Doppler velocimetry in cavitating media

Area of Science:

• Acoustics
• Fluid Dynamics
• Biomedical Engineering

Background:

• Ultrasonic beams are used for flow measurement, but their behavior in complex media like cavitating flows is not well understood.
• Reports of cavitation in mitral bi-leaflet mechanical heart valves highlight the need to study ultrasonic wave propagation in such environments.

Purpose of the Study:

• To develop and apply a numerical model simulating ultrasonic beam propagation in inhomogeneous, moving media, specifically focusing on cavitating flows.
• To investigate how cavitation affects ultrasonic beam path, orientation, and frequency changes.
• To assess the implications for ultrasonic velocimetry accuracy.

Main Methods:

• Developed a numerical model based on high-frequency ray theory for ultrasonic beam propagation.
• Decoupled sound-flow interactions for post-processing application with existing computational fluid dynamics (CFD) data.
• Simulated unsteady cavitating flows using CFD-ACE and applied the ultrasonic beam model to analyze beam behavior.

Main Results:

• The presence of cavitation fundamentally alters ultrasonic beam propagation characteristics.
• Cavitation induces significant variations in local sound speed, causing large distortions in the ultrasonic beam.
• Simple models assuming rectilinear propagation are inadequate for analyzing these complex flow conditions.

Conclusions:

• Cavitation significantly impacts ultrasonic beam path, orientation, and frequency, challenging accurate measurement.
• The developed numerical model accurately captures these complex beam distortions.
• Findings have strong ramifications for the accuracy of ultrasonic velocimetry in cavitating environments, particularly when using simplified interpretation models.