What is it about?
In viscous fluids, the torques that produce turbulent vortices result from the loss of symmetry of the stress tensor, once the viscous friction exceeds the shear stress resistance of the fluid. In wall-bounded flows, in particular, the turbulent vortices form in a thin layer of fluid adjacent to the wall, practically coinciding with the so-called viscous sublayer, where the viscous friction reaches the largest values.
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Why is it important?
Classical fluid mechanics does not contemplate the possibility that spin-producing torques may be generated by friction stress. This makes the theory incapable of predicting the onset of turbulence. The paper determines the diameter, angular velocity, and interaxis of the vortices that are formed near the wall in steady-state conditions. The lifting force that makes the vortices migrate from the wall towards the mainstream flow is also calculated, and the role played by gyroscopic precession in the reorientation of the vortex axis is evidenced.
Perspectives
The role of the angular momentum in turbulent vortex formation has thus far been ignored. The paper shows that the angular momentum balance provides a rationale for the origin of turbulence in viscous fluids. This result should help to foster better ways to model and control the turbulent flow of fluids.
A. Paglietti
University of Cagliari, Italy
Read the Original
This page is a summary of: Angular momentum balance and vortex production in wall-bounded flows, Physics of Fluids, April 2020, American Institute of Physics,
DOI: 10.1063/1.5141513.
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