Engineering Commons^™

Investigation, Modeling And Validation Of Digital Bridge For A New Generation Hot-Wire Anemometer, Karthik Kamalakar Joshi

Mechanical & Aerospace Engineering Theses & Dissertations

The Digital Bridge Thermal Anemometer (DBTA) is a new generation anemometer that uses advanced electronics and a modified half-Wheatstone bridge configuration, specifically a sensor and a shunt resistor in series. This allows the miniaturization of the anemometer and the communication between host computer and anemometer is carried out using serial or ethernet which eliminates the noise due to the use of long cables in conventional anemometer and the digital data sent to host computer is immune to electrical noise. In the new configuration the potential drop across a shunt resistor is used to control the bridge.

This thesis is confined …

Numerical Study Of The Performance Of A Model Scramjet Engine, Ayad Alhumadi

Mechanical & Aerospace Engineering Theses & Dissertations

A computational parametric investigation was conducted to study the effect of variations to several geometric parameters on the performance of a two-dimensional model scramjet engine (square cross section area for 3-D model). Geometric parameters included backstep location, height, and angle and fuel injector angle, diameter, and location. Two- and three-dimensional geometries have been studied, using a finite-volume computational fluid dynamics (CFD) code (FLUENT) with structured grids with sizes between 50,000 and 90,000 cells for the two-dimensional geometry and with structured hexahedral grid sizes between 650,000 and 949,725 cells for the three-dimensional geometry. Otherwise, identical values of program inputs were utilized …

Process Study For The Design Of Small-Scale 2 Kelvin Refrigeration Systems, Peter N. Knudsen

Mechanical & Aerospace Engineering Theses & Dissertations

Helium refrigeration at temperatures below 4.5-Kelvin (K), but greater than 0.8-K typically employ a sub-atmospheric process utilizing a vacuum pumping system. These types of helium refrigerators are of keen interest to present and future particle physics programs utilizing super-conducting magnet or radio-frequency technology. As such, there is a need for small scale 2-K helium refrigeration systems (i.e., those that operated below the lambda temperature) in small laboratories and test facilities at this time. This study establishes the key process parameter choices of flow ratio, heat-exchanger size, and supply pressure, and how they influence the overall system performance for various process …

Two Dimensional Numerical Simulation Of Highly-Strained Hydrogen-Air Opposed Jet Laminar Diffusion Flames, Kyu C. Hwang

Mechanical & Aerospace Engineering Theses & Dissertations

In this study, a detailed 2-D numerical technique is utilized to investigate the structure, and flame extinction and restoration characteristics of laminar hydrogen-air opposed jet diffusion flames, using both plug (uniform) and parabolic inflow boundary conditions for 3 millimeter jet tubes, spaced 6 millimeters apart and imbedded in low velocity coflows.

First, by using the most recent of two chemical kinetic models, excellent agreement was obtained between calculated distributions of temperature and major species, and published UV laser Raman scattering measurements, for 50% and 100% hydrogen-air flames over a range of input strain rates. Agreement with measured OH profiles was …

Numerical Studies On Supersonic Mixing And Combustion Phenomena, Tarek M. Abdel-Salam

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study is conducted to investigate the mixing, combustion, and flow characteristics of different scramjet-combustor configurations. Three-dimensional models for the combustors have been used. Numerical results are obtained using a finite volume computational fluid dynamics (CFD) code with unstructured grids with sizes between 200,000 and 400,000 cells.

In the first part of the current study, the effects of the side angle of the fuel injectors in both mixing and combustion processes are investigated. Raised (compression) and relieved (expansion) wall-mounted ramps are used with side angles of 0 (unswept), 5, and 10 degrees. Results are obtained for nonreacting flows as …

Supersonic Combustion And Mixing Characteristics Of Hydrocarbon Fuels In Screamjet Engines, Ahmed A. Taha

Mechanical & Aerospace Engineering Theses & Dissertations

The combustion characteristics of gaseous propane in supersonic airflow using the rearward-facing step that is swept inward from both end sides is studied. The effect of sweeping the step on the flow field features of propane combustion is investigated.

The study of the supersonic combustion of ethylene is carried out using different combustor configurations, different main fuel equivalence ratios, and different pilot fuel equivalence ratios.

The swept step shows the ability to hold the propane flame in the supersonic air stream without extinction. It was found that the side sweeping of the combustor exhibits the high temperature and combustion products …

Radiative Interactions In Thermochemical Nonequilibrium Expanding Flows, Srikanth B. Pidugu

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study is conducted to investigate radiative interactions in flows with thermal and chemical nonequilibrium. The two dimensional spatially elliptic Navier-Stokes equations have been used to numerically investigate different physical processes in the nozzle flow problem. The system of governing equations are solved using explicit, unsplit MacCormack predictor-corrector scheme. The chemistry source term is treated implicitly to alleviate stiffness associated with fast chemical reactions.

Different physical processes considered in this study are investigated in a systematic manner. Finite chemical processes in chemically reacting supersonic nozzle flows are studied. Five hydrogen-air combustion models have been employed to study the influence …

Numerical Investigation Of Shock-Induced Combustion Past Blunt Projectiles, Jagjit K. Ahuja

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study is conducted to simulate shock-induced combustion in premixed hydrogen-air mixtures at various free-stream conditions and parameters. Two-dimensional axisymmetric, reacting viscous flow over blunt projectiles is computed to study shock-induced combustion at Mach 5.11 and Mach 6.46 in hydrogen-air mixture. A seven-species, seven reactions finite rate hydrogen-air chemical reaction mechanism is used combined with a finite-difference, shock-fitting method to solve the complete set of Navier-Stokes and species conservation equations. In this approach, the bow shock represents a boundary of the computational domain and is treated as a discontinuity across which Rankine-Hugoniot conditions are applied. All interior details of …

Studies On Nonequilibrium Phenomena In Supersonic Chemically Reacting Flows, Rajnish Chandrasekhar

Mechanical & Aerospace Engineering Theses & Dissertations

This study deals with a systematic investigation of nonequilibrium processes in supersonic combustion. The two-dimensional, elliptic Navier-Stokes equations are used to investigate supersonic flows with nonequilibrium chemistry and thermodynamics, coupled with radiation, for hydrogen-air systems. The explicit, unsplit MacCormack finite-difference scheme is used to advance the governing equations in time, until convergence is achieved.

For a basic understanding of the flow physics, premixed flows undergoing finite rate chemical reactions are investigated. Results obtained for specific conditions indicate that the radiative interactions vary substantially, depending on reactions involving HO$\sb2$ and NO species, and that this can have a noticeable influence on …

Laminar And Turbulent Natural Convection Heat Transfer In Trombe Wall Channels, Tony D. T. Chen

Mechanical & Aerospace Engineering Theses & Dissertations

The natural convective heat transfer and air movement in a Trombe wall solar passive system has been studied analytically and numerically. Three Trombe wall channel geometries including the parallel channel with axial inlet and exit, parallel channel with side vents and Trombe wall channel coupled to the room have been considered. Several models representing these Trombe wall geometries have been formulated. For the parallel channel with axial inlet and exit geometry, a momentum-integral method has been used to solve parabolic governing equations for two-dimensional laminar flow. This formulation leads to a second order ordinary differential equation for pressure defect in …

Viscous Shock Layer Analysis Of Hypersonic Flows Over Long Slender Vehicles, Kam-Pui Lee

Mechanical & Aerospace Engineering Theses & Dissertations

A method for solving the viscous shock-layer equations for hypersonic flows over long slender bodies is presented. The governing equations are solved by employing a spatial-marching implicit finite-difference technique. The two first-order equations, continuity and normal momentum, are solved simultaneously as a coupled set. This method yields a simple and computationally efficient technique.

Flows past hyperboloids and sphere cones with body half angles of five to 35 degrees are considered. The flow conditions included are from high Reynolds numbers at low altitudes to low Reynolds numbers at high altitudes. Detailed comparisons have been made with other predictions and experimental data …