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Internal circulation in a drop in an acoustic field
H Zhao1, S S Sadhal, E H Trinh
1Aerospace & Mechanical Engineering Department, University of Southern California, Los Angeles 90089-1453, USA.
The Journal of the Acoustical Society of America
|January 1, 2000
Summary
Researchers studied the internal flow of a liquid drop in a standing wave. A key finding is that the recirculating flow layer disappears under specific conditions related to viscosity and frequency.
Area of Science:
- Fluid Dynamics
- Acoustic Levitation
- Interfacial Phenomena
Background:
- Understanding fluid behavior in acoustic fields is crucial for applications like material processing and microfluidics.
- Previous studies focused on solid spheres, neglecting the complexities of liquid-gas interfaces.
- The behavior of internal flow fields in levitated liquid drops under acoustic forces remains less understood.
Purpose of the Study:
- To investigate the internal flow field within a liquid drop situated at the antinode of a standing acoustic wave.
- To analyze the influence of liquid-gas interface conditions (shear stress, velocity continuity) on the internal flow.
- To determine the conditions under which the predicted recirculating Stokes layer ceases to exhibit recirculation.
Main Methods:
- Theoretical investigation of the internal flow field using a mathematical model.
- Inclusion of shear stress and velocity continuity conditions at the liquid-gas interface.
- Analysis of flow behavior at different orders of calculation, considering time-dependent and steady-state conditions.
Main Results:
- The leading order of calculation reveals a weak, time-dependent internal flow with zero mean flow.
- A higher-order analysis predicts steady internal flows, including a surface-layer recirculation similar to solid spheres.
- The recirculating Stokes layer is predicted to cease recirculation when the ratio of liquid viscosity to gas viscosity and the dimensionless frequency parameter satisfy a specific condition.
Conclusions:
- The internal flow field of a levitated liquid drop exhibits complex behavior influenced by interfacial conditions.
- A novel prediction is the cessation of recirculation in the Stokes layer under specific fluid property and frequency parameters.
- Experimental validation is required to confirm these theoretical predictions, particularly regarding the absence of observed recirculation in some levitated drop experiments.