The Advanced Numerical Simulation Domain

Laurent Cambier

Scientific director
of the Advanced Numerical Simulation domain (SNA)

On October 18, 2022, ONERA co-founded the LARTISSTE scientific interest group (GIS) for the quantification of uncertainties, with Université Paris-Saclay and a very wide range of participants, from academic research to industry, including major organizations such as Airbus, Safran, EDF, CEA, IFPEN, Cerfacs, ENS Paris-Saclay, CentraleSupélec... This GIS, which brings together major players in the energy and aeronautics sectors, will explore important issues of numerical models for the reasoned use of numerical models for prediction and decision-making purposes.

Major HPC challenges for young researchers As its Sator supercomputer ramps up, ONERA has offered its young research engineers a few million hours of computing over two months in autumn 2021. The initiative was spearheaded by Alain Refloch, in charge of the High-Performance Computing mission, and Laurent Cambier, Scientific Director for Advanced Numerical Simulation. See images of some of these challenges.

LMA2S Maths Apps Lab - Laboratory of Applied Mathematics for Aeronautics and Space is a virtual inter-departmental laboratory (created in 2019) that federates ONERA's scientific community of mathematicians and numerical engineers, giving it greater visibility. The aim is to optimize the resources allocated to this discipline by encouraging the pooling of work.. [w3.onera.fr/lma2s]

ONERA is a member of the consortium OpenTURNS is a software library written in Python and C++ dedicated to the treatment of uncertainties in numerical simulation. The consortium includes Airbus, EDF R&D, IMACS (Polytechnique), Phimeca and ONERA.

Scientific Officers

Denis Sipp

DAAA
Aerodynamics, Aerolelasticity, Acoustics Department

Philippe Villedieu

DMPE
Multiphysics for Energy Department

Bertrand Langrand

DMAS
Materials and Structures Department

Hélène Piet-Lahanier

DTIS
Information Processing and Systems Department

This type of calculation is carried out in order to develop a technological test dedicated to be implemented in ONERA's icing wind tunnel. Once a block of ice has formed on a profile, pressurized air is injected to induce detachment, and the characteristics of the detached ice are studied in relation to the aero-icing conditions and the characteristics of the substrate. Calculations are performed using the Z-set code, exploiting its parallel resolution capabilities. This work  is carried out in collaboration with the Multiphysics department for energy as part of the ONERA TRICEPS project.

Finite Volume Axis - Cedre solver Objective: spatial scheme of order greater than 2 on unstructured mesh.

Example of application to primary atomization in cryogenic combustion (VF with 2nd-order multipent MUSCL scheme).

Spectral Difference axis - JAGUAR solver Objective: scheme development on triangle/tetrahedron.

Family of schemes of order 3 to 6 (p=2 to 5) on triangles, convergence of calculations on laminar transonic NACA12 at Minfini=0.8, ;Alpha=10°, Re=500, despite non-alignment of mesh/solution.

JEROBOAM is a collaborative project focusing on discontinuous spectral methods for which the solutions in each cell are defined as polynomials of given degree p, and for which no continuity of fields at cell interfaces is assumed. These approaches provide a class of numerical schemes whose order is controllable, and by their "mathematical nature" enable good scalability on massively parallel machines (here, measured scalability of 96% on more than 121,000 cores for the JAGUAR solver). We are interested in these approaches in a perfect gas and reactive multi-species gas context. At the heart of the project: numerical time integration schemes, spatial numerical schemes including shock capture and entropy schemes, coupling for multiphysics, boundary conditions for large-scale turbulence simulations... Validation of these approaches involves stationary (minority) and especially unsteady flows, in order to demonstrate the LES-like capabilities of the approaches. The project ends fall 2023 and will continue with HOGSMEADE, with a specific focus on multi-species flows, shocks, and Euler/Euler approach for liquid/gaz interaction.

DAAA Florent Renac, Bruno Maugars

• Space and time discretization
• Schemes for hypersonic flows
• Inversion of ill-conditioned linear systems
• Coupling methods for multiphysics
• A posteriori error estimation
• Mesh (h), scheme (p) and model (m) adaptations
• High-order CAD representation
• Methods for long-range noise propagation

Examples

REALITY - High-order numerical schemes for compressible fluid mechanics.  To reduce aircraft design costs, numerical simulation has become an indispensable tool. We are concerned with turbulent flow phenomena characterized by a wide range of time and space scales. The use of high-accuracy methods for their simulation is becoming a necessity as the levels of accuracy requiored in the aeronautical industry tend to become ever higher. In this context, the REALITY project aimed to enhance the robustness and efficiency of high-order simulations of compressible fluid mechanics equations (encompassing turbulence, multi-species and two-phase models) using discontinuous Galerkin methods, where the solution is sought as piecewise polynomials in each element of unstructured polyhedral meshes.

The European CleanSky2 ACONIT project (2020-2023, with ENSAM, Bundeswehr University Munich and CETC), aims to bring fluidic control technology closer to industrial use in aircraft engine compressors, in order to reduce pumping margin.

ONERA's first activity in this project was to evaluate the ability of elsA software to predict the limit of operability (rotating stall) of the CME2 compressor (Laboratoire de Mécanique de Fluides de Lille) using unsteady simulations over its entire circumference. Experimentally, only one stalled cell was observed. The simulations have enabled us to gain a better understanding of the mechanisms involved in the stall of the CME2 compressor rotor in the absence of fluidic control. As a result, elsA is able to reproduce the single-cell rotating stall observed during testing.

AHFIR cooperation One of the objectives of the cooperation between ONERA and the US Army is to evaluate and compare the immersed boundary methods developed by ONERA in the ONERA FAST/IBM environment and by the US Army in HELIOS/ROAM on a rotor-fuselage interaction case and on the evaluation of the drag of a helicopter rotor head in a wind tunnel. The aim is twofold: to be able to carry out CFD simulations in a rapid restitution time around complex geometries, while at the same time capturing the physics in a sufficiently precise way, for which so-called "low-fidelity" methods alone are not appropriate. ONERA has therefore adopted an original approach to calculating this type of configuration. Rotating blades are discretized by moving curvilinear meshes, for which a URANS model is used.  The helicopter fuselage is taken into account by Cartesian meshes using a immersed boundary method. As a result, calculations can be carried out in just a few tens of minutes, even for very complex geometries, as the process is automated.

The coupling between the rotating curvilinear grids and the Cartesian mesh is achieved by an optimized Chimère approach, which limits the transfer time between grids to 20% of the overall time. The calculations are implemented by coupling Python/CGNS HPC modules developed by ONERA/DAAA (Cassiopee, FastS, Quantum...). The first figure illustrates an academic calculation of the wake generated by an isolated blade, while the next two figures represent a more industrial case of a 4-blade rotor in forward flight modeled by a URANS model which takes into account the interaction with the fuselage thanks to a immersed  boundary method.

The calculations were carried out on an unstructured mesh, on ONERA's SPIRO parallel computer, using 32 cores distributed over two computing nodes. By taking charge separation into account and resolving the complete electron dynamics, we were able to demonstrate the appearance of a pulsed Trichel regime, as seen in point-planar discharges. This pulsed regime is linked to the interaction with the flow, which moves the charged particles towards the base of the device and prevents the electric field from being screened.