Spectral Simulations of the Partial Reconnection Phenomena of Aircraft Wake Vortices

Guillaume Beardsell
Master degree student
guillaume.beardsell.1@ulaval.ca

In order to take off and fly, an airplane must generate a force equal to its weight. It is known that when a wing generates lift, it also generates a pair of counter-rotating vortices. These little “tornados” can be very powerful and their intensity is proportional to the weight of the aircraft [1], representing a potential hazard for other aircrafts flying nearby. 

These vortices are the cause of the delays between two takeoffs/ landings in congested airports. The waiting time required between each aircraft is related to the intensity and persistence of these vortices. Dissipation of these structures depends heavily on hydrodynamic instabilities which are the source of fine turbulence in such flow. On their part, instabilities and the wake vortex dynamics depend very much on the internal structure of the vortices, the atmospheric turbulence and eventually the ground effects. Thorough understanding of these dynamics is very important to improve flight safety [2] and to reduce airport congestion. 

My work focuses on the study of the partial reconnection between theses vortices and its impact on the longevity of the vortex system. Partial reconnection occurs when a pair of counter-rotating vortices of varying intensity meets. This happens for example when the tailplane generates downforce at takeoff / landing. Recent studies [3-4] suggest that partial reconnection generates a large spectrum of small-scale turbulent structures that should significantly increase the dissipation rate of the wake vortices.

My project is part of collaboration between Professor Guy Dumas (LMFN) and Professor Louis Dufresne (ETS), both specialists in direct numerical simulations (DNS) [5] applied to fluid dynamics. A spectral solver initially developed by Professor Carati and al. (Université Libre de Bruxelles) and adapted by Professor Dufresne [4] and I can simulate very accurately the evolution of vortex systems in three dimensions. Since large calculations are involved, access to High Performance Computing (HPC) is essential. Special thanks to Compute Canada and the CLUMEQ HPC Consortium at Laval University for providing access to their facilities.

Références

1. SPALART, P.R. (1998) "Airplane trailing vortices." Annual Rev. Fluid Mech., 30, 107-138.

2. JACKSON, W. (Ed.) (2001) "Wake vortex prediction: An overview." Technical Report TP 13629E, Transport Canada.

3. DUFRESNE, L., CHRISTOPHE, J., GOURGUE, O., & WINCKELMANS, G. (2005) "Merging of unequal strength co-rotating vortices." In Bull. Amer. Phys. Soc., 50(9), 218-219, Chicago, IL (É.-U.).

4. DUFRESNE, L. & WINCKELMANS, G. (2005) "LES of the interaction and partial reconnection of unequal strength vortices." In Intl. Conf. High Reynolds Numb. Vortex Interactions, Toulouse (France).

5. DUFRESNE L. & DUMAS G. (2003): "A Spectral/B-spline Method for the Navier-Stokes Equations in Unbounded Domains", J. of Comp. Physics, 185/2, pp. 532-548.