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Input impedance in flow ducts: theory and measurement
S Rodriguez1, V Gibiat, A Lefebvre
1Renault SAS, Centre Technique de Lardy, Département Fluides Moteur, 91510 Lardy, France. rodriguez.samuel@yahoo.fr
The Journal of the Acoustical Society of America
|September 18, 2012
Summary
This study investigates how mean flow affects duct input impedance. Experiments and theory show good agreement for resonant frequencies and magnitude evolution, though experimental amplitude variations are smaller than predicted.
Area of Science:
- Acoustics
- Fluid Dynamics
- Acoustic Engineering
Background:
- The input impedance of a duct is influenced by factors like flow.
- Understanding these influences is crucial for acoustic and fluid dynamic applications.
- Previous studies may not fully capture the interplay of convective, dissipative, and radiation effects.
Purpose of the Study:
- To theoretically and experimentally investigate the influence of mean flow on duct input impedance.
- To analyze the contributions of convective flow, turbulent dissipation, and open-jet radiation.
- To validate theoretical models against experimental data.
Main Methods:
- Developed a theoretical model for axisymmetrical flow duct input impedance.
- Incorporated convective, dissipative, and radiation effects into the model.
- Designed a specialized experimental apparatus utilizing the Two-Microphone-Three-Calibration (TMTC) method to minimize flow noise.
- Conducted experiments on a 1m cylindrical duct with Mach numbers up to 0.15.
Main Results:
- Theoretical predictions and experimental results for resonant frequencies show close agreement (within 3%).
- The relative evolution of magnitude maxima with increasing flow also shows good agreement (within 10%).
- Experimental amplitude variations were 2 to 5 times smaller than theoretical predictions, despite similar trends.
Conclusions:
- The study provides a validated theoretical framework for understanding mean flow effects on duct input impedance.
- Experimental data closely matches theoretical predictions for resonant frequencies and magnitude evolution.
- Discrepancies in amplitude variation suggest further refinement may be needed for experimental conditions or theoretical assumptions.
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