<< Scientists have long used supercomputers to better understand how turbulent flows behave under a variety of conditions. Researchers have now include the complex but essential concept of 'intermittency' in turbulent flows. >>️
<< Despite its seemingly random, chaotic characteristics, researchers have identified some important properties that are universal, or at least very common, for turbulence under specific conditions. (..) Much of that important turbulent motion may stem from what happens in a thin area near the edge of the flame, where its chaotic motions collide with the smoother-flowing fluids around it. This area, the turbulent-non-turbulent interface (TNTI), has big implications for understanding turbulent mixing. >>️
<< Scientists distinguish between internal intermittency, which occurs at the smallest scales and is a characteristic feature of any fully developed turbulent flow, and external intermittency, which manifests itself at the edge of the flame and depends on the structure of the TNTI. >>️
<< For Bode and Gauding (Mathis Bode, Michael Gauding), understanding the small-scale turbulence happening at the thin boundary of the flame is the point. >>
<< Our simulations are highly resolved and are interested in these thin layers, (..) For production runs, the simulation resolution is significantly higher compared to similar DNS (direct numerical simulations ) to accurately resolve the strong bursts that are connected to intermittency. >> Mathis Bode.
️
Simulations of turbulence's smallest structures. Gauss Centre for Supercomputing. Jul 8, 2021.
<< In turbulent jet flows, the phenomenon of external intermittency originates from a sharp layer, known as the turbulent/ non-turbulent interface, that separates the turbulent core from the surrounding irrotational fluid. First, it is shown that low-order and higher-order structure functions in both the core and the shear layer of the jet satisfy complete self-preservation, which means that structure functions are invariant with time and collapse over the entire range of scales, regardless of the set of length and velocity scales used for normalization. Next, the impact of external intermittency on small-scale turbulence is studied along the cross-wise direction by the self-similarity of structure functions. It is shown that structure functions exhibit from the centre toward the edge of the flow a growing departure from self-similarity and the prediction of classical scaling theories. By analysing statistics conditioned on the turbulent portion of the jet, it is demonstrated that this departure is primarily due to external intermittency and the associated similarity-breaking effect. >>️
Michael Gauding, Mathis Bode, et al. Self-similarity of turbulent jet flows with internal and external intermittency. Journal of Fluid Mechanics. 919 , 25, A41. doi: 10.1017/ jfm.2021.399. Jun 1, 2021.
Michael Gauding, Mathis Bode, et al. On the combined effect of internal and external intermittency in turbulent non-premixed jet flames. Proceedings of the Combustion Institute. 38, (2): 2767-2774. doi: 10.1016/ j.proci.2020.08.022. Dec 9, 2020.
keyword 'Intermittency' in ScienceDirect
Also
1939 - stocastici accessi (di traslitteranti ludi). Notes. Jan 11, 2006.
(quasi-stochastic poetry )
2064 - on responses to deviant stimuli.
Notes. Sep 26, 2006. (quasi-stochastic poetry )
