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The wing-tip vortex of a rectangular wing half-model with a model engine is studied experimentally and numerically. The airfoil has a supercritical BAC 3-11/RES/30/21 geometry with a chord length of c=150 mm. The investigations include three different spanwise positions of the engine and two jet velocities with a constant free stream velocity of u∞=27 m/s yielding Rec=2.8×105. The numerical simulation is divided into two parts. First the flow around the airfoil is calculated. In a second step the data is taken as an input to calculate the wake downstream of the trailing edge. Experiments include 2C- and 3C-PIV-measurements for the velocity distribution of the jet and the wing-tip vortices. The experimental and numerical results show the significance of the streamwise velocity component for the analysis of the jet/wing-tip vortex interaction. [Copyright &y& Elsevier]

The drag of airfoils has long been determined from measurements in the wake behind the airfoil. The well-known formula of Squire and Young can be used to transfer the measured data to infinity downstream of the airfoil, where an exact relation to the drag exists. The Squire–Young formula is reviewed and an uncertainty in its derivation is discussed. A new formula of the same type is then derived, which also contains an uncertainty. This uncertainty can be reduced by experimental and numerical investigations of the wake displacement. Conversely, the displacement and the momentum of the wake must be investigated to reduce the uncertainty of the Squire–Young formula. In the second part of the paper, the determination of the drag directly by integration of the skin friction is investigated. Such a calculation is not difficult if the boundary-layer characteristics are computed numerically. An additional pressure drag must be regarded in this case. A new formula for the pressure drag is derived which shows that the uncertainty of the Squire–Young type formulas is contained in the evaluation of the pressure drag. This is another reason for further research on wake displacement. [Copyright &y& Elsevier]