Computational Fluid Dynamics Simulation Of Flow Research Articles

CFD simulation of multiphase flow in an airlift column photobioreactor

<p>A Computational Fluid Dynamics (CFD) simulation using <em>CFX, ANSYS 11.0</em>, has been carried out using a multiphase flow model with an Eulerian-Eulerian approach for an airlift column photobioreactors (PBR). Transient simulations were performed for three inlet air flow, 2, 3 and 5 l/min. The contours for gas holdup, air and water velocity showed that the presence of gas phase (air bubbles) is lower in the downcomer but larger in the riser, which leads to require a vigorous mixing in the riser that will be sufficient for a continuous flow. For air, velocity vectors show that they are smaller in the downcomer than in the riser. Nevertheless, water velocity vectors are organized, pointing down in the downcomer and up in the riser. Water shear stress rate contours analysis showed that, shear stress rate regions are considerably larger in the riser, but lower in the downcomer. Due to fewer restrictions to the liquid phase in the riser, a large amount of energy is dissipated by gas liquid interactions. In the downcomer region, gas phase is almost inexistent, and so are the bubble collisions. Finally, the kinetic energy is larger at the top region of the riser, meanwhile is lower at the downcomer. Similar results are observed for energy dissipation rate.</p> <p> </p>

Potential use of reduced-scale models in CFD simulations to save numerical resources: Theoretical analysis and case study of flow around an isolated building

This study hypothesizes that reduced-scale models for computational fluid dynamics (CFD) simulations of wind flow and related processes can save numerical resources. To test this hypothesis, both theoretical analysis and a numerical case study are conducted. The CFD simulations are validated against a set of wind tunnel experimental data. Both theoretical and numerical results support the hypothesis. It is found that a reduced-scale model requires fewer cells than a full-scale model to achieve a target near-wall z+ value and prediction accuracy and therefore has the potential to save numerical resources. Quantitative analysis shows that this potential is very large, depending on many factors, such as the scaling factor, the target z+ value, and the flow problem. The findings of this study should be useful for CFD simulations of wind flow and related processes, particularly over large areas. However, special attention should be paid to the disadvantages of using reduced-scale models, such as the difficulty to fulfill the similarity requirements.

In vivo measurement of gas flow in human airways with hyperpolarized gas MRI and compressed sensing.

Hyperpolarized (HP) (3) He and (129) Xe are two gases with different fluid dynamic properties, which can be used as tracers for airflow measurement in the lungs with phase contrast velocimetry MRI sequences. In this work, in vivo measurements of velocity maps of airflow in the upper airways and first bronchi of healthy volunteers were obtained with both gases and compared. To reduce the acquisition time, a Compressed Sensing (CS) based acquisition and reconstruction algorithm was developed and optimized for flow measurement in three directions by including the sparsity of the complex difference images as prior knowledge. CS simulations on retrospectively under-sampled images demonstrated a better reconstruction with the inclusion of the complex difference terms in the cost function. The technique was then validated with a prospective acquisition study providing artifact free maps with acceleration factors up to 3. The presented technique opens up the possibility to map velocity inside human lungs. The results are of interest for the validation of computational fluid dynamics flow simulations and for understanding the spatio-temporal evolution of airflow patterns in the airways in vivo with different gas mixtures.

IN CYLINDER COLD FLOW CFD SIMULATION OF IC ENGINE USING HYBRID APPROACH

The design and manufacture of Internal Combustion (IC) Engines is under significant pressure for improvement. The next generation of engines needs to be compact, light, powerful, and flexible, yet produce less pollution and use less fuel. Innovative engine designs will be needed to meet these competing requirements. The time scales of the intake air flow, fuel injection, liquid vaporization, turbulent mixing, species transport, chemistry, and pollutant formation all overlap, and need to be considered simultaneously. Computational Fluid Dynamics (CFD) has emerged as a useful tool in understanding the fluid dynamics of IC Engines for design purposes. . Insight provided by CFD analysis helps guide the geometry design of parts, such as ports, valves, and pistons; as well as engine parameters like valve timing and fuel injection. Using CFD results, the flow phenomena can be visualized on 3D geometry and analyzed numerically, providing tremendous insight into the complex interactions that occur inside the engine. This allows you to compare different designs and quantify the trade-offs such as soot vs NOx, swirl vs tumble and impact on turbulence production, combustion efficiency vs pollutant formation, which helps determine optimal designs. In this paper the In cylinder cold flow CFD simulation of four stroke petrol engine using hybrid approach of ANSYS fluent. The simulation is carried out using parameter and journal files which is a symmetry geometry. Dynamic motion was visualize and velocity magnitude is plotted for crank angle starting from 0 to 720. The engine is simulated for half cylinder cycle. The In cylinder data file is write displaying swirl and tumble for zones of fluid-ch and fluid-piston-layer. The text file is written in working directory containing swirl, x-tumble, y-tumble and moment of inertia as a function of CA.

An Eulerian-Eulerian CFD Simulation of Air-Water Flow in a Pipe Separator

This paper presents a three dimensional Computational Fluid Dynamics (CFD) of air-water flow using Eulerian –Eulerian multiphase model and RSM mixture turbulence model to investigate its hydrodynamic flow behaviour in a 30 mm pipe separator. The simulated results are then compared with the stereoscopic PIV measurements at different axial positions. The comparison shows that the velocity distribution can be predicted with high accuracy using CFD. The numerical velocity profiles are also found to be in good qualitative agreement with the experimental measurements. However, there were some discrepancies between the CFD results and the SPIV measurements at some axial positions away from the inlet section. Therefore, the CFD model could provide good physical understanding on the hydrodynamics flow behaviour for air-water in a pipe separator.

PS206. Use of Computational Fluid Dynamics Studies in Predicting Aneurysmal Degeneration of Acute Type B Aortic Dissections

Although uncomplicated acute type B aortic dissections are often medically managed with good outcomes, a subset will develop subacute or chronic aneurysmal dilatation. We hypothesize that computational fluid dynamics (CFD) simulations may be useful in identifying patients at risk for this complication. Patients with acute type B dissection complicated by rapidly expanding aortic aneurysms (n = 7) were compared with patients with stable aortic diameters (n = 7). Three-dimensional patient-specific dissection geometries were generated from computed tomography angiography and used in CFD simulations of pulsatile blood flow. Hemodynamic parameters, including false lumen flow and wall shear stress, were compared. Patients with rapid aneurysmal degeneration had a growth rate of 5.3 ± 2.7 mm/mon compared with those with stable aortic diameters who had rates of 0.2 ± 0.02 mm/mon. Groups did not differ in initial aortic diameter (36.1 ± 2.9 vs 34.4 ± 3.6 mm; P = .122) or false lumen size (22.6 ± 2.9 vs 20.2 ± 4.5 mm; P = .224). In patients with rapidly expanding aneurysms, a greater percentage of total flow passed through the false lumen (78.3% ± 9.3% vs 56.3% ± 11.8%; P = .016). The time-averaged wall shear stress on the aortic wall was also significantly higher (12.6 ± 3.7 vs 7.4 ± 2.8 Pa; P = .028; Fig). Hemodynamic parameters derived from CFD simulations of acute type B aortic dissections were significantly different in dissections complicated by aneurysm formation. Thus, CFD may assist in predicting which patients may benefit from early stent grafting.

A Virtual Free Surface (VFS) model for efficient wave–current CFD simulation of fully submerged structures

In ocean engineering, complex design problems are frequently analyzed by applying computational fluid dynamics (CFD). When these problems involve waves and currents, a CFD simulation of a multiphase flow is one possible approach to gain valuable information. However, in terms of the computational costs, free surface flow simulations are quite restrictive. Neglecting viscous effects, significantly simpler and faster models are available, but may not provide sufficient information regarding the true nature of the flow. As an alternative, a single phase Virtual Free Surface (VFS) model is introduced in this paper. The methodology allows for efficient CFD simulations of fully submerged structures subjected to pure waves and combined wave–current scenarios, under consideration of wave–current interaction. The velocities and pressures computed with the model are analyzed and compared to theoretical reference solutions. Then, a correction model is introduced that reduces deviations observed in the pressure solution. The model is applied to the investigation of a tidal turbine and its support structure. All results computed with the VFS model are compared to reference free surface computations. Overall the VFS results agree well with the reference solutions, at significantly lower computational cost. Therefore, the method is ideal for optimization problems involving a large number of structural variations subjected to specific offshore conditions.

Abstract 118: Use of Computational Fluid Dynamics Studies in Predicting Aneurysmal Degeneration of Acute Type B Aortic Dissections

Objectives: While uncomplicated acute type B aortic dissections are often medically managed with good outcomes, a subset develop subacute or chronic aneurysmal dilatation. We hypothesize that computational fluid dynamics (CFD) simulations may be useful in identifying patients at risk for this complication. Methods: Patients with acute type B dissection complicated by rapidly expanding aortic aneurysms (N=7) were compared to patients with stable aortic diameters (N=7). Three dimensional patient-specific dissection geometries were generated from CTA and used in CFD simulations of pulsatile blood flow. Hemodynamic parameters including false lumen flow and wall shear stress were compared. Results: Patients with rapid aneurysmal degeneration had a growth rate of 5.3 ± 2.7 mm/month compared to those with stable aortic diameters who had rates of 0.2 ± 0.02 mm/month. Groups did not differ in initial aortic diameter (36.1±2.9 vs 34.4±3.6 mm, P=0.122) or false lumen size (22.6±2.9 vs 20.2±4.5 mm, P=0.224). In patients with rapidly expanding aneurysms, a greater percentage of total flow passed through the false lumen (78.3±9.3 vs 56.3±11.8%, P=0.016). The time averaged wall shear stress on the aortic wall was also significantly higher (12.6±3.7 vs 7.4±2.8 Pa, P=0.028, see Figure). Conclusions: Hemodynamic parameters derived from CFD simulations of acute type B aortic dissections were significantly different in dissections complicated by aneurysm formation. Thus, CFD may assist in predicting which patients may benefit from early stent grafting.

Multiphase flow simulations of a moving fluidized bed regenerator in a carbon capture unit

To accelerate the commercialization and deployment of carbon capture technologies, computational fluid dynamics (CFD)-based tools may be used to model and analyze the performance of carbon capture devices. This work presents multiphase CFD flow simulations for the regenerator—a device responsible for extracting CO2 from CO2-loaded particles before the sorbent is recycled. The use of solid particle sorbents in this design is a departure from previously reported systems, where aqueous sorbents are employed. Another new feature is the inclusion of a series of perforated plates along the regenerator height. The influence of these plates on sorbent distribution is examined for varying sorbent holdup, fluidizing gas velocity, and particle size. The residence time distribution of sorbents is also measured to classify the flow regime as plug flow or well-mixed flow. The purpose of this work is to better understand the sorbent flow characteristics before reaction kinetics of CO2 desorption can be implemented.

Methods of simulating large-scale rod bundle and application to a 17 × 17 fuel assembly with mixing vane spacer grid

In the last decade, a large number of computations were presented using computational fluid dynamics (CFD) for the simulation of thermal-hydraulic problems in the nuclear industry. A common feature in almost all of those simulations is that the geometric models used in the simulations only contained a small number of fuel rods such as 3×3 and 5×5 due to the limit of the computer capacity. However, a typical fuel assembly of pressurized water reactor (PWR) consists of 17×17 rod bundle. This paper concerned on the appropriate numerical methods for CFD simulations of fluid flow and heat transfer in large-scale rod bundle such as 17×17 fuel assembly with mixing vane spacer grid at reasonable computational cost. Firstly, in order to reduce the computational amount in the research, the effectiveness of applying periodic boundary conditions to a central two-subchannel model was validated by comparing the velocity profiles to the experimental and other CFD data. Later, based on the validated two-subchannel model, the methods of domain-divided solving technique and application characteristics of polyhedral meshes for simulating a large-scale rod bundle with mixing grid were investigated. The so-called domain-divided solving technique is a method that the whole rod bundle domain is divided in several sub-domains along the axial direction and each of the sub-domains is simulated separately. The optimal subdivision method and outlet boundary condition of the sub-domain containing mixing vanes were confirmed in the present work. The application characteristics of the polyhedral meshes applied to the rod bundle with mixing grid was investigated and the polyhedral meshes show higher computational efficiency and better convergence properties for the same reasonable accuracy compared to tetrahedral meshes. Finally, a numerical simulation of a typical 17×17 fuel assembly with mixing vane spacer grid was performed by utilizing the methods investigated above. As a result of this study, we have found the appropriate methods to simulate the large-scale rod bundle with mixing grids at full axial length on a conventional computer. The CFD analysis on thermal-hydraulic problems in reactor coolant system can be conducted widely by using a real size fuel assembly in the future.

High resolution microtomography-based CFD simulation of flow and heat transfer in aluminum metal foams

The necessity for devising more effective heat transfer technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this prospect, metal foams are good candidates for improving the thermal efficiency of heat transfer devices and allowing, at the same time, the use of smaller and lighter equipments. For design purposes, the proper characterization and quantification of transport and thermal properties of metal foams is fundamental but far from simple. This lack of information constitutes a fundamental limit in the employment of metal foams in practical and industrial applications. Nowadays, besides classical transport models and correlations, computational fluid dynamics (CFD) at the pore scale, although challenging, are becoming a promising approach for recovering the transport properties of the medium, especially if coupled with a realistic description of the foam structure. In order to precisely describe the microstructure of the foams, a 3D approach based on the X-ray computed microtomography (μ-CT) technique can be adopted. In this work, the results of high resolution μ-CT-based CFD simulations, performed on three different open-cell aluminum foams samples, will be illustrated. The results demonstrate that open-cell aluminum foams are effective means for enhancing heat transfer. Moreover, the procedure proved that μ-CT is a valid tool for capturing the peculiar details of the foam structure, thus to overcome the limits associated to the use of economical, but simplified, geometric models.

Finite element modeling of embolic coil deployment: Multifactor characterization of treatment effects on cerebral aneurysm hemodynamics

Endovascular coiling is the most common treatment for cerebral aneurysms. During the treatment, a sequence of embolic coils with different stiffness, shapes, sizes, and lengths is deployed to fill the aneurysmal sac. Although coil packing density has been clinically correlated with treatment success, many studies have also reported success at low packing densities, as well as recurrence at high packing densities. Such reports indicate that other factors may influence treatment success. In this study, we used a novel finite element approach and computational fluid dynamics (CFD) to investigate the effects of packing density, coil shape, aneurysmal neck size, and parent vessel flow rate on aneurysmal hemodynamics. The study examines a testbed of 80 unique CFD simulations of post-treatment flows in idealized basilar tip aneurysm models. Simulated coil deployments were validated against in vitro and in vivo deployments. Among the investigated factors, packing density had the largest effect on intra-aneurysmal velocities. However, multifactor analysis of variance showed that coil shape can also have considerable effects, depending on packing density and neck size. Further, linear regression analysis showed an inverse relationship between mean void diameter in the aneurysm and mean intra-aneurysmal velocities, which underscores the importance of coil distribution and thus coil shape. Our study suggests that while packing density plays a key role in determining post-treatment hemodynamics, other factors such as coil shape, aneurysmal geometry, and parent vessel flow may also be very important.

Computational fluid dynamics for concentrating solar power systems

Computational fluid dynamics (CFD) can be used to better understand complex processes and to improve designs and system performance in concentrating solar power (CSP) applications. Applications presented in this paper include CFD simulations for collectors, thermal receivers, and thermal storage technologies. CFD simulations of wind flow around collectors such as parabolic troughs and heliostats have been used to determine wind loads, which impact the design and requirements of the support structure. Simulations of the heat transfer and heat loss in solar thermal receivers have been performed to identify designs that optimize thermal efficiency, and to better understand radiative, convective, and conductive heat losses. CFD models have also been developed to understand processes in thermal storage systems, including mixing in thermoclines, heat transfer in solid media, and melting and solidification processes in phase‐change materials. Researchers have generally concluded that CFD modeling is a useful and cost‐effective tool to understand processes and improve designs for CSP systems.This article is categorized under: Concentrating Solar Power > Science and Materials Concentrating Solar Power > Systems and Infrastructure

CFD simulation of flow and dispersion around an isolated building: Effect of inhomogeneous ABL and near-wall treatment

This paper presents a study of the effect of the inhomogeneous atmospheric boundary layer (ABL) and near-wall treatment on a computational fluid dynamics (CFD) simulation of the flow and dispersion around an isolated building. Based on a revised k−ɛ model (MMK), the effect of the inhomogeneous ABL is studied by comparing several sets of inhomogeneous inlet conditions with a homogeneous one, while the roughness-adapted standard wall functions and two-layer model are compared to examine the effect of the near-wall treatment of rough ground. Wind tunnel experimental data from previous investigations are used to validate the numerical simulations. The inhomogeneous ABL has a significant effect on the prediction of the flow and dispersion fields, depending on the percentage deviation of the incident from the inlet conditions. A decreased incident k profile results in a longer reattachment length on the roof and a larger recirculation region in the wake, which in turn produce decreased and increased nondimensional velocity and concentration fields, respectively. An increased incident U profile enlarges the reattachment lengths and raises the k field, which has a similar effect on the nondimensional velocity and concentration fields as decreased k. It is observed that the use of the two-layer model to solve the near-wall viscous sublayer clearly improves the prediction of flow and dispersion, depending on the role of the low-Reynolds-number effect of the near-wall region on the entire wall-bounded turbulent flow.

CFD simulations of turbulent buoyant atmospheric flows over complex geometry: Solver development in OpenFOAM

This paper, first of a two-part work, presents an overview of the development of a computational fluid dynamics (CFD) solver in OpenFOAM platform to simulate the internal ventilation regime within an open pit including the effects of developed turbulence, buoyancy and stratification. To incorporate the effect of stratification in the simulations we have chosen a formulation that includes density as a variable in the system of equations, thus facilitating further study of buoyant flows. Given the importance of turbulence in this type of large-scale flows we have used Large Eddy Simulation (LES) to incorporate it in the calculation, using a Detached Eddy Simulation (DES) approach to solve the flow near walls. Specific initial and boundary conditions were defined.The results presented in this paper, including several tests of the solver where we compared our results with experimental or numerical data, have demonstrated the validity of using OpenFOAM to study this type of complex multiphysics problems. Especially advantageous in this regard are the flexibility provided by the modular structure of the code, the possibility of defining specific boundary and initial conditions for each case, and the ability of generating detailed meshes of complex geometries. Also we probed the benefits of using a DES approach, allowing us to solve developed turbulence and the interaction of the flow with detailed geometry. A second paper associated to this work will expose the application of the solver to large open pit mines, simulating the particular case of Chuquicamata, one of the largest open pit mines in the world, located in northern Chile.

Technical Development of Design & Fabrication of an Unmanned Aerial Vehicle

UAV (Unmanned Aerial Vehicle) is an air vehicle which is largely used for surveillance, monitoring, reconnaissance, data relay, and data collection or to enter the area which is not safe for human i.e. flood affected or virus affected area. This paper represents the unique design of such an UAV which designed at MILITARY INSTITUTE OF SCIENCE & TECHNOLOGY to participate in an international competition SAE Aero Design West-2013. As per competition requirement empty weight of the UAV must be less than 2 lb and must fly with payload as heavy as possible for good scoring. Initially, the model of the UAV was tested in wind tunnel and the test data showed that the model aircraft performance was capable enough for flying and covering an area specified in the competition. Subsequently, an actual aircraft was fabricated of that model and flight tested which proved the match with theoretical, statistical and experimental data that was obtained from wind tunnel test, wing tip test, tensile test of manufacturing material and CFD (Computational Fluid Dynamics) flow simulation over the aerofoil.

Simulation of Deposition the Corrosion Waste in a Water Distribution System

In water distribution systems can be found particles of rust and other mechanical contaminants. The particles are deposited in locations where the low velocity of water flow. Where a can cause the pitting corrosion. Is a concern in the systems made of galvanized steel pipes. The contribution deals with CFD (Computational Fluid Dynamics) simulations of water flow and particles deposition in water distribution system. CFD Simulations were compared with the corrosive deposits in real pipeline. Corrosion is a spontaneous process of destruction of metal material due to electrochemical reactions of metal with the aggressive surrounding. Electrochemical corrosion is caused by the thermodynamic instability of metal and therefore can not be completely suppress, it can only influence the speed of corrosion. The requirement is to keep metal properties during the whole its lifetime. Requested service lifetime the water pipe according to EN 806-2 is 50 years.

Experimental and CFD Studies on the Performance of Microfiltration Enhanced by a Turbulence Promoter

This paper reports experimental and computational fluid dynamics (CFD) studies on the performance of microfiltration enhanced by a helical screw insert. The experimental results show that the use of turbulence promoter can improve the permeate flux of membrane in the crossflow microfiltration of calcium carbonate suspension, and flux improvement efficiency is strongly influenced by operation conditions. The energy consumption analysis indicates that the enhanced membrane system is more energy saving at higher feed concentrations. To explore the intrinsic mechanism of flux enhancement by a helical screw insert, three-dimensional CFD simulation of fluid flow was implemented. It reveals that hydrodynamic characteristics of fluid flow inside the channel are entirely changed by the turbulence promoter. The rotational flow pattern increases the scouring effect on the tube wall, reducing the particle deposition on the membrane surface. The absence of stagnant regions and high wall shear stress are responsible for the enhanced filtration performance. No secondary flow is generated in the channel, owing to the streamline shape of helical screw insert, so that the enhanced performance is achieved at relatively low energy consumption.

CFD simulation of cross-ventilation flow for different isolated building configurations: Validation with wind tunnel measurements and analysis of physical and numerical diffusion effects

Computational Fluid Dynamics (CFD) has become one of the most important tools for the assessment of natural cross-ventilation of buildings. To ensure the accuracy and reliability of CFD simulations, solution verification and validation studies are needed, as well as detailed sensitivity studies to analyse the impact of computational parameters on the results. In a previous study by the present authors, the impact of a wide range of computational parameters on the cross-ventilation flow in a generic isolated single-zone building was investigated. This paper presents the follow-up study that focuses in more detail on validation with wind tunnel measurements and on the effects of physical and numerical diffusion on the cross-ventilation flow. The CFD simulations are performed with the 3D steady Reynolds-Averaged Navier–Stokes (RANS) approach with the SST k–ω model to provide closure. Validation of the coupled outdoor wind flow and indoor airflow simulations is performed based on Particle Image Velocimetry (PIV) measurements for four different building configurations. The analysis of numerical diffusion effects is performed in two parts. First, the effect of physical diffusion is analysed by changing the inlet profiles of turbulent kinetic energy within a realistic range. Second, the effect of numerical diffusion is investigated by changing the grid resolution and by applying both first-order and second-order discretisation schemes. The results of the validation study show a good to a very good agreement for three of the four configurations, while a somewhat less good agreement is obtained for the fourth configuration. The results of the diffusion study show that the effects of physical and numerical diffusion are very similar. Along the centreline between the openings, these effects are most pronounced inside the building, and less pronounced outside the building. The velocity-vector fields however show that increased physical and numerical diffusion decreases the size of the upstream standing vortex and increase the spread of the jet entering the buildings. It is concluded that diffusion is an important transport mechanism in cross-ventilation of buildings, and that special care is needed to select the right amount of physical diffusion and to reduce the numerical diffusion, using high-resolution grids and using at least second-order accurate discretisation schemes.

CFD Simulation of the Gas-Liquid Flow on the Ripple Tray

The ripple tray is a sieve tray without downcomers, in which the liquid contacts with the upward gas counter-currently. The hydrodynamics performance in ripple tray columns was investigated with the computational fluid dynamics (CFD) method. Various superficial gas velocity and liquid loads were simulated for the tray with cylindrical cross sections using the Euler-Euler method. The modeling results were validated by comparing the calculated liquid height on the ripple tray with the experimental values. The developed CFD model is found to be able to predict the two phase flow patterns in ripple tray columns and provide useful information for further design of ripple tray.