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Executive summaries of Action Groups of Group of Responsables in Aerodynamics
This GARTEUR action group was established in January 1999 as a follow-on activity of the successful EU research project EUROSUP. Participants of this group were: Aérospatiale-Matra, BAE Systems, DERA, DLR, INTA, NLR and ONERA; later joined CIRA and Technical University Helsinki (HUT). The objectives of the group were threefold: - Assess the currently available CFD methods for the prediction of high-lift flow; - design a low drag high-lift system and - develop a proposal for a large scale wind tunnel model for a SCT configuration to be used in a future EU project. Due to the fact that based on the initial work of the group an EU project called EPISTLE was launched in March 2000, the GARTEUR activities were finished in September 2000. Therefore, only the first of the three objectives has been worked on and the results of this study have been presented in the final report [1]. The main outcome and the conclusions are briefly summarised: High-lift flow computations were performed by all partners on the EUROSUP low speed configuration representing a generic supersonic commercial transport aircraft, on either a common mesh or on their own meshes. These computations comprised the calculation of the attached, partially and fully separated flow for the EUROSUP configuration with a leading edge high-lift system. Only a limited analysis of the gathered numerical data have been carried out by the partners. The results of this GARTEUR study underlines that it was possible to estimate numerically the measured drag reduction of the high-lift system of the EUROSUP configuration. This holds for attached, partially separated and fully developed vortical flow. Predictions of sufficient accuracy were obtained by all partners independent of the used flow solver and turbulence model at the end of the AG's lifetime. The improvement of the numerical results obtained within the group reduced the scatter in the aerodynamic coefficients. Nevertheless the question arose and was answered by the industrial partners which numerical accuracy level is necessary for this kind of low speed flow predictions. For attached and partially separated flow the configuration drag is predictable to an industry defined level of accuracy. For attached flow the pressure drag level is proved to be mesh converged on the finer meshes used and in good agreement between the different computations. Changing from attached to separated flow the predicted results show increasing differences because of the difficulties in predicting separation onset. The separation onset prediction depends mainly on the capabilities of the used turbulence models. The main reason for differences in drag are due to the different friction drag levels predicted by the turbulence models. Partially separated flows are influenced more by the friction drag due to the influence on separation onset and the resulting vortical flow effecting the pressure drag increments. The friction drag predicted by the turbulence models is therefore a large source of uncertainty. At fully separated flow the pressure drag is again in good agreement between the different computed results. The predicted results are in general in close agreement to the experiment (results are from EU EUROSUP project) and in alignment with the requested accuracy requirements: ?a< 0.5°; ?cD£ 17 dc; ?cM£ -0.0035 for attached (a=6°) and partially separated flows (a=8°). This is exemplified in Fig. 1. The calculated differences increase for separated flows. The local and global comparison of structured and unstructured solutions show that the quite high Y+ values experienced in the unstructured solutions lead to relative low friction drag levels. This was considered to lead to early flow separation and generation of the associated vortices. Fortuitously, the vortex drag balances the low friction drag and good agreement to the measured total aerodynamic coefficients is reached. Quite good agreement of the predicted surface streamlines with oil flow pictures is shown in Fig. 2 for partially separated flow. The work of GARTEUR AD(AG-30) laid the basis for the EU project EPISTLE which was launched in 2000 and which continues the work of AD(AG-30). Within EPISTLE a wind tunnel model of an SCT configuration with high-lift devices has been designed, manufactured and successfully tested in the ONERA F1 wind tunnel. Without the preparatory work in GARTEUR AD(AG-30) the EU project EPISTLE had not been feasible. [1] U. Herrmann, H. Figueiredo: CFD for Supersonic Civil Transport high-lift evaluation and configuration development, Final Report GARTEUR AD(AG-30), GARTEUR TP 137, DLR IB 124-2002/25, 2002.
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