Computational Fluid Dynamics Analysis Of Flow Research Articles

Abstract WP159: Examining The Utility Of 2D DSA For Carotid Stenosis Hemodynamic Pressure Analysis

Introduction: Measurement of local hemodynamic behavior is useful for assessing the pathology of carotid stenosis. In this study, we explore a novel method using two-dimensional digital subtraction angiography (2D DSA) to provide time-dependent pressure data. We performed comparative validation with computational fluid dynamics (CFD) and flow guidewire measurements as reference methods. Methods: A silicone phantom model of a carotid stenosis was prepared, filled with physiological saline, and connected to a flow pump (Vascular Simulations, LLC Left Heart Replicator) applying pulsatile flow. The stenosis model narrowed from a diameter of 1.37 cm to 0.58 cm for a length of 0.64 cm (NASCET=40%). Iodinated contrast media was injected, and time dependent pressure profiles at four regions of interest: 2 cm proximal to the stenosis, proximal end of the stenosis, distal end of the stenosis and 2 cm distal to the stenosis were derived from contrast intensity (I) obtained from 2D DSA background-subtracted intensity plots using previously published PVEC software. A Volcano flow guidewire sensor was utilized at the same four locations to collect flow data. Pulsatile CFD flow analysis was performed to extract flow data. Results: DSA PVEC contrast analysis allowed observation of distinct flow pulsatility. At 30fps, strong agreement of DSA contrast waveform matching CFD and guidewire flow measurements was found at the distal end of the stenosis over a period of linear contrast increase (constant dI/dt). Bland-Altman analysis was used to compare derived pressure with the reference methods over 3.5 cardiac cycles, from 5.9 s to 8.7 s after the initial injection of contrast. 2D DSA-derived pressure showed a mean departure of -10.24% (std. dev 14.65%) pressure obtained from CFD analysis, and a mean departure of -15.32% (std. dev 14.24%) from guidewire measurements for the duration. Conclusion: A novel computational approach suggests 2D DSA can provide real-time results to approximate carotid flow from 2D DSA. We showed using this novel approach the flow data is comparable with guide wire and CFD methods. Future experiments may allow it to provide a supplementary, non-invasive means to examine local hemodynamic behavior that is relevant to the evaluation of carotid stenosis.

Performance analysis of step type solar still and comparison of the performance with evacuated tube collector coupled with single slope step type solar still

This research project aims to address the growing need for freshwater in regions affected by water scarcity, particularly in coastal and desert areas. The focus is on evaluating the effectiveness of a solar-powered desalination system, which utilizes a single slope step type solar still and an Evacuated Tube Collector (ETC) to produce fresh drinkable water. Additionally, Computational Fluid Dynamics (CFD) analysis is conducted to gain insights into the natural convection of heat transfer within a glass tube, which creates a buoyant flow of saline water. The design consists of a solar evacuated tube, which heats up due to the exposure to sun rays and this heat is transferred to the impure/saline water (effluent). The water is then discharged to a single slope step type solar still which absorbs energy from sunlight and increases the evaporation rate in the solar still. Thus, the water evaporates and is then condensed by the inner surface of the glass roof hence purified water is collected. The CFD flow analysis of incompressible fluid under the effect of gravity in the transient condition is carried out for ETC in the ANSYS workbench. Also, fluid flow analysis of single slope step type solar still consisting of ten steps with a water depth of 3 cm in multiphase conditions using the VOF model is carried out to obtain the amount of distillate output per day in fair weather conditions in the location 13.2848⁰ N, 74.7486⁰ E in Katapady, Udupi. The amount of distillate collected as a result of CFD analysis was found to be 5.195 kg/day. The contours obtained from the steady state analysis for solar still showed the distribution of temperature, solar heat flux, and mass flow rate. The transient analysis of the ETC assisted well in obtaining the temperature in the ETC collector tank and the variation in solar radiation throughout the day. The contours of ETC showed the buoyant flow of water under natural convection, velocity distribution, density distribution and solar irradiation distribution on glass walls.

Study for the Comparison of CFD Analysis of Flow through Valves

Control valves are generally flow control equipment is utilized in a variety of sectors. The authors' modeling and simulation studies of various control valves are reviewed in this study. The findings of this research enable users to comprehend the flow pattern of a valve at various flow rates, as well as identify approaches for improving the valve's function. A gate valve was designed using Computational Fluid Dynamics (CFD) and CFD-powered software. The valve coefficient (Cv), often known as the flow coefficient, is a commonly used valve parameter. This paper presents the results of Flow Coefficient Analysis research.

Investigation of Air Filter Properties of Flash-Spinning Nanofiber Non-Woven Fabric

Using computational fluid dynamics (CFD) technology, a stable manufacturing method for polymeric nanofiber non-woven fabrics based on an improved melt-blowing method and flash spinning is realized to achieve mass productivity. Subsequently, a method to predict filter efficiency using two production methods based on the effects of thickness, filling rate, and fiber diameter on filtration performance is developed to establish a filter design via CFD technology. CFD models featuring uniform fiber diameters are proposed. Next, the pressure loss and flow resistivity are calculated using CFD flow analysis software, as in a filter experiment. The proposed fiber diameter distribution model yields results similar to the experimental value, and the relationship among filling rate, fiber diameter, and flow resistivity is verified. The non-woven filter fabricated in this study demonstrates superior filtration properties, based on the results. Additionally, a method to satisfy both low pressure loss (low flow resistivity) and high filtration efficiency is discussed. Although the pressure loss increases, the filter yields a value below the standard for high-performance face masks, since the fiber diameter is on the nano-order.

Computational Fluid Dynamics Analysis of Compressible Flow Through a Converging-Diverging Nozzle using the k-ε Turbulence Model

The thrust produced by a rocket motor is mainly dependent upon the expansion of the product gases through a nozzle. The nozzle is used to accelerate the gases produced in the combustion chamber and convert the chemical-potential energy into kinetic energy so that the gases exit the nozzle at very high velocity. It converts the high pressure, high temperature, and low-velocity gas in the combustion chamber into high-velocity gas of lower pressure and low temperature. The design of a nozzle has particular importance in determining the thrust and performance of a rocket. In recent years, it has received considerable attention as it directly impacts the overall performance of the rocket. This paper aims to analyze the variation of flow parameters like pressure, Mach number, and velocity using Finite Volume Method (FVM) solver with the standard k-ε turbulence model in Computational Fluid Dynamics (CFD). The simulation of shockwave inside the divergent nozzle section through CFD is also investigated. In this regard, a nozzle has been designed using Design Modeler, and CFD analysis of flow through the nozzle has been carried out using ANSYS Fluent. The model results are compared with theoretically calculated results, and the difference is negligible.

Reproducibility of Gaseous Phase Area on Journal Bearing Utilizing Multi-Phase Flow CFD Analysis under Flooded and Starved Lubrication Conditions

It is important to predict the gaseous phase area of journal bearing. However, a detailed calculation method for such gaseous phase areas has not yet been proposed. In this study, the gaseous-phase areas in small bore journal bearings under flooded and starved lubrication conditions are analyzed in terms of the computational fluid dynamics (CFD) of two-phase flow while using a volume of fluid (VOF) method. Furthermore, the influence of surface tension and vapor pressure conditions were investigated, and the analytical and experimental results were compared. The analytical results of VOF for vapor pressure and surface tension were observed to be consistent with the experimental observations under both flooded and starved lubrication conditions. Furthermore, under starved lubrication condition, the analytical results agree well with the observed results for the interface of the oil film and cavitation upon the rupture of the oil film. While using these results, CFD analysis of the two-phase flow of the VOF can be conducted in terms of vapor pressure and surface tension to estimate the gaseous-phase areas of journal bearings under flooded and starved lubrication conditions.

CFD Analysis of flow around fish

The study of fish like bodies in the liquid is a challenging research area in the fields of bio-locomotion and biomimetics. The power and maneuvering of swimming fish will help a lot in the field of underwater vehicles. Mainly the effect of tail oscillation and abdomen oscillation on fluid flow around such a body is highly unsteady, generating vortices and requiring detailed analysis of fluid-structure interactions. In the present context, a computational fluid dynamic (CFD) simulation of a tilapia fish has been developed to study about the fluid flows around this body when moving in water using the k-epsilon turbulence model. A parametric analysis of the variables that affect the flow surrounding the body is presented, along with flow visualizations. In the present study, a detailed unsteady and transient CFD analysis of the effect of tail and abdomen oscillation on the fluid flow around the fish has been studied. The simulation produces a motion of the tail and abdomen in the (x, y) plane, with both the tail and abdomen oscillating in the form of a sinusoidal wave. Detailed CFD analysis is done and results in terms of the aerodynamic force coefficients namely the lift and drag coefficients, pressure contour and velocity contour have been presented and discussed for the linear motion of fish along z-axis along with periodic oscillations of tail and abdomen in the (x,y) plane. It was observed that both the aerodynamic coefficients and forces came out to be very less which paves way for the motion of the fish with high efficiency. The analysis provided by the simulations has allowed the flow surrounding the tilapia fish undergoing periodic oscillations along with a linear motion to be studied in detail.

CFD analysis of flow through Venturi tube and its discharge coefficient

Venturi tube plays a very important role in different fields of engineering. It has a number of industrial applications in which its design is an essential factor. Venturi tube used in gas measurement applications provides an accurate critical gas flow measurement. There is a need to design Venturi tube with an effective analytical tool or software. In this work, two parameters: pressure drop and velocity discharge nozzle were analyzed using Computational Fluid Dynamics (CFD). The results obtained were then analyzed for accurate determination of the Venturi tube's discharge coefficient, Cd. It was found that there is less than 1% difference between the average values of the discharge coefficient obtained from the numerical analysis and experimental results.

Computational and experimental study of the effect of inclination on hydrocyclone performance

In this paper, the effect of inclination on hydrocyclone performance is studied using both computational fluid dynamics (CFD) and experimental methods. Experiments with water medium and the corresponding water–air two-phase CFD simulations in a 75mm diameter cyclone are carried out at various inclined positions to the vertical plane. The two-phase CFD flow analysis shows that the water split to underflow decreases as the inclination increases, which is consistent with the experiments. The predicted flow velocity profiles were analyzed for different inclinations. An increase in the inclination results the air-core size reduction and reduced pressure drop profiles. Experimental classification also performed using the silica slurry. The experimental analysis shows the increased cut-size and the reduced water split with the inclination. Cross validation of inclined cyclone’s CFD data is attempted with Electrical Resistance Tomography (ERT) and High speed video imaging experiments. The inclination effect on hydrocyclone flow field is further analyzed in terms of turbulence parameters; turbulent intensities, and radial RMS velocities. Turbulent dispersion of the particles is calculated using the CFD data and plotted by using a dispersion index formulation. Fish hook phenomena and possible mechanism of particle classification under the influence of inclination is also explained. Experimentally measured cut size and water recovery to underflow for 10wt% silica slurry at various inclinations are compared with numerical predictions. Predicted efficiency curves are found in a close agreement with experiments for all the inclinations.

CFD flow analysis in the centrifugal vortex pump

Purpose – Aging of the oil wells leads to a decrease in reservoir pressure and also to an increase in the water, gas and abrasive particles content. Therefore, there is a need for the oil pumps exploitation characteristics improvements. This paper aims to generate a valuable numerical model which will provide a useful tool to study various cases. Design/methodology/approach – Computational fluid dynamics (CFD) analysis of the generation of so-called coherent structures of eddies and turbulence in the peripheral area of the vortex rotor mounted at the back side of centrifugal rotor was undertaken. After detailed analysis of the influence of the used turbulence models on the results, a hybrid turbulent model Detached Eddies Simulation (DES) was chosen as the most suitable. Findings – Numerical control volume method with unsteady solver and DES turbulence model was proven to be valuable tool for flow analysis in the centrifugal pumps. Having in mind that DES turbulence model consumes much less computational time than large eddies turbulence model, this is a very useful fact that resulted from this research. Practical implications – The proven numerical model is robust and reliable enough to become a standard method in simulating flow and other physical phenomena occurring in centrifugal pumps and similar turbo machines. This makes it possible to easily research different factors that influence their performances. Originality/value – Comprehensive experimental and CFD study was performed which made it possible to conduct detailed validation and verification of described CFD model.

A CFD Analysis of Flow Around a Disc

Discus, disc golf and ultimate Frisbee are all sports that utilise rotating disc projectiles. The aim of this study was to use computational fluid dynamics (CFD) examine the flow over a disc and in doing so determine which CFD model is most suited to examining the aerodynamics of sports disc projectiles. All of the CFD analysis was carried out using ANSYS-Fluent V6.3. The study initially compared experimental and CFD data of flow around a simple non-rotating parametric disc, with a thickness to diameter ratio of 0.1. Aerodynamic coefficients and surface flow visualisations were compared. Three models within ANSYS-Fluent gave steady converged solutions; standard k-å, realizable k-å and standard k-ù. The standard k-ù model gave unrealistic aerodynamic coefficients and was discounted. The two k-å models were used for the second stage of the study, simulating the flow around a disc golf disc, called a Floater. The geometry of the disc was captured using a 3D non-contact laser scanner. Aerodynamic coefficients and surface flow visualisations showed good agreement between the two k-å models. The standard k-å model was deemed the most suitable for a study of flow around a sports disc, mostly due to its more accurate simulations of the parametric disc. The results were used to further examine the flow, looking at separated flow on the discs surface with increasing angle of attack and the structure of the wake. The study identified which CFD model is most suited to the simulation of flow over a sports disc and in doing so provided a platform for using CFD for future disc aerodynamics studies.

Development of an Engineering Education Framework for Aerodynamic Shape Optimization

Design optimization is a mathematical process to find an optimal solution through the use of formal optimization algorithms. Design plays a vital role in the engineering field; therefore, using design tools in education and research is becoming more and more important. Recently, numerical design optimization in fluid mechanics, which uses computational fluid dynamics (CFD), has numerous applications in the engineering field, because of the rapid development of high-performance computing resources. However, it is difficult to find design optimization software and contents for educational purposes in aerospace engineering. In the present study, we have developed an aerodynamic design framework specifically for an airfoil, based on the EDucation-research Integration through Simulation On the Net (EDISON) portal. The airfoil design framework is composed of three subparts: a geometry kernel, CFD flow analysis, and an optimization algorithm. Through a seamless interface among the subparts, an iterative design process is conducted. In addition, the CFD flow analysis and the design framework are provided through a web-based portal system, while the computation is taken care of by a supercomputing facility. In addition to the software development, educational contents are developed for lectures associated with design optimization in aerospace and mechanical engineering education programs. The software and content developed in this study is expected to be used as a tool for e-learning material, for education and research in universities.

Development and Validation of a Three-Dimensional Multiphase Flow Computational Fluid Dynamics Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines, this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach, resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach, including cavitation and air entrainment for high-speed turbomachinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty-type gas turbine journal bearings.

CFD analysis of flow boiling in the ITER first wall

Abstract This paper compares two Computational Fluid Dynamic (CFD) approaches for the analysis of flow boiling inside the first wall (FW) of the International Thermonuclear Experimental Reactor (ITER): (1) the Rohsenow model for nucleate boiling, seamlessly switching to the Volume of Fluid (VOF) approach for film boiling, as available in the commercial CFD code STAR-CCM+, (2) the Bergles–Rohsenow (BR) model, for which we developed a User Defined Function (UDF), implemented in the commercial code FLUENT. The physics of both models is described, and the results with different inlet conditions and heating levels are compared with experimental results obtained at the Efremov Institute, Russia. The performance of both models is compared in terms of accuracy and computational cost.

Model Reduction of Computational Aerothermodynamics for Hypersonic Aerothermoelasticity

A primary challenge for aerothermoelastic analysis in hypersonic flow is accurate and efficient computation of unsteady aerothermodynamic loads. This study examines two model reduction strategies with the goal to enable the use of computational fluid dynamics within a long time-record, dynamic, aerothermoelastic analysis. One approach seeks to exploit the quasi-steady nature of the flow by using steady-state computational fluid dynamics to capture primary flow features, and simple analytical approximations to account for unsteady effects. The second approach seeks to minimize the computational cost of steady-state computational fluid dynamics flow analysis using either kriging or proper orthogonal decomposition-based modeling techniques. These model reduction strategies are assessed, both individually and combined, in the context of a three-dimensional hypersonic control surface. Results computed over a wide range of operating conditions and reduced frequencies indicate that when combined, the considered approaches yield an aerothermodynamic model that is tractable within a dynamic aerothermoelastic analysis, and generally has less than 5% maximum error relative to computational fluid dynamics.

RANS modeling for flow in nuclear fuel bundle in pressurized water reactors (PWR)

This paper presents use of Reynolds-averaged Navier–Stokes (RANS) based turbulence model for single-phase CFD analysis of flow in pressurized water reactor (PWR) assemblies. An open source code called OpenFoam was used for computational fluid dynamics (CFD) study using computational meshes generated using Shari Harpoon. The PWR assembly design used in this analysis represents a 5 × 5 pin design including structural grid equipped with mixing vanes. The design specifications used in this study were obtained from the experimental setup at Texas A&M University and the results obtained are used to validate the CFD software, algorithm, and the turbulence model used in this analysis.

CFD Analysis of Flow and Heat Transfer in a Direct Transfer Preswirl System

The accuracy of computational fluid dynamics (CFD) for the prediction of flow and heat transfer in a direct transfer preswirl system is assessed through a comparison of CFD results with experimental measurements. Axisymmetric and three-dimensional (3D) sector CFD models are considered. In the 3D sector models, the preswirl nozzles or receiver holes are represented as axisymmetric slots so that steady state solutions can be assumed. A number of commonly used turbulence models are tested in three different CFD codes, which were able to capture all of the significant features of the experiments. A reasonable quantitative agreement with experimental data for static pressure, total pressure, and disk heat transfer is found for the different models, but all models gave results that differ from the experimental data in some respect. The more detailed 3D geometry did not significantly improve the comparison with experiment, which suggests deficiencies in the turbulence modeling, particularly in the complex mixing region near the preswirl nozzle jets. The predicted heat transfer near the receiver holes was also shown to be sensitive to near-wall turbulence modeling. Overall, the results are encouraging for the careful use of CFD in preswirl-system design.

MRI-Based CFD Analysis of Flow in a Human Left Ventricle: Methodology and Application to a Healthy Heart

A three-dimensional computational fluid dynamics (CFD) method has been developed to simulate the flow in a pumping left ventricle. The proposed method uses magnetic resonance imaging (MRI) technology to provide a patient specific, time dependent geometry of the ventricle to be simulated. Standard clinical imaging procedures were used in this study. A two-dimensional time-dependent orifice representation of the heart valves was used. The location and size of the valves is estimated based on additional long axis images through the valves. A semi-automatic grid generator was created to generate the calculation grid. Since the time resolution of the MR scans does not fit the requirements of the CFD calculations a third order bezier approximation scheme was developed to realize a smooth wall boundary and grid movement. The calculation was performed by a Navier-Stokes solver using the arbitrary Lagrange-Euler (ALE) formulation. Results show that during diastole, blood flow through the mitral valve forms an asymmetric jet, leading to an asymmetric development of the initial vortex ring. These flow features are in reasonable agreement with in vivo measurements but also show an extremely high sensitivity to the boundary conditions imposed at the inflow. Changes in the atrial representation severely alter the resulting flow field. These shortcomings will have to be addressed in further studies, possibly by inclusion of the real atrial geometry, and imply additional requirements for the clinical imaging processes.

3D solid fin model construction from 2D shapes using non-uniform rational B-spline surfaces

A computer aided design (CAD) tool has been specifically developed for rapid and easy design of solid models for surfboard and sailboard fins. This tool simplifies the lofting of advanced fin cross-sectional foils, in this instance based upon the family of standard airfoil series set by the National Advisory Committee for Aeronautics (NACA), whilst retaining a basic parametric description at each cross-section. This paper describes the way in which non-uniform rational B-spline (NURBS) surfaces are created from 2D profile splines, and are then used to generate 3D geometrical surfaces of the fins, which can be imported directly into commercial software packages for finite element stress analysis (FEA) and computational fluid dynamics (CFD). Pressure distributions, lift and drag forces are determined from a CFD flow analysis for various fins designed with this tool, and the results suggest that the incorporation of advanced foils into surfboard fins could indeed lead to increased performance over fins foiled using current standard techniques.

A three-dimensionally silicon-micromachined fluidic amplifier device

A fluidic proportional amplifier device is fabricated using three-dimensional silicon micromachining. The technology involves deep vertical dry etching to fabricate the amplifier midsection, and three-dimensional passage etching from the back side, followed by glass anodic bonding on the front side. In order to optimize the device performance, the amplifier geometries are designed using three-dimensional CFD (computational fluid dynamics) flow analysis. The device performance is measured using nitrogen as the working fluid. The experimentally measured value of the amplifier gain is 3.15.