Two-sensor power measurements in lossy ducts.

Area of Science:

• Acoustics
• Fluid Dynamics
• Wave Propagation

Background:

• Traditional acoustic power flow measurement relies on intensity-times-area.
• Viscous drag at duct walls can affect acoustic measurements.
• Phase shifts between pressure and velocity are often overlooked.

Purpose of the Study:

• To present a novel theory and measurement technique for acoustic power flow in a duct.
• To incorporate the phase shift caused by viscous drag into power flow calculations.
• To validate the new method against traditional approaches, especially under high standing-wave conditions.

Main Methods:

• Utilized two adjacent pressure sensors to measure acoustic power flow.
• Developed a theoretical model that includes the phase shift due to viscous drag.
• Conducted measurements of simple harmonic sound waves in a duct.

Main Results:

• The proposed method accounts for the phase shift between pressure gradient and velocity.
• Significant differences in power measurements were observed compared to the intensity-times-area method at high standing-wave ratios.
• Measurements confirmed the method's accuracy within 5%, even in turbulent acoustic flow regimes.

Conclusions:

• The novel two-pressure-sensor method accurately measures acoustic power flow, even with viscous effects.
• This approach offers a more accurate alternative to traditional methods, particularly in complex acoustic environments.
• The findings are valid even at high acoustic amplitudes where flow may become turbulent.