Science Pictures

Interaction between a turbulent jet and a wake vortex  

copyright © ONERA 2006 - All rights reserved
Rollup of jet helical structure [red and orange] around an aircraft wingtip vortex [clear tube at center]. LES* computation.
This image won the 2^nd prize at the CMFF'06 / Flow Visualization Gallery, Budapest, 6^th-9^th September 2006 
DSNA

In the near field of the aircraft wake the exhaust jets of the turbines are propelled into the two counter-rotating wingtip vortices. These jets roll up from the sheet of vorticity induced by the wings, at the same time.

Temporal simulations of the interaction between a turbulent jet and a wake vortex were performed in order to understand the complex process of the capture and mixing of a turbulent jet in a wake vortex. Thus, the fluid mechanics equations are solved[compressible Navier-Stokes] for a Mach number* of 0.2 [around 250 km/h] under conditions equivalent to those of a wind tunnel experiment.

First, the vortex velocity induces the capture of the jet around the core, which remains unaffected.  Next, the jet is close enough to the vortex for an interaction to occur, causing the emergence of three dimensional structures, which considerably disturb the vortex core without destroying it.

The main purposes of these studies are to gain an understanding of the vapor contrail formation mechanisms and the reduction of the wake persistence behind the aircraft.

Text and picture: Odile Labbé,
research-engineer in CFD at Onera

Glossary

1. LES - Large Eddy Simulation
   Method for solving the equations of turbulent flows where the large scale eddies are explicitly solved, whereas the small scale ones (size less than the simulation mesh) are computed using a subgrid model. 
2. Mach Number
   In aeronautics, ratio of the speed of a moving body in relation to the air at the speed of sound, at a given altitude.

Last Update: June 1, 2007 - © ONERA 2009 - Terms of use