Effect of free-stream turbulence on conical vortex dynamics
Résumé
The influence of Free-Stream Turbulence (FST) on the space–time dynamics of a conical vortex developing along
a A-pillar is studied experimentally. Measurements of unsteady wall pressure and velocity by High Speed-Stereo
PIV highlight the important effects of turbulence on the mean and instantaneous properties of the vortex. Very
significant increases in Reynolds stresses into the vortex region and in wall fluctuating pressure are observed in
the presence of FST. In smooth flow, the frequency content of the pressure and velocity fields is very rich with
low and high frequency contributions due to the meandering of the vortex and instabilities in the vortex core.
Meandering shows, for the different integral length scales and intensities of turbulence tested, a great receptivity
to the presence of a FST and we observe a global motion of the vortex structure at low frequency. This frequency
is modulated by the value of the integral length scale of the FST. We show that the mean conical structure is a
wave guide for the perturbations of the core but that, with FST, the spatio-temporal evolution of the envelope
overwhelms the intrinsic instability of the vortex core observed in smooth flow