Norbert Kroll

The MEGAFLOW project

Within the framework of the German aerospace research program, the CFD project MEGAFLOW was initiated. Its goal is the development and validation of a dependable and efficient numerical tool for the aerodynamic simulation of complete aircraft in cruise as well as in take-off and landing configurations. In order to meet the requirements for industrial implementation, a concentrated cooperative effort involving the aircraft industry, the DLR and several universities has been set up. This paper gives an overview of the goals and the major achievements of the project. It is concluded with an outlook towards future developments.

ADIGMA - A European Project on the Development of Adaptive Higher-Order Variational Methods for Aerospace Applications

Computational Fluid Dynamics is a key enabler for meeting the strategic goals of future air transportation. However, the limitations of todays numerical tools reduce the scope of innovation in aircraft development, keeping aircraft design at a conservative level. Within the 3rd Call of the 6th European Research Framework Programme, the strategic target research project ADIGMA has been initiated. The goal of ADIGMA is the development and utilization of innovative adaptive higher-order methods for the compressible flow equations enabling reliable, mesh independent numerical solutions for large-scale aerodynamic applications in aircraft design. A critical assessment of the newly developed methods for industrial aerodynamic applications will allow the identification of the best numerical strategies for integration as major building blocks for the next generation of industrial flow solvers. In order to meet the ambitious objectives, a partnership of 22 organizations from universities, research organizations and aerospace industry from 10 countries with well proven expertise in CFD has been set up guaranteeing high level research work with a clear path to industrial exploitation. This paper gives on overview of the goals and the planned activities of the 3-years project.

MEGAFLOW: Parallel complete aircraft CFD

Abstract As a consequence of the worldwide competition in the aircraft market requirements for the accurate prediction of aerodynamic performance and optimization of configurations have increased very much. More sophisticated wind tunnel as well as high quality CFD techniques have become necessary and essential tools for aircraft industry aerodynamic development groups. This requires an ongoing struggle for efficiency improvements where parallel computing is one of the major issues. This paper considers the MEGAFLOW activities in the area of parallel flow solvers including their application and use in the industrial framework. It describes the parallelization principles for the structured multi-block Navier–Stokes code FLOWer and the unstructured Navier–Stokes code TAU. Principle results for industrial applications are given with respect to efficiency, speed-up, load balancing, etc. Computational examples demonstrate the quality of the solvers for 3D flow over wing/body configurations as well as complete transport aircraft.

Fluid-Structure Coupling for Aerodynamic Analysis and Design: A DLR Perspective (Invited)

Accurate prediction of the aerodynamic performance of an aircraft requires coupled fluid/structure simulations. The aerodynamic loads acting on the aircraft result in deformations of its flexible structure, which in turn causes changes in the fluid flow and thus the loads. Static aeroelastic effects are also present in high Reynolds number wind-tunnel testing. For proper comparison of numerical and experimental data the aeroelastic deformations of the wind tunnel model have to be taken into account or modeled within a CFD simulation. At DLR a fully automatic process chain for both steady and unsteady aeroelastic applications has recently been developed, allowing the coupling between the inhouse CFD codes TAU and FLOWer and the commercial FEM codes ANSYS and NASTARAN. The CFD codes have been extended to include functions for aeroelastic simulations, including an interpolation module for the transfer of the aerodynamic loads into structural nodes between the CFD and CSM meshes. Emphasis is put on robust volume mesh deformation translating the structural displacement into the CFD mesh since this is a critical issue in the overall process Steady and unsteady applications are presented to demonstrate the feasibility of the approach for industrial applications, including complex high-lift configurations, a rocket nozzle and maneuvering aircraft. First results for design and optimization based on coupled fluid/structure simulations are also presented. Finally, the paper discusses future developments necessary to further enhance the simulation capabilities for multidisciplinary simulation and optimization.

The DLR Flow Solver TAU - Status and Recent Algorithmic Developments

The only implicit smoothing method implemented in the DLR Flow Solver TAU is the LU-SGS method. It was chosen several years ago because of its low memory requirements and low operation counts. Since in the past for many examples a severe restriction of the CFL number and loss of robustness was observed, it is the goal of this paper to revisit the LU-SGS implementation and to discuss several alternative implicit smoothing strategies used within an agglomeration multigrid for unstructured meshes. Starting point is a full implicit multistage Runge-Kutta method. Based on this method we develop and suggest several additional features and simplifications such that the implicit method is applicable to high Reynolds number viscous flows, that is the required matrices fit into the fast memory of our cluster hardware and the arising linear systems can be approximately solved efficiently. To this end we focus on simplifications of the Jacobian as well as efficient iterative approximate solution methods. To significantly improve the approximate linear solution methods we take care of grid anisotropy for both approximately solving the linear systems and agglomeration strategy. The procedure creating coarse grid meshes is extended by strategies identifying structured parts of the mesh. This seems to improve the quality of coarse grid meshes in the way that an overall better reliability of multigrid can be observed. Furthermore we exploit grid information within the iterative solution methods for the linear systems. Numerical examples demonstrate the gain with respect to reliability and efficiency.

The MEGAFLOW Project — Numerical Flow Simulation for Aircraft

Some years ago the national CFD project MEGAFLOW was initiated in Germany, which combined many of the CFD development activities from DLR, universities and aircraft industry. Its goal was the development and validation of a dependable and efficient numerical tool for the aerodynamic simulation of complete aircraft which met the requirements of industrial implementations. The MEGAFLOW software system includes the block-structured Navier-Stokes code FLOWer and the unstructured Navier-Stokes code TAU. Both codes have reached a high level of maturity and they are intensively used by DLR and the German aerospace industry in the design process of new aircraft. Recently, the follow-on project MEGADESIGN was set up which focuses on the development and enhancement of efficient numerical methods for shape design and optimization. This paper highlights recent improvements and enhancements of the software. Its capability to predict viscous flows around complex industrial applications for transport aircraft design is demonstrated. First results concerning shape optimization are presented.

MEGADESIGN and MegaOpt - German Initiatives for Aerodynamic Simulation and Optimization in Aircraft Design

This volume contains results of the German CFD initiative MEGADESIGN which combines CFD development activities from DLR, universities and aircraft industry. Based on the DLR flow solvers FLOWer and TAU the main objectives of the four-years project is to ensure the prediction accuracy with a guaranteed error bandwidth for certain aircraft configurations at design conditions, to reduce the simulation turn-around time for large-scale applications significantly, to improve the reliability of the flow solvers for full aircraft configurations in the complete flight regime, to extend the flow solvers to allow for multidisciplinary simulations and to establish numerical shape optimization as a vital tool within the aircraft design process. This volume highlights recent improvements and enhancements of the flow solvers as well as new developments with respect to aerodynamic and multidisciplinary shape optimization. Improved numerical simulation capabilities are demonstrated by several industrial applications.

IDIHOM: Industrialization of High-Order Methods - A Top-Down Approach: Results of a Collaborative Research Project Funded by the European Union, 2010 - 2014

The IDIHOM Project.- Research Activities.- Assessment of High-Order Methods.- Conclusion and Recommendations.

The ADIGMA Project

Computational Fluid Dynamics is a key enabler for meeting the strategic goals of future air transportation. However, the limitations of today’s numerical tools reduce the scope of innovation in aircraft development, keeping aircraft design at a conservative level.Within the 3rd Call of the 6th European Research Framework Programme, the strategic target research project ADIGMA was initiated. The goal of ADIGMA was the development and utilization of innovative adaptive higher-order methods for the compressible flow equations, enabling reliable, mesh independent numerical solutions for large-scale aerodynamic applications in aircraft design. A critical assessment of the newly developed methods for industrial aerodynamic applications allowed the identification of the best numerical strategies for integration as major building blocks for the next generation of industrial flow solvers. In order to meet the ambitious objectives, a partnership of 22 organizations from universities, research organizations and aerospace industry from 10 countries with well proven expertise in CFD was set up, guaranteeing high level research work with a clear path to industrial exploitation. The project started September 2006 and finished at the end of 2009.

Numerical Aerodynamics at DLR

Abstract Some years ago the national CFD project MEGAFLOW was initiated in Germany to combine many of the CFD development activities from DLR, universities and aircraft industry. Its goal was the development and validation of a dependable and efficient numerical tool for the aerodynamic simulation of complete aircraft which met the requirements of industrial implementations. The MEGAFLOW software system includes the block-structured Navier-Stokes code FLOWer and the unstructured Navier-Stokes code TAU. Both codes have reached a high level of maturity and they are intensively used by DLR and the German aerospace industry in the design process of new aircraft. Recently, the follow-on project MEGADESIGN and MEGAOPT were set up which focus on the development and enhancement of efficient numerical methods for shape design and optimization. This article highlights recent improvements of the software and its capability to predict viscous flows for complex industrial aircraft applications.