Matching Items (36)

135729-Thumbnail Image.png

In Vitro and In Silico Study of Hemodynamics In Vascular Models: Validating Computational Fluid Dynamics for Medical Application

Description

This study investigates the application of Computational Fluid Dynamics (CFD) to the medical field. An overview of recent advances in computational simulation and modeling in medical applications is provided, with a particular emphasis on CFD. This study attempts to validate

This study investigates the application of Computational Fluid Dynamics (CFD) to the medical field. An overview of recent advances in computational simulation and modeling in medical applications is provided, with a particular emphasis on CFD. This study attempts to validate CFD and demonstrate the possibility for applying CFD to the clinical treatment and evaluation of atherosclerotic disease. Three different geometric configurations are investigated: one idealized bifurcation with a primary diameter of 8 mm, and two different patient-specific models of the bifurcation from the common femoral artery to the superficial and deep femoral arteries. CFD is compared against experimental measurements of steady state and pulsatile flow acquired with Particle Image Velocimetry (PIV). Steady state and pulsatile flow rates that are consistent with those observed in the femoral artery are used. In addition, pulsatile CFD simulations are analyzed in order to demonstrate meaningful clinical applications for studying and evaluating the treatment of atherosclerotic disease. CFD was successfully validated for steady state flow, with an average percent error of 6.991%. Potential for validation was also demonstrated for pulsatile flow, but methodological errors warrant further investigation to reformulate methods and analyze results. Quantities frequently associated with atherosclerotic disease and arterial bifurcations, such as large variations in wall shear stress and the presence of recirculation zones are demonstrated from the pulsatile CFD simulations. Further study is required in order to evaluate whether or not such phenomena are represented by CFD accurately. Further study must also be performed in order to evaluate the practicality and utility of CFD for the evaluation of atherosclerotic disease treatment.

Contributors

Agent

Created

Date Created
2016-05

Quantifying Effects of Stent Treatment on Cerebral Aneurysm Fluid Dynamics using Finite Element Modeling

Description

The purpose of this thesis was to explore how changes in the geometry of a bifurcating cerebral aneurysm will affect the hemodynamics in idealized models after stent treatment. This thesis explores the use of a computationally modeled Enterprise Vascular Reconstruction

The purpose of this thesis was to explore how changes in the geometry of a bifurcating cerebral aneurysm will affect the hemodynamics in idealized models after stent treatment. This thesis explores the use of a computationally modeled Enterprise Vascular Reconstruction Device (Cordis, East Bridgewater, NJ), a high porosity and closed cell design. The models represent idealized cases of saccular aneurysms with dome sizes of either 4mm or 6mm and a dome to neck ratio of either 3:2 or 2:1. Two aneurysm contact angles are studied, one at 45 degrees and the other at 90 degrees. The stent was characterized and deployed with the use of Finite Element Analysis into each model. Computational Fluid Dynamic principles were applied in series of simulations on treated and untreated models. Data was gathered in the neck plane for the average velocity magnitude, root mean squared velocity, average flow vector angle of deflection, and the cross neck flow rate. Within the aneurysm, the average velocity magnitude, root mean squared velocity, and average pressure were calculated. Additionally, the mass flow rate at each outlet was recorded. The results of this study indicate that the Enterprise Stent was most effective in the sharper, 90 degree geometry of Model 3. Additionally, the stent had an adverse effect on the Models 1 and 4, which had the smallest neck sizes. Conclusions are that the Enterprise Stent, as a stand-alone treatment method is only reliable in situations that take advantage of its design.

Contributors

Agent

Created

Date Created
2013-05

147740-Thumbnail Image.png

Fluid flow in a temperature-stratified, parametrically forced regime

Description

This project is a synthesis of the author's learning over the semesters in working with the CFD Group at Arizona State University. The incompressible Navier-Stokes equations are overviewed, starting with the derivation from the continuity equation, then non-dimensionalization, methods of

This project is a synthesis of the author's learning over the semesters in working with the CFD Group at Arizona State University. The incompressible Navier-Stokes equations are overviewed, starting with the derivation from the continuity equation, then non-dimensionalization, methods of solving and computing quantities of interest. The rest of this document is expository analysis of solutions in a confined fluid flow, building toward a parametrically forced regime that generates complex flow patterns including Faraday waves. The solutions come from recently published studies Dynamics in a stably stratified tilted square cavity (Grayer et al.) and Parametric instabilities of a stratified shear layer (Buchta et al).

Contributors

Agent

Created

Date Created
2021-05

152249-Thumbnail Image.png

Parametric analysis of a hypersonic inlet using computational fluid dynamics

Description

For CFD validation, hypersonic flow fields are simulated and compared with experimental data specifically designed to recreate conditions found by hypersonic vehicles. Simulated flow fields on a cone-ogive with flare at Mach 7.2 are compared with experimental data from NASA

For CFD validation, hypersonic flow fields are simulated and compared with experimental data specifically designed to recreate conditions found by hypersonic vehicles. Simulated flow fields on a cone-ogive with flare at Mach 7.2 are compared with experimental data from NASA Ames Research Center 3.5" hypersonic wind tunnel. A parametric study of turbulence models is presented and concludes that the k-kl-omega transition and SST transition turbulence model have the best correlation. Downstream of the flare's shockwave, good correlation is found for all boundary layer profiles, with some slight discrepancies of the static temperature near the surface. Simulated flow fields on a blunt cone with flare above Mach 10 are compared with experimental data from CUBRC LENS hypervelocity shock tunnel. Lack of vibrational non-equilibrium calculations causes discrepancies in heat flux near the leading edge. Temperature profiles, where non-equilibrium effects are dominant, are compared with the dissociation of molecules to show the effects of dissociation on static temperature. Following the validation studies is a parametric analysis of a hypersonic inlet from Mach 6 to 20. Compressor performance is investigated for numerous cowl leading edge locations up to speeds of Mach 10. The variable cowl study showed positive trends in compressor performance parameters for a range of Mach numbers that arise from maximizing the intake of compressed flow. An interesting phenomenon due to the change in shock wave formation for different Mach numbers developed inside the cowl that had a negative influence on the total pressure recovery. Investigation of the hypersonic inlet at different altitudes is performed to study the effects of Reynolds number, and consequently, turbulent viscous effects on compressor performance. Turbulent boundary layer separation was noted as the cause for a change in compressor performance parameters due to a change in Reynolds number. This effect would not be noticeable if laminar flow was assumed. Mach numbers up to 20 are investigated to study the effects of vibrational and chemical non-equilibrium on compressor performance. A direct impact on the trends on the kinetic energy efficiency and compressor efficiency was found due to dissociation.

Contributors

Agent

Created

Date Created
2013

131704-Thumbnail Image.png

Numerical Analysis of the Resistive Drag Force in Competitive Swimming

Description

Competitive Swimming is not only a sport, but also an invaluable life skill. As long as it has existed, people have wondered how to swim faster. There are a multitude of variables that go into any race and shockingly not

Competitive Swimming is not only a sport, but also an invaluable life skill. As long as it has existed, people have wondered how to swim faster. There are a multitude of variables that go into any race and shockingly not much research around to scientifically approach the question. This study aims to investigate the drag forces behind a Swimmer’s race to give better insight as to what will slow a Swimmer down through simulations in ANSYS Fluent. Simple 2D simulations were made with a Swimmer in different positions and a flow of water moved over them. What was found was that different positions, or techniques, yield vastly different results. When following typical good technique, a Swimmer can expect to be approximately 136% less drag forces compared to a typical bad technique. Additionally, small errors such as not being perfectly horizontal can lead to a difference of around 100 Newtons of drag force between perfectly horizontal and a 5-degree angle of attack. Another observation made was that errors are exacerbated by being near a wall, so Swimming in an end lane next to the pool wall leads to about 57% more drag forces that any other lane. Still, there are many more observations to be made as there is so much more to research in swimming.

Contributors

Agent

Created

Date Created
2020-05

Dynamics of Tilted Stably Stratified Square Cavities

Description

The dynamics of a stably and thermally stratified, two dimensional fluid-filled cavity are the subject of numerical study. When gravity is orthogonal to the endwalls, a closed form for a steady state solution with trivial flow may be obtained. However,

The dynamics of a stably and thermally stratified, two dimensional fluid-filled cavity are the subject of numerical study. When gravity is orthogonal to the endwalls, a closed form for a steady state solution with trivial flow may be obtained. However, as soon as the cavity is tilted the flow becomes nontrivial. Previous studies have investigated when this tilt angle is 180 degrees (Rayleigh-Bénard convection), 90 degrees, and 0 degrees, or have done a sweep while solving the steady-state equations. When buoyancy is sufficiently weak the flow is stable and steady up to 90 degrees of tilt. Above a certain level of buoyancy, as measured by the temperature difference between the top and bottom walls, the flow becomes unsteady above a tilt angle less than 90 degrees. Specifically, In this study we examine the relationship between the critical tilt angle and the buoyancy level at the onset of unsteadiness, as well as the dynamical mechanisms by which it occurs.

Contributors

Created

Date Created
2019-05

Design and Analyze a Liquid-Liquid Swirl Coaxial Injector for a small-scale rocket engine using Computational Fluid Dynamics for minimum pressure drop and maximum spray angle.

Description

Atomization of fluids inside combustion chamber has been a very complex and long-lasting subject that is still researched into for maximum efficiency in mixing oxidizer and fuel. This thesis focuses on an injector called the Liquid-Liquid Swirl Coaxial Injector (LLSC)

Atomization of fluids inside combustion chamber has been a very complex and long-lasting subject that is still researched into for maximum efficiency in mixing oxidizer and fuel. This thesis focuses on an injector called the Liquid-Liquid Swirl Coaxial Injector (LLSC) to be used in a small-scale rocket engine due to its high efficiency in spray angles and low pressure drops. Injectors are the elements that exist as a connection in between the plumbing and the combustion chamber of the rocket engine. The performance of injectors can greatly affect the stability and efficiency of the engine. Injectors proportionally help breakup the fluid into small droplets that help in the efficiency of vaporization of fluids while combusting. Helios Rocketry, Arizona State University’s student-led engineering organization, is working to design and successfully launch a small-scale bi-propellant liquid rocket engine to a 100 km (Karman Line) in space as part of the Base11 challenge. For this task a highly efficient injector element needed to be designed that can achieve high amounts of atomization with a large spray angle, to help with combustion in a relatively small sized chamber. The purpose of this thesis is to explore a specific type of injector element called a LLSC injector element. This is performed by simulating it through an LES model in computational fluid dynamics using a Voronoi based meshing scheme, by using codes from Cascade Technologies. In the end a 35-injector element design was used for an injector plate. This helped minimize the pressure drop and keep the wall stress below the safety limit.

Contributors

Agent

Created

Date Created
2019-05

132111-Thumbnail Image.png

The Effect of Spoilers on Vehicle Aerodynamics and Performance

Description

An understanding of aerodynamics is crucial for automobile performance and efficiency. There are many types of “add-on” aerodynamic devices for cars including wings, splitters, and vortex generators. While these have been studied extensively, rear spoilers have not, and their effects

An understanding of aerodynamics is crucial for automobile performance and efficiency. There are many types of “add-on” aerodynamic devices for cars including wings, splitters, and vortex generators. While these have been studied extensively, rear spoilers have not, and their effects are not as widely known. A Computational Fluid Dynamics (CFD) and wind tunnel study was performed to study the effects of spoilers on vehicle aerodynamics and performance. Vehicle aerodynamics is geometry dependent, meaning what applies to one car may or may not apply on another. So, the Scion FRS was chosen as the test vehicle because it is has the “classic” sports car configuration with a long hood, short rear, and 2+2 passenger cabin while also being widely sold with a plethora of aftermarket aerodynamic modifications available. Due to computing and licensing restrictions, only a 2D CFD simulation was performed in ANSYS Fluent 19.1. A surface model of the centerline of the car was created in SolidWorks and imported into ANSYS, where the domain was created. A mesh convergence study was run to determine the optimum mesh size, and Realizable k-epsilon was the chosen physics model. The wind tunnel lacked equipment to record quantifiable data, so the wind tunnel was utilized for flow visualization on a 1/24 scale car model to compare with the CFD.

0° spoilers reduced the wake area behind the car, decreasing pressure drag but also decreasing underbody flow, causing a reduction in drag and downforce. Angled spoilers increased the wake area behind the car, increasing pressure drag but also increasing underbody flow, causing an increase in drag and downforce. Longer spoilers increased these effects compared to shorter spoilers, and short spoilers at different angles did not create significantly different effects. 0° spoilers would be best suited for cases that prioritize fuel economy or straight-line acceleration and speed due to the drag reduction, while angled spoilers would be best suited for cars requiring downforce. The angle and length of spoiler would depend on the downforce needed, which is dependent on the track.

Contributors

Agent

Created

Date Created
2019-12

153954-Thumbnail Image.png

Numerical simulation of dynamic contact angles and contact lines in multiphase flows using level set method

Description

Many physical phenomena and industrial applications involve multiphase fluid flows and hence it is of high importance to be able to simulate various aspects of these flows accurately. The Dynamic Contact Angles (DCA) and the contact lines at the wall

Many physical phenomena and industrial applications involve multiphase fluid flows and hence it is of high importance to be able to simulate various aspects of these flows accurately. The Dynamic Contact Angles (DCA) and the contact lines at the wall boundaries are a couple of such important aspects. In the past few decades, many mathematical models were developed for predicting the contact angles of the inter-face with the wall boundary under various flow conditions. These models are used to incorporate the physics of DCA and contact line motion in numerical simulations using various interface capturing/tracking techniques. In the current thesis, a simple approach to incorporate the static and dynamic contact angle boundary conditions using the level set method is developed and implemented in multiphase CFD codes, LIT (Level set Interface Tracking) (Herrmann (2008)) and NGA (flow solver) (Desjardins et al (2008)). Various DCA models and associated boundary conditions are reviewed. In addition, numerical aspects such as the occurrence of a stress singularity at the contact lines and grid convergence of macroscopic interface shape are dealt with in the context of the level set approach.

Contributors

Agent

Created

Date Created
2015

153834-Thumbnail Image.png

Optimization of complex thermal-fluid processes

Description

First, in a large-scale structure, a 3-D CFD model was built to simulate flow and temperature distributions. The flow patterns and temperature distributions are characterized and validated through spot measurements. The detailed understanding of them then allows for optimization of

First, in a large-scale structure, a 3-D CFD model was built to simulate flow and temperature distributions. The flow patterns and temperature distributions are characterized and validated through spot measurements. The detailed understanding of them then allows for optimization of the HVAC configuration because identification of the problematic flow patterns and temperature mis-distributions leads to some corrective measures. Second, an appropriate form of the viscous dissipation term in the integral form of the conservation equation was considered, and the effects of momentum terms on the computed drop size in pressure-atomized sprays were examined. The Sauter mean diameter (SMD) calculated in this manner agrees well with experimental data of the drop velocities and sizes. Using the suggested equation with the revised treatment of liquid momentum setup, injection parameters can be directly input to the system of equations. Thus, this approach is capable of incorporating the effects of injection parameters for further considerations of the drop and velocity distributions under a wide range of spray geometry and injection conditions. Lastly, groundwater level estimation was investigated using compressed sensing (CS). To satisfy a general property of CS, a random measurement matrix was used, the groundwater network was constructed, and finally the l-1 optimization was run. Through several validation tests, correct estimation of groundwater level by CS was shown. Using this setup, decreasing trends in groundwater level in the southwestern US was shown. The suggested method is effective in that the total measurements of registered wells can be reduced down by approximately 42 %, sparse data can be visualized and a possible approach for groundwater management during extreme weather changes, e.g. in California, was demonstrated.

Contributors

Agent

Created

Date Created
2015