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Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
Nonlinear elastic instability in channel flows at low Reynolds numbers
1Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia 19141, USA.
Physical Review Letters
|May 18, 2013
Summary
Flows of viscoelastic polymer solutions in straight channels are not always stable. Experiments show these flows can become nonlinearly unstable, leading to sudden velocity fluctuations above critical flow rates.
Area of Science:
- Fluid Dynamics
- Polymer Physics
- Rheology
Background:
- Flows of viscoelastic polymer solutions in simple geometries like pipes and channels are generally considered linearly stable.
- Previous research has identified hydrodynamic instabilities in curved geometries for these solutions.
Purpose of the Study:
- To experimentally investigate the nonlinear stability of viscoelastic polymer solution flows in a straight microchannel.
- To determine if subcritical bifurcations occur in such flows.
Main Methods:
- Utilized velocimetry measurements in a long, straight microchannel.
- Introduced controlled flow disturbances at the channel entrance using a variable number of obstacles.
Main Results:
- Observed a sudden onset of large velocity fluctuations above critical flow rate and perturbation size.
- Provided experimental evidence for nonlinear instability and subcritical bifurcation in straight channel flows.
Conclusions:
- Viscoelastic polymer solution flows in straight geometries can exhibit nonlinear instabilities.
- These instabilities manifest as subcritical bifurcations, challenging previous assumptions of linear stability.
- Suggests that polymer solution flows generally become unstable at sufficiently high flow rates, regardless of geometry.
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