Eulerian-Lagrangian Approach for Modeling and Simulations of Turbulent Reactive Multi-Phase Flows under Gas Turbine Combustor Conditions

The work presented in this thesis resulted in the development and application of different mathematical sub-models to describe the physics of turbulent reacting spray typical for gas turbine combustors. The resulting complete models were formulated in the Eulerian-Lagrangian context. Emphases were primarily put on the interaction between solid particles and turbulence seeking a correct prediction of turbulent quantities in turbulent two phase flows. The investigation of the feedback mechanism of particles on the continuous phase within the turbulent two-phase flow which is known as turbulence modulation was carried out with three different modulation models. Computations reveal that the obtained results of the turbulent kinetic energy using the thermodynamically consistent model, reproduce well both the turbulence attenuation and production. Indeed, the standard model underestimates the turbulence. This model is dissipative for small and big particles, whereas the model by Crowe is overall productive. Two evaporation models have been developed, integrated in FASTEST/LAG3D code and subsequently applied. The computations were achieved using a fully two-way coupling process. A systematical study of the interaction processes including turbulence, turbulence modulation, mass and heat transfer has been satisfactory carried out. Simulations showed that non equilibrium model agree most favorably with experimental measurements of the droplet mass flux. In order to characterize the turbulence-droplet vaporization interaction regimes, a vaporization Damkoehler number (Dav) has been introduced. Numerical results have demonstrated that in case of Dav>1 turbulence augmentation enhances the evaporation rate, whereas for Dav¡Ü1 the opposite phenomenon takes place, namely the rate of evaporation is reduced. The spray combustion was studied in a complex industrial configuration, which consists of a single annular combustor that was experimentally measured by Rolls-Royce Deutschland. Simulations were performed using k-eps as well as Reynolds Stress model (Jones Musonge) for turbulence, an assumed shape of probability density function to prescribe turbulence combustion interaction and different models describing the turbulence modulation. Equilibrium and a flamelet chemistry approaches were used. Results showed that predicted RTDF distributions are satisfactory and provide plausible results compared with measurements. The use of the thermodynamically consistent modulation model allows an acceptable behavior of the temperature distribution compared to the standard modulation model. On the other hand, both evaporation models (equilibrium and non-equilibrium) provided similar results for the temperature distribution. Numerical computations including the flamelet turbulent combustion model predicted a lower peak reaction temperature and a more gradual temperature decrease than predictions using equilibrium chemistry. As final conclusion one can reiterate that the combination of the following sub-models: thermodynamically consistent model for the turbulence modulation, Langmuir-Knudsen non-equilibrium model for the evaporation, Reynolds Stress Model for the turbulence and flamelet model for the chemistry establish a reliable complete model that seems to allows a better description of reactive multi-phase flow studied in the frame of this work

Numerical Modelling of Air Pollutant Dispersion in Complex Urban Areas: Investigation of City Parts from Downtowns Hanover and Frankfurt

Hazardous gas dispersion within a complex urban environment in 1:1 scaled geometry of German cities, Hanover and Frankfurt, is predicted using an advanced turbulence model. The investigation involves a large group of real buildings with a high level of details. For this purpose, Computer Aided Design (CAD) of two configurations are cleaned, then fine grids meshed in. Weather conditions are introduced using power law velocity profiles at inlets boundary. The investigation focused on the effects of release locations and material properties of the contaminants (e.g., densities) on the convection/diffusion of pollutants within complex urban area. Two geometries demonstrating different topologies and boundaries conditions are investigated. Pollutants are introduced into the computational domain through chimney and/or pipe leakages in various locations. Simulations are carried out using Large Eddy Simulation (LES) turbulence model and species transport for the pollutants. The weather conditions are accounted for using a logarithmic velocity profile at inlets. CH₄ and CO₂ distributions, as well as turbulence quantities and velocity profiles, show important influences on the dispersion behavior of the hazardous gas

Numerical modelling of air pollutant dispersion in complex urban areas: investigation of city parts from downtowns Hanover and Frankfurt

Hazardous gas dispersion within a complex urban environment in 1:1 scaled geometry of German cities, Hanover and Frankfurt, is predicted using an advanced turbulence model. The investigation involves a large group of real buildings with a high level of details. For this purpose, Computer Aided Design (CAD) of two configurations are cleaned, then fine grids meshed in. Weather conditions are introduced using power law velocity profiles at inlets boundary. The investigation focused on the effects of release locations and material properties of the contaminants (e.g., densities) on the convection/diffusion of pollutants within complex urban area. Two geometries demonstrating different topologies and boundaries conditions are investigated. Pollutants are introduced into the computational domain through chimney and/or pipe leakages in various locations. Simulations are carried out using Large Eddy Simulation (LES) turbulence model and species transport for the pollutants. The weather conditions are accounted for using a logarithmic velocity profile at inlets. CH₄ and CO₂ distributions, as well as turbulence quantities and velocity profiles, show important influences on the dispersion behavior of the hazardous gas

Experimental investigation of central jet displacements on the turbulence and gas dynamics of a coaxial burner

International audienc

Numerical and experimental study of central jet displacement effects on the dynamics of a coaxial burner

International audienc

Experimental and Numerical Study of Swirling Diffusion Flame Provided by a Coaxial Burner: Effect of Inlet Velocity Ratio

This paper reports an experimental and numerical investigation of a methane-air diffusion flame stabilized over a swirler coaxial burner. The burner configuration consists of two tubes with a swirler placed in the annular part. The passage of the oxidant is ensured by the annular tube; however, the fuel is injected by the central jet through eight holes across the oxidizer flow. The experiments were conducted in a combustion chamber of 25 kW power and 48 × 48 × 100 cm3 dimensions. Numerical flow fields were compared with stereoscopic particle image velocimetry (stereo-PIV) fields for non-reacting and reacting cases. The turbulence was captured using the Reynolds averaged Navier-Stokes (RANS) approach, associated with the eddy dissipation combustion model (EDM) to resolve the turbulence/chemistry interaction. The simulations were performed using the Fluent CFD (Computational Fluid Dynamic) code. Comparison of the computed results and the experimental data showed that the RANS results were capable of predicting the swirling flow. The effect of the inlet velocity ratio on dynamic flow behavior, temperature distribution, species mass fraction and the pollutant emission were numerically studied. The results showed that the radial injection of fuel induces a partial premixing between reactants, which affects the flame behavior, in particular the flame stabilization. The increase in the velocity ratio (Rv) improves the turbulence and subsequently ameliorates the mixing. CO emissions caused by the temperature variation are also decreased due to the improvement of the inlet velocity ratio