Rigorous Computational Fluid Dynamics Research Articles

Numerical investigation of the erosion reduction in elbows using separate and helical inner ring

This study presents a comprehensive numerical investigation of erosion in bends equipped with inner rings as a novel geometric concept for erosion control. The research aims to assess the effectiveness of these innovative configurations in reducing erosion through rigorous computational fluid dynamics (CFD) simulations. Numerical modeling for the gas-solid two-phase flow has been carried out based on one-way coupling using an Eulerian-Lagrangian approach. The CFD model employed in this work incorporates the RNG k-ε turbulence model for flow solution, the Oka model for simulating surface erosion, and the Grant and Tabakoff model to account for particle-wall collisions. The primary focus of the investigation is to evaluate the erosion reduction capabilities of different inner ring configurations. By systematically varying the number of inner rings, the study elucidates the influence of this parameter on erosion mitigation. The obtained numerical results are analyzed in terms of erosion patterns, erosion reduction percentages, and the integral erosion surface criterion. The findings reveal the elbow with two separate inner rings as the most effective configuration, exhibiting a remarkable decrease in erosion of up to 43 % compared to the standard elbow. Moreover, based on the integral erosion surface criterion, the elbow with five separate inner rings emerges as a more desirable alternative to the standard elbow. In addition, the study investigates the impact of an elbow with helical inner rings configuration on erosion. It is observed that this configuration intensifies flow velocity, thereby accelerating particle motion and leading to increased erosion along the outer wall.

Prediction of the impact of biofouling roughness on a full-scale planing boat performance using CFD

This study investigates the crucial role of surface roughness caused by biofouling in contributing to increased drag in fast planing vessels. Through rigorous computational fluid dynamics (CFD) simulations using a full-scale reference hull, the impact of surface roughness on planing hull performance is examined. The results show that heavy slime roughness on the hull surface causes a significant increase in total resistance, ranging from 10% at low speeds to 80% at high speeds. Skin friction was identified as the most affected component of resistance, with additional changes in residual resistance. Although the change in residual resistance is relatively small, they give rise to dynamic phenomena such as variations in pressure distribution, wave elevation, and wave making formation. The study also explores the influence of surface roughness on dynamic lift forces, observing an increase in upward friction forces but ultimately concludes that overall hull performance was hampered due to the disproportionately higher increase in resistance caused by roughness (biofouling). Changes in dynamic trim, dynamic sinkage, and dynamic wetted surface area due to this roughness are also discussed.

A CFD study of a direct solar-driven desorption process for carbon capture under transient conditions

Solvent-based post-combustion carbon capture (PCC) is the most accessible technology to reduce the greenhouse gas (GHG) emissions from coal-fired power plants, however with a substantial energy penalty. This study investigates a novel concept of solar-powered solvent-based PCC, replacing the traditional stripper unit with a solar collector field (SCF) pipe network. This SCF pipe network consists of modular units termed “solar-strippers” (So-St)s that function to desorb the CO2 gas directly within the solar collector tubes. The internal design complexities of the So-St unit are poorly understood and yet to be optimised. Computational fluid dynamics (CFD) is ideal for modelling complex thermo-physical phenomena that appear in the So-St, including boiling flow, heat transfer, reaction kinetics and thermodynamics. This study develops a rigorous CFD model for a single So-St segment; the first of its kind. The model is used to assess possible design improvements using methods of enhanced heat transfer (EHT), in particular the insertion of porous and solid baffles which increase thermal efficiency and boost vapour formation. The porous and solid baffles are estimated to reduce the So-St field size by 56% and 65%, however demanding 2.5 and 6 times more pumping power, respectively. These incremental design enhancements display the utility of CFD in enabling the So-St concept to become a sustainable low-emissions carbon capture & storage (CCS) technology for cleaner energy production.

High-Thrust Aerostatic Bearing Design Through Transient Perturbation Modeling With Numerical Validation

A simple perturbation flow model is formulated and validated by a rigorous computational fluid dynamics (CFD) study for designing a counterbalanced vertical-axis aerostatic thrust bearing. The flow model of the orifice at the entry of the stator manifold involves natural transition between the choked and free flows. While the air distribution network of holes in the stator and one air gap at the inner radius of the stator constitute the fixed part, the variable part is comprised of two air gaps at the top and bottom of the stator interconnected by the inner air gaps. The top and the inner gaps receive air by a circular array of holes. While the basic flow of the perturbation model is taken as steady corresponding to fixed air gaps, the transient effect is captured by a squeezing flow due to the variations of the top and bottom gaps. The overall flow including that in the network is assumed as compressible and isothermal. This model has been validated through a transient axisymmetric CFD study using dynamic meshing and the coupled lifting dynamics of the payload. The validated model has been used to find the appropriate counterbalancing, the orifice diameter, the air gap sizes, and the location of the air holes feeding the top gap. This clearly shows the worth of the model for carrying out an extensive design analysis that would have been very costly and even unachievable for small gaps that would occur during system transients.

Modeling of CO2 Decompression across the Triple Point

The formation of significant quantities of solid CO2 as a result of surpassing its triple point during rapid decompression of CO2 pipelines employed as part of the carbon capture and sequestration (CCS) chain can present serious operational and safety challenges. In this paper, the development, testing and validation of a rigorous computational fluid dynamics (CFD) flow model for predicting solid CO2 formation during decompression is presented. Multiphase flow is modeled by assuming homogeneous equilibrium, and the pertinent thermodynamic data are computed using real-fluid equations of state. The flow model is validated against pressure and temperature data recorded during the decompression of an extensively instrumented 144 m long, 150 mm i.d. CO2 pipe initially at 5.25 °C and 153.3 bar. For the conditions tested, the simulated results indicate CO2 solid mass fractions as high as 35% at the rupture plane, whose magnitude gradually decreases with distance toward the pipe’s intact end.

Computational Fluid Dynamics Simulation Study of a Novel Membrane Contactor for Simultaneous Carbon Dioxide Absorption and Stripping

Physical absorption is a potential technology for economic carbon capture due to its low energy consumption, however, the absorption efficiency of current systems must be improved. In this study, novel hybrid absorption/stripping membrane contactors (HASMCs) for physical solvent carbon capture are proposed. The simultaneous absorption and stripping within one module provides instant regeneration of the solvent and results in the enhancement of absorption. HASMCs with parallel-flow and cross-flow configurations and using empty or spacer-filled channels are investigated by rigorous computational fluid dynamics simulation. The internal profiles of transmembrane mass fluxes reveal that cross-flow HASMCs are much more effective than the parallel-flow ones and the modules using spacer-filled channels give better performance than the ones using empty channels. The mass transfer coefficients of HASMCs are much higher than predicted by correlations in the literature.

Robust Optimization of Variable-Camber Continuous Trailing-Edge Flap Static Aeroelastic Action

A robust optimization method is described in this paper, focusing on the optimization of a variable-camber continuous trailing-edge flap system for drag reduction in transonic cruise. The variable-camber continuous trailing-edge flap, through the rich combination of shapes it can attain, has the potential to provide greater design and operation freedom than conventional flap systems as well as greater efficiency in drag reduction and performance improvement. The deformation shape optimization of such a system, however, when based on rigorous computational fluid dynamics simulations, presents a significant computational challenge because of the high cost of repetitive analyses required. The construction of surrogate models and their use in the optimization process is one common way to tackle this challenge. Here, stochastic kriging is used, extending the commonly used deterministic kriging. Accounting for the intrinsic uncertainty of data, stochastic kriging and the optimization based on it are well suited for addressing uncertain flight conditions as well as math modeling limitations. An optimization process for the variable-camber continuous trailing-edge flap system that couples shape synthesis with high-fidelity aerodynamic simulations, accounting for static aeroelastic interactions and load distribution constraints, is presented. A potential for robust optimal drag subject to flight Mach number uncertainties is shown.

Analysis of Turbulence and Convective Inertia in a Water-Lubricated Tilting-Pad Journal Bearing Using Conventional and CFD Approaches

ABSTRACTThe influence of turbulence and convective fluid inertia in a water-lubricated journal bearing was investigated using two types of models: a “conventional” solution based on traditional lubrication theory (Reynolds equation) and a more rigorous computational fluid dynamics (CFD) program containing a full Navier-Stokes solution. The calculations reveal that turbulence accounts for around 50% of the load capacity in the water-lubricated bearing studied, highlighting the importance of accurate characterization of turbulence in such applications. Convective inertia, also referred to as transport inertia because it depends only on the spatial parameters within the film rather than time-dependent journal motions, was found to lower the static film pressures (load capacity) by about 6% compared to an inertialess solution.Hydrodynamic pressures calculated by the conventional Reynolds solution were initially about 30% lower than those of the more rigorous CFD model for the water-lubricated bearing operating in the turbulent regime. The mesh spacing of the conventional model was refined and a method was developed to adjust the turbulence model within the Reynolds solution as a function of the pivot Reynolds number. These refinements brought the calculated bearing load capacities and power losses of the conventional Reynolds model into better agreement with those of the CFD model for a broad range operating conditions.

Smart Manufacturing Approach for Efficient Operation of Industrial Steam-Methane Reformers

Steam methane reforming is a mature and complex process extensively used worldwide for hydrogen production from methane. The process takes place in a steam methane reformer (SMR), with the endothermic reforming reactions being carried out in catalyst-filled tubes placed in a gas-fired furnace. The SMR is an energy-intensive process unit, and maximizing energy efficiency is of primary interest. However, the high-temperature conditions and large physical scale of the process (hundreds of tubes and burners) pose several operational challenges related to distributed sensing, actuation, and feedback control. Various efforts have been reported on optimization of furnace operation using rigorous computational fluid dynamics (CFD)-based models but, being computationally intensive, these models are unsuitable for real-time optimization. In this paper, we present an integrated framework that relies on the use of advanced temperature sensors, soft sensors, and reduced-order and rigorous SMR CFD models for distribute...

Computational fluid dynamics modeling of laboratory flames and an industrial flare

A computational fluid dynamics (CFD) methodology for simulating the combustion process has been validated with experimental results. Three different types of experimental setups were used to validate the CFD model. These setups include an industrial-scale flare setups and two lab-scale flames. The CFD study also involved three different fuels: C3H6/CH4/Air/N2, C2H4/O2/Ar, and CH4/Air. In the first setup, flare efficiency data from the Texas Commission on Environmental Quality (TCEQ) 2010 field tests were used to validate the CFD model. In the second setup, a McKenna burner with flat flames was simulated. Temperature and mass fractions of important species were compared with the experimental data. Finally, results of an experimental study done at Sandia National Laboratories to generate a lifted jet flame were used for the purpose of validation. The reduced 50 species mechanism, LU 1.1, the realizable k-ϵ turbulence model, and the EDC turbulence–chemistry interaction model were used for this work. Flare efficiency, axial profiles of temperature, and mass fractions of various intermediate species obtained in the simulation were compared with experimental data and a good agreement between the profiles was clearly observed. In particular, the simulation match with the TCEQ 2010 flare tests has been significantly improved (within 5% of the data) compared to the results reported by Singh et al. in 2012. Validation of the speciated flat flame data supports the view that flares can be a primary source of formaldehyde emission.ImplicationsValidated computational fluid dynamics (CFD) models can be a useful tool to predict destruction and removal efficiency (DRE) and combustion efficiency (CE) under steam/air assist conditions in the face of many other flare operating variables such as fuel composition, exit jet velocity, and crosswind. Augmented with rigorous combustion chemistry, CFD is also a powerful tool to predict flare emissions such as formaldehyde. In fact, this study implicates flares emissions as a primary source of formaldehyde emissions. The rigorous CFD simulations, together with available controlled flare test data, can be fitted into simple response surface models for quick engineering use.

Parametric Study of Ethylene Flare Operations Using Numerical Simulation

In addition to CO2 and H2O, industrial flares may also release Volatile Organic Compounds (VOCs), NOx, and CO among others. Since experimental measurements of these emissions are expensive, rigorous computational fluid dynamics (CFD) simulations and the accrued correlations are viable tools to understand and analyze factors affecting flare operations. In this paper, parametric studies of air and steam assisted ethylene flares based on CFD modeling were employed to investigate important flare operating parameters such as vent gas velocity, crosswind velocity, stoichiometric air ratio, steam-to-fuel ratio and heat content of the vent gas. The CFD modeling utilized a 50-species reduced mechanism (LU 1.1) based on rigorous combustion chemistry. Validation results of LU 1.1 are also presented. The destruction/removal efficiency and the combustion efficiency (DRE & CE) were computed along with HRVOCs/VOCs/NOx emission rates to quantify the flare performance. Correlations between DRE/CE and major parameters (crosswind, jet velocity, and combustion zone heating value) were developed using the results obtained from the case studies. A modified combustion zone heating value definition was proposed to compute a comprehensive heating value in the combustion zone.

CFD Simulation of Propane Cracking Tube Using Detailed Radical Kinetic Mechanism

In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics (CFD) model. The eddy-dissipation-concept (EDC) model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Considering the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Large scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of operating conditions including the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.

Radiation Boundary Conditions for Computational Fluid Dynamics Models of High-Temperature Cavity Receivers

Rigorous computational fluid dynamics (CFD) codes can accurately simulate complex coupled processes within an arbitrary geometry. CFD can thus be a cost-effective and time-efficient method of guiding receiver design and testing for concentrating solar power technologies. However, it can be computationally prohibitive to include a large multifaceted dish concentrator or a field of hundreds or thousands of heliostats in the model domain. This paper presents a method to allow the CFD code to focus on a cavity receiver domain alone, by rigorously transforming radiance distributions calculated on the receiver aperture into radiance boundary conditions for the CFD simulations. This method allows the incoming radiation to interact with participating media such as falling solid particles in a high-temperature cavity receiver. The radiance boundary conditions of the CFD model can take into consideration complex beam features caused by sun shape, limb darkening, slope errors, heliostat facet shape, multiple heliostats, off-axis aberrations, atmospheric effects, blocking, shading, and multiple focal points. This paper also details implementation examples in ansys fluent for a heliostat field and a dish concentrator, which are validated by comparison to results from delsol and the ray-tracing code asap, respectively.

Biomedical systems research—New perspectives opened by quantitative medical imaging

Recent advances in quantitative imaging allow unprecedented views into cellular chemistry of whole organisms in vivo. These novel imaging modalities enable the quantitative investigation of spatio-temporal reaction and transport phenomena in the living animal or the human body. This article will highlight the significant role that rigorous systems engineering methods can play for interpreting the wealth of in vivo measurements. A methodology to integrate medical imaging modalities with rigorous computational fluid dynamics entitled image-based computational fluid dynamics ( iCFD) will be introduced. The quantitative analysis of biological systems with rigorous mathematical methods is expected to accelerate the introduction of novel drugs by providing a rational foundation for the systematic development of new medical therapies. Rigorous engineering methods not only advance biomedical research, but also aid the translation of laboratory research results into the bedside practice.

Neural network computer simulation of medical aerosols.

Preliminary investigations have been conducted to assess the potential for using artificial neural networks to simulate aerosol behaviour, with a view to employing this type of methodology in the evaluation and design of pulmonary drug-delivery systems. Details are presented of the general purpose software developed for these tasks; it implements a feed-forward back-propagation algorithm with weight decay and connection pruning, the user having complete run-time control of the network architecture and mode of training. A series of exploratory investigations is then reported in which different network structures and training strategies are assessed in terms of their ability to simulate known patterns of fluid flow in simple model systems. The first of these involves simulations of cellular automata-generated data for fluid flow through a partially obstructed two-dimensional pipe. The artificial neural networks are shown to be highly successful in simulating the behaviour of this simple linear system, but with important provisos relating to the information content of the training data and the criteria used to judge when the network is properly trained. A second set of investigations is then reported in which similar networks are used to simulate patterns of fluid flow through aerosol generation devices, using training data furnished through rigorous computational fluid dynamics modelling. These more complex three-dimensional systems are modelled with equal success. It is concluded that carefully tailored, well trained networks could provide valuable tools not just for predicting but also for analysing the spatial dynamics of pharmaceutical aerosols.

A novel method to capture mass transfer phenomena at free fluid–fluid interfaces

A rigorous Computational Fluid Dynamics (CFD) based approach incorporating interfacial mass transfer at moving interfaces has been developed. The peculiarity of this approach is that it is able to govern multicomponent systems as well as interfacial boundary conditions in an arbitrary form. This is important in order to properly handle the typical concentration jump at the phase interface and to avoid an assumption of a constant distribution coefficient which is seldom met in real separation units. As a test system, the movement of a rising toluene droplet in quiescence aqueous phase is studied, whereas acetone is used as the transferring component. The level set method is applied for the description of the droplet movement. To give a first validation to the developed CFD model, the toluene droplet is first assumed to be stagnant and the mass transfer from/to the continuous aqueous phase is considered. A good agreement with analytical results from the literature is found in terms of the asymptotic value of mass transfer rate. Further, simulations for rising droplet are performed to incorporate the coupling between the momentum and mass transfer. The method provides concentration fields that are in qualitative agreement with the available data from the literature. Another test accomplished with an increased distribution coefficient also yields reasonable results.

Atmospheric Dispersion of Sodium Aerosol due to a Sodium Leak in a Fast Breeder Reactor Complex

Liquid sodium at high temperatures (470 K to 825 K) is used as the primary and secondary coolant in Liquid Metal cooled Fast Breeder Reactors (LMFBR). In the event of a postulated sodium leak in the Steam Generator Building (SGB) of a LMFBR, sodium readily combusts in the ambient air, especially at temperatures above 523 K. Intense sodium fire results and sodium oxide fumes are released as sodium aerosols. Sodium oxides are readily converted to sodium hydroxide in air due to the presence of moisture in it. Hence, sodium aerosols are invariably in the form of particulate sodium hydroxide. These aerosols damage not only the equipment and instruments due to their corrosive nature but also pose health hazard to humans. Hence, it is essential to estimate the concentration of sodium aerosols within the plant boundary for a sodium leak event. The Gaussian Plume Dispersion Model can obtain the atmospheric dispersion of sodium aerosols in an open terrain. However, this model does not give accurate results for dispersion in spaces close to the point of release and with buildings in between. The velocity field due to the wind is altered to a large extent by the intervening buildings and structures. Therefore, a detailed 3-D estimation of the velocity field and concentration has to be obtained through rigorous computational fluid dynamics (CFD) approach. PHOENICS code has been employed to determine concentration of sodium aerosols at various distances from the point of release. The dispersion studies have been carried out for the release of sodium aerosols at different elevations from the ground and for different wind directions.

Deposition of Ultrafine Particles at Carinal Ridges of the Upper Bronchial Airways

Bifurcations of the upper bronchial airways are primary hot spots for deposition of inhaled particles and noxious gases. Deposition of coarse particles in the carinal ridges results from inertial impaction, and deposition distal to these sites is attributed to secondary flows. Diffusional deposition of ultrafine particles on carinae surfaces is studied here. Similarity solutions for both the flow and concentration fields at the respective boundary layers that develop near the surface of a wedge are presented, corresponding to a relatively high Re number. The expressions developed for the deposition efficiency compare favorably to those obtained by rigorous computational fluid dynamics simulations. Yet unlike simulation-derived expressions that pertain to the specific geometry and flow conditions studied, our expressions are robust and can account for different branching angles, airflow rates, and particle sizes. The average diffusive flux toward the carina walls is in good agreement with experimental deposition data, as well as with simulation results specifically designed to account for deposition hot spots at airway bifurcations. The expressions obtained can be easily implemented in algebraic inhalation dosimetry models to estimate deposition profiles along the whole respiratory system.