Home | Project | Software | Gallery | News | Documentation
Last delivery
Restricted acces either to user or developer of elsA Download
© 1999-2016 ONERA Terms of use

Presentation of elsA software package

The presentation of elsA software concerns the :

Outstanding features  

The elsA software capitalizes many years of CFD research and thereby opens new prospects of research. The development of elsA relies on Object-Oriented techniques for design and implementation, which allows an important integration flux of new research results. Thus, elsA software takes advantage of this proximity to CFD research, and new versions of elsA always include recent CFD progress. Among the outstanding features of elsA today, we may mention:

  • the ability to compute both internal and external flows;
  • the high performance level obtained on large steady configurations, due to numerical efficiency, CPU performances on parallelization;
  • the advanced capabilities for unsteady aerodynamics ;
  • the ability to take into account complex configurations, due to advanced methods of block matchings (for example, totally non-coincident matchings, or Chimera technique) ;
  • the large panel of capabilities for turbulence and transition modelling ;
  • the ability to perform accurate fluid/structure coupling simulations;
  • the robustness of RANS adjoint for the calculation of gradients for optimum design.
The elsA software has today become a very important tool for ONERA and for several major aerospace industry partners, such as Airbus, Safran group or Eurocopter.

CFD main capabilities  

elsA is a multi-application CFD simulation platform dealing with internal and external aerodynamics from the low subsonic to the high supersonic flow regime. The compressible 3-D Reynolds averaged Navier-Stokes equations for arbitrary moving bodies are solved by a cell centered finite-volume method with second order upwind or central space discretization with scalar or matrix artificial dissipation on multi-block structured meshes. A high flexibility in the multi-block approach is achieved in elsA through patched grid, Hierarchical Mesh Refinement and Chimera techniques. The discrete equations are integrated either by multistage Runge-Kutta schemes with implicit residual smoothing, or, which in general leads to a better efficiency, by backward Euler integration with implicit LU schemes. For time accurate computations, the implicit dual time stepping method or the Gear integration scheme are employed. Preconditioning is used for low speed flow simulations. A large variety of turbulence models are available, ranging from eddy viscosity to full differential Reynolds stress models, and including options for Detached Eddy Simulation (DES) and Large Eddy Simulation (LES). Various transition models are also available for complex geometry configurations.
elsA software package includes an important software module dealing with aeroelasticity [8], [9]. Also, a module dealing with calculation of gradients by linearized equation or by adjoint solver techniques is very useful for aerodynamic optimization.

OO design  

elsA (standing for "Ensemble Logiciel pour la Simulation en Aérodynamique") is a software package based on object-oriented (OO) solutions for fluid dynamics numerical simulation. The scope is to solve the Computational Fluid Dynamics (CFD) problems with high demands on the expressiveness, extensibility and flexibility as well as on the efficiency of the implementation. When the elsA project started about ten years ago, CFD softwares were mainly traditional functional codes written in FORTRAN. These softwares may be very efficient for their particular tasks, but they have also proved to be quite awkward when it comes to integrate and maintain a combination of new developments. OO programming is an appropriate approach to alleviate this drawback. The crucial factors for success are then the following.

  • Software development approach has to scale with the complexity and capability of the code. Ability to incorporate new algorithms and/or physical models is of the utmost importance./
  • High performance has to be achieved for various and changing computer architectures. As a matter of fact, it is sometimes thought that OO implementation can lead to a significant loss of efficiency. One constant ambition of the elsA project is to find the wise edge between OO abstraction and numerical efficiency.
  • elsA system is also used for research work. Here, the numerical efficiency may be less important; instead, ease of extension is mandatory.
The computational part of the software is a set of classes which implements the CFD functionalities. During the initial phase of the elsA project, We defined an original OO consistent model based on the experience of the previous 20 years of CFD numerical computations at ONERA. This original OO design of elsA was successful, since the enrichment or the adaptation of this initial design has allowed the integration of many new capabilities, a lot of which were not initially planned.

Package structure  

The elsA main release is first composed of the elsA kernel and its companion Python-elsA user interface. The user interface is built with the freely available interpreted Object-Oriented Python language. Python has an elegant syntax, is easy to learn, and is available on virtually every computing platform.
The elsA main release also includes additional user-oriented tools, such as :

  • a Python tool providing classes and methods to define a reference flow state from various combinations of pressure, density and Reynolds number ;
  • a Python tool to interactively prepare the transition-related additional files ;
  • a Python tool to concatenate splitted result files when the blocks of the original configuration have been splitted for parallel computations.
The elsA main release is also composed of the elsAxdt Python-CGNS interface used for input and output of in-memory CGNS compliant trees and for coupling with external tools.

(updated $Date: 2016/06/14 14:04:08 $)Home Site map Contacts