Stefan Keye

Investigation of Aeroelastic Effects on the NASA Common Research Model

Static fluid-structure coupled simulations were performed on NASA’s Common Research Model to assess the influence of aeroelastic effects on the numerical prediction of the overall aerodynamic coefficients and wing static pressure distributions. The numerical results of both rigid steady-state computational fluid dynamics and static aeroelastic coupled simulations were compared to the experimental data from wind tunnel test campaigns at NASA’s National Transonic Facility and the NASA Ames Research Center’s 11-Foot Transonic Wind Tunnel Facility. Coupled analyses were performed using an in-house simulation procedure built around the German Aerospace Research Center’s flow solver TAU and the commercial finite element analysis code NASTRAN®. The results show a considerable reduction of deviations between the computational results obtained during the fourth and fifth AIAA Computational Fluid Dynamics Drag Prediction Workshops and the measured data when aeroelastic wing deformations are taken into account.

Fluid-Structure Coupled Analysis of a Transport Aircraft and Flight-Test Validation

The estimation of aerodynamic loads of a transport aircraft taking into account static aero-elastic deformations at steady-state flight conditions is described. Within the scope of a pilot study a fluid-structure coupled (FSC) simulation approach based on state of the art numerical fluid dynamics and structural analysis methods has been applied to an Airbus A340-300 aircraft in both cruise and high-lift configurations. Coupled analyses were performed using an in-house simulation procedure linking DLR’s flow solver TAU and the commercial finite-element code NASTRAN™. Numerical results were validated against flight test data generated in the research project AWIATOR (Aircraft Wing with Advanced Technology Operation) funded by the European Union. A good agreement of simulation results and flight test data, including both fluid dynamics and structural deformation properties, was observed. Aero-elastic effects in cruise flight were found to be larger than in high-lift, where only slats and the wing’s leading edge region are affected. Work presented in this paper is part of a co-operation between DLR and Airbus Deutschland within the joint research project HIT (High-Lift Innovative Technologies).

DLR Results from the Fourth AIAA CFD Drag Prediction Workshop

A summary about the DLR, German Aerospace Center, results from the fourth AIAA Computational Fluid Dynamics (CFD) Drag Prediction Workshop (DPW) is presented. Compared to the investigations in the previous three workshops the latest workshop had a stronger focus on drag and trim drag predictions as well as pitching moment calculations. Therefore the new Common Research Model (CRM) developed by NASAs Subsonic Fixed Wing Aerodynamics Technical Working Group is applied. It represents a state of the art transonic transport aircraft configuration and in contrast to the configurations previously used it includes a horizontal tail plane (HTP) with three different tail settings.

Summary of Data from the Sixth AIAA CFD Drag Prediction Workshop: CRM Cases 2 to 5

Results from the Sixth AIAA CFD Drag Prediction Workshop Common Research Model Cases 2 to 5 are presented. As with past workshops, numerical calculations are performed using industry-relevant geometry, methodology, and test cases. Cases 2 to 5 focused on force/moment and pressure predictions for the NASA Common Research Model wing-body and wing-body-nacelle-pylon configurations, including Case 2 - a grid refinement study and nacelle-pylon drag increment prediction study; Case 3 - an angle-of-attack buffet study; Case 4 – an optional wing-body grid adaption study; and Case 5 – an optional wing-body coupled aero-structural simulation. The Common Research Model geometry differed from previous workshops in that it was deformed to the appropriate static aeroelastic twist and deflection at each specified angle-of-attack. The grid refinement study used a common set of overset and unstructured grids, as well as user created Multiblock structured, unstructured, and Cartesian based grids. For the supplied common grids, six levels of refinement were created resulting in grids ranging from 7x106 to 208x106 cells. This study (Case 2) showed further reduced scatter from previous workshops, and very good prediction of the nacelle-pylon drag increment. Case 3 studied buffet onset at M=0.85 using the Medium grid (20 to 40x106 nodes) from the above described sequence. The prescribed alpha sweep used finely spaced intervals through the zone where wing separation was expected to begin. Although the use of the prescribed aeroelastic twist and deflection at each angle-of-attack greatly improved the wing pressure distribution agreement with test data, many solutions still exhibited premature flow separation. The remaining solutions exhibited a significant spread of lift and pitching moment at each angle-of-attack, much of which can be attributed to excessive aft pressure loading and shock location variation. Four Case 4 grid adaption solutions were submitted. Starting with grids less than 2x106 grid points, two solutions showed a rapid convergence to an acceptable solution. Four Case 5 coupled aerostructural solutions were submitted. Both showed good agreement with experimental data. Results from this workshop highlight the continuing need for CFD improvement, particularly for conditions with significant flow separation. These comparisons also suggest the need for improved experimental diagnostics to guide future CFD development.

Investigations of Fluid-Structure-Coupling and Turbulence Model Effects on the DLR Results of the Fifth AIAA CFD Drag Prediction Workshop

Static Fluid-Structure-Coupled (FSC) simulations were performed on NASAs Common Research Model (CRM) to assess the influence of aeroelastic effects on the numerical prediction of overall aerodynamic coefficients and wing static pressure distributions. Numerical results of both rigid steady state Computational Fluid Dynamics (CFD) and static aeroelastic coupled simulations were compared to experimental data from wind tunnel test campaigns in NASAs National Transonic Facility (NTF) and the Ames 11-Foot Transonic Wind Tunnel Facility (TWT). Coupled analyses were performed using an in-house simulation procedure built around DLRs flow solver TAU and the commercial finite-element analysis code NASTRAN\textsuperscript{\textregistered}. Results show a considerable reduction of deviations between computational results obtained during the 4th and 5th AIAA CFD Drag Prediction Workshops (DPW) and measured data when aeroelastic wing deformations are taken into account.

Fluid-Structure Coupled Loads Analysis of DLR's F6 Wing-Body Configuration

The activities associated with the preparation of the DLR-F6 wind tunnel model for testing in NASA Langley’s National Transonic Facility (NTF) in September 2007 are described. The purpose of this test was to provide validation-quality experimental data for comparison to existing results from the third AIAA Computational Fluid Dynamics (CFD) Drag Prediction Workshop (DPW-3) held in 2006. As the aerodynamic forces associated with the required flow conditions exceed the model’s design load limits various model modifications were implemented and comprehensive fluid-structure coupled analyses were performed for the desired flow conditions in order to meet NTF safety requirements.

Development of Deformed CAD Geometries of NASA's Common Research Model for the Sixth AIAA CFD Drag Prediction Workshop

A method for modifying the shape of digital geometry representations used in Computer Aided Design (CAD) applications according to experimental pointwise deflection data is described. In the pilot study presented here the method is applied to the CAD geometry of an aircraft wing which is deformed using measured deflections obtained from the associated wing model during a wind tunnel test. The method provides various advantages in Computational Fluid Dynamics (CFD) and other applications. Numerical grids generated on the deformed geometry yield an improved correlation of CFD results to wind tunnel data without the need for aeroelastic computations, which require coupling to a structural model. Additionally, the method is beneficial in aerodynamic optimization, where the optimized shape is usually given in the form of a CFD surface mesh or nodal deflections, which, for further processing or manufacturing purposes, need to be transferred into a CAD geometry description. The paper presents an application to NASAs Common Research Model (CRM) transport aircraft configuration, where deformation measurements from a test campaign in the European Transonic Wind Tunnel (ETW) are processed to provide deformed CAD geometries for use in the forthcoming 6th AIAA CFD Drag Prediction Workshop (DPW-6).

Summary Data from the Sixth AIAA CFD Drag Prediction Workshop: CRM Cases

Results from the Sixth AIAA CFD Drag Prediction Workshop Cases 2 to 5 are presented. These cases focused on force/moment and pressure predictions for the NASA Common Research Model wing–body and wi...

Aero-Structural Optimization of the NASA Common Research Model

A combined aerodynamic and structural, gradient-based optimization has been performed on the NASA/Boeing Common Research Model civil transport aircraft configuration. The computation of aerodynamic performance parameters includes a Reynolds-averaged Navier-Stokes CFD solver, coupling to a linear static structural analysis using the finite element method to take into account aero-elastic effects. Aerodynamic performance gradients are computed using the adjoint approach. Within each optimization iteration, the wings structure is sized via a gradient-based algorithm and an updated structure model is forwarded for the performance analysis. In this pilot study wing profile shape is optimized in order to study engine installation effects. This setting was able to improve the aerodynamic performance by 4%.

Development of a Parallel Fluid-Structure Coupling Environment and Application to a Wind Tunnel Model under High Aerodynamic Loads

Accurate measurements of the aerodynamic performance in wind tunnel experiments require to retain dynamic similarity to represent the flow characteristics of real aircraft configurations. High Reynolds numbers for a full-scale aircraft in cruise flight are realized in wind tunnels by reducing the temperature to cryogenic conditions and increasing the static pressure to compensate for the smaller reference lengths. Clearly, this increases the aerodynamic loads to an extent that even rigid models show a significant deflection, depending on the flow conditions. Consequently the aeroelastic deflections have to be taken into account in a numerical simulation of a wind tunnel experiment.Usually this is done by coupling fluid dynamics and structural mechanics (see [3]).