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

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

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

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

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

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

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 179-12 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)

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?

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

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.

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-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. Coe, C.F. Nute, J.B. "Steady and Fluctuating Pressures at Transonic Speeds on Hammerhead Launch Vehicles," NASA TM X-778, December 1962.

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.

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 66059. p. 15.

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

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.

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.)

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

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