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Measuring intense rotation and dissipation in turbulent flows
Benjamin W Zeff1, Daniel D Lanterman, Ryan McAllister
1Department of Physics, IPST and IREAP, University of Maryland, College Park, Maryland 20742-4111, USA.
Nature
|January 10, 2003
Summary
Turbulent flows exhibit intense bursts of vorticity and strain. New observations reveal that these events start with rapid strain, followed by rising vorticity, offering insights into turbulence intermittency.
Area of Science:
- Fluid dynamics
- Turbulence research
- Non-gaussian statistics
Background:
- Turbulent flows are characterized by high intermittency, with intense bursts of vorticity and strain.
- Kolmogorov theory explains energy cascades but not the causes of non-gaussian intermittency.
- Turbulence intermittency impacts chemical mixing, pressure drops, cavitation, and atmospheric vortices.
Purpose of the Study:
- To investigate the causes of high intermittency in turbulent flows.
- To simultaneously measure velocity components and gradients to determine dissipation and enstrophy.
- To analyze the sequence of events during intense turbulent bursts.
Main Methods:
- Simultaneous measurement of three velocity components and nine velocity gradients within a small volume.
- Analysis of flow dissipation (strain) and enstrophy (vorticity).
- Statistical analysis of measurements and individual burst evolution.
Main Results:
- A typical intense event sequence begins with rapid strain growth.
- This is followed by rising vorticity and a sudden decline in stretching.
- The study provides detailed observations of velocity and velocity gradients during turbulent bursts.
Conclusions:
- The observed sequence of strain and vorticity provides new insights into turbulence intermittency.
- Two potential mechanisms are proposed for these characteristics: advection of coherent structures or local causes.
- Understanding these mechanisms is crucial for predicting and controlling turbulent phenomena.
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