Gas Phase Turbulence Research Articles

Multiphase flow simulation and industrial application of an in-line gasifier for NOx emissions control from cement kiln

Following the power and steel industries, nitrogen oxides (NOx) in the cement industry have become an important part of the next stage of air pollutant control. Consequently, the multiphase flow simulation of an in-line coal gasification denitration system was carried out using the computational fluid dynamics (CFD) approach. Among them, the solid phase is simulated by the Multiphase Particle-In-Cell (MP-PIC) method, and the gas phase turbulence is accurately captured by the large eddy simulation (LES) method. The flow field characteristics distribution and the reaction kinetic of NO under different parameters (coal, raw meal, tertiary air) in the gasifier were investigated, and the operating condition values for guiding industrial applications are obtained. The simulation results show that the gasifier can completely remove NOx from the rotary kiln at 2.8 kg/s for coal, 30 kg/s for raw meal and 2.5 kg/s for tertiary air. The application results show that under 1.6 kg/t.cl of ammonia water combined with SNCR, NOx emission and ammonia slip can be controlled below 50 mg/Nm3 and 5 mg/Nm3, respectively. Compared to similar denitrification technologies, this technology shows the potential to achieve ultra-low NOx emission levels in the cement industry.

Liquid jet breakup in a subsonic cross airflow: An experimental study of the effect of the gas phase turbulence

Liquid jet breakup in a subsonic cross airflow: An experimental study of the effect of the gas phase turbulence

Detailed comparison of physical fining methods in an industrial glass melting furnace using coupled CFD simulations

Melting and primary fining represent the most essential steps in the glass manufacturing process. Electric boosting and bubbling are common methods used to optimize these processes by improving the product quality and energy efficiency. However, a structured overview of their impacts on the operation of the total melting furnace has not previously been published. The present paper provides a thorough comparison of these technologies applied to an industrial melting furnace, including the effects on temperatures, melt flow patterns, glass quality, as well as the heat fluxes and process efficiency. In this work, extensive numerical simulations were performed. Unlike other studies described in the literature, a validated CFD model of exceptionally high accuracy was employed. Furthermore, the entire melting furnace was considered, such that the glass tank was coupled to detailed simulations of the turbulent gas-phase combustion. A novel method for combustion modeling in glass manufacturing was applied, and user-defined functions supported an analysis of glass quality. Substantial differences were observed between the furnaces with electric boosting and bubbling. For the first time, interrelated effects could be described in detail, providing a comprehensive overview of the entire operation. Based on the presented results, the targeted use of both electrodes and gas nozzles is suggested for future melting processes.

Eulerian-Eulerian Modeling of the Features of Mean and Fluctuational Flow Structure and Dispersed Phase Motion in Axisymmetric Round Two-Phase Jets

The features of the local mean and fluctuational flow structure, carrier phase turbulence and the propagation of the dispersed phase in the bubbly and droplet-laden isothermal round polydispersed jets were numerically simulated. The dynamics of the polydispersed phase is predicted using the Eulerian–Eulerian two-fluid approach. Turbulence of the carrier phase is described using the second-moment closure while taking into account the presence of the dispersed phase. The numerical analysis was performed in a wide range of variation of dispersed phase diameter at the inlet and particle-to-fluid density ratio (from gas flow laden with water droplets to carrier fluid flow laden with gas bubbles). An increase in the concentration of air bubbles and their size leads to jet expansion (as compared to a single-phase jet up to 40%), which indicates an increase in the intensity of the process of turbulent mixing with the surrounding space. However, this makes the gas-droplet jet narrower (up to 15%) and with a longer range in comparison with a single-phase flow. The addition of finely dispersed liquid droplets to an air jet suppresses gas phase turbulence (up to 15%). In a bubbly jet, it is found that small bubbles (Stk < 0.1) accumulate near the jet axis in the initial cross-sections, while concentration of the large ones (Stk > 0.2) along the jet axis decreases rapidly. In the gas-droplet jet, the effect of dispersed phase accumulation is also observed in the initial cross-section, and then its concentration decreases gradually along the jet axis. For gas bubbles (Stk < 0.1), small turbulence attenuation (up to 6%) is shown.

Large Eddy Simulation of Gasoline Sprays in a Lagrangian–Eulerian Framework Using the High-Order Spectral Element Method

Abstract Predicting the spray evolution using simulations requires accurate modeling of the turbulent gas-phase flow field. In this study, the high-order spectral-element method (SEM), implemented in the code Nek5000, was used to provide highly resolved solutions to the turbulent flow field. Spray modeling capabilities were implemented into the Nek5000 code. The spray is modeled in a Lagrangian–Eulerian (LE) framework, where the liquid is represented by discrete parcels of droplets. The method for coupling liquid and gas in the context of SEM is described, which allows for very fine meshes to be used without affecting the stability of the solution. Large-eddy simulations (LES) of the eight-hole ECN Spray G gasoline injector were conducted. Numerical results are compared against experimental data for liquid penetration, droplet size and gas velocity. The morphology of the multiplume spray is compared against experimental data. The effect of different spray injection inputs is analyzed. It was found that using a plume direction of 33 deg and an injection cone angle of 30 deg produced the best results overall. This work shows the applicability of SEM for spray modeling applications, where use of a high-order flow solver can help us understand the multiplume spray aerodynamics and how it leads to plume collapse under certain conditions. Results also highlight the need for tuning spray input parameters in the LE framework, even when high-fidelity gas flow solutions are possible.

RANS Modeling of Turbulent Flow and Heat Transfer in a Droplet-Laden Mist Flow through a Ribbed Duct

The local structure, turbulence, and heat transfer in a flat ribbed duct during the evaporation of water droplets in a gas flow were studied numerically using the Eulerian approach. The structure of a turbulent two-phase flow underwent significant changes in comparison with a two-phase flow in a flat duct without ribs. The maximum value of gas-phase turbulence was obtained in the region of the downstream rib, and it was almost twice as high as the value of the kinetic energy of the turbulence between the ribs. Finely dispersed droplets with small Stokes numbers penetrated well into the region of flow separation and were observed over the duct cross section; they could leave the region between the ribs due to their low inertia. Large inertial droplets with large Stokes numbers were present only in the mixing layer and the flow core, and they accumulated close to the duct ribbed wall in the flow towards the downstream rib. An addition of evaporating water droplets caused a significant enhancement in the heat transfer (up to 2.5 times) in comparison with a single-phase flow in a ribbed channel.

Turbulence in Two-Phase Flows with Macro-, Micro- and Nanoparticles: A Review

Turbulent flows are nonstationary in nature. Since the turbulent fluctuations of most flow parameters satisfy a symmetric Gaussian distribution, the turbulent characteristics have the property of symmetry in the statistical meaning. A widespread simplest model of turbulent flows is the model of “symmetric” turbulence, namely, homogeneous isotropic turbulence (HIT). The presence of particles with non-uniform distribution of their concentration in the turbulent flow, even under HIT conditions, can lead to redistribution of different components of fluctuation velocities of the carrier gas, i.e., to the appearance of asymmetry. The subject of the review is turbulent flows of gas with solid particles. Particular attention is paid to the problem of the back influence of particles on carrier gas characteristics (first of all, on the turbulent kinetic energy). A review of the results of experimental and computational-theoretical studies of the effect of the presence of the dispersed phase in the form of particles on the parameters of the turbulent flow of the carrier gas phase has been carried out. The main physical mechanisms and dimensionless criteria determining the direction and magnitude of the impact of particles of different inertia on the carrier gas phase turbulence energy are described and analyzed. The peculiarities of the influence of particles on the turbulence energy of the gas for different classes of flows: homogeneous isotropic turbulence, homogeneous shear flow, and wall turbulence in a pipe (channel) have been considered. For the near-wall flow in the pipe, it is shown that the turbulizing effect of extremely low-inertia particles of sub-micrometer size (nanoparticles) is replaced by the laminarizing effect of low-inertia particles of micrometer size (microparticles), and then again it is replaced by turbulizing due to additional generation of turbulence in the wakes of large particles of millimeter size (macroparticles). The review is intended to some extent to fill in the currently existing gap associated with the absence of dimensionless criteria (or complexes of physical parameters) responsible for the direction (attenuation or enhancement) of turbulence modification, and the value of this change. Possible directions for further researches are given in the conclusion of the review.

An enhanced mesoscale model for laminar and turbulent three-dimensional simulations of the gas phase flow with concentration mixing in structured packing columns

This work presents a mesoscale model (MSM) simulating the laminar and turbulent gas phase fluid dynamics and concentration mixing in structured packings, used in absorption and distillation columns or static mixers. The MSM aims to provide computationally efficient predictions of the three-dimensional distributions of pressure, velocity and concentration in the structured packing’s gas phase. The MSM is successfully calibrated and validated with virtual experiments obtained from DNS (direct numerical simulations) of a single structured packing section featuring concentration mixing under uniform and maldistributed velocity inlet profiles. The packing section scenarios exhibit a variety of physical effects, like backflow, high-velocity fronts and blockage at the packing’s borders to the wall, which are all predicted correctly by the MSM. The physical effects have an impact on concentration mixing and velocity smoothing and are particularly interesting for applications of structured packings in dividing-wall columns or static mixers. Finally, the MSM is set up to simulate cylindrical columns with alternately rotated structured packing sections, including wall regions and wipers. MSM simulations of three packed columns of varying diameter are compared against experimental data and correctly predict the pressure drop dependence on the diameter, demonstrating the MSM’s potential for scale-up predictions.

CFD simulation aided glass quality and energy efficiency analysis of an oxy-fuel glass melting furnace with electric boosting

• Inexpensive coupled CFD simulations of glass furnace with verified numerical models. • Link between specific power input and glass quality was established and quantified. • Space utilisation increased when specific heat input over free glass surface increased. • Space utilisation increased when pull rate was reduced or fuel mass flow increased. Determining glass quality has been a focal point of CFD studies of glass furnaces for several decades. Previous research identified the utilisation of glass tank space by inhomogeneities as a crucial quantity for the scrutinization of glass quality. However, the majority of previous CFD based parametric studies were conducted on idealized glass tank models, which neglected the influence of the turbulent gas phase in the combustion chamber on the heat transfer. Consequently, not all of the findings are universally applicable in practical settings. Hence, the present work aims at closing this research gap by introducing two improvements over the current state-of-the-art in a parametric study by: 1) Employing a verified, computationally inexpensive, coupled numerical model in the complete CFD simulation of a glass melting furnace and 2) Establishing and quantifying the link between variations of the specific power input and common glass quality indicators. It was shown that due to the cross-fired configuration of the burners, increasing the specific power input over the free glass surface resulted in higher transversal velocities and temperature gradients, which favoured the development of helical flow in the melt and thus increased the critical residence time and by extension, the glass quality.

Numerical Studies on Particle Dynamics in a Spouted Bed

A coupled computational fluid dynamics (CFD)-discrete element method (DEM) technique has been adopted to examine the dynamic behavior of particles in a rectangular spouted bed. Eulerian method has been used to solve the Navier–Stokes equation for the gas phase (for the CFD) and Lagrangian method (for the DEM) for the particle phase, where the k–ϵ two-equation turbulence model has been used to capture the effect of gas-phase turbulence. In the present work, we sought to predict the minimum spouting velocity (Ums) numerically for a fixed bed height and particular particle properties. The effects of the inelastic collision and the friction on translational and rotational dynamics of the particles in spout, annulus, and fountain zones have been brought out with the intensive parametric study. The results reported here would be a way forward for a better understanding of the spouted bed processing where translational and rotational dynamics of particles play a key role.

Numerical study on the mixing and evaporation process of a liquid kerosene jet in a scramjet combustor

The mixing and evaporation process of a liquid kerosene jet in a scramjet combustor with dual-cavity is investigated by two-phase Large Eddy Simulation. The gas-droplet flow system is solved through a two-way coupled Eulerian-Lagrangian method. The primary and secondary breakup processes of the liquid fuel jet are taken into account. The Langmuir-Knudsen evaporation model, which considers the non-equilibrium effect, is used to calculate the evaporation process of the droplets. The penetration depth of the jet is in good agreement with the experimental value. The dynamic process of the liquid jet breakup, spray evaporation, and fuel transportation within the combustor are well described by the numerical results. The distribution and evaporation characteristics of the spray are analyzed and most droplets are evaporated within 30 mm downstream of the jet orifice. However, a small portion of droplets with high velocity and low temperature can survive for a long distance. The influence of injection pressure on the mixing process near the cavity is also analyzed, and it is found that the injection pressure affects the total quantity of fuel entrained into the cavity by affecting the fuel distribution in the near-wall region and the total fuel mass flow rate. The local distribution of the liquid and gas phase fuels, local temperature and turbulence characteristics in the cavity are analyzed, and the ignition environment on the development path of the flame kernel is discussed. The results indicate that the injection pressure and the distance between the cavity and the orifice have a critical effect on the quantity of the kerosene entrained into the cavity, which then have a great influence on the ignition environment in the cavity.

Validation of a coupled 3D CFD simulation model for an oxy-fuel cross-fired glass melting furnace with electric boosting

Glass furnaces represent a continuous challenge for CFD simulations, which is attributed to the complex description of multiple phases: the turbulent gas phase, raw materials from a solid glass batch and the laminar liquid phase of the glass melt. Prevalence of unsuitable oxy-fuel combustion models, like the eddy-dissipation model, and the lack of advanced coupling methods for the coupling of combustion chamber and glass tank domains have been identified as research gaps in glass furnace simulations. These are tackled in a 3D CFD simulation model for an oxy-fuel glass furnace with electric boosting by introducing two significant improvements compared to previous approaches: (1) The partially-premixed steady diffusion flamelet model in combination with a skeletal25 reaction mechanism was used for combustion modelling. (2) An advanced iterative coupled simulation method is presented, which introduces damping of the solution and a rigorous termination condition. By employing the presented models, the respective temperatures in the combustion chamber and the glass tank were predicted within less than 1.93% and 3.81% of the experimental data.

Numerical study of preheating primary air on pinewood and corn straw co-combustion in a fixed bed using Eulerian-Eulerian approach

The effect of preheating primary air on the co-combustion characteristics of a 50–50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 °C. The co-combustion characteristics were included the co-combustion behaviors and emissions. In order to reveal the features of the combustion process in the porous bed, a two-dimensional unsteady state model was employed to investigate the combustion process in a fixed bed of blended biomass on the combustion process in a fixed bed reactor. Conservation equations of the bed were implemented to describe the combustion process. The gas phase turbulence was modeled using the k-ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. Results showed that by increasing primary air temperature the residual mass on bed decreased, while the average burning rates and ignition front propagation velocity increased At the primary air temperature of 85 °C the smallest unburned carbon was left in the ash, and the emissions of nitrogen-compounds were relatively small. In contrast, the primary air temperature of 85 °C was found to be well-operating condition, which can be suggested for industrial boiler during blend co-combustion. The simulation results were then compared with experimental data for different temperature, which shows that the combustion process in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data.

Turbulence Regulates the Rate of Planetesimal Formation via Gravitational Collapse

Abstract We study how the interaction between the streaming instability (SI) and intrinsic gas-phase turbulence affects planetesimal formation via gravitational collapse in protoplanetary disks. Turbulence impedes the formation of particle clumps by acting as an effective turbulent diffusivity, but it can also promote planetesimal formation by concentrating solids, for example, in zonal flows. We quantify the effect of turbulent diffusivity using numerical simulations of the SI in small local domains, forced with velocity perturbations that establish approximately Kolmogorov-like turbulence. We find that planetesimal formation is suppressed by turbulence once velocity fluctuations exceed ≃ (10−3.5–10−3) . Turbulence whose strength is just below the threshold reduces the rate at which solids are bound into clumps. Our results suggest that the well-established turbulent thickening of the midplane solid layer is the primary mechanism by which turbulence influences planetesimal formation and that planetesimal formation requires a midplane solid-to-gas ratio ϵ ≳ 0.5. We also quantify the initial planetesimal mass function using a new clump-tracking method to determine each planetesimal mass shortly after collapse. For models in which planetesimals form, we show that the mass function is well described by a broken power law, whose parameters are robust to the inclusion and strength of imposed turbulence. Turbulence in protoplanetary disks is likely to substantially exceed the threshold for planetesimal formation at radii where temperatures T ≳ 103 K lead to thermal ionization. Planetesimal formation may therefore be unviable in the inner disk out to 2–3 times the dust sublimation radius.

Numerical investigation of swirl-stabilized pulverized coal flames in air and oxy-fuel atmospheres by means of large eddy simulation coupled with tabulated chemistry

This paper investigates a self-sustained swirl-stabilized pulverized coal combustion chamber, specially designed to validate numerical models under atmospheric and oxy-fuel conditions. For this purpose, a comprehensive model, which accounts for both atmospheric and oxy-fuel conditions, is developed based on Large Eddy Simulation. To describe the turbulent gas-phase chemistry, a 4D Flamelet Generated Manifold based tabulated chemistry model is coupled with the artificially thickened flame approach and implemented in an Euler–Lagrange framework. The chemistry model is able to account for finite rate chemistry, heat losses, mixing devolatilization gases and char off-gases. Radiative heat transfer is included by solving the radiative transfer equation, applying the discrete ordinate method for angular discretization and a weighted sum of gray gas model for the spectral resolution, while particles are treated as gray. The simulation results from the combustion chamber are extensively validated against the available measurement data. Operating conditions with different atmospheres are investigated to validate the models’ prediction accuracy for air and oxy-fuel atmospheres. The validation process is carried out using velocity fields, particle temperature measurements and the gas-species concentrations. Overall, the comparisons between simulations and measurements reveal a favorable agreement with only small differences near the burner opening. These results demonstrate the suitability of large-eddy simulation combined with tabulated chemistry for predicting the combustion of pulverized coal in conventional air and oxy-fuel atmospheres. Further analyses of the self-sustained coal flames are carried out; in particular, the influence of different atmospheres on the interaction of coal particles with the gas phase is studied.

Particle Concentration Distribution in a Gas–Droplet Confined Swirling Flow: Euler and Lagrange Approaches

This paper considers the problem of the numerical simulation of the propagation dynamics of a dispersed admixture and heat transfer in a swirling turbulent gas–droplet flow behind a sudden tube expansion. The gas phase is described by a system of three-dimensional Reynolds-Averaged Navier-Stokes equations with taking into account the effect of particles on the transport processes in the carrier phase. The gas-phase turbulence is calculated with the Reynolds stress transport model with allowance for the effect of the dispersed phase. The Euler and Lagrangian descriptions give qualitatively similar results for small droplet sizes of up to d1 ≤ 30 μm; it is only for the largest particles studied in this paper (with an initial diameter of d1 = 100 μm) did the difference in the calculation results exceed 15%.

Evolution and Physical Characteristics of a Raceway Based on a Transient Eulerian Multiphase Flow Model

In industrial processes, a semi-cavity area formed by airflow wherein the particles circulate is called a “raceway”. In a blast furnace, the role of the raceway is particularly important. To understand and predict the evolution and physical characteristics of the raceway, a three-dimensional transient Eulerian multiphase flow model in a packed particle bed was developed. In the model, it was assumed that the gas and solid (particle) phases constitute an interpenetrating continuum. The gas-phase turbulence was described as a k–ε dispersed model. The gas-phase stress was considered in terms of the effective viscosity of the gas. The solid-phase constitutive relationship was expressed in terms of solid stress. It was found that the evolution process of the raceway can be divided into three stages: (1) rapid expansion, (2) slow contraction, and (3) gradual stabilization. When the blast velocity was increased from 150 m/s to 300 m/s, the surface area of the raceway increased from 0.194 m2 to 1.644 m2. The depth and height of the raceway increased considerably with velocity, while the width slightly increased.

Numerical analysis of swirling turbulent droplet-laden flow and heat transfer in a sudden pipe expansion

The effect of swirling intensity on the structure and heat transfer of a turbulent gas–droplet flow after a sudden pipe expansion has been numerically simulated. Air is used as the carrier phase, and water, ethanol, and acetone are used as the dispersed phase. The Eulerian approach is applied to simulate the dynamics and heat transfer in the dispersed phase. The gas phase is described by a system of Reynolds-averaged Navier-Stokes (RANS) equations, taking into account the effect of droplets on mean transport and turbulent characteristics in the carrier phase. Gas phase turbulence is predicted using the second-moment closure. A swirling droplet-laden flow is characterized by an increase in the number of small particles on the pipe axis due to their accumulation in the zone of flow recirculation and the action of the turbulent migration (turbophoresis) force. A rapid dispersion of fine droplets over the pipe cross-section is observed without swirling. With an increase in swirling intensity, a significant reduction in the length of the separation region occurs. The swirling of a two-phase flow with liquid droplets leads to an increase in the level of turbulence for all three types of liquid droplets investigated in this work due to their intensive evaporation. It is shown that the addition of droplets leads to a significant increase in heat transfer in comparison with a single-phase swirling flow. The greatest effect of flow swirling on heat transfer intensification in a two-phase gas-droplet flow is obtained for the droplets of ethanol and water and smallest effect is for the acetone droplets.

Changes in the Number of Membership Functions for Predicting the Gas Volume Fraction in Two-Phase Flow Using Grid Partition Clustering of the ANFIS Method.

A 2D-bubble column reactor (BCR) including gas and liquid phases is simulated, and fluid characteristics such as gas-phase volume fraction and gas-phase turbulence are extracted from the CFD simulations. A type of heuristic algorithm called adaptive network-based fuzzy inference system (ANFIS) is applied here to simulate the gas-phase volume fraction in a physical system. Indeed, the x direction, the y direction, and gas-phase turbulence are considered as the ANFIS inputs. Changes in the number of inputs as well as membership functions are evaluated and studied to obtain a high level of ANFIS intelligence. By implementing the highest ANFIS intelligence, a surface is predicted, which suggests that the gas-phase volume fraction is based on x and y directions. It provides capability to achieve the amount of gas-phase volume fraction in different points of a 2D-BCR.

Particle dynamics in a gas assisted coal combustion chamber using advanced laser diagnostics

Coal combustion is strongly influenced by the interaction of gas phase turbulence, particle dynamics and chemistry. To advance the understanding of these mutually coupled processes, experiments under well-controlled inflow and boundary conditions are needed that provide access to non-intrusive multi-parameter measurement techniques. Following this idea, in this work gas-assisted coal flames with power up to 40 kWth are investigated in an optically accessible combustion chamber including a quartz glass quarl of the swirl burner assembly. A Two-phase particle image/tracking velocimetry (PIV-PTV) technique is applied for the first time in coal combustion to measure simultaneously velocities of small and large particles. Due to the wide particle size distribution of the grinded coal small particles can be used as tracers for the gas flow while the velocity of large particles can be measured with particle tracking velocimetry (PTV) simultaneously. For this purpose Mie-scattering is imaged by a single camera. Large and small particles are separated in the post-processing based on apparent size and signal intensity of each particle individually. By measuring quasi-simultaneously laser-induced fluorescence of intermediate hydrocarbons released from coal particles during their devolatilization process, regions of intense pyrolysis are identified. Flames operated with different coal types and thermal powers in air and oxy-fuel atmospheres are compared to each other. Additionally, advantages and limits of the measurement techniques are discussed in the context of coal combustion.