Flow-noise and turbulence in two tidal channels

Area of Science:

• Oceanography
• Acoustics
• Fluid Dynamics

Background:

• Flow-noise from oceanic turbulence interferes with low-frequency ambient noise measurements (<100 Hz).
• This noise is significant in turbulent environments like tidal channels with high current velocities (>3 m/s).

Purpose of the Study:

• To investigate and model flow-noise in high-current tidal channels.
• To develop and validate semi-empirical models for predicting flow-noise from 20 to 500 Hz.

Main Methods:

• Conducted measurements in Chacao Channel, Chile, and Admiralty Inlet, Puget Sound, WA.
• Developed two semi-empirical models based on mean velocity, turbulence spectra, and scaling arguments.
• Applied models to predict flow-noise using measured environmental data.

Main Results:

• Observed significant flow-noise pressure spectral densities up to 500 Hz in both locations.
• Flow-noise at 20 Hz exceeded ambient noise levels by over 50 dB.
• Both models showed good agreement in Chacao Channel; only the velocity and turbulence spectra model performed well in Admiralty Inlet.

Conclusions:

• Semi-empirical models can predict flow-noise in turbulent oceanic environments.
• Model performance depends on the validity of turbulence scaling assumptions.
• Accurate flow-noise prediction is crucial for low-frequency underwater acoustic measurements.