Conferences - Seminars

17JAN
2017
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  Tuesday 17 January 2017 11:15 - 12:15 ME B1 B10

Stability analysis of three-dimensional open flows

By Lorenzo Siconolfi, University of Pisa
Bio: Since 2013, Lorenzo Siconolfi is a PhD student at University of Pisa under the supervision of Prof. S. Camarri and Prof. M.V. Salvetti with a thesis entitled “Stability and sensitivity analysis for flow control”. His academic work is focused on two main research topics: the study of passive methods for laminar to turbulent transition delay in boundary layers and the sensitivity analysis of globally unstable flows aimed at the stability control. Through these activities and the collaboration with professors and researchers from other universities, he has developed a strong expertise in stability analysis and numerical simulation of complex flows.

The characterisation of instabilities in spatially-developing open flows is a key result in fluid dynamics. In the last decades, the dramatic increase of the computational power has allowed to investigate the stability properties of complex flow configurations.
 
In the first part of the seminar, some examples of global and local stability analysis for three-dimensional flow cases will be presented, oriented to the design of flow control strategies.
 
In the second part, weakly non-parallel flows are considered, where the WKBJ asymptotic analysis provides a rigorous strategy to link the local and global stability approach (Huerre & Monkewitz, Annual Review of Fluid Mechanics, Vol. 22 (1990)). As already shown by several papers, at the geometrical optics, WKBJ approximation is generally able to provide satisfactory results, even for configurations where the parallel flow assumption is questionable, as in the wake past of bluff bodies (see, for example, Juniper & Pier, EJMFLU Vol. 49B (2015)).
 
It will be shown that, considering the physical optics level in the WKBJ approximation allows to provide very accurate estimations of the global eigenfrequencies, reducing the error by about one order of magnitude compared to the geometrical optics approximation. Moreover, the proposed approach is used to analyze three-dimensional flow configurations, such as wakes past bluff bodies, obtaining good results if compared to full three-dimensional global stability analysis at highly reduced computational costs.

Organization François Gallaire

Contact François Gallaire

Accessibility General public

Admittance Free