Mechanical Engineering Commons^™

Natural Convection In Shallow Inclined Enclosures, Effendy Arif

Mechanical & Aerospace Engineering Theses & Dissertations

A two dimensional natural convective flow in a shallow inclined enclosure has been considered. A mathematical model has been developed to simulate the flow. The system of governing equations has been solved using finite-differencing techniques and the alternating direction implicit method.

The effect of the Raleigh number, the enclosure aspect ratio and orientation on the heat transfer and flow development have been studied by determining the Nusselt numbers and analyzing a number of contour maps of temperature and stream function fields, and velocity profiles. The Nusselt number has been found to increase with the Raleigh number, the enclosure aspect ratio, …

An Apparatus For Measuring The Thermal Conductivity Of Cast Insulation Materials, Christine A. Wilkins, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

A steady-state apparatus has been developed for measuring the thermal conductivity of cast materials. The design has employed a novel thermal symmetry arrangement which can permit total electrical isolation of the test material from its surroundings. © 1980 American Institute of Physics

Influence Of Nonequilibrium Radiation And Shape Change On The Flowfield Of A Jupiter Probe With Ablation And Mass Injection, Sundaresa Venkata Subramanian

Mechanical & Aerospace Engineering Theses & Dissertations

The influence of nonequilibrium radiative energy transfer and the effect of probe configuration changes on the flow phenomena around a Jovian entry body is investigated. The radiating shock-layer flow is assumed to be axisymmetric, viscous, laminar and in chemical equilibrium. The radiative transfer equations are derived under nonequilibrium conditions which include multi-level energy transitions. The equilibrium radiative transfer is calculated with an existing nongray radiation model which accounts for molecular band, atomic line and continuum transitions. The nonequilibrium results are obtained with and without ablation injection in the shock layer. The nonequilibrium results are found to be influenced greatly by …

Analytic And Experimental Studies Of A True Airspeed Sensor, Joseph Yao-Cheng Shen

Mechanical & Aerospace Engineering Theses & Dissertations

The objective of this study was to analyze and design a true airspeed sensor which will replace the conventional pitot-static pressure transducer. This sensor should have the following characteristics: the flow phenomenon is vortex procession, or the "vortex whistle", it should have no moving parts, and also is to be independent of temperature, density, altitude or humidity changes. This sensor has been designed mainly for small commercial aircraft with the airspeed up to 321.9 km/hr (200 mph).

In an attempt to model the complicated fluid mechanics of the vortex precession, three-dimensional, inviscid, unsteady, incompressible fluid flow was studied by using …

Finite Element Model Of A Timoshenko Beam With Structural Damping, Louis Ablen Roussos

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical integration technique, a modified version of the Newmark method, is applied to transient motion problems of systems with mass, stiffness, and small nonlinear damping. The nonlinearity is cast as a pseudo-force to avoid repeated recalculation and decomposition of the effective stiffness matrix; thus, the solution technique is dubbed the "pseudo-force Newmark method." Comparisons with exact and perturbation solutions in single-degree-of-freedom problems and with a Gear-method numerical solution in a cantilevered Timoshenko beam finite element problem show the solution technique to be efficient, accurate, and, thus, feasible provided the nonlinear damping is small. As a preliminary step into the …

Curing And Flow Of Thermosetting Resins For Composite Materials Pultrusion, Howard L. Price Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Fibrous composite materials for mechanical and structural applications often are expensive due to high labor costs. One economical way of making composites is pultrusion, a manufacturing process in which resin-impregnated fibers are pulled at a constant speed through a heated die which shapes the resin-fiber mass and cures the resin. Most of the work which has been done on the process has been of an empirical nature, with limited understanding of the process principles. Most of the experience with pultrusion has been gained with polyester resins and glass fibers. Very little experience has been gained with higher performance, more costly …

Effect Of Precursor Heating On Radiating And Chemically Reacting Viscous Flow Around A Jovian Entry Body, Kuo Yen Szema

Mechanical & Aerospace Engineering Theses & Dissertations

The influence of changes in the precursor region flow properties (resulting from absorption of the radiation from the shock layer) on the entire shock layer flow phenomena around a Jovian entry body is investigated under physically realistic conditions. In the precursor region, the flow is considered to be inviscid and the variations in flow properties are determined by employing the small perturbation technique as well as the thin layer approximation. The flow in the shock layer is assumed to be steady, axisymmetric and viscous. The analysis is carried out by considering both the chemical equilibrium and nonequilibrium composition of the …

Inviscid Two-Dimensional Vortex-Panel Method For Calculating The Pressure Distribution Over Noncircular Cylinders At Various Flow Incidence Angles, Sophia Kokkinos Ashley

Mechanical & Aerospace Engineering Theses & Dissertations

A method. has been implemented to calculate the potential flow pressure distribution over noncircular cylinders at various flow incidence angles. The inviscid, solution has been obtained by replacing the surface of a noncircular cylinder with a vortex sheet. The surface has been approximated by a number of flat panels. Each vortex panel has been assumed to have a constant vorticity, and the condition of no-circulation applied.. Solutions yield the local tangential velocity and pressure coefficient at each point.

The accuracy of the method has 'been established through comparison of the predicted results with existing exact theoretical results.

Comparisons of the …

Design, Calibration, And Application Of A Sensor For Measuring Time Dependent Angle Of Attack Of Helicopter Blades, Weiyuan Henry Liu

Mechanical & Aerospace Engineering Theses & Dissertations

Various pressure probes were designed and tested which could be attached to helicopter blades when a helicopter is in flight. The pressure probes consisted of spherical heads which were held in place by cylindrical shanks. Built inside the heads were transducers to measure the pressure differential between pressure ports which were located on the front portion of the spherical head facing the airstream. Data was obtained over a range of airstream velocity of 11,6 to 88.4- m/s (38 to 290 ft/sec), corresponding to Reynolds numbers of 0.24 to 1.84x10⁵ based on the sphere diameter. Both static and dynamic tests …

Analysis Of Moisture Absorption And Diffusion In Fiber Reinforced Polymeric Resin-Matrix Composite Materials, Stephen Stern Tompkins

Mechanical & Aerospace Engineering Theses & Dissertations

The diffusion of moisture through fiber reinforced polymeric-matrix composite materials has been studied analytically. The diffusion in the orthotropic, nonhomogeneous material was modeled, in detail, with a two-dimensional transient diffusion analysis. An effective diffusivity for the composite was determined in terms of the fiber volume fraction and the resin diffusivity. This effective diffusivity is in better agreement with recent data than those previously determined using less complex models.

The influence of both material and environmental parameters on the moisture content of the composite was determined analytically. Predicted moisture contents were compared over a wide range of values for emittance, solar …

Optimal Control Of A Large Space Telescope Using An Annular Momentum Control Device, Arun Anant Nadkarni

Mechanical & Aerospace Engineering Theses & Dissertations

Application of a new development in the field of momentum storage devices, the Annular Momentum Control Device (AMCD), to the twin problems of large angle maneuvers and fine pointing control is considered. The basic concept of the AMCD consists of a spinning rim, with no central hub area, suspended by a minimum of three magnetic bearings, and driven by a noncontacting electromagnetic spin motor. The dissertation considers in detail the design of an optimal controller to achieve both large angle maneuvers and the fine pointing control of a Large Telescope (LST) with a single configuration, consisting of a single AMCD …

Static Temperature Measurements In Supersonic Flow Using Lasar Raman Spectroscopy, Paul A. Nystrom

Mechanical & Aerospace Engineering Theses & Dissertations

Laser Raman spectroscopy is a nonintrusive technique which can generate mean static temperature (MST) data within flow fields. By ratioing two simultaneously gathered portions of the Raman scattered spectrum, absolute intensity measurements were not needed. This method was applied to a supersonic cold air jet, where the NST ranged from 160'K to 300'K. Accurate measurements were not realized due to the presence of flow contaminates, especially water vapor.

Effect Of Compliant Wall Motion On Turbulent Boundary Layers, Dennis M. Bushness, Jerry N. Hefner, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

A critical analysis of available compliant wall data which indicated drag reduction under turbulent boundary layers is presented. Detailed structural dynamic calculations suggest that the surfaces responded in a resonant, rather than a compliant, manner. Alternate explanations are given for drag reductions observed in two classes of experiments: (1) flexible pipe flows and (2) water-backed membranes in air. Analysis indicates that the wall motion for the remaining data is typified by short wavelengths in agreement with the requirements of a possible compliant wall drag reduction mechanism recently suggested by Langley. Copyright © 1977 American Institute of Physics.

Evaluation Of Upwelling Infrared Radiance In A Nonhomogeneous Nonequilibrium Atmosphere, Sundaresa Venkata Subramanian

Mechanical & Aerospace Engineering Theses & Dissertations

The primary purpose of this study was to investigate the influence of vibrational nonequilibrium upon upwelling infrared radiance from the earth's atmosphere. Basic equations are presented for calculating the atmospheric transmittance, heating rates, and equilibrium and nonequilibrium upwelling radiances. By employing the Lorentz line-by-line model for spectral absorption, heating rates and upwelling radiances were calculated for equilibrium as well ·as nonequilibrium conditions in the spectral range of 4.6 μ CO and 3.3 μ 'CH₄ bands. For the spectral range of CO fundamental band, the influence of different 1~arameters on the upwelling radiance was also investigated. The results indicate that …

Similitude Of Mass Transfer Processes In Distorted Froude Model Of An Estuary, Carvel Hall Blair

Mechanical & Aerospace Engineering Theses & Dissertations

The project began with the design and construction of a hydraulic Froude model of the Lafayette River, a small well mixed estuary in Norfolk, Virginia. Horizontal scale is 1/540, vertical scale 1/12 yielding a vertical distortion of 45. Adjustment by roughness strips and screens produced close agreement of model-prototype tide heights, currents, and salinities in the deep reaches comprising 80% of the estuary volume. Some scale effect in velocity and tide height could not be eliminated in the shallow upper branches of the estuary, probably because of the high geometric distortion and the narrowness of the channel at kilometer 6.7. …

Analysis Of Spread Multi-Jet Vtol Aircraft In Hover, Leroy F. Albang

Mechanical & Aerospace Engineering Theses & Dissertations

An investigation of VTOL aircraft lift losses in hover has been conducted to evaluate a method for a simplified test technique. Three flat plate models were tested to determine their usefulness in predicting hover characteristics by comparing results between plate and three­ dimensional models. Attempts to correlate the out of ground effect results for the plate models with the empirical expression for calculating jet-induced loads were successful for the models which used engine simulators producing efflux characteristics similar to the three­ dimensional model engines. Data for the model using engine simulators with characteristics unlike those of the three-dimensional model simulators …

Effect Of Rod Gap Spacing On A Suction Panel For Laminar Flow And Noise Control In Supersonic Wind Tunnels, William D. Harvey

Mechanical & Aerospace Engineering Theses & Dissertations

It has been well established that the test section flow of conventional supersonic and hypersonic wind tunnels contains significant levels of disturbances. These disturbances are mainly caused by the radiation of aerodynamic noise from the turbulent boundary layer on the nozzle walls. This noise level has been shown to have an important effect on boundary layer transition measured on models in tunnels. The purpose of this thesis is to present results of a coordinated experimental and theoretical study of a sound shield concept which aims to provide a means of noise reduction in .the test section of supersonic wind tunnels …

An Experimental Investigation Of A Cold Jet With Solid Centerbody Emitting From A Flat Plate Into A Subsonic Free Stream, Danny K. Livingston

Mechanical & Aerospace Engineering Theses & Dissertations

A study of the influence of a solid center body on lift loss and pitching moment has been conducted. It has been well established that a round free jet emitted from a flat plate at right angles to a cross flow causes an induced pressure distribution on the plate which adversely affects the lift and pitching stability of the flat plate.

This investigation has employed a 2.58 - cm diameter round jet with a 1.91 - cm diameter solid rounded core in order to modify the induced flow field and attempt to reduce the lift loss and pitching moment. Preliminary …

A Method For Improving The Accuracy In Phase Change Heat Transfer Data Through Increased Precision In Thermophysical Property Determinations, John Philip Drummond

Mechanical & Aerospace Engineering Theses & Dissertations

Wind tunnel model materials typically have thermophysical properties that vary with both position and temperature. A numerical study using a finite difference representation of the heat conduction equation has been performed on several of these model materials to determine their thermal response under a specified heat loading. This study has confirmed the feasibility of using an effective thermophysical property to account for the existence of variable thermal properties when a model undergoes aero­ dynamic heating. The effective property, when used in the reduction of phase-change heat transfer data, forced agreement of the actual transient behavior of a model with the …

Dynamics Of Explosion Remnants In Earth-Orbits, Joseph T. Fuss

Mechanical & Aerospace Engineering Theses & Dissertations

Explosions in space produce particles that are hazardous to space vehicles. Some of these particles are not trackable and their locations must be predicted by dynamical methods.

This investigation sheds light on three different, areas, First, ignoring perturbations, the characteristics of a three dimensional envelope outlined by the sum of individual particle orbits is determined, Second, the distribution of the particles is found as a function of time, Finally, the movement, of the body via secular perturbations is investigated. Magnitudes of the explosion, the point of. detonation in the parent satellite's orbit, and the radius of perigee of the parent …

Application Of Boundary Layer Theory To Suction Through Streamwise Slots In Wind Tunnel Walls, Michael Harold Berger

Mechanical & Aerospace Engineering Theses & Dissertations

A theoretical investigation at Mach 6 and 8 has been conducted on a model of a wind tunnel sound shield. The flat plate model consists of interchangeable circular and wedge shaped longitudinal rods with gaps between the rods for boundary layer removal. One­ dimensional gas dynamics results have been applied to model the pressure distribution for the array of cylinders. Comparisons with experimental pressure distributions and numerical potential flow solutions indicate good agreement. It has been demonstrated that stagnation line heat transfer can be accurately predicted for laminar and-turbulent flow for circular cylinders. The flow around the wedge rods was …

The Effect Of Unreinforced Cutouts On The Buckling Of Thin Conical Shells Loaded By Central Axial Compression, Garla Arjuna

Mechanical & Aerospace Engineering Theses & Dissertations

Analytical trends for the linear bifurcation buckling of thin isotropic right-circular-conical shells with unreinforced cutouts are investigated. Clamped, constant-thickness conical shells with homogeneous, isotropical material properties are analyzed for uniform axial compression. The buck­ ling loads are obtained by the use of the STAGS (Structural Analysis of General Shells) computer program which is based on a finite difference numerical approach. Variables defining the geometry of the cutout and the cone are nondimensionalized and the relationship between the nondimensional buckling load and nondimensional cutout parameter is established. A range of the cutout sizes is investigated for which linear bifurcation buckling results …

An Experimental And Theoretical Study Of The Flow Phenomena Within A Vortex Sink Rate Sensor, Dashrath Khodidas Patel

Mechanical & Aerospace Engineering Theses & Dissertations

The objective of this investigation was to obtain a detailed description of the flow field within a vortex sink rate sensor and to observe the influence of viscous effects on its performance.

The sensor basically consists of a vortex chamber and a sink tube. The vortex chamber consists of two circular coaxial disks held apart, at their periphery, by a porous coupling. One circular disk has an opening to permit the mounting of the sink tube, in such a manner that the vortex chamber as well as the sink tube have a common axis of rotation.

Air was supplied radially …

The Design And Performance Of A Fiber Optic Pressure Transducer, Raymond Henry Pahler Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Design and performance characteristics of a fiber optic pressure transducer are presented and discussed. The transducer consists of a cylindrical metal housing with a specular reflecting aluminum diaphragm at the distal end and a circular array of fiber optic light guides at the proximal end. The center bundle is connected to a light source with the surrounding bundles carrying reflected light to a photodetector. A change in pressure on the diaphragm causes a deflection which in turn causes a change in intensity over the light receiving fibers. The intensity is converted to a voltage signal by the photodetector circuit. Thus, …

A Finite Element Analysis Of Unsymmetrically Laminated Rectangular Plates, Stanley F. C. Tseng

Mechanical & Aerospace Engineering Theses & Dissertations

The behavior of laminated plates with coupled extension-bending was investigated using the finite element method. A stiffness matrix for a rectangular element with 20 degrees of freedom was developed using a symbolic mathematics interpreter program. A finite element analysis program was written for the analysis of flat plate. Results i for plate deformations and internal moment distributions are compared with existing exact solutions or experimental data and excellent agreement is obtained.

An Investigation Of A Free Jet At Low Reynolds Numbers, George C. Greene

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis presents a comparison of the measured and calculated flow field properties of a nozzle of unusual design which was used to produce an incompressible, low Reynolds number ]et. The "nozzle" is essentially a porous metal plate which covers the end. of a pipe. Results are presented for nozzle Reynolds numbers from 50 to 1000 with velocities of 100 or 200 ft/sec. The nozzle produces s, uniform velocity profile at nozzle Reynolds numbers well below those at, which conventional contoured nozzles are completely filled with the boundary layer. A Jet mixing analysis based on the boundary layer equations accurately …

Computer-Aided Design Of Light Aircraft To Meet Certain Aerodynamic And Structural Requirements, Joanne Lynn Walsh

Mechanical & Aerospace Engineering Theses & Dissertations

Nonlinear mathematical programming techniques are applied to a particular aircraft design problem, that of determining the maximum range design for light aircraft subject to certain aerodynamic and structural requirements. Search techniques available in an existing nonlinear optimization computer program, AESOP, are applied to the design problem. Seven design variables are used to define the wing dimensions, the wing skin thickness, the cruise velocity, the amount of fuel carried, and the engine horsepower. The influence of different design requirements on the range is observed and discussed.

Numerical Study Of The Turbulent Boundary Layer In A Hypersonic Nozzle, Joan Patricia Gosink

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study of the turbulent boundary layer in a hypersonic nozzle is presented. The boundary layer equations are solved by a second order, implicit finite difference scheme developed at Langley Research Center. The technique is applicable to laminar, transitional or turbulent compressible or incompressible boundary layer flows for planar or axisymmetric geometries. A technique is presented for utilizing experimental data to start the finite difference solution.

Turbulent boundary-layer measurements on axisymmetric nozzle walls at Mach number 6 are presented and compared with numerical predictions obtained by starting the solution in the stagnation chamber and from a downstream experimental station. …

A Theoretical And Experimental Study Of An Unsteady Pressure Measuring System, Ramesh R. Batki

Mechanical & Aerospace Engineering Theses & Dissertations

Experiments were performed to determine the frequency response of gas filled instrument tubes, and the results were correlated with a theoretical model. The theoretical model developed by Bergh and Tijdeman for a series connection of thin circular tubes and volumes was studied in full detail and employed. A measuring system was designed and built to measure pressure ratio and phase lag employing thin nylon or vinyl tubes and strain gage transducers. 1'leasurements were performed using cathode ray tube, strip chart, analog techniques and also a commercial electronic function analyzer and the various results were compared. The theoretical and experimental influence …

An Experimental Investigation Of The Vortex Sink Rate Sensors, Nelson L. Lu

Mechanical & Aerospace Engineering Theses & Dissertations

The vortex sink rate sensor device consists basically of an ideal sink flow between two coaxial disks. A sink tube was located at the center of one disk. The vortex was created by the rotation of the unit about its axis of symmetry. Five inch and 10 inch diameter of porous couplers were used for the air chamber here in this investigation. Several slenderness parameters, i.e., the ratio of the sink tube diameter to the height of the air chamber ^ro/n were conducted. Two probes were used to measure the static pressure and stagnation pressure respectively at various positions …