François Morency

Computation of ice shedding trajectories using cartesian grids, penalization, and level sets

We propose to model ice shedding trajectories by an innovative paradigm that is based on cartesian grids, penalization and level sets. The use of cartesian grids bypasses the meshing issue, and penalization is an efficient alternative to explicitly impose boundary conditions so that the body-fitted meshes can be avoided, making multifluid/multiphysics flows easy to set up and simulate. Level sets describe the geometry in a nonparametric way so that geometrical and topological changes due to physics and in particular shed ice pieces are straight forward to follow. The model results are verified against the case of a free falling sphere. The capabilities of the proposed model are demonstrated on ice trajectories calculations for flow around iced cylinder and airfoil.

Numerical validation of conjugate heat transfer method for anti-/de-icing piccolo system

An anti-/de-icing conjugate heat transfer method based on a ANSYS-CFX flow solver and FENSAP-ICE software is presented. The ANSYS-CFX flow solver is used as the flow solver module with the k-ω shear stress transport turbulence model. DROP3D is used as the droplet impingement module. ICE3D is used as the ice accretion and water film runback module. CHT3D/CFX is used for the thermal coupling of all modules. Before solving for the temperature distribution in a three-dimensional antiicing system geometry based on a piccolo tube with three jet rows, a test case consisting of a two-stream parallel gas-to-gas microheat exchanger will validate the CHT3D/CFX procedure. For the antiicing system in wet air mode, the temperature results at corresponding experimental locations are presented and compared to results from the literature.

Aerodynamic force evaluation for ice shedding phenomenon using vortex in cell scheme, penalisation and level set approaches

In this work, we propose a formulation to evaluate aerodynamic forces for flow solutions based on Cartesian grids, penalisation and level set functions. The formulation enables the evaluation of forces on closed bodies moving at different velocities. The use of Cartesian grids bypasses the meshing issues, and penalisation is an efficient alternative to explicitly impose boundary conditions so that the body fitted meshes can be avoided. Penalisation enables ice shedding simulations that take into account ice piece effects on the flow. Level set functions describe the geometry in a non-parametric way so that geometrical and topological changes resulting from physics, and particularly shed ice pieces, are straightforward to follow. The results obtained with the present force formulation are validated against other numerical formulations for circular and square cylinder in laminar flow. The capabilities of the proposed formulation are demonstrated on ice trajectory calculations for highly separated flow behind a bluff body, representative of inflight aircraft ice shedding.

Modelling nanoparticle transport in an animal exposure chamber: a comparison between numerical and experimental measurements

Nanoparticles transport in an exposure chamber is investigated using computational fluid dynamics (CFD). This exposure chamber is used to assess the lung toxicity in rats resulting from the inhalation of airborne NPs. The mathematical model for airflow is based on the three-dimensional Reynoldsaveraged Navier-Stokes equations with turbulence modelling. Simulations of airborne NPs are based on assumptions such that their motions are similar to the ones of a single sized diameter distribution of a passive contaminant.

Simulation of ice shedding around an airfoil

In this work we propose to model ice shedding by an innovative paradigm that is based on cartesian grids, penalization and level sets. The use of cartesian grids bypass the meshing issue in complex geometries and moreover allows extensions to higher order accuracy in a natural and simple way. Penalization is an efficient alternative to explicitly impose boundary conditions so that the body fitted meshes can be avoided, making multi fluid/multi physics flows easy to set up and simulate. Level sets describe the geometry in a non-parametric way so that geometrical and topological changes due to physics and in particular ice-shedding are straight forward to follow.

Numerical investigation of wall mounting effects in semi-span wind-tunnel tests

In this paper, the effects of installing an aircraft half-model on a sidewall of a wind tunnel are investigated. Three-dimensional RANS computations are performed on a geometry representative of an actual modern widebody airliner. The influence of a non-metric spacer, introduced between the half-model and the sidewall, is studied. The study focuses on the effects of the spacer presence on the lift coefficient and the pressure distribution around the model. Computational results show a significant change of the flow field in the case of the half-span installation compared to the full-span case. Unlike several previous investigations showing that the lift usually increases with increasing spacer height, the present study shows that the influence of the spacer is strongly dependent on the Mach number and the angle of attack. It is also found that changing the spacer height may have positive impact on the correlation between semi-span and full-span results for the lift coefficient at specific Mach numbers and angles of attack, while also negatively affecting the correlations of the same coefficient for other flow conditions.

Effect of Compressibility on Contrail Ice Particle Growth in an Engine Jet

Abstract In order to understand the formation process of condensation trails (contrails), the flow in the near field of an aircraft engine jet is studied by using the three-dimensional Large Eddy Simulation technique. The configuration consists of a hot round jet laden with soot particles. The particles are tracked using the Lagrangian approach, and their growth is calculated by a microphysics water vapour deposition model. A series of simulations are performed at a realistic Reynolds number (Re = 3.2 · 106) for two different jet Mach numbers: quasi-incompressible jet flow (M = 0.2) and compressible jet flow (M = 1). Whatever the Mach number used the ice crystals first appear at the edges of the jet where the hot and moist flow mixes with the cold and dry ambient air. Both the thermal transfers and the mass coupling, which are more significant for the quasi-incompressible jet flow, control the growth process.

Evaluation of diffusion models for airborne nanoparticles transport and dispersion

The diffusion coefficient is a property that plays a significant role in the transport of airborne nanoparticles. However, there seems to be no general agreement in the literature on the most appropriate model to use for nanoparticle numerical simulations to be used in risk exposure assessments. This paper begins by presenting a brief review of some of the main models for small particles diffusion. A general dynamic equation for aerosol transport is briefly discussed next. Since the particle diffusion coefficient can be expressed in terms of a friction coefficient, three relationships are then presented and their influences on the friction and diffusion coefficients are considered for the particular case of TiO2 nanoparticles. Although, all the models studied here predict a decrease in the value of the diffusion coefficient with increasing particle diameter, some significant variations can be observed between the models. A specific diffusion model, chosen between those studied, is finally applied to estimate the purge time of airborne TiO2 nanoparticles in a simple closed space the size of a glovebox. It is shown that the sedimentation and the diffusion processes do not play a major role in the evaluation of the purge time.

A SIMPLIFIED APPROACH FOR MODELLING AIRBORNE NANOPARTICULES TRANSPORT AND DIFFUSION

A simplifi ed approach is proposed and used to study the TiO 2 nanoparticle transport and diffusion in an exposure chamber. This exposure chamber is used to assess lung toxicity in rats resulting from the inhalation of airborne nanoparticles. The simplifi ed approach uses computational fl uid dynamics (CFD) commercial software. The mathematical model for airfl ow is based on the three-dimensional Reynoldsaveraged Navier–Stokes equations with turbulence modeling. The mathematical model for airborne nanoparticles transport is based on assumptions such that their motions are similar to those of a singlesized diameter distribution of a passive contaminant. This model is valid as long as the nanoparticle concentration is low and the particle diameter is small enough that settling is negligible, which is the case for the exposure chamber studied. With this model, the diffusion coeffi cient is a property that plays a signifi cant role in the transport of airborne nanoparticles. The particle diffusion coeffi cient can be expressed in terms of a friction coeffi cient, and three possible relationships to model particle diffusion are presented. Their infl uences on the friction and diffusion coeffi cients are considered for the particular case of TiO 2 nanoparticles. Although all the models studied here predict a decrease in the value of the diffusion coeffi cient with increasing particle diameter, some signifi cant variations can be observed between the models. A specifi c diffusion model is selected and then used with the simplifi ed approach. The simplifi ed approach is fivalidated against available correlations for particle deposition on walls. Correlation for deposition loss rate in the case of a room agrees with numerical prediction for particle diameter between 10 and 200 nm. Particle mass concentration distribution inside the exposure chamber is also studied. The computed concentration distribution is quite uniform inside the exposure chamber and corresponds to single point measurements.

Numerical prediction of heat transfer in the case of a heated leading edge

The k ω - , SST and BSL Reynolds stress turbulence models from a commercial flow solver are used to compute heat transfer from impinging jets to curved surfaces. The geometry of the test case is representative of an a irfoil leading edge and is cited from experimental results found in the literature. Nuss elt numbers are computed for two geometries and three Reynolds numbers. The spanwise averaged Nusselt numbers computed are higher than the experimental ones. Computed Nusselt numbers agree among turbulence models and dependence on Reynolds numbers agree with experimental results.