1. Source Modelling II: Airframe Noise W. Dobrzynski * and S. Guérin **
Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) *Institut für Aerodynamik und Strömungstechnik Braunschweig/Göttingen
**Institut für Antriebstechnik / Abt. Turbulenzforschung Berlin
MIT / DLR / DLH Workshop on Noise Abatement Procedures 17 – 19 August 2004, Seeheim / Germany
MIT/DLR/DLH-Workshop, / Seeheim

2. Analysis of Wind Tunnel and Flyover Noise Data
Objectives:
Development of noise source models for
Airbus aircraft landing gears and
high lift systems.
Approach:
Quantification of noise radiation characteristics through analysis of
wind tunnel data on scaled and full scale aircraft/components and
A319 flyover noise data (array and single lateral microphones).
MIT/DLR/DLH-Workshop, / Seeheim

3. Landing Gear Noise Data from Full-scale Wind Tunnel Tests
Noise data available from full-scale wind tunnel tests (DNW-LLF):
Main landing gears: A320 -> 2-wheel and 4-wheel configurations A340 -> 4-wheel and 6-wheel configurations
Nose landing gears: A340 -> 2-wheel configuration
Wind tunnel noise data analysis:
Effect of speed
Radiation directivity
MLG installation effects (wing circulation)
Harmonisation with flyover test results
Modelling of noise characteristics for impact prediction
A320 MLG
A340 MLG
A340 NLG
MIT/DLR/DLH-Workshop, / Seeheim

4. Empirical Landing Gear Noise Model
Frequency [Hz]
Spectra of main / nose gear
MIT/DLR/DLH-Workshop, / Seeheim

5. Landing Gear Noise Directivity
Test range in DNW-LLF
Dipolmodel:
Low Frequencies
High Frequencies
Flow
MIT/DLR/DLH-Workshop, / Seeheim

6. Installation Effects U = U¥ – v Zirkulation G z v
Local velocity at gear position under the wing as function of circulation:
Zirkulation G z v
U = U¥ – v
(Kutta-Joukowski) and
(with chord s and span l)
Thus circulation can be expressed as
and
which results in
MIT/DLR/DLH-Workshop, / Seeheim

7. Clean aircraft with LG down:
Landing Gear Noise Data from Flyover Noise Measurements (Array)
Microphone array source localisation and data analysis:
Compute source maps for selected radiation directions
Determine acoustic energy of components re total aircraft
j = 90°
f = 4 kHz
Clean aircraft with LG down:
Spectra from Array Data Analysis:
1/3-oct. Band Frequency
NLG
MLG-1
MLG-2
MIT/DLR/DLH-Workshop, / Seeheim

8. Comparison of Landing Gear Noise Spectra from W/T and F/T
Normalized 1/3-oct. SPL
Strouhal Number
Airbus Nose Landing Gear
Airbus Main Landing Gear
j = 90°
Future work:
Harmonisation of results from wind tunnel and flight tests.
MIT/DLR/DLH-Workshop, / Seeheim

9. High Lift Devices Noise Data from Wind Tunnel and Flyover Noise Tests
Noise data available from model and full scale wind tunnel (DNW-LLF) and A319 flyover noise tests.
A320 Modell
A320
A319
Noise data analysis:
Effects of - aircraft speed - aircraft angle-of-attack - slat/flap deflection
Quantification and extrapolation of measured directivities
Development of scaling laws
Validation / harmonisation with flyover test results
Modelling of noise characteristics for impact prediction
MIT/DLR/DLH-Workshop, / Seeheim

10. Baseline “landing” noise spectrum:
Semi-empirical Slat Noise Model
The analysis of aircraft noise characteristics showed:
slats represent dominating noise components
spectra scale with slat chord
noise intensity scales with v4.5
levels peak in the rear arc
Baseline “landing” noise spectrum:
Maximum noise level:
Compact dipole model:
Aircraft Axis
Slat a x e d z j
Effect of slat deflection:
Linear dependence of level on deflection angle
Only low frequency (Strouhal number) effect
MIT/DLR/DLH-Workshop, / Seeheim

11. Normalised Spectra for j = 90° Polar Directivity for St = 1.8
Slat Noise Model Validation
Normalised Spectra for j = 90°
Polar Directivity for St = 1.8
Comparison between wind tunnel and flyover data show good agreement in terms of level, spectral shape and directivity.
MIT/DLR/DLH-Workshop, / Seeheim

12. Summary
Aiming at the development of airframe noise source models for the prediction of noise contours, wind tunnel and flyover noise data are analysed.
Landing gear noise:
Determine radiation characteristics (speed, directivity),
Quantify effects of gear geometry on noise
Describe under the wing installation effects.
High lift devices noise:
Rank order high lift components in terms of noise
Determine radiation characteristics (speed, slat/flap deflection, directivity)
Determine scaling laws
For both landing gears and high lift devices initial (semi)-empirical source models have been developed.
MIT/DLR/DLH-Workshop, / Seeheim