1. Derivation of Preliminary Ascent Vibro-Acoustic Environments for the Crew Exploration Vehicle
Presented by:
Mike Yang / ATA Engineering
Nancy Tengler / Lockheed Martin Corporation at
Spacecraft 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
Space Shuttle fleet will be retired in 2010.
CEV designed to go to ISS, Moon, Mars, and beyond.
Crew of 4-6
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
M=1.4
q represents the fluid kinetic energy. q = ½*rho*u^2
From conservation of linear momentum for an incompressible gas: p + q = total pressure
Plots were provided by LM

6. Aeronoise Models are Comprised of Three Components
RMS
Autospectra
Cross-spectra
Increasing Uncertainty
Derived loads are dependent on:
Flight Parameters
Spacecraft Geometry
Dynamic Pressure (q)
Mach (M)
Atmospheric Properties (altitude)
Density ()
Speed of sound (c)
Ratio of specific heats ()
Kinematic viscosity ()
Determines flow regime
Affects RMS Pressure for some flow regimes

7. RMS Pressure is Typically Expressed as a Fluctuating Pressure Coefficient
Cp Equations
Plateau
Peak
Attached TBL
Compression Regime
Transonic
Supersonic
Expansion Regime
What are the general range of values for these constants.
Shock wave angle is a function of the GEOMETRY of the vehicle
NOTE: compression regime equations assume there are no protuberances (like LAS nozzles) – see TM
Peak expansion equation includes a correction factor for the expansion angle (THIS IS NEW)
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)

8. Peak Expansion and Compression Shock Regimes have Highest Cp Values
Peak Expansion Shock
Peak Compression Shock
What range of mach numbers were used to derive these equations?

9. C is regime-dependent, and shifts curve to the left Generally:
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
Increasing C
+10 dB/decade
-10 dB/decade

10. Default VA-One Cross-Correlation Coefficients were Used
Along Flow
Cross Flow
Default values are cz(w)=.1, ch(w)=.72, a(w)=1, b(w)=0, s=0
We compared these with cross-correlation models in the literature and found that the VA-One coefficients were generally conservative.

11. Different Geometries Used to Verify Aeronoise Model
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 May p. 32.
Shelton, J.D. "Collation of Fluctuating Buffet Pressures for the Mercury/Atlas and Apollo/Saturn configurations." NASA CR 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 p. 7.
Coe, C.F. Nute, J.B. "Steady and Fluctuating Pressures at Transonic Speeds on Hammerhead Launch Vehicles," NASA TM X-778, December 1962.

12. Predicted Autospectra Anchored to Flight Data
Expansion Peak
Expansion Plateau
Attached Turbulent Boundary Layer
SPL (dB)
Derived aeronoise model envelopes majority of data
Two lines on expansion plateau plot are peak and plateau models.

13. Aeronoise RMS Levels Anchored to Wind Tunnel Data
Apollo/Saturn-like Wind Tunnel Model T1 T2
No autospectra data available – wind tunnel data was taken back in the 70’s.
Shelton, J.D. "Collation of Fluctuating Buffet Pressures for the Mercury/Atlas and Apollo/Saturn configurations." NASA CR 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?
Slices near nozzle have more high frequency content
Also known as “Eldred’s Method”
Prediction also affected by:
Thrust level – proportional
Nozzle diameter – smaller diameter increases high frequency component

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:
Liftoff
DAF excitation
Sea-level
Nominal Ascent
TBL excitation
Altitude ~ 15K feet
LAS Abort
TBL and DAF excitation
Altitude ~ 31K feet
Point over different components of model: LAS, CM, SM (EM and PM), Spacecraft Adapter, pressurized and unpressurized cavities, etc.

16. SEA Results Reveal Critical Events
SPL in Cavity 1
SPL in Cavity 2
Crew Module
Highest noise levels occur during LAS Abort
Spacecraft Adapter
Highest noise levels occur during Liftoff
Why is SPL in “Cavity 2” really low at low frequencies for nominal ascent?
Liftoff – DAF – Uses SEA formulation to compute modes (function of wavespeed and size of subsystem)
Nominal Ascent – TBL – Uses modal formulation (assumes simply-supported boundary conditions and calculates modes based on closed-form solution for simple plates, etc.)

17. VA-One’s hybrid analysis capability was used
Hybrid FEM-SEA Model Used to Compute Low-Frequency Response of Thrust Cone
Hybrid model is aft end of CEV model.
Hybrid model used to evaluate results at low frequencies, where SEA can be inaccurate.
“Dip” at 15 Hz is due to low number of modes (First flexible mode at ~20 Hz)
“Dip” at 500 Hz is due to modal truncation (Modes solution was run out to 500 Hz)
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

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:
RMS Pressure
Peak expansion and peak compression regimes are highest
Autospectra
Shape of spectrum is function of the flow regime
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