Vortex methods and their application to trailing wake vortex simulations

Vortex methods are competitive for simulating incompressible unsteady flows, because they have negligible dispersion error and good energy conservation. The various methods are presented, including the recent developments: particle redistribution, diffusion, relaxation (by projection), efficient solvers (fast multipole method, vortex-in-cell method, hybrid method) and parallel computer implementations. Examples relating to wing/aircraft trailing wake vortices are presented: 2-D and 3-D, inviscid and viscous, direct numerical simulation and large eddy simulation. We consider wake roll-ups, vortex tube dynamics, 3-D instabilities and the complexity/turbulence they produce. A vortex system in ground effects is also presented

Dynamics and decay of spatially-evolving two- and four-vortex wakes near the ground

The purpose of the Task 3.1 was to investigate the dynamics and decay of wake vortices near the ground in idealized and controlled computational and laboratory conditions (i.e wake vortices released over a flat ground, without wind or turbulence). The outcome of this task, together with Task 3.2, also served as input to Task 3.3 which concerns the improvement of real-time operational models. This task was divided in two main subtasks. The first subtask (3.1.1) con- cerns longitudinally uniform wakes (time developing wakes) while the second one (3.1.2) concerns spatially evolving wakes. The present deliverable reports on the second subtask. It is made of four detailed technical reports (annexed). We here only summarize the main outcomes (executive summary)

Direct Numerical Simulation and Large-Eddy Simulation of wake vortices: Going from laboratory conditions to flight conditions

This paper aims at presenting DNS and LES as applied to the simulation of vortex wakes: in laboratory conditions (moderate to medium Reynolds numbers) and up to real aircraft conditions (high to very high Reynolds numbers). Only incompressible flows are considered. DNS and LES are able to capture complex 3-D physics provided one uses high quality numerical methods: methods with negligible numerical dissipation (i.e., methods that conserve energy in absence of viscosity and/or subgrid modelling) and with low dispersion errors (to properly transport complex vortical structures). Methods that can do that are: spectral methods, high order finite difference methods, and vortex-in-cell (VIC) methods. As the problems of interest are of large spatial extent and contain vortices with small cores, it is also essential that the methods be efficiently parallelized. As to LES of wake vortex flows, this require subgrid scale (SGS) models that are essentially inactive during the gentle, well-resolved, phases of the flow and within the vortex cores, and that become active only during the complex turbulent phases of the flow. The recent multiscale models, that act solely on the high wavenumbers modes of the LES, are seen to be most appropriate. We present some illustrative examples of DNS and LES results that were obtained within our group