Bulk-driven acoustic streaming at resonance in closed microcavities.

Area of Science:

• Fluid Dynamics
• Acoustics
• Microfluidics

Background:

• Bulk-driven acoustic streaming (Eckart streaming) arises from acoustic energy flux in fluids.
• It's often overlooked in acoustofluidics compared to boundary-driven (Rayleigh) streaming.
• Double modes in microcavities can create rotating acoustic energy flux.

Purpose of the Study:

• To investigate rotating bulk-driven acoustic streaming in closed microcavities.
• To derive analytical solutions for double modes in rectangular cavities.
• To determine optimal geometries for exciting rotating streaming via non-rotating actuation.

Main Methods:

• Derivation of analytical solutions for double modes in rectangular cavities with viscous boundary layers.
• Mapping of potential rotating bulk-driven acoustic streaming patterns.
• Simulation of streaming-roll patterns (2x2, 4x4, 6x6) in optimal geometries.

Main Results:

• Double modes support rotating acoustic energy flux and bulk-driven streaming.
• Rotating streaming can be excited by non-rotating actuation.
• Optimal geometries were identified to maximize streaming excitation.
• High-frequency patterns (6x6) are dominated by bulk-driven streaming, while low-frequency patterns (2x2) are dominated by boundary-driven streaming.

Conclusions:

• Rotating bulk-driven acoustic streaming is a significant phenomenon in microcavities with double modes.
• Acoustic streaming patterns are dependent on frequency and cavity geometry.
• This work provides insights into controlling and optimizing acoustic streaming in microfluidic devices.