Thomas Jaravel

Stanford University | SU · Department of Mechanical Engineering

This study aims at estimating the inherent variability of microscale boundary-layer flows and its impact on the air pollutant dispersion in urban environment. For this purpose, we present a methodology combining a high-fidelity Large-Eddy Simulation (LES) model and a stationary bootstrap algorithm, to estimate the internal variability of time-avera...

Study of the impact of thermo-diffusive instabilities on the acceleration of very lean H2/air mixtures in a tube

Alkali metal compounds, such as (NaHCO3)s and (Na2CO3)s, are widely used fire suppressants that can be spread as powders or aqueous solutions. Their efficiency depends strongly on the capacity of the alkali metal particles to decompose inside the flame front. The paper aims at providing a theoretical basis for: (1) manufacturing efficient powders;...

Infrasound observations are increasingly used to constrain properties of volcanic eruptions. In order to better interpret infrasound observations, however, there is a need to better understand the relationship between eruption properties and sound generation. Here we perform two-dimensional computational aeroacoustic simulations where we solve the...

Deep learning has recently emerged as a successful approach to produce accurate subgrid-scale (SGS) models for Large Eddy Simulations (LES) in combustion. However, the ability of these models to generalize to configurations far from their training distribution is still mainly unexplored, thus impeding their application to practical configurations....

We propose an on-the-fly statistical learning method to take a qualitative reduced-order model of the dynamics of a premixed flame and make it quantitatively accurate. This physics-informed data-driven method is based on the statistically optimal combination of (i) a reduced-order model of the dynamics of a premixed flame with a level-set method, (...

We propose an on-the-fly statistical learning method to take a qualitative reduced-order model of the dynamics of a premixed flame and make it quantitatively accurate. This physics-informed data-driven method is based on the statistically optimal combination of (i) a reduced-order model of the dynamics of a pre-mixed flame with a level-set method,...

The understanding of flame blow-out is of fundamental importance for practical applications. In particular, the reliable prediction of blow-out limits is of direct relevance for the design of gas turbine combustors that operate under fuel-lean conditions. The objective of this work is to investigate the physical mechanisms and parameters that contr...

Efficient reduction techniques are necessary for the construction of compact chemical kinetic mechanisms to enable the application to large-scale simulations. In this work, a new formulation is proposed to derive skeletal mechanisms by species elimination. The proposed method relies on a gradient-based non-linear optimization (NLO) method, allowing...

In the present work, the flame structure and dynamics of a swirl-stabilized methane/air flame near and at blow-out conditions are investigated using large-eddy simulations (LES). To this end, simulations at stable conditions and during a transient blow-out sequence are performed employing a flamelet/progress variable (FPV) model and a thickened fla...

Spray combustion is of practical importance to various applications. To study spray flames, benchmark cases were investigated both experimentally and numerically. Previous numerical studies of these flames have identified sensitivities to gas-phase combustion models and the description of the droplet evaporation. The objective of this work is to ex...

This study extends the Pareto-efficient combustion (PEC) framework to adaptive LES combustion simulations of turbulent flames. With the focus on improving predictions of CO emissions, PEC is employed to augment a flamelet/progress variable (FPV) model through local sub-model assignment of a finite-rate chemistry (FRC) model. A series of LES-PEC cal...

This study examines the effect of turbulence on the ignition of multicomponent surrogate fuels and its role in modifying preferential evaporation in multiphase turbulent spray environments. To this end, two zero-dimensional droplet models are considered that are representative of asymptotic conditions of diffusion limit and the distillation limit a...

Ensuring robust ignition is critical for the operability of aeronautical gas-turbine combustors. For ignition to be successful, an important aspect is the ability of the hot gas generated by the spark discharge to initiate combustion reactions, leading to the formation of a self-sustained ignition kernel. This study focuses on this phenomena by per...

The need for improved engine efficiencies has motivated the development of high-pressure combustion systems, in which operating conditions achieve and exceed critical conditions. Associated with these conditions are strong variations in thermo-transport properties as the fluid undergoes mixing and phase transition, and two-stage ignition with low-t...

Large Eddy Simulation (LES) with direct integration of reduced chemical kinetics including NO chemistry is performed on the Sandia flame D. This approach allows a detailed analysis of the flame structure and pollutant formation. The Analytically Reduced Chemistries (ARCs) are obtained using Directed Relation Graph method with Error Propagation (DRG...

In the application of the combustion models based on low-dimensional manifolds (for instance flamelet models) to large-eddy simulation (LES) of reactive turbulent flows, the modeling simplifications of the combustion process is a critical source of uncertainty in addition to those due to the turbulent closure model and numerical discretization. The...

This numerical study deals with the distinction between autoignition and propagation driven reaction zones using an autoignition index (AI). It allows a clear identification of the two burning regimes based on the relative contribution of two reactions for hydroperoxyl (HO2) chemistry. AI was applied to a lifted methane–air jet in a hot (1350 K) vi...

Complying with stringent pollutant emission regulations requires a strong optimization of modern gas turbine combustors, for which Large Eddy Simulation (LES) is a promising tool at the design stage. Yet the accurate prediction of pollutant formation remains a challenge because of the complex flame structure in this type of configuration. The strat...

This paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predic...

This study concerns the problem of the reconstruction of inclusions embedded in a conductive medium in the context of electrical impedance tomography (EIT), which is investigated within the framework of a non-iterative sampling approach. This type of identification strategy relies on the construction of a special indicator function that takes, roug...