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PhD position on Active control of wall drag. Transverse motion of the wall and chaotic synchronization, LEGI, Univ. Grenoble-Alpes (France)

Du 1 septembre 2020 au 31 août 2023

3 years contract
Starting from October 2020
Site actualite
LEGI
Grenoble - France
Contact :
Sedat.Tardu@legi.grenoble-inp.fr

The main objective of the present proposal is to develop feasible efficient active drag reduction strategies based on chaos control concepts. The methodology we introduce is new and promises to be interesting in wall turbulence and active drag control research.

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CONTRAT DOCTORAL 2020-2021

Laboratoire des Ecoulements Géophysiques et Industriels, LEGI-UMR 5519 Année universitaire de 1ère inscription en doctorat : 2020
Date de début de la thèse page1image37079488
1er octobre 2020
Directeur de thèse 
: Sedat TARDU

CONTACTER : Sedat.Tardu@legi.grenoble-inp.fr

Contrôle actif de la traînée turbulente. Mouvement transverse de la paroi et la synchronisation chaotique.

Active control of wall drag. Transverse motion of the wall and chaotic synchronization.

1 - Turbulent drag reduction 2 -Active control

Thesis overview

The dynamical system approach to turbulence that regards the Navier -Stokes equation as a manifestation of deterministic chaos is not new. Simplified dynamical models such as coupled maps or amplitude equations put on together with the use of chaos quantifiers such as Lyapounov phenomenological treatment of turbulence. Besides the fact that turbulence in general, and wall turbulence in particular can be seen as an infinite dimensional chaotic system, compact and robust objects called as coherent structures in turbulence community are a common feature of most of turbulent flows and play key roles in the momentum and scalar transport. We could sort out the noisy synchronization hidden in the wall turbulence to clarify the results we obtained in wall turbulence control. We analyzed the statistical characteristics of the constant phase periods and shown the existence of type-I intermittency.

The objectives of the present proposal are divided into two main parts that are not separate but closely linked together. Special care will be paid to the synergy between these two groups. The largest Reynolds number we resolved contains the ensemble of the key elements of the near wall physics. In any case, investigations dealing with drag control have never been realized in the range of the Reynolds numbers we propose to analyze. Some of the unique contributions to the field coming from this proposal will be:

A- Active drag control

1.Revisit through direct numerical simulation the effect of the amplitude and frequency modulation on the efficiency of periodical transverse motion of the wall.

2. Revisit through direct numerical simulations the effect of localized unsteady blowing through optimized distribution of spanwise thin slots at the wall. Thus, it is aimed to see the impact of this active control strategy not through a single intervention but by using a distributed network of such wall perturbations.

3. Assess the validity of classical schemes such as ad-hoc and suboptimal controls at large Reynolds numbers.

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B-Imperfect Synchronization of wall turbulence its characterization and control

1. Constant phase zones are reminiscent in both direct numerical simulations and experiments. Abrupt and thin phase shift zones that are characteristic of phase lock phenomena in chaotic synchronization separate them. It is however unclear at the present time, to what precisely correspond these regions. Several quantities, such as vorticity, dissipation, helicity, enstrophy and the invariants of the velocity gradient tensor will be analyzed to determine the relevant parameters that merely govern the constant phase zones.

2. The high number experimental data will be analyzed in the frame of stochastic synchronization. References

• F. Bauer, S. Tardu, O. Doche, Comp. Fluids, 0.1016/j.compfluid.2014.10.009. (2014) • S. Tardu, J. Fluid Mech., 43, 217, 2001.
• S. Tardu, Exp. Fluids, 33, p. 640, (2002).
• S. Tardu, O. Doche Phys. Fluids, 19,108103-107, (2007).

• S. Tardu Phys. Fluids 20, 045105 (2008).

• S. Tardu, O. Doche, Exp. Fluids47(1), 19-26, (2009-b).
• S. Tardu J. of Turbulence 12: N26, pp. 1-29, DOI:10.1080/14685248.2011.572887 (2011).
• S. Tardu Wall turbulence control John Wiley & Sons, ISTEISBN: 978-1-84821-559-7, 198 pp., 2017

Profile :

Basic knowledge in fluid dynamics and turbulence in general, and wall turbulence in particular is compulsory. Competences in parallel computing are very wall come but they can also be acquired in our team at the beginning of the thesis, since the main computational routines have already been developed and they are operational.