Experimental observations of trailing vortices at high Reynolds numbers
A. Gallardo-Clarosa, J.J. Serano-Aguilerab, L. Parrasa and C. del Pinoa
Experimental techniques applied to the study of wingtip vortices are of great interest for the 
Fluid Mechanics Community. The available experimental techniques to obtain new insights into 
trailing vortices, focus on quantitative methods, e.g. Particle Image Velocimetry (PIV)1,2. In fact, 
this  technique  requires  high  costs  associated  not  only  to  equipments  but  also  to  image 
processing that is a complex, and time consuming task. A novel,  easier,  faster and cheaper 
experimental  procedure  is  presented  in  this  research  work  to  compute  experimentally  the 
vortex structure in comparison to a theoretical model.
Different theoretical models have  described the velocity field for  every cross section along 
the axial coordinate, once  the vortex was created  at the wing tip. These models depend on 
several parameters and provide the axial evolution of the velocity field. We used in this study a 
q-vortex or  Batchelor’s3 model, based only on two free parameters: swirl  value,  q,  and the 
virtual  origin  in  the  axial  coordinate,  z0.  These  parameters  have been processed  with  the 
experimental trailing vortex formed by a NACA0012 aerofoil over a Reynolds number range of 
105.
The experimental setup consists of one smoke wire device together with a laser beam, and a 
digital camera installed in a subsonic wind tunnel. A smoke segment was generated upstream 
the model, but near the wing edge. This line followed the main stream passing through the wing 
tip. Lift  forces produced the characteristic vortex pattern, highlighted by the swirling smoke 
segment, and whose topological structure was recorded by a digital camera. Several sections at 
different axial distances from the wing edge have been analyzed. The integration of the velocity  
field in the theoretical model allowed us to know two theoretical parameters in order to obtain 
similar experimental streaklines at a given axial position, as shown in figure 1. The experimental 
results using this procedure were in agreement with those found in the literature1.
This work has been supported by the Grant Proyecto de Excelencia nº TEP-7776.
a ETSI Industriales, C/ Doctor Ortiz Ramos S/N, 29071 Málaga, Spain. 
b CIEMAT-Plataforma Solar de Almería, Crta. de Senés, km. 4.5, E04200 Tabernas, Almería, Spain
 
1  C. del Pino, L. Parras, M. Felli y R. Fernández-Feria. Structure of trailing vortices: Comparison between particle 
image velocimetry measurements and theoretical models. Physics of Fluids. 23, 013602 (2011).
2 Myong Hwan Sohn, Jo Won Chang. Visualization and PIV study of wing-tip vortices for three different tip 
configurations. Aerospace Science and Technology. 16(1), 40 (2012).
3  G. K. Batchelor. Axial Flow in trailing line vortices. J. Fluid Mech. 20,645 (1964).
Figure 1: Processed image: Smoke (black) and theoretical streakline (green) for a trailing vortex.