Twin fluid atomizers allow for two different spray forming modes, flow focusing and flow blurring, depending on the operating, geometric, and thermophysical properties of the working liquids. In flow focusing mode, the liquid jet breaks outside the injector, whereas in flow blurring mode, the liquid jet breaks inside the atomizer. Operating conditions are believed to play an essential role in determining

The effects of different baffled configurations of acoustic dampers placed downstream of the dump plane of a combustor on the mean flowfield, coherent structures, acoustics, stability and dynamics of partially premixed methane flames were experimentally investigated. Particle image velocimetry (PIV) was used to capture the instantaneous flowfield downstream of the dump plane or the baffles and proper

A new explicit algebraic wall law for the Large Eddy Simulation of flows with adverse pressure gradient is proposed. This new wall law, referred as adverse pressure gradient power law (APGPL), is developed starting from the power-law of Werner and Wengle (Turbulent Shear Flows, vol 8, Springer, New York, pp 155–168, 1993) in order to mimic an implicit non-equilibrium log-law based on Afzal’s law (Afzal

The article ‘Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture’, written by Minh Bau Luong, Swapnil Desai, Francisco E. Hernández Pérez, Ramanan Sankaran, Bengt Johansson, and Hong G. Im was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 29th May 2020 with open access.

A novel multiple mapping conditioning (MMC) approach has been developed for the modelling of turbulent premixed flames including mixture inhomogeneities due to mixture stratification or mixing with the cold surroundings. MMC requires conditioning of a mixing operator on characteristic quantities (reference variables) to ensure localness of mixing in composition space. Previous MMC used the LES-filtered

A new opposite facing oscillator pair is presented where shared feedback channels enable synchronized sweeping of the exiting jets. The design has no moving parts and the oscillator pair is composed in a back-to-back configuration. The synchronized operation generates a near-field acoustic tonality and the objective is to determine the emitted directivity. The acoustic generation mechanisms were determined

In recent years Computational Fluid Dynamics (CFD) has become a widespread practice in industry. The growing need to simulate off-design conditions, characterized by massively separated flows, strongly promoted research on models and methods to improve the computational efficiency and to bring the practice of Scale Resolving Simulations (SRS), like the Large Eddy Simulation (LES), to an industrial

Head-on quenching is a canonical configuration for flame-wall interaction. In the present study, the transient process of a laminar premixed flame impinging on a wall is investigated for different strain rates, while previous studies with detailed chemistry and transport focused only on unstrained conditions. Increasing strain rate leads to a reduction in the normalized quenching distance, and an increase

A three-dimensional Direct Numerical Simulation of an open turbulent jet spray flame representing a laboratory-scale burner configuration has been used to analyse the statistical behaviours of the magnitude of reaction progress variable gradient \(\left| {\nabla c} \right|\) [alternatively known as the Surface Density Function (SDF)] and the strain rates, which affect its evolution. The flame has been

Data-driven modelling in fluid mechanics is a promising alternative given the continuous increase of computational power and data-storage capabilities. Highly non-linear flows which include turbulence and reaction are challenging to model, and accurate algebraic closures for the unresolved terms in large eddy simulations of such flows are difficult to obtain. In this study, an artificial neural network

Production of functional nanoparticles and nanoscaled powders is a key process in several recent industrial applications. In this work, the flame process in nanoparticle production in sprays is analyzed. Specific focus is on the flow behavior, the temperature distribution, and the residence-time of particles in the hot (reactive) regions in a flame spray reactor that are analyzed by numerical simulations

Spray combustion is one of the most important applications connected to modern combustion systems. Direct numerical simulations (DNS) of such multiphase flows are complex and computationally very challenging. Ideally, such simulations account for atomization, breakup, dispersion, evaporation, and finally ignition and combustion; phase change, heat and mass transfer should be considered as well. Considering

Large eddy simulations (LES) of a scramjet combustor are reported in this paper. The case under study is a cavity-based combustion chamber that is experimentally studied at the US Air Force Research Laboratory. The chamber is fed by eleven injectors. The computational domains are either simplified including only one or two injectors or complete with the 11 injectors. A good agreement is found between

This paper illustrates recent progresses in the development of the smoothed particle hydrodynamics (SPH) method to simulate and post-process liquid spray generation. The simulation of a generic annular airblast atomizer is presented, in which a liquid sheet is fragmented by two concentric counter swirling air streams. The accent is put on how the SPH method can bridge the gap between the CAD geometry

Three-dimensional direct numerical simulations of V-flames interacting with chemically inert walls in a fully developed turbulent channel flow have been performed under adiabatic and isothermal wall boundary conditions using single-step chemistry. These simulations are representative of stoichiometric methane-air mixture at unity Lewis number under atmospheric conditions. The turbulence in the non-reacting

Macroscopic properties of sedimenting suspensions have been studied extensively and can be characterized using the Galileo number (Ga), solid-to-fluid density ratio (\(\pi _p\)) and mean solid volume concentration (\({\bar{\phi }}\)). However, the particle–particle and particle–fluid interactions that dictate these macroscopic trends have been challenging to study. We examine the effect of concentration

Among the technological solutions proposed to reduce air pollutants and greenhouse gas emissions, the so-called “downsizing” operating mode for internal combustion engines is considered one of the most promising. By boosting the intake air pressure, this operating mode achieves higher efficiency, thus reducing pollutant emissions. Modelling the combustion process in these drastic conditions (high pressure

New insights into how different ground simulation methods affect road vehicle aerodynamics are presented. Experiments are conducted on a 1/24th-scale model, representative of a Heavy Goods Vehicle, at a Reynolds number, based on width of 2.3 × 105. Particular focus lay in characterising differences in unsteady wake development, with mean drag, base pressures, and wake velocities quantified, compared

To study combustion fundamentals of complex fuels under well-defined boundary conditions, a novel Temperature Controlled Jet Burner (TCJB) system is designed that can stabilise both gaseous or pre-vaporised liquid fuels. In a first experimental exploratory study, piloted turbulent jet flames of pre-vaporised methanol, ethanol, 2-propanol and 2-butanol mixtures are compared to methane/air as a reference

A data-driven approach to classify combustion regimes in detonation waves is implemented, and a procedure for domain-localized source term modeling based on these classifications is demonstrated. The models were generated from numerical datasets of canonical detonation simulations. In the first phase, delineations of combustion regimes within the detonation wave structure were analyzed through a clustering

This work predicts the evolution of self-excited thermo-acoustic instabilities in a gas turbine model combustor using large eddy simulation. The applied flow solver is fully compressible and comprises a transported sub-grid probability density function approach in conjunction with the Eulerian stochastic fields method. An unstable operating condition in the PRECCINSTA test case—known to exhibit strong

Eddy viscosity-based and regularization-based subgrid-scale (SGS) models are quantitatively assessed for large eddy simulations (LES) of stratified Taylor–Green vortex (TGV). LES calculations using the dynamic Smagorinsky, Leray-\(\alpha\), LANS-\(\alpha\) and Clark-\(\alpha\) models are conducted using a pseudo-spectral formulation on a \(128^{3}\) grid and using \(\alpha =\frac{1}{160}\) (for all

We present a novel mathematical model of two-phase interfacial flows. It is based on the Entropically Damped Artificial Compressibility (EDAC) model, coupled with a diffuse-interface (DI) variant of the so-called one-fluid formulation for interface capturing. The proposed EDAC-DI model conserves mass and momentum. We find appropriate values of the model parameters, in particular the numerical interface

Direct numerical simulation based on incompressible Navier–Stokes equations with an immersed boundary method is used to simulate accelerating porous media flow through a bed of uniform spheres arranged in hexagonal close packing order. The transient flow is realised by driving initially resting fluid by a constant pressure gradient. A wide spectrum of Reynolds number based on the sphere diameter and

Air entrainment within water is a common feature of flows over hydraulic works – spill over a dam, wave breaking on a dike, etc. – and its accurate modeling is a key to better design such structures. The Smoothed Particle Hydrodynamics (SPH) method appears as a natural way to model such highly distorted flows. To avoid computationally prohibitive costs related to the full discretization of bubbles

The influences of characteristic Lewis number \( \hbox{Le} \) on the statistics of density-weighted displacement speed and consumption speed in spherically expanding turbulent premixed flames have been analysed using three-dimensional direct numerical simulations data for \( \hbox{Le} = 0.8 \), 1.0 and 1.2 under statistically similar flow conditions. It has been found that the extents of flame wrinkling

Large Eddy Simulations of the Sydney mixed-mode flame with inhomogeneous inlet (FJ200-5GP-Lr75-57) are performed using the Eulerian Stochastic Fields (ESF) transported probability functions method to account for the sub-grid scale turbulence–chemistry interaction, to demonstrate the suitability of the ESF method for mixed-mode combustion. An analytically reduced 19-species methane mechanism is used

The downward shift of the mean velocity profile in the logarithmic region, known as roughness function, \(\Delta U^+\), is the major macroscopic effect of roughness in wall bounded flows. This speed decrease, which is strictly linked to the friction Reynolds number and the geometrical properties which define the roughness pattern such as roughness height, density, shape parameters, has been deeply

The effects of turbulence on knock development and intensity for a thermally inhomogeneous stoichiometric ethanol/air mixture at a representative end-gas autoignition condition in internal combustion engines are investigated using direct numerical simulations with a skeletal reaction mechanism. Two- and three-dimensional simulations are performed by varying the most energetic length scale of temperature

A DNS study of the interaction between an oblique laminar jet and a particle-laden crossflow is presented. The delivery tube is included in the simulation and jet in crossflow blowing ratio is set equal to 0.5, typical for gas turbine film cooling applications. The solid phase is polydisperse and it is simulated by adopting a Lagrangian two-way coupling point-particle approach. Wall-particle interaction

Synthetic (zero net mass flux) jets are an active flow control technique to manipulate the flow field in wall-bounded and free-shear flows. The present paper focuses on the role of the periodic actuation mechanisms on the boundary layer of a SD7003 airfoil at \(Re=U_{\infty } C/\nu =6\times 10^4\). Here, Reynolds number is defined in terms of the free-stream velocity \(U_{\infty }\) and the airfoil

Physiologically, sinus ventilation is a critical aspect of good functionality for human respiratory function, the understanding of which is still unclear. In this study we develop a method to measure sinus ventilation. Spatial and temporal features of the sinus recirculation are provided through dynamic mode decomposition (DMD). We associate the recirculation feature on the sinus epithelial surface

The statistical behaviour and modelling of the sub-grid variance of reaction progress variable have been analysed based on a priori analysis of direct numerical simulation (DNS) data of turbulent premixed Bunsen burner flames at different pressure levels. An algebraic expression for sub-grid variance, which can be derived based on a presumed bi-modal sub-grid distribution of reaction progress variable

The effect of pressure on hydrogen (H2) enriched natural gas jet flames in crossflow is experimentally investigated here. Simultaneously acquired high speed OH* chemiluminescence, OH planar laser induced fluorescence (PLIF), and stereoscopic particle image velocimetry are used to study flames at conditions typical of a gas turbine premixer, i.e. at elevated pressure, preheated crossflow, and in confinement

The aerodynamic performance of a maglev (magnetic levitation) train (MT) passing through a two-sided noise barrier was simulated by the improved delayed detached eddy simulations. The influence of the presence of noise barrier on both sides on the flow field around the MT and the pressure field in the noise barrier area are analyzed. The effect of changes of the noise barrier height and the centre

Temporal evolution of an ignition kernel in a spark ignited turbulent hydrogen–air mixing layer is studied using the large eddy simulation approach with an implicit treatment of the reaction source terms. The applied numerical code is based on a high-order compact difference approximation combined with a weighted essentially non-oscillatory scheme, which provide an accurate resolution of the small

This work is a first direct numerical simulation of a configuration closely related to the SpraySyn burner (Schneider et al. in Rev Sci Instrum 90:085108, 2019). This burner has been recently developed at the University of Duisburg-Essen to investigate experimentally nanoparticle synthesis in spray flames for a variety of materials. The present simulations are performed for ethanol and titanium tetraisopropoxide

The behaviours of bubble-induced turbulence (BIT) have been demonstrated to be different from the homogeneous isotropic single-phase turbulence on the turbulence energy spectrum. The description of bubble/eddy-bubble collision to cause bubble coalescence and breakage are usually based on the classical Kolmogorov − 5/3 scaling law for the inertial subrange of the turbulence energy spectrum function

Dynamic mode decomposition (DMD) and deep learning are data-driven approaches that allow a description of the target phenomena in new representation spaces. This fact motivates their comparison in the analysis of flow data, generated through experimental setups and numerical simulations. The focused application is the processing of high-speed videos of horizontal two-phase stratified and slug flows

The implementation of adaptive mesh refinement (AMR) in the spectral-element method code Nek5000 is used for the first time on the well-resolved large-eddy simulation of the turbulent flow over wings. In particular, the flow over a NACA4412 profile with a \(5^\circ\) angle of attack at chord-based Reynolds number \({\text {Re}}_c=200{,}000\) is analyzed in the present work and compared with a previous

This paper investigates the collision between a droplet and a spherical particle for non-reacting, isothermal flows based on the design of computer experiment and statistical learning methods, using the Volume of Fluid method along with a momentum conserving formulation on an adaptive octree grid. It has increasingly been a subject of numerical investigation due to the growing demand for full industrial

Near-wall processes in internal combustion engines strongly affect heat transfer and pollutant emissions. With continuously improving capabilities to model near-wall processes, the demand for corresponding measurements increases. To obtain an in-depth understanding of the near-wall processes within spark-ignition engines, flame distributions and flow fields were measured simultaneously near the piston

The local heat-release rate and the thermo-chemical state of laminar methane and dimethyl ether flames in a side-wall quenching configuration are analyzed. Both, detailed chemistry simulations and reduced chemistry manifolds, namely Flamelet-Generated Manifolds (FGM), Quenching Flamelet-generated Manifolds (QFM) and Reaction-Diffusion Manifolds (REDIM), are compared to experimental data of local heat-release

Different strategies to account for the heat and mass transfer between liquid droplets and their carrier phase within the Artificially Thickened Flame (ATF) approach are analyzed and compared. Herein, two approaches are introduced to take into account the droplet movement relative to the thickened flame front orientation. While the first approach achieves this behavior through scalar modifications

This paper presents a comparison of experimental and numerical results for a series of turbulent reacting jets where silica nanoparticles are formed and grow due to surface growth and agglomeration. We use large-eddy simulation coupled with a multiple mapping conditioning approach for the solution of the transport equation for the joint probability density function of scalar composition and particulate

In several technical combustion systems for lean, premixed combustion, mixture stratification plays an important role, such as in stationary and aero gas turbines. The current paper focuses on a detailed characterization of a dual-swirl gas turbine model combustor operated in a stratified regime. The influence of mixture stratification on flame stabilization and self-induced thermo-acoustic oscillations

The dynamics of three-phase flows involves phenomena of high complexity whose characterization is of great interest for different sectors of the worldwide industry. In order to move forward in the fundamental knowledge of the behavior of three-phase flows, new experimental data has been obtained in a facility specially designed for flow visualization and for measuring key parameters. These are (1)

In the framework of local volume-averaging for two-way coupling simulation of particle-laden flows, we have developed a force model that represents the particle reaction to the fluid. By considering the stress profile on the surface of finite size particles, our previous model was capable of representing the reaction force distribution even without fully resolving the boundary layer around the particle

While fuel combustion in oxygen-enriched environments provides a number of significant advantages, such as reduced nitrogen oxide emissions and high carbon dioxide purity for carbon sequestration, it is characterized by different physico-chemical oxidation behavior than combustion in air. Compared to nitrogen, carbon dioxide has different specific heat and effective Lewis number, and is chemically

In this paper we examine droplet behavior and macroscopic atomization characteristics of a non-reactive liquid spray via a series of large-eddy simulations. In our numerical study we examine three popular models for spray atomization, namely, the Taylor analogy breakup (TAB), Reitz–Diwakar and Pilch–Erdman models, and compare their predictions against available experimental data. According to our simulations

Hydraulic fracturing is a non-linear and multi-physics problem involving the break up of a solid medium due to the action of hydrodynamic forces. Fluid and solid mechanics are involved at the same time together with fracture mechanics. Despite its relevance in many scientific and engineering fields, the theoretical and numerical description of hydraulic fracturing remains a challenging matter and the

The current work presents a study on spray dynamics in aeronautical injectors. More particularly, the experimental characterization of a liquid jet in an oscillating gaseous cross flow (LJIOGCF) atomization is presented and compared to numerical simulations. The experimental setup consists of a water jet transversally injected into an oscillating subsonic air flow at ambient conditions. In a first

A new reaction rate source term \(\omega _m(c)\) for modelling of premixed combustion with a single progress variable c is proposed. \(\omega _m(c)\) mimics closely the Arrhenius source term \(\omega _A(c)\) for a large range of activation energies and density ratios while admitting analytic evaluation of many quantities of interest. The analytic flame profile \(c_m(\xi )\) very closely approximates

High-speed turbulent boundary layers of a dense gas (PP11) and a perfect gas (air) over flat plates are investigated by means of direct numerical simulations and large eddy simulations. The thermodynamic conditions of the incoming flow are chosen to highlight dense gas effects, and laminar-to-turbulent transition is triggered by suction and blowing. In the paper, the behavior of the fully developed

This paper presents results for the experimental vector velocity field obtained through spatial filter velocimetry in a triangular tube bundle with tubes of 20 mm O.D. and a transverse pitch of 25.2 mm. The experiments were conducted for single-phase water flows with Reynolds numbers ranging from 447 to 1842, and for air–water two-phase bubbly flow with liquid Reynolds number of 909 and gas Reynolds

Shock-wave/boundary-layer interactions (SBLI) are an important feature of high-speed gas dynamics. In many numerical studies of SBLI span-periodicity is assumed to reduce computational complexity. However, span-periodicity is not a valid assumption for aeronautical applications such as supersonic engine intakes where lateral confinement leads to highly three-dimensional behaviour. In this work transitional

We carried out high-fidelity large-eddy simulations to investigate the effects of uniform blowing and uniform suction on the aerodynamic efficiency of a NACA4412 airfoil at the moderate Reynolds number based on chord length and incoming velocity of \(Re_c=200{,}000\). We found that uniform blowing applied at the suction side reduces the aerodynamics efficiency, while uniform suction increases it. This

Particle–particle interactions, quantified by particle–particle restitution coefficient (e) and particle diameter (\(d_s\)) are two crucial parameters governing the flow hydrodynamics of dispersed gas–particle flows. In this work, a detailed numerical analysis has been carried out in order to get an insight into the effects of these two parameters on the jet penetration characteristics inside a bubbling

This work investigates microbubble dynamics in four-way (with coalescence) coupled microbubble-laden turbulent channel flows. Upward and downward flows of water at a shear Reynolds number of Reτ = 150 are predicted using direct numerical simulation (DNS). Microbubbles, assumed to be non-deformable and spherical, are injected into the water flow and tracked using a Lagrangian approach. One-way and two-way

Direct Numerical Simulation (DNS) data obtained earlier from two statistically stationary, 1D, planar, weakly turbulent premixed flames are analyzed in order to examine the influence of combustion-induced thermal expansion on the flow structure within the mean flame brushes and upstream of them. The two flames are associated with the flamelet combustion regime and are characterized by significantly