Two-dimensional wind tunnel measurement corrections by the singularity method/Korekcije rezultata dvodimenzijskih aerotunelskih mjerenja metodom singulariteta

The correction method for pressure coefficient distribution around an airfoil is developed for the purpose of the postprocessing of wind tunnel data, obtained from the model pressure measurements. Pressure coefficient distribution around the airfoil, directly obtained by wind tunnel measurements, is corrected numerically in order to compensate for the interference effects of the wind tunnel test section walls. In this paper, the airfoil NACA0012 is approximated by linear vortex segments, which are then mirrored using sufficient number of images with respect to the ceiling and the floor of the test section, to model the flow pattern around an airfoil in the wind tunnel test section with solid walls. Flow calculations, both with the tunnel wall presence and in the free stream, are then performed. The numerically obtained pressure coefficient difference between these two cases should be superimposed to the pressure coefficient distribution measured in the wind tunnel, for the same nominal airflow parameters and angle of attack, at the corresponding points, resulting in the corrected experimental pressure coefficient distribution. The values of corrections generally increase with the reduction of the wind tunnel test section relative height. The paper is focused on the verification of lift curve slope corrections, where very good agreements have been obtained with several well-known classical correction methods.