Engineering Commons^™

Control Of Low-Speed Turbulent Separated Flow Over A Backward-Facing Ramp, John C. Lin

Mechanical & Aerospace Engineering Theses & Dissertations

The relative performance and flow phenomena associated with several devices for controlling turbulent separated flow were investigated at low speeds. Relative performance of the devices was examined for flow over a curved, backward-facing ramp in a wind tunnel, and the flow phenomena were examined in a water tunnel using dye-flow visualization. Surface static pressure measurements and oil-flow visualization results from the wind tunnel tests indicated that transverse grooves, longitudinal grooves, submerged vortex generators, vortex generator jets (VGJ’s), Viets’ fluidic flappers, elongated arches +a + a (positive angle of attack), and large-eddy breakup devices (LEBU’s) +a + a placed near the …

A Computational Aerodynamic Design Optimization Method Using Sensitivity Analysis, Mohamed E. Eleshaky

Mechanical & Aerospace Engineering Theses & Dissertations

A new and efficient procedure for aerodynamic shape optimization is presented. The salient lineaments of this procedure are: (1) using a discrete sensitivity analysis approach to determine analytically the aerodynamic sensitivity coefficients; (2) obtaining the flowfield solution either by a computational fluid dynamics (CFD) analysis or, alternatively, by a flowfield extrapolation method which is based on a truncated Taylor's series; (3) defining the aerodynamic shape in such a way that it is not restricted to any class of surfaces and the optimizer automatically shapes the aerodynamic configuration to any arbitrary geometry; and (4) requiring no expertise other than that needed …

Shape Sensitivity Analysis And Optimization Of Skeletal Structures And Geometrically Nonlinear Solids, Ching-Hung Chuang

Mechanical & Aerospace Engineering Theses & Dissertations

Formulations and computational schemes for shape design sensitivity analysis and optimization have been developed for both skeletal structures and geometrically nonlinear elastic solids. The continuum approach, which is based on the weak variational form of the governing differential equation and the concept of the material derivative, plays a central role in such a development.

In the first part of this work, the eigenvalue and eigenvector sensitivity equations for skeletal structures are derived with respect to configuration variables of joint and support locations. This derivation is done by the domain method as well as the boundary method. The discrete approach for …

Unsteady Euler And Navier-Stokes Computations Around Oscillating Delta Wing Including Dynamics, Ahmed Abd-El-Bar Ahmed Salman

Mechanical & Aerospace Engineering Theses & Dissertations

Unsteady flows around rigid or flexible delta wings with and without oscillating leading-edge flaps are considered. These unsteady flow problems are categorized under two classes of problems. In the first class, the wing motion is prescribed a priori and in the second class, the wing motion is obtained as a part of the solution. The formulation of the first class includes either the unsteady Euler or unsteady Navier-Stokes equations for the fluid dynamics and the unsteady linearized Navier-displacement (ND) equations for the grid deformation.

The problem of unsteady transonic flow past a bicircular-arc airfoil undergoing prescribed thickening-thinning oscillation is studied …

Improving The Throughput Of Plasticating Extruders : Manufacture Of Non-Circular Pellets, Measurement Of Their Interparticulate Friction Coefficient, And Implications For Screw Design, Chia-Ying Liu

Dissertations

This dissertation addresses the hypothesis that the interparticulate friction coefficient of a bed of polymeric particulates is a function of the cross-section of the pellets. Most pellets have a circular cross-section especially those that are strand cut. But when such pellets constitute a particulate bed there are few restrictions to adjacent pellets turning with respect to each other, or of the beds rupturing under shear load. This rupture can occur in plasticating extrusion, and it results in a poorly mixed melt with an inhomogeneous temperature distribution. The temperature fluctuations cause viscosity fluctuations which in turn cause pressure fluctuations. The pressure …

Computer Aided Shape Optimization Using Finite Element Analysis, Charanpreet Singh Bagga

Theses

Various theories behind Computer Aided Shape Optimization are studied. A special attention is paid to the shape representation, mesh generation and refinement during the shape optimization process. Shape optimization process for a wall bracket is performed using the Computer Aided Engineering package of I-DEAS. Finite element analysis of the wall bracket is done and the stress distribution over the bracket is studied. The bracket is trimmed in the selected low stress regions using shape optimization capability of I-DEAS and an optimized shape of the wall bracket is obtained. The end product is evaluated using Supertab module of I-DEAS as well …

A Finite Element Thermal And Diffusion Analysis At Bearing Metal Interface In Extrusion Processes, Biju Dennis

Theses

A mathematical model is developed to study the effect of extrusion speed and the bearing length on the surface temperature along the die billet interface. The surface temperature distribution resulting from the plastic work done on the die billet interface is studied. Finite element analysis is done on the model incorporating the mass transport effect occurring during the extrusion process and the interdependence of various parameters are presented. Die wearing problem is analyzed considering the effect of diffusion. Thermal analogy of the diffusion problem is utilized in the development of the mathematical model for diffusion problem and finite element analysis …

Computer Numerical Controlled (Cnc) Machining Of Screws And Dies For Plasticating Extruders : Determination Of The Criteria For Implementing Cnc Machining, Nilesh H. Desai

Theses

The work of this thesis is dedicated to the manufacturing industry making production equipment to manufacture plastic products. The main theme of the thesis is to determine the criteria for implementing Computer Numerical Control machining to make parts with complex geometries for production equipment.

A small manufacturing company with job shop type of production was chosen as the subject and study of extruder manufacturing process was performed. The various available alternatives of CNC manufacturing units available in the market were chosen and their feasibility examined.

At present a large variety of CNC machine tools are available in the market, offered …

Microchannel Fluid Flow In A Silicon Chip, Ronald R. Ulseth

Retrospective Theses and Dissertations

The objective of this study was to analyze theoretically and experimentally the fluid characteristics of forced flow in microchannels. An apparatus was designed and constructed to allow microflow through a 450 μm wide by 17. 5 μm deep microchannel in a silicon chip. The flow through the chip was laminar with Reynolds numbers not exceeding 100. Tuckerman and Pease (1981) theorized that microscopic heat exchangers etched in the back of silicon chips could provide for efficient heat removal from the chips at rates much higher than the conventional methods could attain. The best technologies available provided for heat removal rates …

Particle Size And Velocity Measurements In Two Phase Flows Using Laser Doppler Velocimetry, Joseph Parker

Honors Theses

Laser Doppler Velocimetry is used in fluid mechanics to measure the velocity of particles in fluid flows. A small particle exhibits motion closely corresponding to the fluid behavior because of its ability to follow high frequency flow fluctuations. Large particles do not follow the flow field precisely but represent a second phase. This project used LDV to measure the size and velocity of particles in two phase flows by computer analysis of the Doppler signal.

Hypoid Gear Optimization, Selvaraj Ramachandran

Dissertations and Theses

A hypoid gear optimization procedure using the method of feasible directions has been developed. The objective is to reduce the gear set weight with bending strength, contact strength and facewidth-diametral pitch ratio as constraints. The objective function weight, is calculated from the geometric approximation of the volume of the gear and pinion. The design variables selected are number of gear teeth, diametral pitch, and facewidth. The input parameters for starting the initial design phase are power to be transmitted, speed, gear ratio, type of application, mounting condition, type of loading, and the material to be used. In the initial design …

Non-Destructive Evaluation Of Space Shuttle Thermal Protection System Tile Bond Integrity, George David Mulligan

Retrospective Theses and Dissertations

Experimental modal analysis (EMA) is used as a non-destructive technique for the evaluation of Space Shuttle thermal protection system (TPS) tile bond integrity. Finite element (FE) models for tile systems were developed and were used to generate their vibration characteristics (i.e. natural frequencies and mode shapes). Various TPS tile assembly configurations as well as different bond conditions were analyzed. Results of finite element analyses demonstrated a drop in natural frequencies and a change in mode shapes which correlate with both size and location of disband. Results of experimental testing of tile panels correlated with FE results and demonstrated the feasibility …

Transition From Laminar To Turbulent Flow Around An Airfoil, Chang-Ren Chen

Doctoral Dissertations

"A computational fluid dynamics (CFD) code has been developed for two-dimensional incompressible turbulent flows and employed to solve the Navier Stokes equations around an airfoil of arbitrary shape. A low-Reynolds-number k — e turbulence model including curvature effect was used to consider the gain and loss of turbulent kinetic energy. To include laminar sublayer into the computational domain, a multi-layer grid and a cubic-slpine grid were introduced through a conservative form of coordinate transformation. The flow structure varies with the Reynolds numbers. For an airfoil at low Reynolds numbers (below ten thousand), distinct vortex shedding patterns can be found in …

Explicit Multistage Schemes For The Solution Of The Three-Dimensional Compressible Euler/Navier-Stokes Equations, Alaa Ahmed Elmiligui

Mechanical & Aerospace Engineering Theses & Dissertations

The objective of this study was to develop a high-resolution-explicit-multi-block numerical algorithm, suitable for efficient computation of the three-dimensional, time-dependent Euler and Navier-Stokes equations. The resulting algorithm has employed a finite volume approach, using MUSCL-type differencing to obtain state variables at cell interface. Variable interpolations were written in the $\kappa$-scheme formulation. Inviscid fluxes were calculated via Roe's flux-difference splitting, and van Leer's flux-vector splitting techniques, which are considered state of the art. The viscous terms were discretized using a second-order, central-difference operator.

Two classes of explicit time integration has been investigated for solving the compressible inviscid/viscous flow problems--two-stage predictor-corrector schemes, …