Vortex Particle-Mesh with Immersed Lifting Lines for Aerospace and Wind Engineering

AbstractWe present the treatment of lifting lines with a Vortex Particle-Mesh (VPM) methodology. The VPM method relies on the Lagrangian discretization of the Navier-Stokes equations in vorticity-velocity formulation. The use of this hybrid discretization offers several advantages. The particles are used solely for the advection, thereby waiving classical time stability constraints. They also exploit the compactness of vorticity support, leading to high computational gains for external flow simulations. The mesh, on the other hand, handles all the other computationally intensive tasks, such as the evaluation of the differential operators and the use of fast Fourier-based Poisson solvers, which allow the combination of unbounded directions and inlet/outlet boundaries. Both discretizations communicate through high order interpolation. The mesh and the interpolation also allow for additional advances; they are used to handle Lagrangian distortion by reinitializing the particle positions onto a regular grid. This crucial step, referred to as remeshing, guarantees the accuracy of the method. In addition, the resulting methodology provides computational efficiency and scalability to massively parallel architectures.Sources of vorticity are accounted for through a lifting line approach. This line handles the attached and shed vorticity contributions in a Lagrangian manner. Its immersed treatment efficiently captures the development of vorticity from thin sheets into a three-dimensional field. We apply this approach to the simulation of wake flows encountered in aeronautical and wind energy applications. An important aspect in these fields is the handling of turbulent inflows. We have developed a technique for the introduction of pre-computed or synthetic turbulent flow fields in vorticity form. Our treatment is based on particles as well and consistent with the Lagrangian character of the method. We apply here our method to the investigation of wind turbine wakes over very large distances, reaching cluster or wind farm sizes

Imaging Features of Hypertrophic Olivary Degeneration

Hypertrophic olivary degeneration (HOD) is a unique form of transneuronal degeneration caused by a disruption of the dentato-rubro-olivary pathway, also known as the triangle of Guillain-Mollaret. The triangle of Guillain-Mollaret is involved in fine voluntary motor control and consists of both the inferior olivary nucleus and the red nucleus on one side and the contralateral dentate nucleus. Clinically, patients classically present with symptomatic palatal myoclonus. Typical magnetic resonance imaging findings include T2-hyperintensity and enlargement of the inferior olivary nucleus evolving over time to atrophy with residual T2-hyperintensity. In this article, we provide a case-based illustration of the anatomy of the Guillain-Mollaret-triangle and the typical imaging findings of hypertrophic olivary degeneration

Wake Vortex Detection and Tracking for Aircraft Formation Flight

Formation flying is known to improve the aerodynamic efficiency of a follower aircraft flying close to the wake vortices of a leader. In this study, two wake sensing strategies designed to locate these vortices are exposed. The first one is based on dedicated measurements of the follower wing circulation distribution and on the control surfaces deflections. The second one relies on measurements from its flight dynamics (position, velocity) and control surfaces. Both techniques implement an Ensemble Kalman Filter for the propagation in time of the non-linear surrogate model, which involves Prandtl lifting lines for the aerodynamics, and a simplified equation of motion. The resulting estimators are tested under steady and unsteady flight conditions, using reference data obtained from the numerical simulation of the associated wake flows using CFD. As a result, an accurate estimation of thewake parameters is produced by both methods, even in configurations where a symmetry was known to hamper the filter efficiency. Noisy configurations are also considered through the addition of ambient turbulence in the simulations. In that case, the second method proves more sensitive to external perturbations