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Turbulence, Instability and Numerical Simulations

last modified 6 April 2012

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Partnerships

Industrial, governmental and academic partnerships

  • University of St Andrews,
  • IMFT,
  • CEA (Commissariat à l’Énergie Atomique),
  • RTRA/STAE (Réseau Thématique de Recherche Avancée/Sciences et Technologies de l’Aéronautique et de l’Espace),
  • CNRS-IDRIS (Institut du Développement et des Ressources en Informatique Scientifique).

Permanent staff:L. Joly, S. Jamme, J. Fontane, Y. Bury, J. Gressier, G. Grondin, P. Chassaing

Post-docs: O. Chikhaoui

PhD students: A. Lopez-Zazuetta

Contact: laurent.joly@isae.fr, phone: 33 (0)5 61 33 91 65


The research conducted in the field of turbulence and instability aims at achieving better understanding of the physics of transition and turbulence in flows with large density variations (due to mixing, thermal inhomogeneity, or compressibility) and flows developing in the vicinity of solid walls. This research targets improving statistical prediction methods and devising flow-control strategies. At the present time, the following specific topics are undergoing study.

Stability of variable-density shear flows

The mixing of inhomogeneous fluids mainly depends on the onset and growth of the large-scale organized structures that result from the amplification of unstable modes in shear layers. This question is addressed by experimental studies of the unstable modes in a round air-helium jet developing in ambiant air. We also perform linear stability analyses of the three-dimensional secondary modes starting from the case of the plane mixing layer and proceeding toward the case of the round jet.

Variable-density vortex dynamics

Vortex dynamics play a crucial role in aeronautical as well as geophysical flows. They also provide an interesting guide to the understanding of elementary events in fully-developed turbulence. Vortex stability and dual-vortex interactions are the main topics investigated here to address the questions of promotion/preclusion of mixing and persistence of aircraft wing-tip vortices.

Compressible flows

The interaction between various types of turbulence and a shock wave is studied for its relevance to high-speed aerodynamics. Direct numerical simulations of the interaction are performed in order to gain a better understanding of the corresponding physics and to gather reference databases for compressible turbulence modeling. Theoretical analyses (LIA) are also conducted for validation and comparison purposes.

Wall turbulence

The questions addressed here draw from intrinsic features of this type of turbulence. Thus, the effect of kinematic blocking is studied through direct numerical simulation to elucidate the physical mechanisms involved in intercomponent energy transfer close to a solid wall or a free surface. Conversely, cases in which proximity to a solid wall is combined with another kind of complicating effect (Coriolis accelerations, presence of free-stream boundaries, etc.) are studied from a theoretical point of view in order to analyze the mathematical behavior of turbulence models.

Numerical Simulation

Despite significant improvements in current computational and data processing resources, the continued growth in requirements for computational fluid dynamics remains unsatisfied. For example, the simulation of complex turbulent flows at high Reynolds numbers encountered in technical applications remains a challenge requiring higher accuracy modeling such as LES, which is very costly, especially for complex configurations with both academic and industrial relevance.

In order to fulfill these needs, the department is focusing on the study of numerical methods for the resolution of the Navier-Stokes compressible equations, taking into account realistic constraints such as the potential severity of test cases and the eventuel geometrical complexity. Current investigations covers the following topics:

Methods based on unstructured partitioned grids

The codes based on unstructured formulations are preferred due to their flexibility and ability to describe all geometries. Furthermore, the grid partitioning is inevitable for significant and realistic applications.

Adaptive grid refinement

This is one of the most commonly used methods to achieve the desired level of accuracy. This method is investigated particularly in a context of unsteady flow (monitoring physical phenomena).

High order Extension

Theoretically, this method ensures the highest accuracy for a given simulation. However, it is very difficult to achieve and maintain on unstructured mesh of irregular quality.

Stability of numerical schemes

It order to ensure the generalization of a given method, it is necessary to show that it can handle arbitrarily severe cases without creating non-physical issues that might block the computation.

The latest investigations focus on high-order methods (typically 4 to 5) using compact spectral methods (Spectral Volume Method) compatible with unstructured grids.

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