Fifth Drag Prediction Workshop: ONERA Investigations with Experimental Wing Twist and Laminarity

Abstract

This article is aimed at presenting the computational studies which have been performed at ONERA in 2013 in the framework of the 5 th AIAA Drag Prediction Workshop (DPW-5). As data concerning the Common Research Model (CRM) configuration was collected from the NASA Langley and Ames wind tunnels, a significant discrepancy appeared between the experimental and computational pitching moment evaluations. Investigations carried out by NASA in 2012 showed that the experimental model and the numerical geometry were slightly different. Indeed, the wing twist measured in the wind tunnels was different from the one that was used for the computational analyses. Therefore, new Computational Fluid Dynamics (CFD) studies using the CRM Wing-Body configuration with the corrected wing twist have been completed at ONERA. The common Multi-Block (MB) grids provided by the DPW-5 Committee have been adequately modified before being computed with the ONERA-elsA Reynolds-averaged Navier-Stokes (RANS) solver and the ONERA-ffd72 software. This paper exhibits the results of the new grid convergence process and buffet study (cases 1 and 2 of DPW-5). The impacts of the wing twist modification on drag and moment productions are investigated. The grid convergence study led with the as-tested shape in fully turbulent conditions gives an extrapolated drag value close to 254 counts, which is 4 counts higher than the drag produced by the original CFD geometry. Moreover, to further match the wind tunnel conditions, computations including a laminar zone up to 10% of the wing chord have been performed. These calculations with experimental wing twist and laminar / turbulent transition significantly improve the agreement between the numerical and experimental data.

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“…Nevertheless, these differences are very limited in amplitude. In [26], it can be seen that the difference of wing twist values between the experimental and numerical models reveals much more significant discrepancies on pressure distributions at wingtip than what is shown in Fig. 27.…”

“…Furthermore, in the experiments, laminar zones were present up to 10% chord whereas the CFD calculations are fully turbulent. These two differences impact the agreement that can be achieved (nevertheless it happens that they almost compensate each other [26]). Finally, the closest reference data that can be used for this paper corresponds to the numerical results obtained with the DPW-5 common grids described above.…”

“…Besides, support system effects are not taken into account. More detail about CRM WB numerical and experimental comparisons is available in [26].…”

“…The CRM is an open geometry representative of current wide-body commercial aircraft [23], for which a wealth of experimental and numerical data is available. This configuration has been deeply studied at ONERA [24][25][26] in the framework of DPW-4 (San Antonio, 2009) and DPW-5 (New Orleans, 2012) which was focused on a deep grid convergence study.…”

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“…Additionally, the investigations of Rivers et al [15] also led to the discovery of a large discrepancy between the as-built and tested wind-tunnel model wing twist and the DPW-IV computational wing twist. Hue [16] showed that including the experimentally measured twist distribution reduced lift and improved the comparison with wind-tunnel measurements. Keye et al [17] also applied fluid-structure coupling and confirmed the shift in predicted forces and moments due to wing twist.…”