Xavier Vancassel

Large-eddy simulation of a turbulent jet and a vortex sheet interaction : particle formation and evolution in the near field of an aircraft wake

Aircraft are prolific sources of particles (soot, liquid aerosols and contrails) that can impact cloudiness and affect the Earths radiative budget balance. In order to study the formation and evolution of these particles, a numerical approach has been developed combining large-eddy simulation (LES) and a detailed microphysical model. Generally very detailed microphysical models are run along a single average trajectory, without any temperature fluctuation. However, this approach may lead to significant differences in particle properties and particle size distribution as it oversimplifies dynamical and mixing processes compared to multidimensional descriptions of aircraft wakes. This may affect the initialisation of meso-scale models, such as, for example, the formation of cloud condensation nuclei from persistent contrails, and heterogeneous chemical reactions. In this paper, we present the results of detailed microphysical processes calculations applied to a large number of fluid parcels trajectories, generated by a LES two-phase flow solver.

Experimental and Numerical Study of Scallop Ice on Swept Cylinder

LaMP, Blaise PASCAL University, BP2235, 03101 Montlucon Cedex Under specific conditions, scallop ice shape appears: this latter is found intrinsically depending on geometry parameters and aero-thermal conditions. This work deals with the trigger of the scallop ice shape formation and how to simulate it. Several tests have been performed using a plain cylinder for several sweep angles, velocity, temperature, median volume diameter and liquid water content. They were conducted at the CEPr (French engine test center) on swept cylinder in order to provide large sets of data for numerical simulation by the analysis of each ice shape formed for various conditions. First we developed a reference model for 3D scallop ice simulation. Then, we built a full 3D numerical scallop ice formation that consists of injecting supercooled droplets through a 2D window. Each droplet is assumed as an aggregate including 1000 of 20

Spatial Simulation of Contrail Formation in Near-Field of Commercial Aircraft

During this study, three-dimensional numerical simulations of contrails generated by commercial aircraft in cruise conditions were performed. The objective was to study the early development of contrails in the near field of an aircraft, including engine core and bypass flows. Computational fluid dynamics simulations, based on the three-dimensional Reynolds-averaged Navier–Stokes approach, were carried out on a realistic aircraft geometry. A microphysical model was implemented in the computational fluid dynamics code to simulate particle growth using an Eulerian approach. Results showed that the mixing processes in the bulk plume were in good agreement with the literature. Then, the early growth of a contrail in the near wake of the aircraft was investigated for two ambient relative-humidity conditions. This parameter played a significant role in contrail local properties. Increased relative humidity led to an increase in the fraction of particles under the supersaturated condition and condensation rate. ...

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.

Numerical simulation of aerosols in an aircraft wake using a 3D LES solver and a detailed microphysical model

The global impact of aviation on the atmosphere is generally determined using the total amount of gas and particulate matter emitted at the aircraft engine exit but generally ignore some of the physical transformations occurring at much smaller scales in the aircraft wake. In this work, we present an offline alternative method based on the use of a detailed plume aerosol model combined to fluid trajectories calculated from 3D large-eddy simulations (LESs). The study has been limited to the first 10 s behind a type Airbus 340 aircraft. The results have been compared to those obtained from a one-way coupling approach including a simple microphysics water vapour deposition model on soot cores. The respective evolutions of average ice particles radius are in good agreement. Furthermore, different types of aerosol properties are examined including the charged volatile particles, the dry and activated soot and the ice crystals from homogeneous and heterogeneous freezing. The variability of the aerosol size distribution clearly illustrates the influence of the mixing, as a function of the position in the aircraft plume. Finally, the volatile particles distribution exhibits a bimodal shape resulting from the presence of charges, in agreement with that observed experimentally.

Aero-thermodynamic and chemical process interactions in an axial high-pressure turbine of aircraft engines

Precise investigation of aero-thermodynamic and chemical processes relating to environmental precursor pollutants in an aircraft turbine is challenging because of the complexity of transformation processes at high temperature and high pressure. We present here, for the first time, new insights into the study of aero-thermodynamic processes, formation of nitrate and sulfate aerosol precursors, and investigate the influence of chemical processes on aero-thermodynamics. We also shed light on the effect of three-dimensional blade profile, radial spacing, and rotor speed on the performance of a high-pressure turbine. We highlight that flow vortex and the variation of chemical formation which appear in both rear stator blades and rear rotor blades. We found that the chemical processes were affected by the evolution of temperature (maximum of 16.9%) and flow velocity (maximum of 38.8%). Contrary to the conservative one-dimensional and two-dimensional modeling, which provide only the flow trends and flow evolution at cylindrical surface, respectively, our three-dimensional modeling approach offers the possibility of combining information on radial spacing and rotor-speed effect by providing three-dimensional images of spatial-geometry effect on aero-thermodynamic and chemical processes. Quantitatively, the magnitude of change in aero-thermodynamics and nitrogen oxidation may be expected to be up to 17% and 48%, respectively, over a stage of the high-pressure turbine.

Numerical Simulation of Contrail Formation Using a Simplified Wing-Injector Configuration

Contrail formation is a complex topic, since several physical processes are involved, covering a large range of space and time scales, from the engine exit to the atmospheric global scale. In the near field of the aircraft, contrail formation is mainly dominated by microphysics and mixing processes between the propelling jets and the external flow and more precisely during the jet-vortex interaction. In this paper, we present a new approach to focus on the influence of the wing/nacelle configuration on contrail onset. The originality of this work is to provide a preliminary study in order to take into account a complex aircraft geometry in further jet vortex numerical simulations using the ONERA multiphysics code CEDRE.