Section: New Results
Modelling of icing and de-icing of aircrafts
Flying debris is generated in several situations: when a roof is exposed to a storm, when ice accretes on rotating wind turbines, or during inflight aircraft deicing. Four dimensionless parameters play a role in the motion of flying debris. The goal of our work was to investigate the relative importance of four dimensionless parameters: the Reynolds number, the Froude number, the Tachikawa number, and the mass moment of inertia parameters. Flying debris trajectories have been computed with a fluid-solid interaction model formulated for an incompressible 2D laminar flow. The rigid moving solid effects are modelled in the Navier-Stokes equations using penalization. A VIC scheme was used to solve the flow equations. The aerodynamic forces and moments are used to compute the acceleration and the velocity of the solid. A database of 64 trajectories has been built using a two-level full factorial design for the four factors. The dispersion of the plate position at a given horizontal position decreases with the Froude number. Moreover, the Tachikawa number has a significant effect on the median plate position.
Ice release is of concern to aircraft manufacturers due to the potential damage that the ice debris can cause on aircraft components. This raises the need for accurate ice trajectory simulation tools to support pre-design, design and certification phases while improving cost efficiency. High-fidelity models involve fully coupled time-accurate aerodynamic and flight mechanics simulations and thus require the use of emerging simulation tools, such as approaches based on immersed boundary methods or chimera grids. The developments of current simulations tools for ice block trajectories performed in the scope of the recently completed research project STORM have been described and validated against a STORM experimental data base of trajectories created by the German Aerospace Center (DLR) in collaboration with the German-Dutch Wind Tunnel foundation.
Immersed boundary methods (IBM) are alternative methods to simulate fluid flows around complex geometries. The grid generation is fast as it does not need to conform to the fluid-solid interface. However, special treatments are needed in the flow equations to properly take into account the wall proximity. The penalization method is a particular case of the IBM in which the wall boundary conditions are imposed via continuous forcing terms into the governing equations. Reynolds Averaged NavierâStokes (RANS) equations completed with a turbulence model are still the most common way to model turbulence in engineering applications. However, RANS turbulence model implementation with penalization into a vortex formulation is not straight forward, in part because of the variable turbulent viscosity and partly because of the boundary conditions. Our work extends the penalization technique to turbulent flows. The objective is to validate the use of the SpalartâAllmaras turbulence model in the context of penalization and vortex formulation. Details of the resolution using a Vortex In Cell (VIC) numerical scheme are given. The proposed scheme is based on the advection of particles of vorticity and particles of turbulent viscosity. A Lagrangian framework is chosen to solve the advection part. The remaining parts of the system of equations are solved with an Eulerian framework using a Cartesian uniform grid. To avoid fine meshes near the wall, a wall function compatible with the penalization method and the vortex formulation is proposed. The formulation and the coding are validated against the wellknown periodic channel flow. Velocity profiles are computed without and with the wall function. Results agree with analytic law of the wall solutions, showing that RANS simulations can be conducted with VIC schemes and penalization.
Ice formation can reduce the efficiency of aircraft lifting surfaces. Experiments proved that even the onset of icing (increased roughness) could cause an increase of 63% on the minimum drag coefficient of a NACA0015 airfoil when compared to a smooth airfoil. To investigate stall behavior due to ice formation, a roughness wall extension for the Spalart-Allmaras turbulence model was implemented in the open-source code SU2 so that the onset of ice formation could also be evaluated.