Browsing by Subject "CFD"

Now showing 1 - 6 of 6
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    Computational Fluid Dynamics for Modeling and Simulation of Intraocular Drug Delivery and Wall Shear Stress in Pulsatile Flow
    (2020-08) Abootorabi, Seyedalireza; Yu, Huidan; Nematollahi, Khosrow; Yokota, Hiroki
    The thesis includes two application studies of computational fluid dynamics. The first is new and efficient drug delivery to the posterior part of the eye, a growing health necessity worldwide. Current treatment of eye diseases, such as age-related macular degeneration (AMD), relies on repeated intravitreal injections of drug-containing solutions. Such a drug delivery has significant cant drawbacks, including short drug life, vital medical service, and high medical costs. In this study, we explore a new approach of controlled drug delivery by introducing unique porous implants. Computational modeling contains physiological and anatomical traits. We simulate the IgG1 Fab drug delivery to the posterior eye to evaluate the effectiveness of the porous implants to control the drug delivery. The computational model was validated by established computation results from independent studies and experimental data. Overall, the results indicate that therapeutic drug levels in the posterior eye are sustained for eight weeks, similar to those performed with intravitreal injection of the same drug. We evaluate the effects of the porous implant on the time evaluation of the drug concentrations in the sclera, choroid, and retina layers of the eye. Subsequent simulations were carried out with varying porosity values of a porous episcleral implant. Our computational results reveal that the time evolution of drug concentration is distinctively correlated to drug source location and pore size. The response of this porous implant for controlled drug delivery applications was examined. A correlation between porosity and fluid properties for the porous implants was revealed in this study. The second application lays in the computational modeling of the oscillating
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    Coupled thermal-fluid analysis with flowpath-cavity interaction in a gas turbine engine
    (2013-12) Fitzpatrick, John Nathan; Wasfy, Tamer; Nalim, M. Razi; Yu, Huidan (Whitney); Anwar, Sohel
    This study seeks to improve the understanding of inlet conditions of a large rotor-stator cavity in a turbofan engine, often referred to as the drive cone cavity (DCC). The inlet flow is better understood through a higher fidelity computational fluid dynamics (CFD) modeling of the inlet to the cavity, and a coupled finite element (FE) thermal to CFD fluid analysis of the cavity in order to accurately predict engine component temperatures. Accurately predicting temperature distribution in the cavity is important because temperatures directly affect the material properties including Young's modulus, yield strength, fatigue strength, creep properties. All of these properties directly affect the life of critical engine components. In addition, temperatures cause thermal expansion which changes clearances and in turn affects engine efficiency. The DCC is fed from the last stage of the high pressure compressor. One of its primary functions is to purge the air over the rotor wall to prevent it from overheating. Aero-thermal conditions within the DCC cavity are particularly challenging to predict due to the complex air flow and high heat transfer in the rotating component. Thus, in order to accurately predict metal temperatures a two-way coupled CFD-FE analysis is needed. Historically, when the cavity airflow is modeled for engine design purposes, the inlet condition has been over-simplified for the CFD analysis which impacts the results, particularly in the region around the compressor disc rim. The inlet is typically simplified by circumferentially averaging the velocity field at the inlet to the cavity which removes the effect of pressure wakes from the upstream rotor blades. The way in which these non-axisymmetric flow characteristics affect metal temperatures is not well understood. In addition, a constant air temperature scaled from a previous analysis is used as the simplified cavity inlet air temperature. Therefore, the objectives of this study are: (a) model the DCC cavity with a more physically representative inlet condition while coupling the solid thermal analysis and compressible air flow analysis that includes the fluid velocity, pressure, and temperature fields; (b) run a coupled analysis whose boundary conditions come from computational models, rather than thermocouple data; (c) validate the model using available experimental data; and (d) based on the validation, determine if the model can be used to predict air inlet and metal temperatures for new engine geometries. Verification with experimental results showed that the coupled analysis with the 3D no-bolt CFD model with predictive boundary conditions, over-predicted the HP6 offtake temperature by 16k. The maximum error was an over-prediction of 50k while the average error was 17k. The predictive model with 3D bolts also predicted cavity temperatures with an average error of 17k. For the two CFD models with predicted boundary conditions, the case without bolts performed better than the case with bolts. This is due to the flow errors caused by placing stationary bolts in a rotating reference frame. Therefore it is recommended that this type of analysis only be attempted for drive cone cavities with no bolts or shielded bolts.
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    Modeling and design optimization of a microfluidic chip for isolation of rare cells
    (2013-12) Gannavaram, Spandana; Zhu, Likun; Yu, Huidan (Whitney); Xie, Jian; Anwar, Sohel
    Cancer is still among those diseases that prominently contribute to the numerous deaths that are caused each year. But as technology and research is reaching new zeniths in the present times, cure or early detection of cancer is possible. The detection of rare cells can help understand the origin of many diseases. The current study deals with one such technology that is used for the capture or effective separation of these rare cells called Lab-on-a-chip microchip technology. The isolation and capture of rare cells is a problem uniquely suited to microfluidic devices, in which geometries on the cellular length scale can be engineered and a wide range of chemical functionalizations can be implemented. The performance of such devices is primarily affected by the chemical interaction between the cell and the capture surface and the mechanics of cell-surface collision and adhesion. This study focuses on the fundamental adhesion and transport mechanisms in rare cell-capture microdevices, and explores modern device design strategies in a transport context. The biorheology and engineering parameters of cell adhesion are defined; chip geometries are reviewed. Transport at the microscale, cell-wall interactions that result in cell motion across streamlines, is discussed. We have concentrated majorly on the fluid dynamics design of the chip. A simplified description of the device would be to say that the chip is at micro scale. There are posts arranged on the chip such that the arrangement will lead to a higher capture of rare cells. Blood consisting of rare cells will be passed through the chip and the posts will pose as an obstruction so that the interception and capture efficiency of the rare cells increases. The captured cells can be observed by fluorescence microscopy. As compared to previous studies of using solid microposts, we will be incorporating a new concept of cylindrical shell micropost. This type of micropost consists of a solid inner core and the annulus area is covered with a forest of silicon nanopillars. Utilization of such a design helps in increasing the interception and capture efficiency and reducing the hydrodynamic resistance between the cells and the posts. Computational analysis is done for different designs of the posts. Drag on the microposts due to fluid flow has a great significance on the capture efficiency of the chip. Also, the arrangement of the posts is important to contributing to the increase in the interception efficiency. The effects of these parameters on the efficiency in junction with other factors have been studied and quantified. The study is concluded by discussing design strategies with a focus on leveraging the underlying transport phenomena to maximize device performance.
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    Numerical simulation of combustion and unburnt products in dual-fuel compression-ignition engines with multiple injection
    (2015-12) Jamali, Arash; Nalim, Mohamed Razi; Yu, Whitney; Zhu, Likun; Chen, Jie
    Natural gas substitution for diesel can result in significant reduction in pollutant emissions. Based on current fuel price projections, operating costs would be lower. With a high ignition temperature and relatively low reactivity, natural gas can enable promising approaches to combustion engine design. In particular, the combination of low reactivity natural gas and high reactivity diesel may allow for optimal operation as a reactivity-controlled compression ignition (RCCI) engine, which has potential for high efficiency and low emissions. In this computational study, a lean mixture of natural gas is ignited by direct injection of diesel fuel in a model of the heavy-duty CAT3401 diesel engine. Dual-fuel combustion of natural gas-diesel (NGD) may provide a wider range of reactivity control than other dual-fuel combustion strategies such as gasoline-diesel dual fuel. Accurate and efficient combustion modeling can aid NGD dual-fuel engine control and optimization. In this study, multi-dimensional simulation was performed using a nite-volume computational code for fuel spray, combustion and emission processes. Adaptive mesh refinement (AMR) and multi-zone reaction modeling enables simulation in a reasonable time. The latter approach avoids expensive kinetic calculations in every computational cell, with considerable speedup. Two approaches to combustion modeling are used within the Reynolds averaged Navier-Stokes (RANS) framework. The first approach uses direct integration of the detailed chemistry and no turbulence-chemistry interaction modeling. The model produces encouraging agreement between the simulation and experimental data. For reasonable accuracy and computation cost, a minimum cell size of 0.2 millimeters is suggested for NGD dual-fuel engine combustion. In addition, the role of different chemical reaction mechanism on the NGD dual-fuel combustion is considered with this model. This work considers fundamental questions regarding combustion in NGD dual-fuel combustion, particularly about how and where fuels react, and the difference between combustion in the dual fuel mode and conventional diesel mode. The results show that in part-load working condition main part of CH4 cannot burn and it has significant effect in high level of HC emission in NGD dual-fuel engine. The CFD results reveal that homogeneous mixture of CH4 and air is too lean, and it cannot ignite in regions that any species from C7H16 chemical mechanism does not exist. It is shown that multi-injection of diesel fuel with an early main injection can reduce HC emission significantly in the NGD dual-fuel engine. In addition, the results reveal that increasing the air fuel ratio by decreasing the air amount could be a promising idea for HC emission reduction in NGD dual-fuel engine, too.
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    Tire Deformation Modeling and Effect on Aerodynamic Performance of a P2 Race Car
    (2021-08) Livny, Rotem; Dalir, Hamid; Borm, Andy; Finch, Chris
    The development work of a race car revolves around numerous goals such as drag reduction, maximizing downforce and side force, and maintaining balance. Commonly, these goals are to be met at the same time thus increasing the level of difficulty to achieve them. The methods for data acquisitions available to a race team during the season is mostly limited to wind tunnel testing and computational fluid dynamics, both of which are being heavily regulated by sanctioning bodies. While these methods enable data collection on a regular basis with repeat-ability they are still only a simulation, and as such they come with some margin of error due to a number of factors. A significant factor for correlation error is the effect of tires on the flow field around the vehicle. This error is a product of a number of deficiencies in the simulations such as inability to capture loaded radius, contact patch deformation in Y direction, sidewall deformation and overall shifts in tire dimensions. These deficiencies are evident in most WT testing yet can be captured in CFD. It is unknown just how much they do affect the aerodynamics performance of the car. That aside, it is very difficult to correlate those findings as most correlation work is done at WT which has been said to be insufficient with regards to tire effect modeling. Some work had been published on the effect of tire deformation on race car aerodynamics, showing a large contribution to performance as the wake from the front tires moves downstream to interact with body components. Yet the work done so far focuses mostly on open wheel race cars where the tire and wheel assembly is completely exposed in all directions, suggesting a large effect on aerodynamics. This study bridges the gap between understanding the effects of tire deformation on race car aerodynamics on open wheel race cars and closed wheel race cars. The vehicle in question is a hybrid of the two, exhibiting flow features that are common to closed wheel race cars due to each tire being fully enclosed from front and top. At the same time the vehicle is presenting the downstream wake effect similar to the one in open wheel race cars as the rear of the wheelhouse is open. This is done by introducing a deformable tire model using FEA commercial code. A methodology for quick and accurate model generation is presented to properly represent true tire dimensions, contact patch size and shape, and deformed dimension, all while maintaining design flexibility as the model allows for different inflation pressures to be simulated. A file system is offered to produce CFD watertight STL files that can easily be imported to a CFD analysis, while the analysis itself presents the forces and flow structures effected by incorporating tire deformation to the model. An inflation pressure sweep is added to the study in order to evaluate the influence of tire stiffness on deformation and how this results in aerodynamic gain or loss. A comparison between wind tunnel correlation domain to a curved domain is done to describe the sensitivity each domain has with regards to tire deformation, as each of them provides a different approach to simulating a cornering condition. The Study suggests introducing tire deformation has a substantial effect on the flow field increasing both drag and downforce.In addition, flow patterns are revealed that can be capitalized by designing for specific cornering condition tire geometry. A deformed tire model offers more stable results under curved and yawed flow. Moreover, the curved domain presents a completely different side force value for both deformed and rigid tires with some downforce distribution sensitivity due to inflation pressure.
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    Towards a high performance parallel library to compute fluid flexible structures interactions
    (2015-04-08) Nagar, Prateek; Song, Fengguang; Zhu, Luoding; Mukhopadhyay, Snehasis
    LBM-IB method is useful and popular simulation technique that is adopted ubiquitously to solve Fluid-Structure interaction problems in computational fluid dynamics. These problems are known for utilizing computing resources intensively while solving mathematical equations involved in simulations. Problems involving such interactions are omnipresent, therefore, it is eminent that a faster and accurate algorithm exists for solving these equations, to reproduce a real-life model of such complex analytical problems in a shorter time period. LBM-IB being inherently parallel, proves to be an ideal candidate for developing a parallel software. This research focuses on developing a parallel software library, LBM-IB based on the algorithm proposed by [1] which is first of its kind that utilizes the high performance computing abilities of supercomputers procurable today. An initial sequential version of LBM-IB is developed that is used as a benchmark for correctness and performance evaluation of shared memory parallel versions. Two shared memory parallel versions of LBM-IB have been developed using OpenMP and Pthread library respectively. The OpenMP version is able to scale well enough, as good as 83% speedup on multicore machines for <=8 cores. Based on the profiling and instrumentation done on this version, to improve the data-locality and increase the degree of parallelism, Pthread based data centric version is developed which is able to outperform the OpenMP version by 53% on manycore machines. A distributed version using the MPI interfaces on top of the cube based Pthread version has also been designed to be used by extreme scale distributed memory manycore systems.