Olivier Desjardins

• Professor (Associate) at Cornell University

The interaction between turbulence and surface tension is studied numerically using the one-dimensional-turbulence (ODT) model. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It p...

The accurate reconstruction of immiscible fluid-fluid interfaces from the volume fraction field is a critical component of geometric Volume of Fluid (VOF) methods. A common strategy is the Piecewise Linear Interface Calculation (PLIC), which fits a plane in each mixed-phase computational cell. However, recent work goes beyond PLIC by using two plan...

The accurate reconstruction of immiscible fluid–fluid interfaces from the volume fraction field is a critical component of geometric Volume of Fluid methods. A common strategy is the Piecewise Linear Interface Calculation (PLIC), which fits a plane in each mixed-phase computational cell. However, recent work goes beyond PLIC by using two planes or...

The mesh-dependency of the breakup of liquid films, including their breakup length scales and resulting drop size distributions, has long been an obstacle inhibiting the computational modeling of large-scale spray systems. With the aim of overcoming this barrier, this work presents a framework for the prediction and modeling of subgrid-thickness li...

This paper evaluates and compares the accuracy and robustness of curvature estimation methods for three-dimensional interfaces represented implicitly by discrete volume fractions on a Cartesian mesh. The height function (HF) method is compared to three paraboloid fitting methods: fitting to the piecewise linear interface reconstruction centroids (P...

We provide closed-form expressions for the first moments (i.e., the volume and volume-weighted centroid) of a polyhedron clipped by a paraboloid, that is, of a polyhedron intersected with the subset of the three-dimensional real space located on one side of a paraboloid. These closed-form expressions are derived following successive applications of...

A volume-filtered Large Eddy Simulation (LES) of oscillatory flow over a mobile rippled bed is conducted using an Euler–Lagrange approach. The modeling is done to complement the experimental work, which shows quasi-steady state ripples in a sand bed under oscillatory flow, as observed in unsteady marine flows over sedimentary beds. Simulations appr...

Non-invasive visualization techniques for multiphase flows are critical to understanding primary atomization and sprays. We use back-lit imaging to identify the liquid-gas interface of two-phase flows at high temporal and spatial resolutions and employ Dynamic Mode Decomposition (DMD) to study the shape and frequency of instabilities of a liquid je...

Utilizing recent advancements in computational schemes for compressible, multiphase flows, this work features a parametric study of a pure liquid jet in supersonic crossflow that involves simulating the atomization process for four values of momentum-flux ratio. These simulations are validated against experimental results measured with high-speed X...

The shear instability occurring at the interface between a slow water layer and a fast air stream is a complex phenomenon driven by momentum and viscosity differences across the interface, velocity gradients as well as by injector geometries. Simulating such an instability under experimental conditions is numerically challenging and few studies exi...

Intersecting a polyhedron with a half-space or another polyhedron is required in various fields, including computer graphics, computer-aided design, and many methods used in computational physics. Often, the polyhedra involved are complicated non-convex objects, and intersecting them constitutes a significant computational cost. To address this, we...

Liquid-gas flows that involve compressibility effects occur in many engineering contexts, and high-fidelity simulations can unlock further insights and developments. Introducing several numerical innovations, this work details a collocated, volume-of-fluid, finite volume flow solver that is robust, conservative, and capable of simulating flows with...

In simulations, artificial boundaries need to be introduced to limit the size of computational domains and thereby lower computational cost. At these boundaries, flow variables need to be calculated in a way that will not induce any perturbation of the interior solution, which poses a great challenge in incompressible flows. In this paper, we demon...

Particle-laden flow in a vertical channel was simulated using a Reynolds-averaged Navier-Stokes two-fluid model including a Reynolds-stress model (RSM). Two sets of cases varying the overall mass loading were done using particle sizes corresponding to either a large or small Stokes number. Primary and turbulent statistics extracted from counterpart...

Particle‐laden flows in a vertical channel were simulated using an Eulerian–Eulerian, Anisotropic Gaussian (EE‐AG) model. Two sets of cases varying the overall mass loading were done using particle sizes corresponding to either a large or small Stokes number. Primary and turbulent statistics were extracted from these results and compared with count...

In this study, we address the modification of sheared turbulence by dispersed inertial particles. The preferential sampling of the straining regions of the flow by inertial particles in turbulence leads to an inhomogeneous distribution of particles. The strong gravitational loading exerted by the highly concentrated regions results in anisotropic a...

In this study, we address the modification of sheared turbulence by dispersed inertial particles. The preferential sampling of the straining regions of the flow by inertial particles in turbulence leads to an inhomogeneous distribution of particles. The strong gravitational loading exerted by the highly concentrated regions results in anisotropic a...

This work demonstrates a computational framework for simulating vaporizing, liquid-gas flows. It is developed for the general vaporization problem which solves the vaporization rate based as from the local thermodynamic equilibrium of the liquid-gas system. This includes the commonly studied vaporization regimes of film boiling and isothermal evapo...

The interface/turbulence interaction between two fluids in a turbulent environment has an important role in many technical processes, e.g. primary liquid atomization in combustion devices. Primary atomization has a significant role in spray formation and its characteristics. The resulting dynamics typically span 4–6 orders of magnitude in length sc...

Turbulence is a complex, multi-scale fluid process that can be strongly modified by the presence of multiple phases. In this work, we will discuss various aspects of the interaction between turbulence and interfaces with surface tension, as commonly encountered in liquid-gas flows. This study is based on a series of direct numerical simulations of...

Predictive simulations of multiphase flows require high fidelity numerical schemes and well resolved flow features. In this paper, we integrate the all-Mach multiphase flow algorithm that has been developed in [1] into AMReX-a framework for massively parallel, block-structured adaptive mesh refinement applications [2]. The compressible multiphase f...

The conditional hyperbolic quadrature method of moments (CHyQMOM) was introduced by Fox et al. [19] to reconstruct 1- and 2-D velocity distribution functions (VDF) from a finite set of integer moments. The reconstructed VDF takes the form of a sum of weighted Dirac delta functions in velocity phase space, and provides a hyperbolic closure for the s...

Particle-laden flows of sedimenting solid particles or droplets in a carrier gas have strong inter-phase coupling. Even at low particle volume fractions, the two-way coupling can be significant due to the large particle to gas density ratio. In this semi-dilute regime, the slip velocity between phases leads to sustained clustering that strongly mod...

Particle-laden flows of sedimenting solid particles or droplets in a carrier gas have strong inter-phase coupling. Even at low particle volume fractions, the two-way coupling can be significant due to the large particle to gas density ratio. In this semi-dilute regime, the slip velocity between phases leads to sustained clustering that strongly mod...

This note introduces a regression technique for finding a class of nonlinear integro-differential operators from data. The method parametrizes the spatial operator with neural networks and Fourier transforms such that it can fit a class of nonlinear operators without needing a library of a priori selected operators. We verify that this method can r...

The efficiency of a gas turbine is largely dependent on the combustion process between the liquid fuel and the oxidizer. The mixing of the the fuel vapours and the incoming air is critical to the combustion process, and the primary factor affecting vaporization is the atomization of the fuel spray. Experiments [1, 2] have shown that high-amplitude...

Turbulent wall-bounded flows exhibit a wide range of regimes with significant interaction between scales. The fluid dynamics associated with single-phase channel flows is predominantly characterized by the Reynolds number. Meanwhile, vastly different behaviour exists in particle-laden channel flows, even at a fixed Reynolds number. Vertical turbule...

Fiber-based coalescers are widely used in the chemical industry to separate two immiscible fluids. Due to the complex structure inside a coalescer and the opaque nature of the fiber material, it is impractical to perform direct visualization and measurement of the multiphase flow inside a coalescer. One fundamental problem in understanding the phys...

A recurring challenge among the variety of existing biomass‐to‐biofuel conversion technologies is the need to ensure optimal and homogeneous contact between the various phases involved. The formulation of robust design rules from an empirical standpoint alone remains difficult due to the wide range of granular flow regimes coexisting within a given...

Many common engineering problems involve the study of turbulence interaction with other physical processes. For many such physical processes, solutions are expressed most naturally in physical space, necessitating the use of physical space solutions. For simulating isotropic turbulence in physical space, linear forcing is a commonly used strategy b...

Simulations of homogeneously sheared turbulence (HST) are conducted until a universal self-similar state is established at the long non-dimensional time $\unicode[STIX]{x1D6E4}t=20$ , where $\unicode[STIX]{x1D6E4}$ is the shear rate. The simulations are enabled by a new robust and discretely conservative algorithm. The method solves the governing e...

One fundamental problem in understanding two-phase flows in coalescers is determining how large of a drop can attach to and subsequently remain on a fiber. Droplet detachment can be caused by gravity or shear from the cross-flow overcoming the adhesion between the drop and the fiber. Previous studies have found the critical size of a drop on a hydr...

Particle-laden flows of sedimenting heavy solid particles or droplets in a carrier gas have strong inter-phase coupling even at low volume fractions. The slip velocity between phases lead to sustained clustering that can strongly modulate the overall flow. Simulations of homogeneously sheared flow are conducted in the Euler-Lagrange and Euler-Euler...

We present a verification study of three simulation techniques for fluid–particle flows, including an Euler–Lagrange approach (EL) inspired by Jackson's seminal work on fluidized particles, a quadrature–based moment method based on the anisotropic Gaussian closure (AG), and the traditional two-fluid model. We perform simulations of two problems: pa...

This paper presents an accurate and robust reinitialization equation for the conservative level set that does not significantly deform stationary surfaces. The compression and diffusion term of the reinitialization equation are reformulated to use a distance level set directly mapped from the conservative level set. The normals are calculated using...

Compressible fuel injection is a critical process in the operation of scramjet engines, but a challenging area for experimentation. Accurate numerical simulations based on first principles can help elucidate the limiting physics in these flows and provide guidance for engineering design. However, most computational studies of liquid jet atomization...

Risers are used in a variety of industries, where rapid mixing between gas and solid particles is essential. More recently, risers are gaining importance in some of the novel combustion technologies, such as Chemical-looping combustion and thermochemical conversion of biomass. These reactor configurations provide challenging modeling issues, as the...

Euler-Lagrange methods are popular approaches for simulating particle-laden flows. While such approaches have been rigorously verified in the dilute limit (where particles do not noticeably alter their carrier flow), much less verification has been attempted for cases where the coupling between the two phases leads to non-negligible modifications i...

Numerical simulations of a planar air/water air-blast atomization are performed using an in-house multiphase Navier–Stokes solver which uses a semi-Lagrangian geometric volume of fluid method to track the position of the interface. This solver conserves mass exactly and mitigates momentum and kinetic energy conservation errors. Excellent agreement...

An Euler-Euler anisotropic Gaussian approach (EE-AG) for simulating gas-particle flows, in which particle velocities are assumed to follow a multivariate anisotropic Gaussian distribution, is used to perform mesoscale simulations of homogeneous cluster-induced turbulence (CIT). A three-dimensional Gauss–Hermite quadrature formulation is used to cal...

Simulations of strongly coupled (i.e., high-mass-loading) fluid-particle flows in vertical channels are performed with the purpose of understanding the fundamental physics of wall-bounded multiphase turbulence. The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions are presented, and the unclosed terms that are retained in the...

In Part I, simulations of strongly coupled fluid-particle flow in a vertical channel were performed with the purpose of understanding, in general, the fundamental physics of wall-bounded multiphase turbulence and, in particular, the roles of the spatially correlated and uncorrelated components of the particle velocity. The exact Reynolds-averaged (...

Scaling of volume fraction and velocity fluctuations with domain size is investigated for high-mass-loading suspensions of finite-size inertial particles subject to gravity. Results from highly resolved Euler-Lagrange simulations are evaluated via an adaptive spatial filter with an averaging volume that varies with the local particle concentration....

At sufficient mass loading and in the presence of a mean body force (e.g. gravity), an initially random distribution of particles may organize into dense clusters as a result of momentum coupling with the carrier phase. In statistically stationary flows, fluctuations in particle concentration can generate and sustain fluid-phase turbulence, which w...

Acoustic standing wave fields are widely used in MEMS applications to separate micron sized particles from fluids. However, the use and understanding of macro scale ultrasonic separators are still limited and challenging. New macro-scale, ultrasonic separators are presented that use multidimensional standing waves to trap and generate tightly packe...

Wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence in practical systems. This work aims at investigating the effects of particle clustering on the carrier-phase turbulence in both dilute and moderately dilute channel flows via highly resolved Euler-Lagrange si...

Acoustic standing wave fields are widely used in MEMS applications to separate micron sized particles from fluids. However, the use and understanding of macro scale ultrasonic separators are still limited and challenging. These systems rely on acoustic radiation forces for trapping and clumping of dispersed phase particles. The clumps of particles...

We examine the linear stability of a homogeneous gas-solid suspension of small Stokes number particles, with a moderate mass loading, subject to a simple shear flow. The modulation of the gravitational force exerted on the suspension, due to preferential concentration of particles in regions of low vorticity, in response to an imposed velocity pert...

In this paper, a mesh-decoupled height function method is proposed and tested. The method is based on computing height functions within columns that are not aligned with the underlying mesh and have variable dimensions. Because they are decoupled from the computational mesh, the columns can be aligned with the interface normal vector, which is foun...

Wall-bounded disperse multiphase flows are common in many environmental and industrial applications, and are often turbulent. Some examples include liquid-solid slurry pipelines, solid deposition in marine flows, and foreign debris in gas turbine engines. In vertical risers of circulating fluidized bed (CFB) reactors, strong coupling between the ph...

Fluid-particle flows are ubiquitous in engineering and environmental applications, and are often turbulent. In systems with heavy particles and significant mass loading, momentum coupling between the phases leads to the spontaneous generation of dense clusters that result in cluster-induced turbulence (CIT). To aid in the development of turbulence...

A volume-filtered Euler-Lagrange large eddy simulation methodology is used to predict the physics of turbulent liquid-solid slurry flow through a horizontal pipe. A dynamic Smagorinsky model based on Lagrangian averaging is employed to account for the sub-filter scale effects in the liquid phase. A fully conservative immersed boundary method is use...

A conjugate heat transfer (CHT) immersed boundary (IB and CHTIB) method is developed for use with laminar and turbulent flows with low to moderate Reynolds numbers. The method is validated with the canonical flow of two co-annular rotating cylinders at $Re=50$ which shows second order accuracy of the $L_{2}$ and $L_{\infty}$ error norms of the temp...

Starting from the kinetic theory (KT) model for monodisperse granular flow, the exact Reynolds-average (RA) equations were recently derived for the particle phase in a collisional gas-particle flow by Fox [1]. The turbulence model solves for the RA particle volume fraction, the phase-average (PA) particle velocity, the PA granular temperature, and...

In this work, a novel computational framework for calculating convection fluxes is developed and employed in the context of the piecewise linear interface calculation (PLIC) volume-of-fluid (VOF) method. The scheme is three-dimensional, unsplit, discretely conservative, and bounded. The scheme leverages the idea of semi-Lagrangian transport to esti...

We present a computational study of cluster-induced turbulence (CIT), where the production of fluid-phase kinetic energy results entirely from momentum coupling with finite-size inertial particles. A separation of length scales must be established when evaluating the particle dynamics in order to distinguish between the continuous mesoscopic veloci...

This paper aims at investigating the capability of numerical models to ac- curately capture the physical characteristics of particle clustering in vertical risers. Within the energy sector, particle clustering in vertical risers of circu- lating fluidized bed reactors are known to play a key role in the multiphase dynamics as well as secondary proc...

Numerical simulation of air-blast breakup of a three-dimensional planar liquid layer is performed, which provides a simplified framework to study the instabilities present in realistic coaxial injectors of propulsion devices during the primary stage of atomization. The computation remains robust and accurate despite the high shear and large density...

In this work, large-eddy simulation of the atomization of a liquid jet in cross-flow is performed. Two different injector geometries are investigated that result in significantly different liquid jets. One of the injectors, referred to as the round-edged injector, produces a laminar flow at the exit plane. The other injector, known as the sharp-edg...

Through a linear stability analysis of a gas-solid suspension of particles with low Stokes number and moderate mass loading, we demonstrate that the modulation of the gravitational force exerted on the suspension due to preferential concentration of particles in regions of low vorticity can destabilize a homogeneous linear shear flow of a gas-solid...

Starting from the kinetic theory (KT) model for granular flow, the exact Reynolds-average (RA) equations have been derived for the particle phase in a collisional gas-particle flow. The corresponding equations for a constant-density gas phase have been derived from a model that includes drag and buoyancy coupling with the particle phase. The fully...

A recurring challenge among the variety of existing biomass-to-biofuel conversion technologies is the need to ensure optimal and homogeneous contact between the various phases involved. One example can be found in the catalytic upgrading of bio-oil vapors, a bi-phasic process critical in pyrolysis-based conversion, typically performed in circulatin...

The accurate conservative level set (ACLS) method of Desjardins et al. [O. Desjardins, V. Moureau, H. Pitsch, An accurate conservative level set/ghost fluid method for simulating turbulent atomization, J. Comput. Phys. 227 (18) (2008) 8395–8416] is extended by using a discontinuous Galerkin (DG) discretization. DG allows for the scheme to have an a...

Turbulent gas-particle flows in vertical pipes are ubiquitous for a range of industrial processes. Within the energy sector, such flows are used in circulating fluidized bed reactors for thermochemical decomposition of coal and biomass. However, the non-deterministic nature of the gas-phase turbulence coupled with an assembly of interacting particl...

In this work, we present a computational methodology for simulating multiphase flows that is designed to be mass and momentum conserving through discrete consistency between interface and momentum transport. The method uses a novel volume-of-fluid (VOF) scheme to transport the interface. The VOF scheme is second order accurate, un-split, conservati...

A detailed understanding of the driving mechanisms behind primary atomization is crucial to the optimization of sprays for efficient combustion in modern propulsion systems. Many challenges are associated with simulating realistic turbulent atomization, such as the multiplicity of length and time scales of the turbulent flow field and gas-liquid in...

Biomass thermochemical conversion, often done in fluidized beds, recently gained a lot of attention due to its potential to efficiently produce renewable liquid fuels. Optimization of reactor design and operating conditions, however, requires a fundamental understanding of bed dynamics. In this work, a numerical framework based on an Euler–Lagrange...

Three-dimensional n-heptane spray flames in a swirl combustor are investigated by means of direct numerical simulation (DNS) to provide insight into realistic spray evaporation and combustion as well as relevant modeling issues. The variable-density, low-Mach number Navier–Stokes equations are solved using a fully conservative and kinetic energy co...

Fluidization is a technique of choice for the thermochemical conversion of biomass. At conversion temperatures however, the amount of gases released by the biomass is large enough to impact the mixing of the reactive particles with the inert sand, and modify the bubbling frequency and intensity. This, in turn, may significantly affect the chemical...

Atomization of hydrocarbon fuels is of critical importance to the transportation sector, in particular for aircraft gas turbine engines. In this work, simulations of a Delevan pressure swirl injector with realistic geometry was investigated. Results were compared with simulations performed by Fuster et al. (Int J Multiphase Flow, 2009) of a swirl j...

Direct Steam Generation (DSG), a technology that uses parabolic solar reflectors to generate steam from water flowing through horizontal pipes located at the focal points of the reflectors, often requires an annular pipe flow in which the liquid is distributed as a thin film around the circumference of the pipe. The distribution of the gas-liquid i...

Turbulent particle-laden flows in the form of fluidized bed reactors display good mixing properties, low pressure drops, and a fairly uniform temperature distribution. Understanding and predicting the flow dynamics within the reactor is necessary for improving the efficiency, and providing technologies for large-scale industrialization. A numerical...

Turbulent gas-particle flows play fundamental roles in a wide range of technical systems. Understanding and predicting particle-laden turbulent flows is key to ensuring optimal performance and improving the design of devices such as fluidized bed reactors. In this work, a Lagrangian description of the particles is combined with state-of-the-art sch...

Air-blast atomization of hydrocarbon fuels is of critical importance to the transportation sector, in partic-ular for aircraft gas turbine engines. In this work, a co-annular air-blast n-dodecane injector is studied both experimentally and numerically. Experiments combine high-resolution and high-speed imaging of the near-field region, with Global...