National Aeronautics and Space Administration

www.nasa.gov

Structural Acoustics Branch at NASA

Langley Research Center

Overview by Noah H. Schiller

noah.h.schiller@nasa.gov

2010 CAV Workshop, Penn State

Kevin P. Shepherd

Head

Richard J. Silcox

Asst. Head

Where we fit

Aeronautics

Science

Exploration

Space Operations

Overview– 2 of 22

Where we fit

Aeronautics

Fundamental

Aeronautics

Subsonic Fixed

Wing

Subsonic Rotary

Wing

Supersonics

Hypersonics

Airspace

Systems

Environmentally

Responsible Aviation

Integrated Systems

Research

Aviation Safety

Aeronautics

Test

Science

Exploration

Space Operations

Overview– 3 of 22

What we do

Structural Acoustics

Interior Noise Sonic Fatigue

Human Response

Psychoacoustics

Engine Nacelle Acoustics

Noise Impact Modeling

Acoustic DesignMaterial Characterization

Sonic Boom, Flyover

Noise, Interior Noise

Simulation & Assessment

Sound Propagation

Noise MetricsResponse Modeling

Qual Testing

Fatigue Mitigation

Transmission Modeling

Measurement Methods

Active/passive Control

Normal/Flow Impedance

Flow resistivity

Propagation constant

Duct propagation/radiation

Liner design

Nacelle designOverview– 4 of 22

Facilities

Overview– 5 of 22

Anechoic Room: TL Testing of Aircraft panel

Reverberant Room: Qualification Testing of

X-37 Article

Structural Acoustic Test Facilities

Thermal Acoustic Fatigue Apparatus

Overview– 6 of 22

Human Response Test Facilities

Interior Effects

Room

Exterior Effects

Room

Sonic Boom

Simulator

Overview– 7 of 22

Normal Incidence Tube (NIT)

Acoustic Liner Technology Facility

Raylometer

Grazing Flow Impedance Tube

Curved Duct Test Rig

Overview– 8 of 22

Recent Activities

Overview– 9 of 22

Quiet Honeycomb Panels

Recessed Core Panel

Voided Core Panel

Solid Core Panel Overview– 10 of 22

Structural Concepts: Polyimide Foam

Collaboration between NASA, PolyuMAC, Purdue, Gulfstream, Boeing

•relate acoustic performance to physics-based empirical model

•couple chemistry/fabrication process with desired acoustic performance

Advantages of Polyimide foam:

•formed at room temperature, cured using microwave energy

•low density: 0.2 to 1.0 pcf

•reduced flammability relative to fiberglass insulation

Overview– 11 of 22

Gulfstream/Boeing/NASA Flight Test

Objective:

Accurate characterization of TBL for

structural-acoustic modeling

Approach:

Heavily instrument a large window blank in a

Gulfstream GV

Instrumented Window

Exterior View Interior View Improved Model

62 flush-mounted sensors

28 surface-mount sensors

Overview– 12 of 22

NASA Langley Gulfstream

Lockheed-Martin

Sonic Boom Testing - Simulation & Flight

NASA Dryden

Overview– 13 of 22

Quiet rotorcraft cabins

Overview– 14 of 22

Technical Challenge: Quiet Cabin

Goal: Cabin noise 77 dBA SPL with no additional weight penalty

Powertrain noise is important

• high frequency tones

Approach:

• reduce source noise

• improve modeling tools

• develop novel structural concepts

Overview– 15 of 22

High Frequency Vibroacoustic Modeling

support beams, trans.

housing: long wavelength

acoustic space,

sidewall panels: short

wavelength

Goal: Get noise into vehicle design

• Statistical Energy Analysis (SEA) is preferred

• expertise required

• separate model must be generated

• Energy finite elements (EFE) are alternative

• analyzes coarse finite element model

• automates structure partitioning

Overview– 16 of 22

Test Structure: Composite Cylinder

Overview– 17 of 22

Automated Impulse Response Decay Method

0 0.05 0.1 0.15-30

-25

-20

-15

-10

-5

0

5

Measured FRFs* Impulse responses

Schroeder decays Fit initial [-2,-17] dB

of decay

FFT-1

*Important details: Jacobsen and Bao, JSV, 115(3): 521-537, 1987.

• loss factor:

• goodness of fit

metric: R2

(0<R2<1)

regression: fit with

single exponential

Results

filter*

1/3-octave response

Overview– 18 of 22

Vibroacoustic modeling

drive point

Horizontal variation of v2 at 2 kHz

v2 prediction in 2 kHz 1/3-octave

band using default power

transmission coefficients

due to errors

in pwr. trans.

coeffs

due to

model

errors

Overview– 19 of 22

Estimate damping and statistics

Overview– 20 of 22

Propagate damping uncertainty through model

Overview– 21 of 22

Concluding remark

Structural Acoustics Branch conducts research to

understand and control noise and its effects on

aircraft, passengers, crew, and the community

Overview– 22 of 22