Drag Induced by Flat-Plate Imperfections in Compressible Turbulent Flow Regimes

This paper presents the results of a coupled experimental and numerical study aimed at evaluating the influence of typical aircraft surface imperfections on the flat-plate drag production in fully turbulent conditions. A test campaign involving high- level measurement techniques, such as microdrag evaluation, near- wall laser Doppler velocimetry, and oil- film interferometry, has been carried out at several Mach numbers from 0.5 to 1.3 to quantify the impact of a large range of flat- plate imperfections. Forward- facing and backward- facing plain and chamfered steps of different heights have been studied. A whole numerical study, based on Reynolds- averaged Navier- Stokes computations, has been completed and used for validation purposes. Given the very small order of magnitude of the forces to be measured and calculated, the relative comparison between experimental and numerical outcomes is satisfactory. Even if some local discrepancies exist, results show an overall good agreement in the positioning of the different imperfection drag productions. Such investigations are of prime interest to determine industrialization tolerances or excrescence geometries offering the best compromises between manufacturing costs and aerodynamic performances.