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Hydrocylones offer a process intensified environment for rapid, high-throughput and relatively sharp particle classification or phase separation. One of the main performance limitations of hydrocyclone is bypassing of fines to the underflow. To address this limitation, a novel design modification of fitting thin concentric rings to the cylindro-conical section has been proposed. The Computational Fluid Dynamics (CFD) modeling based methodology has been adopted to validate the hypothesis. Predictions using Realizable k-e, Reynolds Stress Model (RSM), and Large Eddy Simulation Wall Adopting Local Eddy viscosity (LES-WALE) turbulence models has revealed that LES-WALE matched better with the experimental observations. The experimental data included overall performance parameters and detailed observations of axial and tangential velocity profiles across the hydrocyclone. The validated CFD model and the methodology was then used to predict the behavior of the proposed designs. They established that the modifications held promise in reducing the bypass with additional benefits of sharper separation curve and finer D50.

In a fuel-efficient extended formation flight of commercial airplanes, the aerodynamic benefits depend on one’s ability to surf wake vortices. This paper presents a wake vortex detection scheme bas...

This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. As a case study, Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties like the Plant Area Density and the tree heights are extracted from the Airborne Laser Scanning (ALS) 3D data, thus the forest is heterogeneous. To emphasize the impact of the local topography and surface roughness on the wind field, the wind turbines are not included in the numerical simulations. The predicted wind speeds using LES are compared to wind speed from the nacelle-mounted anemometers taken from the wind farm's turbine SCADA data, focusing on the wake-free turbines. A sufficient degree of match is observed, supporting the accuracy of the numerical simulations. The results show that inflow variables i.e., mean wind speed, shear exponent and turbulence intensity vary at each wind turbine location justifying the need for turbine-specific assessment of the wind resource in a wind farm located in forested complex terrain. The inter-turbine (between turbines in the wind farm) differences in wind resource is quantified in terms of the difference in turbine-specific structural and mechanical loads by running wind turbine mechanical simulations using the extracting the wind fields predicted by the LES. The results show that not only inter-turbine loads varying significantly in the wind farm, but the turbine loads also differ significantly if a homogeneous assumption is made for the forest. Most importantly, it was found that the homogeneous forest assumption predicted a higher turbulence intensity compared to a heterogeneous forest resulting.

Environmental flows are generally characterized by complex bed morphology and high current speeds. Such configurations favor the formation of vortex structures that strongly affect hydrody-namics and sediment transport. Large-Eddy Simulation (LES) enables investigation of the dynam-ics of the largest turbulence scales and, thanks to enhanced calculation resources, has now become applicable for simulating environmental flows. In this paper, a LES approach is developed in a CFD code (TELEMAC-3D), which was originally developed to simulate free surface flows using RANS methods. The present developments involve implementing subgrid models, boundary con-ditions and numerical schemes suitable for LES. The LES version of TELEMAC-3D was validated by comparing results on the model with experimental data for flow past a cylinder. Then, the model was applied to a test case representing flow over dunes. After validating the hydrodynamics, the model was used to assess the bottom shear stress, using both a RANS and a LES approach. Com-parison highlighted the potential contribution of LES to investigating the hydrodynamic forces acting on the bottom.

When the number of wind farms increases, the number of wind turbines placed in forested areas will also increase, this is because of the large forest areas in Sweden. When the wind turbines are placed in forested areas the fatigue loads increase drastically, so their maintenance costs increase making them less profitable. In this work clearings in forest are studied to be able to increase the electrical power generated by the wind turbines and decrease the fatigue loads to make them more profitable. The approach in this work is to use Computational Fluid Dynamics (CFD) with the Large Eddy Simulation (LES) turbulence model coupled to an aero elastic solver that solves the dynamic response of the wind turbine. Here Ryningsnas in Sweden is investigated with a homogeneous forest, the current clearing and an extended clearing. The electrical generator power was highest for the current clearing. But the fatigue loads were both higher and lower than the homogeneous forest depending on which part of the wind turbine that was investigated. The extended clearing nearly always had the lowest fatigue loads but unfortunately also the lowest electrical generator power. Further optimization of the clearings and the wind turbine locations in relation to them is needed to find the sweet spot where the fatigue loads are lower and the electrical generator power is higher.

The crossflow is the key phenomenon in turbulent flow inside rod bundles. In order to establish confidence on application of computational fluid dynamics (CFD) to simulate the crossflow in rod bundles, three Reynolds-Averaged Navier Stokes (RANS) models i.e. the realizable k-e model, the k-ω SST model and the Reynolds stress model (RSM), and the Large Eddy simulations (LES) with the Wall-Adapting Local Eddy-viscosity (WALE) model are validated based on the Particle Image Velocimetry (PIV) flow measurement experiment in a 5 × 5 rod bundle. In order to investigate effects of periodic boundary condition in the gap, the numerical results obtained with four inner subchannels are compared with that obtained with the whole 5 × 5 rod bundle. The results show that periodic boundaries in the gaps produce strong errors far downstream of the spacer grid, and therefore the full 5 × 5 rod bundle should be simulated. Furthermore, it can be concluded, that the realizable k-e model can only provide reasonable results very close to the spacer grid, while the other investigated models are in good agreement with the experimental data in the whole downstream flow in the rod bundle. The LES approach shows superiority to the RANS models.

In response to the rapid growth of energy consumption in urban cities, rooftop wind turbines (RWT) have emerged as a powerful technique for providing sustainable energy and strategically minimizing the carbon footprint of buildings. However, significant knowledge gaps exist regarding how RWT respond to the complex urban environmental flows modified by the coexisting buildings and trees. This study conducts idealized numerical experiments using an open-source large-eddy simulation model to investigate the interactions between actuator-disc turbines, street trees and buildings. We found that trees taller than the mean building height modifies the existing roof-level strong shear layer by extracting energy from the mean momentum. A significant change in the mean kinetic energy budget is induced, drastically increasing turbulence production of the flow, which leads to lower power output of RWT. Trees lower than the buildings hardly alter the mean flow field but they reduce turbulence production near the roof level. As a result, improved power output (16%) and decreased normalized power fluctuation (5.2%) are observed compared to the control case without trees. The results highlight that it is important to assess effects of different street tree morphologies on the performance of RWT in their design and implementation processes.

Three square plan shaped tall buildings are arranged at the vertices of an equilateral triangle of varying size. The octagonal plan shaped principal building is also positioned randomly such that the position of the principal building is never overlapped with the square plan shaped buildings. The effect of interference of the square buildings on the wind-induced responses of the principal building is thoroughly measured by computational fluid dynamics using large eddy simulation turbulence model. Metamodels for drag and lift coefficients of the principal building in the interfering conditions are established. Interference factors for the pressure coefficients at different faces of the principal building is calculated and cast into efficient mathematical models. Pareto optimality for the maximum interference criterion is obtained. The optimal positions of the principal and interfering buildings for maximum interference are plotted. Selected cases from the Pareto optima are analysed to obtain the transient wind effects for those interference cases. The peak and root-mean-square pressure coefficients of these interfering conditions are compared with that of the isolated condition. The difference between the power spectra of the isolated and interfering conditions are also depicted.

In this research work, numerical simulations were conducted to examine the effect of baffles on flow activity in a stirred tank bioreactor fitted with two six-blade Rushton turbines, at Reynolds number (Re) = 40,000. The lattice Boltzmann method (LBM) was used as a numerical technique to discretize the flow domain. Large Eddy Simulation (LES) method was applied for turbulence modeling. The small-scale turbulent structures were resolved by using the conventional Smagorinsky subgrid-scale (SGS) model. The action of the reactor components (i.e., cylindrical wall, baffles, shaft, and Rushton turbines) on the flow field were obtained by using the immersed boundary (IB) method. The simulations were performed for three different geometries of stirred tank reactors, differentiated based on the impeller clearance. The study shows the impact of baffles on all the three employed geometries. For each of the geometries, simulations were performed with and without the baffles. A uniform, cubic computational grid of $$150^{3}$$ lattice nodes was constructed for the simulation. The computer code was developed for performing the simulation. The complexity of the geometry and different physical processes involved make the simulation more challenging and time-consuming. Thus, to get the results in an adequate time, the computer code was parallelized to run on a multicore Graphical Processing Unit (GPU) platform. The results are demonstrated in the form of phase average flow velocities as well as in turbulent properties, with validation from the available experimental data reported in the literature.

The coupling of mesoscale and microscale simulation methods represents a significant challenge of wind energy research. Conventional approaches used to address this problem often combine Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) equation elements, which has two significant disadvantages. First, Wyngaard’s Terra Incognita challenge cannot be addressed because there is no reflection of the amount of flow resolution in such equations. Second, (because of the lack of theoretical guidance) there is a relatively large number of influence factors that can affect such simulations. The study of implications of such options continues for decades, and (following the same approach) it is likely that this will go on for a long time. Substantial progress in this regard requires a novel simulation concept that provides strong theoretical guideline via solving Wyngaard’s Terra Incognita challenge. The paper shows that the latter can be accomplished by applying new simulation concepts developed for engineering flows to the problem considered. Essential advantages compared to existing mesoscale to microscale couplings are described.

Studying of gas deflagration is important for a safety purpose in gas industry. A modelling approach based on large eddy simulation (LES) technique for modelling turbulent flow combined with the species mass fraction equations for modelling combustion is used. Different flame acceleration mechanisms, hydrodynamic & thermo-diffusive instabilities, turbulence, and their interaction in addition to flame quenching model are used to model chemical reaction rate. An algebraic model for flame-generated turbulence is incorporated. The model is tested against large scale open atmosphere hydrogen-air experiment. The flame propagation radius and the overpressures are qualitatively compared well with experiment and the state-of-the-art simulations.

The scour and flow field patterns with accumulation of debris around bridge piers are completely different due to the reduction of flow area and the increase in depth average velocity. Accordingly, the risks of bridge piers failure are increased due to the evolution of scour depth. This paper aims to analyse the effect of rectangular debris accumulation around single and dual cylindrical piers on river bed morphology in three dimensional simulation under clear water conditions. An experimental and numerical investigations were conducted to implement computational fluid dynamic (CFD) models that reveal the influence debris accumulation on the characteristics of scour hole and the increase in depth average velocity. The large eddy simulation model (LES) was coupled with three morphological models (Meyer-Peter, and Muller; Van Rijn model, and Nielsen) to assess the performance of simulation and produce efficient CFD morphological models. It was found that coupling of LES turbulence model and Nielsen morphological model yield best agreement with measured scour depth and scour hole characteristics according to the indication of statistical analysis, while the under prediction was noted for other models. As compared with temporal scour development and scour hole morphology of experiments of this study, good agreement was achieved for implemented CFD morphological models for single pier and dual piers with debris accumulation for (6.2 and 16.6% obstructed area to the flow area) respectively. According to the indications of this study, the increase in depth average velocity due to debris accumulation can be ranged from 26 to 44% and from 17 to 41% during the first ten minutes of accumulation around single and dual piers respectively. More consideration should be taken to mitigate bridge piers from debris accumulation.

Hazardous materials are stored in the large tanks in the industry, e.g., a single LNG tank can be as large as 230,000 m3. Therefore, a catastrophic tank failure can cause a disastrous incident. A secondary containment, such as a bund, is required by regulations to control the risk; however, the released liquid may overtop from the bund due to its high kinetic energy converted from potential energy. Computational Fluid Dynamic (CFD) is a proper tool for the bund overtopping study, but there has been significant discrepancy among previous CFD studies. This work developed 2D CFD models of bund overtopping using the axisymmetric approach. A screening study on several turbulence models was performed, and RNG k-e Standard Wall Functions (RNG k-e SWF1) and Large Eddy Simulation WALE (LES WALE) were selected for a detailed comparison in terms of overtopping fraction and flow dynamic behaviour. Both RNG k-e and LES models were systematically validated against experimental data, and the results indicate that LES model is slightly better than RNG k-e model, and both models are acceptable based on the criteria of statistical performance measures.

Modern buildings and structures are commonly equipped with fire safety detection and protection systems. Owing to the complexity in building architectures, performance-based fire engineering designs are often applied to achieve safety compliance criteria in stipulated fire events. With the uprising popularity of computer simulation fire predictive models benefited by the rapid improvement in computing speed and modelling techniques, the use of computational fluid dynamics (CFD) based fire field models has become an integrated component in fire tenability and assessment studies. This article delivers a comprehensive review on the history, past developments, and current state-of-the-art of CFD models for enclosure fires, as well as providing an in-depth review on the advancement in other sub-modelling components including turbulence, combustion, radiation, and soot models. Additionally, two types of multiphase modelling approaches involving solid-gas and liquid-gas phase models are reviewed. As for the preceding, the consideration of the solid phase combustibles is generally achieved via pyrolysis modelling under the context of CFD. Recent advancements in CFD-based pyrolysis studies are extensively discussed, including the consideration of porous media, charring layer formation, and kinetics search algorithms to describe the solid decomposition and charring processes. Meanwhile, fire suppression models involving the discrete phase model (DPM) approach are reviewed. This includes previous developments in simulation methods of water droplets, coupling approaches with the fire dynamics in the large eddy simulation (LES) framework. Finally, a future perspective regarding the need to develop a melting/dripping sub-model for building materials is discussed, whose reaction kinetics can be supported by molecular dynamics (MD).

In a diesel-like condition, kerosene behaves differently from that in the aircraft engine. In order to understand the process, large eddy simulations are conducted to predict the high injection pre...

The design and financing of commercial‐scale floating offshore wind projects require a better understanding of how power generation differs between newer floating turbines and well‐established fixed‐bottom turbines. In floating turbines, platform mobility causes additional rotor motion that can change the time‐averaged power generation. In this work, OpenFAST simulations examine the power generated by the National Renewable Energy Laboratory's 5‐MW reference turbine mounted on the OC3‐UMaine spar and OC4‐DeepCWind semisubmersible floating platforms, subjected to extreme irregular waves and below‐rated turbulent inflow wind from large‐eddy simulations of a neutral atmospheric boundary layer. For these below‐rated conditions, average power generation in floating turbines is most affected by two types of turbine displacements: an average rotor pitch angle that reduces power, caused by platform pitch; and rotor motion upwind‐downwind that increases power, caused by platform surge and pitch. The relative balance between these two effects determines whether a floating platform causes power gains or losses compared to a fixed‐bottom turbine; for example, the spar creates modest (3.1%–4.5%) power gains, whereas the semisubmersible creates insignificant (0.1%–0.2%) power gains for the simulated conditions. Furthermore, platform surge and pitch motions must be analyzed concurrently to fully capture power generation in floating turbines, which is not yet universal practice. Finally, a simple analytical model for predicting average power in floating turbines under below‐rated wind speeds is proposed, incorporating effects from both the time‐averaged pitch displacement and the dynamic upwind‐downwind displacements.

Fire events in nuclear power plants represent a significant potential hazard and are an important contributor to the overall operational risks of these facilities. Consequently, a detailed understanding of fire and smoke propagation behaviour in such applications is required for fire performance-based engineering and risk assessment. This paper presents computational fluid dynamics modelling of a postulated fire scenario and occupant evacuation in a typical multi compartment nuclear building. The NIST Fire Dynamic Simulator (FDS) was used to model fire and smoke propagation by adopting large eddy simulation turbulence modelling approach. FDS simulation benchmarking was first performed against available experimental data of a two-storey compartment. Following this, a study was conducted to understand the smoke propagation, distribution of temperature, toxic gas concentrations, and smoke optical density inside a typical multi-compartment nuclear building. The effect of ventilation on the fire and smoke spread was also investigated. Human evacuation modelling was conducted to determine the required evacuation time and toxic gas dose for each occupant. The FDS predicted smoke parameters, including smoke optical density and toxic gas concentrations, were used as inputs to the evacuation modelling. The results suggest that ventilation flows decrease the smoke optical density due to smoke dilution and thereby result in a shorter time for the occupants to evacuate.

Owing to the well-established Eulerian-Lagrangian framework on mixture fluids, computational fluid dynamics coupled with discrete element model (CFD-DEM) is an effective while appropriate tool to predict the complex interactive fire behaviours associate with suppression effects. Although suppression behaviours between hydrocarbon-fuelled fire and water-based suppression agents were extensively studied both numerically and experimentally, lack of numerical studies was conducted on fires involving water-reactive chemicals (i.e., Na, Li, and LiH), where extinguishment is barely performed by water-based active suppression system, as violent and explosive decomposition occurred between water and reactive fuel. In this research, a numerical investigation has been conducted on expandable graphite (EG) application for water-reactive fire suppression. Based on the discrete phase model (DPM) framework, a novel EG particle model is proposed to characterise the particle expansion that couples with superior thermal properties and chemical stability. A numerical assessment on large eddy simulation (LES) has been performed to study the temporal fire behaviours and the suppression effect of EG against the flame plume in various subgrid-scale (SGS) models. Four SGS models were adopted, which were namely Smagorinsky-Lilly, WALE, dynamic kinetic energy, and dynamic Smagorinsky-Lilly. As a result, the WALE SGS model was observed to be in a better agreement compared with the experimental data owing to its significant enhancement in flow diffusivity modelling. The WALE SGS model has achieved a more accurate temperature prediction and finer resolved turbulence compared with other SGS models.

Three-dimensional computational fluid dynamic (CFD) methods were used to simulate a cough jet that contains droplets. The turbulent cough flow is modelled using large-eddy simulation with a dynamic structure model. An Eulerian–Lagrangian approach was adopted to model the two-phase flows. Droplet breakup, evaporation, dispersion and drag forces were considered in the model. Two different inlet velocity profiles, which are based on constant mouth opening area and variable mouth opening area, were considered in the CFD model. The numerical model was validated by comparing with the available experimental measurements. The results show that the use of the fixed mouth opening area in the geometric model shows the inlet velocity profile of the ‘variable area’ matched better with the experimental data than with the ‘constant area’ inlet velocity profile. Droplet dynamics were analysed with a focus on the droplet penetration and droplet distribution in space during the whole coughing process. The droplet penetration shows two-stage profiles, both of which can be described by logarithmic functions. This is consistent with the analytical results of the simplified drag model. The droplets generated during the mouth opening or closing periods have a higher velocity and longer droplet penetration. With a higher room temperature, the droplet penetration is shorter.

Different drag laws and turbulence models were compared to evaluate gas distribution and fluid flow velocities in a Rheinstahl–Heraeus (RH) reactor. The discrete phase model was adopted to track injected gas bubbles, and the volume of fluid model was applied to describe a more actual free surface. The prediction accuracy of the numerical model was evaluated by the measured flow velocity in an air-water model and the measured circulation flow rate of molten steel in a real RH system. Results indicate that Morsi’s drag law predicts more accurate local velocity compared with Schiller’s and Harmathy’s laws. The influence of turbulent dispersion on the injected gas bubbles is non-negligible for predicting the gas–liquid flow in a RH reactor. In addition, although the large eddy simulation (LES) approach predicts more actual free surface fluctuation, the realizable k-e model shows better agreement with the measured local velocity in the furnace.

The present research work introduces a novel combustion model formulation based on the flamelet concept suitable to investigate characteristic flow conditions in rocket engine thrust chambers. The ...

Modeling flow in vegetative fuel beds is a key component in any detailed physics-based tool for simulating wildland fire dynamics. Current approaches for drag modeling, particularly those employed in multiphase computational fluid dynamics (CFD) models, tend to take a relatively simple form and have been applied to a wide range of fuel structures. The suitability of these approaches has not been rigorously tested for conditions which may be encountered in a wildland fire context. Here, we focus on beds of Pinus rigida needle litter and undertake a two-part study to quantify the drag and evaluate the capabilities of a multiphase large eddy simulation CFD model, the NIST Fire Dynamics Simulator. In the first part, bed drag was measured in a wind tunnel under a range of conditions. The results were fit to a Forchheimer model, and the bed permeability was quantified. A traditional approach employed in the multiphase formulation was compared to the parameterized Forchheimer equation and was found to over-predict the drag by a factor of 1.2–2.5. In the second part, the development of a velocity profile above and within a discrete fuel layer was measured. Using the Forchheimer equation obtained in the first part of the study, the CFD model was able to replicate a qualitatively consistent velocity profile development. Within the fuel bed, the model appeared to under-predict the velocity magnitudes, which may be the result of unresolved pore-scale flow dynamics.

The chemical absorption reaction of CO2 in a circular bubble column reactor was simulated with an Euler/Lagrange CFD method and results were compared with data from a laboratory scale bubble column. The experimental data comprises gas holdup and bubble size distributions obtained with ultrafast X-ray tomography and hydroxide ion conversion obtained with a wire-mesh sensor. Large Eddy Simulation (LES) is used for calculating the fluid flow and modelling the turbulence in the continuous phase, considering the effect of sub-grid-scale (SGS) turbulence on bubble motion, and also SGS turbulence modification by bubbles. Lagrangian bubble tracking is conducted considering all relevant forces, bubble oscillation via stochastic generation of eccentricity and motion angle and consequently non-steady mass transfer via a dynamic Sherwood number. The comparison of experimental and simulation results shows very good agreement for the given data.

The study considers the operation of an unmanned aerial vehicle in hovering mode over a flat landing platform. As a propulsion system, impellers are used, which are a system of a propeller rotating inside an air ring. The air ring is a body of revolution with an aerodynamic profile in cross section. The paper investigates the effect of unsteady interaction of vortex flows with the design of an aircraft by two alternative numerical methods, one of which is vortex-resolving. Numerical calculations are performed using the traditional turbulence modeling approach based on the averaged Navier–Stokes equations (RANS, Reynolds Averaged Navier–Stokes), where the turbulence is assumed to be isotropic, and the eddy-resolving Large Eddy Simulation method. The main feature of the latter is as follows: a turbulent flow is represented as the superposition of the motion of large-scale and small-scale turbulences. After discretizing the flow using a filtering operation, large-scale turbulence, which depends directly on the boundary conditions, is solved from the full Navier–Stokes equations. Small-scale turbulence has isotropic properties and is modeled similarly to semi-empirical RANS methods. The technique allows one to accurately calculate the vortex structure of any flow directly from the equations of motion using relatively low computing power, in contrast to the RANS models, which simulate the flow using a simplified mathematical model and can provide satisfactory accuracy only for a limited range of problems. The results indicate that eddy-resolving methods for modeling turbulence, in contrast to the methods based on averaged Navier–Stokes equations, make it possible to estimate the effect of aperiodic perturbations on the design of aircraft arising from the interaction of large eddies with each other and with the underlying surface. Such phenomena are accompanied by side impacts of a shock nature on the impeller rings, which can lead to loss of aircraft stability. Under conditions of a small propeller step, the use of an air ring results in a significant increase in the air flow passing through the rotor rotation loop, an increase in thrust due to the creation of flow circulation around the airfoil of the ring, and a decrease in the power on the propeller. Even though the effect of using an air ring disappears with a large incoming flow, this design is considered very promising for use on aircraft with vertical takeoff and landing. This mode of operation is the most energy-consuming and determines the greatest requirements for the lifting force of the power plant. The results of this work have demonstrated that numerical methods based on averaging the Navier–Stokes equations and the use of classical turbulence models of the k–ω or k–ε type, which are widely used in numerical modeling of propellers, in takeoff and landing modes fail to detect aperiodic unsteady phenomena associated with the interaction of large eddies, in contrast to eddy-resolving methods for modeling turbulence.

Accurate parameterization of wind farms’ equivalent roughness heights is critical to meso-scale climate simulations as well as power predictions of wind turbines. A notable inadequacy of the existing models is that the results sensitively depend on s x / s y , where s x and s y are the dimensionless streamwise and spanwise spacing of the turbines. To understand the issue, we conduct large-eddy simulations (LESs) for three types of quasi-infinite wind farms with moderate, large, and small s x / s y . We find that the wind speed at the rotor is different from the horizontally averaged wind speed at the hub height, and this is particularly true for wind farms with small s x / s y . This flow inhomogeneity at the hub height plays an important role in determining wind farms’ equivalent roughness height but is often neglected in the existing models. Accounting for the flow inhomogeneity at the hub height, we propose a new coupled top-down/bottom-up model for the equivalent roughness heights of wind farms. Our model is compared with the existing models and our LESs. The results show that the proposed model is able to predict the equivalent roughness height of all types of wind farms irrespective of s x / s y ’s value.

Despite many advances in numerical simulation of stable boundary layers (SBL), most of the models developed are complex and computationally expensive. A computational fluid dynamics (CFD) strategy is proposed that combines very large eddy simulation (VLES) with a reductionist inflow turbulence generator and wall modeling aimed at affordable and practical simulation of SBL. Unlike the standard LES requiring the filter width to be of the scale of grid size, the filter width in VLES can be set at a value between the grid size and the large characteristic length scales of the flow. This strategy, along with the application of wall treatments, results in the significant reduction of computational costs. Moreover, the reductionist approach of the inflow turbulence generator minimizes the number of required input parameters to the model, which makes the model suitable for practical applications. A series of sensitivity studies are conducted to refine the numerical parameters including the grid resolution, filter width, and the inflow turbulence generator variables controlling the length and time scales of the eddies generated at the inlet. The performance of the model is successfully evaluated against wind-tunnel measurements for mean velocity, mean temperature, and turbulence profiles for four different thermal stability levels ranging from weak to strong stability. The spectral analysis of the model for velocity components, temperature, momentum, and heat fluxes showed that the model is capable of successfully resolving the energy cascade for almost two orders of magnitude of wave numbers and partially matching the well-known log-log slopes for the inertial subrange.

Accurate prediction of film cooling flow is a necessity in the design of high-pressure turbine components given the temperature of hot gas exceeds the melting point of the component material; temperatures that are necessary to achieve high thermal efficiency. Nowadays, Computational Fluid Dynamics (CFD) methods are becoming increasingly popular to predict film cooling flows. When compared to large eddy simulation (LES) and direct numerical simulation (DNS), the Reynolds Averaged Navier-Stokes (RANS) method is most frequently employed due to its much lower computational cost, though it struggles to accurately solve the highly three-dimensional and anisotropic cooling flows. However, few publications have focused on the mesh sensitivity problem of RANS simulations. And yet mesh generation is fundamental to CFD simulations and directly affects the accuracy of the calculated solution. Two typical film cooling hole geometries, namely cylindrical and fan-shaped, are utilised to investigate the mesh sensitivity of RANS simulations with low, medium, and high blowing ratios. Seven mesh sizes ranging from super coarse to super fine (4000 times larger) are employed for analysis. In general, the comparisons show that the computational results are close to the experimentally observed film features and averaged effectiveness, while also demonstrating that mesh convergence becomes challenging for RANS modelling, especially for the fan-shaped hole.

The study presents an experimental and numerical investigation to determine the role of adiabatic lame temperature on controlling the operability of a micromixer-based gas turbine model combustor holding premixed CH4/CO2/O2 non-swirl jet flame for carbon capture. The experimental test rig consists of a mixing pipe and multihole/micromixer-like burner of 61 tubes. The numerical aspect of the study is achieved using the computational fluid dynamic (CFD) approach. Models of the ansys Fluent are used to solve elliptical governing equations involved in the combustion system. Since flames under consideration are jet premixed releasing into a quiescent atmosphere, the partially premixed combustion of species model is used. Large eddy simulation (LES) is used as the turbulence model while radiative transfer equation (RTE) is solved using discrete ordinate (DO). A good agreement between experimental and numerical results is achieved. Results indicated that adiabatic flame temperature (Tad) controls the flame macrostructure, oxygen fraction (OF) controls the peak of the product formation rate rather than Tad, and positions of OH radical reaffirmed that Tad controls the flame macrostructure and increasing the OF leads to reaction rate dominancy and, hence, increases the Damkohler number.

In a large wind farm, the wakes of upstream and downstream wind turbines can interfere with each other, affecting the overall power output of the wind farm. To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence, this work proposes some improvements to the actuator line-large-eddy simulation (AL-LES) method. Based on the dynamic k-equation large-eddy simulation (LES), this method uses a precursor method to generate atmospheric inflow turbulence, models the tower and nacelle wakes, and improves the body force projection method based on an anisotropic Gaussian distribution function. For these three improvements, three wind tunnel experiments are used to validate the numerical accuracy of this method. The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results. After modeling the tower and nacelle wakes, the wake velocity distribution is consistent with the experimental result. The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s, which is about 6% different from the experimental value and improves the prediction accuracy of the tip vortex radial movement. The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.

High-fidelity simulations of the unsteady flow and radiated noise of an unmanned aerial vehicle’s propeller are presented herein. The aim of this study is to capture the broad-band noise associated...

Numerical studies on internal fire whirls (IFW) generated in a vertical shaft model with a single corner gap were reported in this paper. The generation of IFW, burning rate of fuel and temperature were studied experimentally first. Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results. Typical transient flame shape was studied and then simulated numerically by using temperature. The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results. The predicted results were validated by comparing with experimental data, which demonstrated that an IFW can be simulated by Computational Fluid Dynamics. Numerical results for flame surface, temperature, and flame length agreed well with the experimental results. The IFW flame region and intermittent region were longer than those for an ordinary pool fire. The modified empirical formula for centerline temperature was derived. Variations of vertical and tangential velocity in axial and radial directions were also shown. The vortex core radius was found to be determined by the fuel bed size. Velocity field was not measured extensively due to resources limitation. Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate, air flow and pressure gradient.

Turbulent particle flow is modeled using CFD to predict the erosion rate in the pipe. Anisotropic turbulence of the Reynolds Stress Model (RSM) is used in modeling turbulent fluid (natural gas) and...

Prediction of turbulent flow is required for design and assessment of clarifier systems that have been implemented throughout history to treat water in the urban water cycle through physical clarification. Yet, turbulent flow modeling is a relatively new tool that has not existed until the last half-century and can be, and often is, a tenuous component in a computational fluid dynamics simulation of unit operations and processes. Common Reynolds-averaged Navier–Stokes equation (RANS) approaches can be inadequate to obtain consistent and accurate flow solutions. In contrast, this study presents an application of large-eddy simulations (LES) for a clarification system with a high-order spectral element method employing 48 million degrees of freedom. Turbulent and unsteady flow characteristics are investigated, and statistics are examined for such a system. Simulation results are compared with laser Doppler anemometry measurements for mean flow velocity, turbulence kinetic energy, and Reynolds shear stress. LES results agree well with measurements, and the differences between LES and measurements are generally less than the reported measurement error. LES results capture the transition behavior from a jet-like flow at the near-inlet region to an open-channel flow at the downstream end of the system. Furthermore, LES results reveal that the widely adopted log-law of a classical turbulent boundary layer is not established in the system even at the most downstream location. Preliminary examination of commonly used RANS models identifies the challenges in application of RANS to such systems. The results from this study provide a benchmark for turbulence modeling of common water clarification systems.

The formation of explosive gas zones (EGZs) from flammable vapors, gases, or dust pose safety hazards to many industries. In many cases, explosions may occur in confined areas with obstacles in the path of flame expansion. By studying the effects of obstacle shape, turbulence model, and spark location on flame propagation and turbulence, a more complete understanding of the flame and fluid dynamics interaction has been achieved. Reynolds Averaged Navier-Stokes (RANS) models were tested to determine if these simplified turbulence models could capture the flame dynamics and propagation velocities using fewer computational resources compared to the higher fidelity Large Eddy Simulation (LES) turbulence model. Results showed that square obstacles caused faster flame propagation compared to hexagons and circles. The square had an average flame propagation velocity 26 % faster than the circle, and the hexagon was 16 % faster than the circle using a k-ω model. Modeling results indicate variation of spark location by as small as 10 % of the obstacle diameter can result in a difference of the flame propagation. Findings on turbulence model accuracy and computational time along with shape comparison can be applied in future modeling of large systems, providing crucial information for safety planning and explosion prevention.

The most common type of cardiac arrhythmia is atrial fibrillation (AF), which is characterised by irregular and ineffective atrial contraction. This behaviour results into the formation of thrombi, mainly in the left atrial appendage (LAA), responsible for thromboembolic events. Very different approaches are considered as therapy for AF patients. Therefore, it is necessary to yield insight into the flow physics of thrombi formation to determine which is the most appropriate strategy in each case. Computational Fluid Dynamics (CFD) has proven successful in getting a better understanding of the thrombosis phenomenon, but it still requires validation by means of accurate flow field in vivo atrial measurements. As an alternative, in this paper it is proposed an in vitro flow validation, consisting in an idealised model that captures the main flow features observed in the human LA which, once combined with Particle Image Velocimetry (PIV) measurements, provides readily accessible, easy to emulate, detailed velocity fields. These results have been used to validate our laminar and Large Eddy Simulation (LES) simulations. Besides, we have run a parametric study of different boundary conditions sets previously employed in the literature. These data can be used as a benchmark for further development of LA CFD models.

In the present study, we report the first large eddy simulation (LES) study of the Cambridge CCB2 coal flames, one of the target flames in the Workshop on Measurement and Simulation of Coal and Biomass Conversion, with an extended flamelet progress variable (FPV) model. The extended FPV model is based on two mixture fractions considering the volatiles and char off-gases. The normalized total enthalpy is used for the interphase heat transfer modelling. Turbulence-chemistry interaction is treated with an assumed probability density function approach. The results show that the present LES can generally capture the flow field and particle distribution, while there are considerable deviations in the OH prediction due to the boundary treatment of using a mixture of volatiles and carrier gas to replace the methane-containing mixtures in the primary and pilot flow. It indicates that for such gas-assisted coal flames, the pilot fuel stream needs to be rigorously considered in the flamelet tabulation that could be resolved by extending the two-mixture-fraction model into a three-mixture-fraction model. The instantaneous Lagrangian particles histories show that the increasing of coal load has a negligible effect on devolatilization, but delays the char conversion.

A deep neural network (DNN) based large eddy simulation (LES) model for progress variable dissipation rate in turbulent premixed flames is presented. The DNN model is trained using filtered data from direct numerical simulations (DNS) of statistically planar turbulent premixed flames with n-heptane as fuel. Training data was comprised of flames with varying turbulence levels leading to a range of Karlovitz numbers. Through a-priori tests the DNN model is shown to predict the subfilter contribution to progress variable dissipation rate accurately over a range of filter widths and for all Karlovitz numbers examined in this study. Superior performance of the DNN model relative to an established physics-based model is also demonstrated. Additionally, transferability of the DNN model is highlighted by a-priori evaluation of the model using filtered DNS data from multiple cases with different Karlovitz numbers and fuel species than those that were used for training the model.

A moving-domain computational fluid dynamics (CFD) solver is designed by deploying the Arbitrary Lagrangian Eulerian Variational Multi-scale Formulation (ALE-VMS) enhanced with weak enforcement of essential boundary conditions (weak BC) into the open-source finite element automation software FEniCS. The mathematical formulation of ALE-VMS, which is working as a Large Eddy Simulation (LES) model for turbulent flows, and weak BC, which is acting as a wall model, are presented with the implementation details in FEniCS. To validate the CFD solver, simulations of flow past a stationary sphere are performed with moving meshes first. Refinement study shows the results quickly converge to the reference results with fixed grids. Then, the solver is utilized to simulate a tidal turbine rotor with uniform and turbulent inflow conditions. Good agreement is achieved between the computational results and experimental measurements in terms of thrust and power coefficients for the uniform inflow case. The effect of the inflow turbulence intensity on the tidal turbine performance is quantified.

In this paper, A computational study is performed in this paper to investigate the influence of natural surfactant in a 90° bend on the flow properties of heavy Crude Oil. In ANSYS Fluent, computational fluid dynamics (CFD) code is used to investigate the flow phenomena in horizontal pipe bends. A suitable approach for transporting heavy oil through pipes is blending of surfactant with heavy crude oil for 'core annular flow' (CAF). This analysis analyzes the core annular flow numerically using the Large Eddy Simulation (LES). The prime objective of present work is to achieve understanding of the actions of high-sulphur crude oil flow across turbulent core annular flow in transporting pipes line. High-sulphur crude oil blended and additives are the two-phases in horizontal pipe.

The processes of sediment transport in high flow intensity are studied through numerical simulation using a coupled CFD (computational fluid dynamics)-DPM (discrete particle method) model with a fo...

Purpose This study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime. Design/methodology/approach The CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method. Findings By comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs. Research limitations/implications The proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement. Practical implications This CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species. Originality/value The incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.

Different methods are used at Corteva® Agriscience to improve our understanding of mixing in large-scale mechanically agitated fermentors. These include (a) use of classical empirical correlations, (b) use of small-scale models, and (c) computational fluid dynamics (CFD). Each of these approaches has its own inherent strengths and limitations. Classic empirical or semi-empirical correlations can provide insights into mass transfer, blending, shear, and other important factors but are dependent on the geometry and condition used to develop the correlations. Laboratory-scale modelling can be very useful to study mixing and model the effect of heterogeneity on the culture, but success is highly dependent on the methodology applied. CFD provides an effective means to accelerate the exploration of alternative design strategies through physics-based computer simulations that may not be adequately described by existing knowledge or correlations. However, considerable time and effort is needed to build and validate these models. In this paper, we review the various approaches used at Corteva Agriscience to deepen our understanding of mixing in large-scale fermentation processes.

In this study, the flamelet/progress-variable (FPV) approach was applied to a large eddy simulation of a pulverized coal jet flame. The FPV approach considers the characteristics of the pulverized coal flame, e.g., non-adiabatic system and several types of fuel streams, via additional representative variables. First, the applicability of the FPV approach to a turbulent flame with pulverized coals was confirmed through a comparison of the numerical solutions and experimental data. In this study, the pure pilot case was also investigated to clarify the effects of pulverized coals on the flame. The flame structure changes significantly upon the injection of pulverized coals, and the flame index suggests the coexistence of premixed and diffusion combustion modes even in the downstream region. In particular, the combustion mode fluctuates with time in the middle region of the flame. The fuel gas released from the pulverized coals should increase in this region; therefore, the release and combustion behavior of the volatile matter must be involved in the combustion mode variation. The evaluation of the combustion modes of fuel gas in the coal flame is useful for the design and optimization of pulverized coal combustors with next-generation technologies.

Multi-cycle large-eddy simulations (LES) are performed to investigate combustion cycle-to-cycle variability (CCV) in a gasoline spark ignited optical access engine operating under homogeneous stoichiometric conditions. Combustion is addressed with the Thickened Flame Model (TFM) and finite rate chemistry is accounted for through a reduced oxidation reaction mechanism. In view of the fact that computational costs of LES engine simulations are still very high today, this work investigates the use of adaptive mesh refinement (AMR) in the flame zone in conjunction with the artificial flame thickening applied by the TFM model. The paper discusses how the resulting coupled TFM-AMR combustion model allows good resolution of the flame, maintaining accuracy at acceptable costs. First, the details of the coupled model are presented and the effects of the parameters are explored, highlighting their impact on the combustion prediction. Then, computational fluid dynamics (CFD) simulation results are validated against experimental data collected in a low-speed low-load engine point, by comparing 20 LES cycles and 100 measured cycles, for mass fraction burned, combustion phasing, flame images and CCV indices. Lastly, a detailed investigation on the fastest and slowest numerical cycles is presented, analyzing instantaneous flame structures, ignition behaviors, propagation speeds, and probability density function (PDF) of the instantaneous velocity fluctuation around the spark region. The results show that combustion variability is highly correlated to the resolved velocity field and the resolved turbulence intensity, which is found to be the main cause of CCV and affects the early flame kernel growth. This work is an early attempt to use TFM-AMR combustion model for LES simulations of internal combustion engines.

In this work, a deep neural network is presented which is trained on flamelet/progress variable (FPV) tables and validated in a combustion large eddy simulation (LES) of the Sydney/Sandia flame wit...

Urban wind power shows a great potential and plays a significant role for a sustainable city. As a fundamental issue, the interaction between the wind-turbine wake and a building array is studied here via large eddy simulation. The standard actuator disc model is used to model the wind turbine, and 16 cube-shaped buildings are used to represent the urban district. It is found that due to the blocking effect of the downstream urban district, a high-pressure region is formed upstream, which dramatically changes the trajectory of the wind-turbine wake and results in a fast wake recovery. In addition, the wind-turbine wake suppresses the vertical momentum flux and thereby reduces the wind speed in the streamwise streets. At the top region of the urban block below the trajectory of the turbine wake, the turbulence intensity substantially increases at the entrance region of the building array, while the overall turbulence intensity is considerably reduced at the bottom of the block.

Subchannel code is one of the effective simulation tools for thermal-hydraulic analysis in nuclear reactor core. In order to reduce the computational cost and improve the calculation efficiency, empirical correlation of turbulent mixing coefficient is employed to calculate the lateral mixing velocity between adjacent subchannels. However, correlations utilized currently are often fitted from data achieved in central channel of fuel assembly, which would simply neglect the wall effects. In this paper, the CFD approach based on spectral element method is employed to predict turbulent mixing phenomena through gaps in 3 × 3 bare tight lattice rod bundle and investigate the flow pulsation through gaps in different positions. Re = 5000,10000,20500 and P/D = 1.03 and 1.06 have been covered in the simulation cases. With a well verified mesh, lateral velocities at gap center between corner channel and wall channel (W–Co), wall channel and wall channel (W–W), wall channel and center channel (W–C) as well as center channel and center channel (C–C) are collected and compared with each other. The obvious turbulent mixing distributions are presented in the different channels of rod bundle. The peak frequency values at W–Co channel could have about 40%–50% reduction comparing with the C–C channel value and the turbulent mixing coefficient β could decrease around 25%. corrections for β should be performed in subchannel code at wall channel and corner channel for a reasonable prediction result. A preliminary analysis on fluctuation at channel gap has also performed. Eddy cascade should be considered carefully in detailed analysis for fluctuating in rod bundle.

Aim The first dedicated neonatal continuous positive airway pressure (CPAP) device using variable flow was the Infant Flow. The system was pressure stable with a low resistance to breathing. The aim of this study was to describe the flow and function of the Infant Flow geometry using simulated breathing and computational fluid dynamics. Method The original Infant Flow geometry was used with simulated term infant breathing at three levels of CPAP. The large eddy simulation methodology was applied in combination with the WALE sub-grid scale model. Results The simulation fully resolved the flow phenomena in the Infant Flow geometry. The main flow feature during inspiration was support by gas entrainment and mixing. During expiration, the jet deflected towards the outlet with unstable impingement of the jet at the opposing edge. Conclusion The proposed mechanism has previously been based on theoretical reasoning, and our results present the first detailed description of the Infant Flow. The pressure stability was based on a jet supporting inspiration by gas entrainment and then being deflected during exhalation. This confirmed previously assumed principles of function and flows within the geometry and provided a base for further developments.

The co-firing of coal and biomass in fluidized beds under oxy-fuel conditions is an important approach with significant industrial prospects, for both carbon dioxide capture and disposal of biomass waste produced by agriculture and forestry. Numerical simulation is essential in the design of structural and operational parameters for oxy-fuel fluidized beds, as is experimentation. Following our previous research on the oxy-fuel combustion of coal in a fluidized bed (Powder Technol. 2019, 349, 40–51), this paper develops 3D Eulerian-Lagrangian simulations for the co-firing of coal and biomass in an oxy-fuel fluidized bed based on the multiphase particle-in-cell (MP-PIC) scheme. The particle field is described by the discrete particle method (DPM) and the gas field is calculated by large eddy simulation (LES). Different models are used for the reaction of coal and biomass, including devolatilization, combustion of char and volatiles, and the production of pollutants. The numerical simulation was verified by combustion experiments carried out in a micro-fluidized bed reactor with an online mass spectrometer. Based on the simulations, the effects of biomass mass ratio, combustion atmosphere, oxygen concentration, and combustion temperature on the co-firing of coal and biomass in an oxy-fuel fluidized bed are discussed.