Abstract
We study the flow topology dynamics in terms of the paramount nonlinearities of enstrophy and strain production at hard turbulent regimes of Rayleigh-Bénard convection (RBC). To do so, a data set of direct numerical simulations for air turbulent RBC at Rayleigh numbers is analyzed. Considering the bulk dynamics therein, the classical two-dimensional mean Lagrangian evolution of and invariants of is extended to three dimensions by decomposing into two parts: the strain production and the enstrophy production . In this way, the three-dimensional phase space allows us to identify separately the nonlinear straining and rotational mechanisms in turbulence. The main resultant observations attest that, when the turbulent regime is notably hard, a rising local self-amplification of the velocity gradient takes place in strain-dominated areas. This process is strongly aided by vortex contraction. Concomitantly, a pronounced increase in the linear contributions of vortex stretching is also identified, particularly relevant to strain-dominated slots.
1 More- Received 12 April 2019
- Accepted 28 January 2020
DOI:https://doi.org/10.1103/PhysRevFluids.5.024603
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