Drag prediction and decomposition, from wake surveys and calculations, in subsonic flows

Abstract

This paper focuses on methods of drag calculation from flow field wake surveys and CFD results. The analysis is based upon a far-field approach, which enables both the decomposition and the accurate prediction of the aerodynamic drag. The chosen test-case for this study is a subsonic bi-turboprop aircraft model, in its simplest configuration (fuselage and wings uniquely), but with different wing tip devices. The main purpose is to discriminate both components of induced and viscous drag, thanks to an experimental methodology and associated numerical tools. Besides, the whole has to be accurate enough to be able to compare 2 very close configurations in terms of drag. Furthermore, CFD calculations have been achieved on the same configuration, with several solvers (inviscid, viscous/inviscid interaction and eventually NavierStokes codes), in order to establish comparisons with experimental measurements. The results issued from CFD were post-processed with a far-field drag analysis code, developed by ONERA with contributions from EADS Airbus SA, whose main advantage is to enable the elimination of spurious drag sources. For each method, successful results, as well as obvious difficulties, are reported. Finally, the study shows the capability of the different tools to predict drag with a good accuracy, and points out the improvements that need to be accomplished.