Browsing by Subject "Finite volume method"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item A numerical study of heat and momentum transfer over a bank of flat tubes(Texas A&M University, 2005-11-01) Bahaidarah, Haitham M. S.The present study considers steady laminar two-dimensional incompressible flow over both in-line and staggered flat tube bundles used in heat exchanger applications. The effects of various independent parameters, such as Reynolds number (Re), Prandtl number (Pr), length ratio (L/Da), and height ratio (H/Da), on the pressure drop and heat transfer were studied. A finite volume based FORTRAN code was developed to solve the governing equations. The scalar and velocity variables were stored at staggered grid locations. Scalar variables (pressure and temperature) and all thermophysical properties were stored at the main grid location and velocities were stored at the control volume faces. The solution to a one-dimensional convection diffusion equation was represented by the power law. The locations of grid points were generated by the algebraic grid generation technique. The curvilinear velocity and pressure fields were linked by the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. The line-by-line method, which is a combination of the Tri-Diagonal Matrix Algorithm (TDMA) and the Gauss-Seidel procedure, was used to solve the resulting set of discretization equations. The result of the study established that the flow is observed to attain a periodically fully developed profile downstream of the fourth module. The strength increases and the size of the recirculation gets larger as the Reynolds number increases. As the height ratio increases, the strength and size of the recirculation decreases because the flow has enough space to expand through the tube passages. The increase in length ratio does not significantly impact the strength and size of the recirculation. The non-dimesionalized pressure drop monotonically decreased with an increase in the Reynolds number. In general, the module average Nusselt number increases with an increase in the Reynolds number. The results at Pr = 7.0 indicate a significant increase in the computed module average Nusselt number when compared to those for Pr = 0.7. The overall performance of in-line configuration for lower height ratio (H/Da = 2) and higher length ratio (L/Da = 6) is preferable since it provides higher heat transfer rate for all Reynolds numbers except for the lowest Re value of 25. As expected the staggered configurations perform better than the in-line configuration from the heat transfer point of view.Item A STUDY OF SOLVING NAVIER-STOKES EQUATIONS WITH A FINITE VOLUME METHOD BASED ON POLYGONAL UNSTRUCTURED GRIDS AND THE COMPUTATIONAL ANALYSIS OF GROUND VEHICLE AERODYNAMICS(2010-12) Tan, JiannanNavier-Stokes (N-S) equations describe the motion of fluid flow in the nature and they are called the governing equations of fluid flows. Solving Navier-Stokes equations is of great interest to the scientists and researchers. Due to the high nonlinearity, achieving the analytical solutions for the N-S equations is extremely difficult, if not impossible. Thus, people have to switch to numerical solutions with putting on certain restrictions on the N-S equations. This leads to the development of Computational Fluid Dynamics (CFD). This dissertation contains two major sections. The first section is about theoretical study of CFD. We go through the whole process that a CFD analysis normally requires: generating mesh, setting boundary conditions and achieving numerical solutions of N-S equations, and post-processing to achieve flow field plots. An in-house 2- D CFD code based on unstructured polygonal mesh is presented, in which a new momentum interpolation method is developed and implemented to calculate the flow flux on the cell faces. The 2-D code is also validated by comparing the numerical results with widely-known analytical results, if available, or by benchmarking with the results produced by commercial CFD software packages. The second section of this dissertation is about one of the applications of CFD in modern auto industry – ground vehicle aerodynamics. The cross wind effect on a sport utility vehicle (SUV) is studied and analyzed using CFD methods and compared with available wind tunnel experimental results. The first section contributes to the philosophy of mechanical physics and the second section aims to fulfill the purpose of engineering.Item Development and validation of a system identification methodology for the characterization of contaminated sites(Texas Tech University, 1998-12) Jayakody, Kankanamalage Geethani KumariThe quality of groundwater has become a major concern in the United States and many other industrialized countries since the discovery of numerous sites with contamination from hazardous wastes and leaked fuels. Investigation and monitoring have begun at many of these sites, but execution of remedial plans has often been delayed due to regulatory and financial constraints as well as limited understanding of the processes that control the distribution of contaminants in the subsurface. One of the primary difficulties encountered in the site remediation process is the inability to determine the site heterogeneity in an adequate manner. In this research, a mathematical technique known as System Identification Methodology (SID) is used in conjunction with the flow and contaminant transport equations to address the above problem. In this mathematical procedure, a finite volume formulation with an upwind velocity scheme was used to discretize the flow and transport equations. In order to determine site heterogeneity, independent contaminant transport parameters were assigned to each rectangular element in the flow domain. The finite volume formulations of groundwater flow and contaminant transport equations were then reorganized into the standard state-space form that is commonly used in system identification procedures. The determination of the distribution of unknown parameters at the site was then accomplished by minimizing the error between both measured contaminant concentration and hydraulic head and calculated contaminant concentration and hydraulic head by the above finite volume models for groundwater flow and contaminant transport. The Levenberg-Marquardt algorithm was used as the optimization scheme. Once the mathematical model was developed, test cases were run to verify the mathematical accuracy of the model. Sensitivity analyses were performed to determine the relative significance of the heterogeneities in dispersion, retardation, and decay terms on contaminant flow. The model was validated by applying it to actual observations from four selected case studies. As the first step in the validation, the SID methodology was applied to contaminant concentration data obtained from large-scale sand tank tests. Subsequently field validation was accomplished by applying the SID methodology to site in the Southern High Plains of Texas, Jordan aquifer in Iowa and landfill site at Borden.Item Fluid-structure interactions in microstructures(2013-05) Das, Shankhadeep; Murthy, Jayathi; Mathur, SanjayRadio-frequency microelectromechanical systems (RF MEMS) are widely used for contact actuators and capacitive switches. These devices typically consist of a metallic membrane which is activated by a time-periodic electrostatic force and makes periodic contact with a contact pad. The increase in switch capacitance at contact causes the RF signal to be deflected and the switch thus closes. Membrane motion is damped by the surrounding gas, typically air or nitrogen. As the switch opens and closes, the flow transitions between the continuum and rarefied regimes. Furthermore, creep is a critical physical mechanism responsible for the failure in these devices, especially those operating at high RF power. Simultaneous and accurate modeling of all these different physics is required to understand the dynamical membrane response in these devices and to estimate device lifetime and to improve MEMS reliability. It is advantageous to model fluid and structural mechanics and electrostatics within a single comprehensive numerical framework to facilitate coupling between them. In this work, we develop a single unified finite volume method based numerical framework to study this multi-physics problem in RF MEMS. Our objective required us to develop structural solvers, fluid flow solvers, and electrostatic solvers using the finite volume method, and efficient mechanisms to couple these different solvers. A particular focus is the development of flow solvers which work efficiently across continuum and rarefied regimes. A number of novel contributions have been made in this process. Structural solvers based on a fully implicit finite volume method have been developed for the first time. Furthermore, strongly implicit fluid flow solvers have also been developed that are valid for both continuum and rarefied flow regimes and which show an order of magnitude speed-up over conventional algorithms on serial platforms. On parallel platforms, the solution techniques developed in this thesis are shown to be significantly more scalable than existing algorithms. The numerical methods developed are used to compute the static and dynamic response of MEMS. Our results indicate that our numerical framework can become a computationally efficient tool to model the dynamics of RF MEMS switches under electrostatic actuation and gas damping.Item Mimetic finite differences for porous media applications(2014-05) Al-Hinai, Omar A.; Wheeler, Mary F. (Mary Fanett)We connect the Mimetic Finite Difference method (MFD) with the finite-volume two-point flux scheme (TPFA) for Voronoi meshes. The main effect is reducing the saddle-point system to a much smaller symmetric-positive definite matrix. In addition, the generalization allows MFD to seamlessly integrate with existing porous media modeling technology. The generalization also imparts the monotonicity property of the TPFA method on MFD. The connection is achieved by altering the consistency condition of the velocity bilinear operator. First-order convergence theory is presented as well as numerical results that support the claims. We demonstrate a methodology for using MFD in modeling fluid flow in fractures coupled with a reservoir. The method can be used for nonplanar fractures. We use the method to demonstrate the effects of fracture curvature on single-phase and multi-phase flows. Standard benchmarks are used to demonstrate the accuracy of the method. The approach is coupled with existing reservoir simulation technology.Item Numerical modeling of flow around ducted propellers(2006-05) Gu, Hua, 1975-; Kinnas, Spyros A.An iterative method, coupling a vortex lattice method (VLM) based potential solver and a finite volume method (FVM) based Euler solver, is used to model the flow around ducted propellers. The VLM is applied to the blade inside the duct, solves for the potential flow in the vicinity of the blade and predicts the pressures, forces, moments and cavity patterns. The FVM is applied to the whole fluid domain with the duct. The Euler equations are solved with the pressure difference across the blades being converted into body force terms and the duct being modeled as solid wall boundaries. The effective velocities are then evaluated by subtracting the induced velocities from the total velocities. The VLM is applied again with the updated effective velocities and the iteration between VLM and FVM continues until the thrust and torque converge. The interaction between duct and propeller is included with such an iterative procedure. Some special treatments on the ducted propeller are presented. A simplified image model is applied to account for the nonaxisymmetric duct wall effects. A gap model, based on an orifice equation, is implemented to predict the influence of the viscous gap region on the overall performance of ducted propellers. A computational viscous model is used to assess the discharge coefficient in the current method. Some approaches to predict the effective velocities with accuracy are discussed. Systematic validations for the current method with other numerical methods and experiments are given. Finally an approach to model the tip leakage vortex is presented. The tip leakage vortices are aligned via a free wake relaxation method. Convergence and parameter studies are given for this model.