000 10000
Frequency (Hz)
SP
L (
dB
)
Peak
Plateau
Shape of Autospectra Curve is Function of a Parameter which is Regime-Dependent
• C is regime-dependent, and shifts curve to the left
• Generally:
– Cpeak > Cplateau
– Ccomp > Cexp > CTBL
• Slope of 1/3-octave band spectrum:– -10 dB/dec. at low freqs.– +10 dB/dec. at high freqs.
• Function always integrates to 1
+10 dB/decade -10 dB/decade
Increasing C
10
Default VA-One Cross-Correlation Coefficients were Used
• Default values are c()=.1, c()=.72, ()=1, ()=0, =0
kekeR ii
kkckkc
coscos,,
2
*22
2
*22
3
1
3
1
'CU
k
'CU
k UUC '
Along Flow Cross Flow
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2
Distance
Cro
ss-C
orr
elat
ion
Co
effi
cien
t
Along Flow
Across Flow
11
Different Geometries Used to Verify Aeronoise Model
Coe, C.F. Nute, J.B. "Steady and Fluctuating Pressures at Transonic Speeds on Hammerhead Launch Vehicles," NASA TM X-778, December 1962.
Jones, George W. Jr., and Foughner, Jerome T. Jr. "Investigation of Buffet Pressures on Models of Large Manned Launch Vehicle Configurations." NASA Technical Note D-1633. May 1963. p. 32.
Shelton, J.D. "Collation of Fluctuating Buffet Pressures for the Mercury/Atlas and Apollo/Saturn configurations." NASA CR 66059. p. 15.
Coe, Charlie F., and Kaskey, Arthur J. "The Effects of Nose Bluntness on the Pressure Fluctuations Measured on 15 degree and 20 degree Cone-Cylinders at Transonic Speeds." NASA TM X-779. January 1963. p. 7.
12
Predicted Autospectra Anchored to Flight Data
125
130
135
140
145
150
155
10 100 1000 10000
Frequency (Hz)
120
125
130
135
140
145
150
155
160
10 100 1000 10000
Frequency (Hz)
120
125
130
135
140
145
150
10 100 1000 10000
Frequency (Hz)
Expansion Peak Expansion Plateau
Attached Turbulent Boundary Layer
SP
L (d
B)
SP
L (d
B)
SP
L (d
B)
• Derived aeronoise model envelopes majority of data
13
Aeronoise RMS Levels Anchored to Wind Tunnel Data
Compression Regime with Modifications Made to ModelDC offset = 0.025
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
0.180
0.5 1 1.5 2 2.5Mach
De
lta C
p
Compression Shock - Plateau Compression Shock - Peak
CR 66059 - T1 CR 66059 - T2
8% Tower 3 Freon - Mic 1 8% Tower 1 air - Mic 1
8% Tower 1 Freon - Mic 1 8% Tower 2 freon - Mic 1
1.6% Tower 1 - Mic 1 1.6% Tower 2 - Mic 1
Apollo/Saturn-like Wind Tunnel Model
T1
T2
Shelton, J.D. "Collation of Fluctuating Buffet Pressures for the Mercury/Atlas and Apollo/Saturn configurations." NASA CR 66059. p. 15.
14
NASA-SP-8072 Used to Predict LAS Abort Engine Noise
• “Method 2” divides the plume into slices– Each slice has a different sound power spectrum– SPL at CEV surface calculated by acoustically radiating sound back to
surface– An additional 1-3 dB were added to account for surface reflections
• This method assumes that there is no plume impingement.– How would we handle this if there was impingement?
Zone 9-4
Zone 9-3
Zone 9-2
Zone 9-1
Zone 8-2
Zone 8-1
Zone 7-2
Zone 7-1
Zone Center
LAS Motor Noise Spectrum
100
110
120
130
140
150
160
1 10 100 1000 10000
Frequency (Hz)
SP
L (r
ef =
20
mic
roP
a) Zone 7-1
Zone 7-2
Zone 8-1
Zone 8-2
Zone 9-1
Zone 9-2
Zone 9-3
Zone 9-4
15
Internal Responses were Computed using SEA
• Models created in VA-One
• SEA is ideally suited for vibroacoustic predictions at high frequencies
• Symmetric half-model was used to reduce computation time.
Three models:
1. Liftoff
• DAF excitation
• Sea-level
2. Nominal Ascent
• TBL excitation
• Altitude ~ 15K feet
3. LAS Abort
• TBL and DAF excitation
• Altitude ~ 31K feet
16
SEA Results Reveal Critical Events
• Crew Module– Highest noise levels occur during LAS Abort
• Spacecraft Adapter – Highest noise levels occur during Liftoff
Crew Module Cavity SPL
60.0
70.0
80.0
90.0
100.0
110.0
120.0
130.0
140.0
10 100 1000 10000
Frequency (Hz)
Ca
vit
y S
PL
, dB
(R
ef
= 2
0 m
Pa
)
Liftoff
Nominal Ascent
LAS Abort
Spacecraft Adapter Cavity SPL
60.0
70.0
80.0
90.0
100.0
110.0
120.0
130.0
140.0
10 100 1000 10000
Frequency (Hz)
Ca
vit
y S
PL
, dB
(R
ef
= 2
0 m
Pa
)
Liftoff
Nominal Ascent
SPL in Cavity 1 SPL in Cavity 2
17
Hybrid FEM-SEA Model Used to Compute Low-Frequency Response of Thrust Cone
• VA-One’s hybrid analysis capability was used• “Sensors” were placed at several nodes on Cone FE subsystem
– Sensor response was averaged (spatial average)• Low-frequency response of Thrust Cone was verified
Thrust Cone Vibration During Nominal Ascent
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
10 100 1000
Frequency (Hz)
g^
2/H
z
SEA
Hybrid
18
Summary & Conclusions
• Flow around a vehicle can be divided into flow regimes– These flow regimes will have different environments
• Aeronoise model consists of three parts:1. RMS Pressure
• Peak expansion and peak compression regimes are highest2. Autospectra
• Shape of spectrum is function of the flow regime3. Cross-spectra
• Decaying sine along flow, decaying exponential across flow• Aeronoise model was anchored to flight & experimental data
– Saturn/Apollo– Titan– Others (not shown)
• NASA-SP-8072 was used to predict LAS Abort Motor Noise– How can we predict noise due to plume impingement?
• SEA and Hybrid FEA-SEA analysis was used to predict internal CEV responses
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