Experimental study in near-and far-field of trailing vortices and their active control

Abstract

In order to predict the axial development of the wingtip vortices strength, an accurate theoretical model is required. Several experimental techniques have been used to that end, e.g. PIV or hotwire anemometry, but they imply a significant cost and effort. For this reason, we have carried out experiments using the smokewire technique to visualize smoke streaks in six planes perpendicular to the main stream flow direction. Using this visualization technique, we obtained quantitative information regarding the vortex velocity field by means of Batchelor’s model for two chord based Reynolds numbers, ������ = 3.33 ⋅ 104 and 105. Therefore, this theoretical vortex model has been introduced in the integration of ordinary differential equations which describe the temporal evolution of streak lines as a function of two parameters: the swirl number, ��, and the virtual axial origin, ��0. We have applied two different procedures to minimize the distance between experimental and theoretical flow patterns: individual curve fitting at six different control planes in the streamwise direction as well as the global curve fitting which corresponds to all the control planes simultaneously. Both sets of results have been compared with those provided by del Pino et al. [2011a], finding good agreement. Finally, we have observed a weak influence of the Reynolds number on the values �� and ��0 at low-to-moderate ������. This experimental technique is proposed as a low cost alternative to characterize wingtip vortices based on flow visualizations. Secondly, we present a detailed analysis of experimental and numerical results for the flow of wingtip vortices behind a NACA0012 airfoil. Particular attention is paid to a specific value of the angle of attack, ��=9∘, and ultra-low and low chord-based Reynolds numbers ranging from ����=0.3×103 to 20×103.