Aerodynamics and Fluid Mechanics Commons^™

Flow Separation Control Using Synthetic Jets On A Flat Plate, Karunakaran Saambavi

Doctoral Dissertations and Master's Theses

The primary goal of this thesis is to assess the effect of synthetic jets on flow separation. CFD simulation is conducted for laminar flow over a flat plate using the commercial software ANSYS FLUENT. The oscillating zero mass jet flow is simulated by imposing a harmonically varying boundary condition on the wall surface.

In this work, the effect of synthetic jets for different angles of attack and different frequencies ranging from 200 Hz to 800 Hz was assessed. The application of the synthetic jet actuators is based in their ability to energize the boundary layer, thereby providing significant increase in …

Slosh Damping With Floating Magnetoactive Micro-Baffles, Vijay Santhanam

Doctoral Dissertations and Master's Theses

Liquid sloshing within propellant tanks of launch vehicles and other major vehicles has been a major concern. Various methods have been utilized for the damping of slosh through Propellant Management Devices (PMD) accomplishing a wide range of results. Exploratory research conducted at the Embry-Riddle Aeronautical University Fuel Slosh Test Facility in development of an innovative PMD is presented. Embedding floating micro-baffles with a magnetoactive material such that the baffle can be manipulated when exposed to a magnetic field preserves the benefits of both floating and static baffle designs. Activated micro-baffles form a rigid layer at the free surface and provide …

Influence Of Mach Number And Dynamic Pressure On Cavity Tones And Freedrop Trajectories, Justin D. Merrick

Theses and Dissertations

Weapons release at supersonic speeds from an internal weapons bay is a highly desirable capability. To ensure a successful release at multiple Mach numbers, the aerodynamic environment must be well-understood and repeatable, with a robust system for safe testing of store separation. For this reason, experimental methods were used to investigate the characteristics of a scaled WICS bay with a length-to-depth ratio of 4.5 at multiple Mach numbers and stagnation pressures. Three new nozzles were designed, manufactured, and characterized for the AFIT small supersonic tunnel, yielding freestream Mach numbers of 2.22, 1.84, and 1.43. In addition, a control valve was …

On The Growth Rate Of Turbulent Mixing Layers: A New Parametric Model, Jeffrey L. Freeman

Master's Theses

A new parametric model for the growth rate of turbulent mixing layers is proposed. A database of experimental and numerical mixing layer studies was extracted from the literature to support this effort. The domain of the model was limited to planar, spatial, nonreacting, free shear layers that were not affected by artificial mixing enhancement techniques. The model is split into two parts which were each tuned to optimally fit the database; equations for an incompressible growth rate were derived from the error function velocity profile, and a function for a compressibility factor was generalized from existing theory on the convective …

Flight And Stability Of A Laser Inertial Fusion Energy Target In The Drift Region Between Injection And The Reaction Chamber With Computational Fluid Dynamics, Tiffany Leilani Mitori

Master's Theses

A Laser Inertial Fusion Energy (LIFE) target’s flight through a low Reynolds number and high Mach number regime was analyzed with computational fluid dynamics software. This regime consisted of xenon gas at 1,050 K and approximately 6,670 Pa. Simulations with similar flow conditions were performed over a sphere and compared with experimental data and published correlations for validation purposes. Transient considerations of the developing flow around the target were explored. Simulations of the target at different velocities were used to determine correlations for the drag coefficient and Nusselt number as functions of the Reynolds number. Simulations with different target angles …

Experimental Study On Influence Of Pitch Motion On The Wake Of A Floating Wind Turbine Model, Stanislav Rockel, Elizabeth Camp, Jonas Schmidt, Joachim Peinke, Raúl Bayoán Cal, Michael Höllimg

Mechanical and Materials Engineering Faculty Publications and Presentations

Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind …

Experimental And Numerical Study Of Carbon Fiber Oxidation, Francesco Panerai, Nagi N. Mansour, Jean Lachaud, Alexandre Martin

Mechanical Engineering Faculty Publications

The oxidation at high Knudsen number of FiberForm® , the matrix material of NASA's Phenolic Impregnated Carbon Ablator, is investigated both experimentally and numerically. The experimental setup consists of a quartz tube through a clamshell heater. Mass loss and recession of carbon preform samples are measured at temperatures between 700 and 1300 K and pressures around 2000 Pa. A volume average fiber-scale oxidation model is used to model the setup and extract the effective reactivity of the material. New values for carbon fiber reactivity are suggested and discussed.

Evolution Of Perturbations In Flow Field Mechanics, Samantha R. Bell, David Forliti, Nils Sedano, Kriss Vanderhyde

STAR Program Research Presentations

This project explores the stability analysis of a given flow field. Specifically, where the peak disturbance occurs in a flow as this is the disturbance that is most likely to occur. In rocket combustion, it is important to understand where the maximum disturbance occurs so that the mixing of fuel can be stabilized. The instabilities are the results of frequencies in the area surrounding the flow field. The linear stability governing equations are employed to better understand the disturbance. The governing equations for continuity and momentum in the x and y directions are used to form an equation for the …

High-Efficiency Thrust Vector Control Allocation, Jeb S. Orr, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions thatsatisfles the constraints. In this paper, the control …

Gust Mitigation Of Micro Air Vehicles Using Passive Articulated Wings, Adetunji Oduyela, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Birds and insects naturally use passive flexing of their wings to augment their stability in uncertain aerodynamic environments. In a similar manner, micro air vehicle designers have been investigating using wing articulation to take advantage of this phenomenon. The result is a class of articulated micro air vehicles where artificial passive joints are designed into the lifting surfaces. In order to analyze how passive articulation affects performance of micro air vehicles in gusty environments, an efficient 8 degree-of-freedom model is developed. Experimental validation of the proposed mathematical model was accomplished using flight test data of an articulated micro air vehicle …

Nonlinear Dynamics And Anisotropic Structure Of Rotating Sheared Turbulence, Abdelaziz Salhi, Frank G. Jacobitz, Kai Schneider, Claude Cambon

School of Engineering: Faculty Scholarship

Homogeneous turbulence in rotating shear flows is studied by means of pseudospectral direct numerical simulation and analytical spectral linear theory (SLT). The ratio of the Coriolis parameter to shear rate is varied over a wide range by changing the rotation strength, while a constant moderate shear rate is used to enable significant contributions to the nonlinear interscale energy transfer and to the nonlinear intercomponental redistribution terms. In the destabilized and neutral cases, in the sense of kinetic energy evolution, nonlinearity cannot saturate the growth of the largest scales. It permits the smallest scale to stabilize by a scale-by-scale quasibalance between …

Nondestructive Analysis Of Advanced Aerospace Materials Via Spectroscopy And Synchrotron Radiation, Albert Manero

Electronic Theses and Dissertations

Advanced aerospace materials require extensive testing and characterization to anticipate and ensure their integrity under hostile environments. Characterization methods utilizing synchrotron X-Ray diffraction and spectroscopy can decrease the time required to determine an emerging material's readiness for application through intrinsic information on the material response and failure mechanisms. In this study, thermal barrier coating samples applicable to turbine blades of jet engines were studied using Raman and Photoluminescence spectroscopy as well as Synchrotron X-ray diffraction while Kevlar based fiber composites applicable to ballistic resistant armor were studied using Raman spectroscopy to investigate the mechanical state and corresponding damage and failure …

A Wedge Impact Theory Used To Predict Bow Slamming Forces, Ashok Benjamin Basil Attumaly

LSU New Orleans Theses and Dissertations

The pressures and impact forces acting on a hull while experiencing bow wave slamming is analyzed using Vorus' Impact Theory. The theory extends the hydrodynamic analysis of planing hulls from simple wedges to irregular shapes using a Boundary Element Method. A Fortran-based code developed by the Author is used to analyze hullforms. Linear strip theory is used to extend the analysis over a three dimensional hull. Post-processing of output data gives hull pressure distributions at different time steps and is visually presentable.

Impact pressure, Impact force, Planing, Wave slamming, Bow impact, Vorus' theory, Boundary Element Method, Linear strip theory

Experimental Investigation Of Mist Film Cooling And Feasibility Study Of Mist Transport In Gas Turbines, Reda M. Ragab

LSU New Orleans Theses and Dissertations

In the modern advanced gas turbines, the turbine inlet temperature may exceed 1500°C as a requirement to increase power output and thermal efficiency. Therefore, it is imperative that the blades and vanes are cooled so they can withstand these extreme temperatures. Film cooling is a cooling technique widely used in high-performance gas turbines. However, the film cooling effectiveness has almost reached plateau, resulting in a bottleneck for continuous improvement of gas turbines' efficiency.

In this study, an innovative cooling scheme, mist film cooling is investigated through experiments. A small amount of tiny water droplets with an average diameter about 10-15 …

Adaptive Control Techniques For Transition-To-Hover Flight Of Fixed-Wing Uavs, Brian Decimo Marchini

Master's Theses

Fixed-wing unmanned aerial vehicles (UAVs) with the ability to hover combine the speed and endurance of traditional fixed-wing fight with the stable hovering and vertical takeoff and landing (VTOL) capabilities of helicopters and quadrotors. This combination of abilities can provide strategic advantages for UAV operators, especially when operating in urban environments where the airspace may be crowded with obstacles. Traditionally, fixed-wing UAVs with hovering capabilities had to be custom designed for specific payloads and missions, often requiring custom autopilots and unconventional airframe configurations. With recent government spending cuts, UAV operators like the military and law enforcement agencies have been urging …

Experimental Study On The Effect Of Air Flow On Soap Bubble Formation, John M. Davidson

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Soap bubbles are a common interfacial fluid dynamics phenomenon having applications such as buoyant hollow spherical fillers and flow visualization of large scale airflows. In contrast to the dynamics of liquid drops in gas and gas bubbles in liquid, the dynamics of soap bubbles has not been well documented, possibly because soap bubbles have gas-liquid-gas interfaces. Having the thin-liquid-film interface seems to alter the characteristics of the bubble/drop creation process. Thus, the main objective of this study is to experimentally examine how airflow develops and interacts with the soap liquid film as the film stretches and finally collapses to pinch-off. …

Computational And Experimental Comparison Of A Powered Lift, Upper Surface Blowing Configuration, Jay M. Marcos

Master's Theses

In the past, 2D CFD analysis of Circulation Control technology have shown poor comparison with experimental results. In Circulation Control experiments, typical results show a relationship between lift coefficient, CL, vs blowing momentum coefficient, Cμ. CFD analysis tend to over-predict values of CL due to gridding issues and/or turbulence model selection. This thesis attempted to address both issues by performing Richardson’s Extrpolation method to determine an acceptable mesh size and by using FLUENT’s 2-equation turbulence models. The experimental results and CAD geometry were obtained from Georgia Tech Research Institute for comparison with the CFD analysis.

The study showed that 3D …

Advanced Visualization Techniques Of Hot-Jet Combustion Of Lean And Ultra-Lean Substances, Timothy I. Machin, Li Qiao

The Summer Undergraduate Research Fellowship (SURF) Symposium

Research has been conducted on ignition of natural gas as a potential replacement for fossil fuels. A reason natural gas is not widely used and adapted is because of the harmful emissions created when combusted in rich mixtures, but if the gas can be burned at a lean or ultra-lean equivalence ratio, these emissions can be reduced or even eliminated. One method of burning lean and ultra-lean substances is by use of hot-jet ignition. This method ignites the substance near its combustion temperature, reducing the harmful emissions. This method is not yet fully understood, and so research must be done …

High-Order Shock Capturing For Computational Aeroacoustics, Samuel Otto, Gregory Blaisdell

The Summer Undergraduate Research Fellowship (SURF) Symposium

Jet noise is not only an annoyance to passengers and communities near airports, it is a major contributor to hearing loss in veterans who served on aircraft carriers, as well as a significant limiting factor for the growth of commercial airlines. High-fidelity large eddy simulation (LES) is an important tool for analyzing and predicting jet noise; however the utilized non-dissipative high order finite difference schemes produce instabilities at shock waves. Schemes for capturing shock waves, however, are more dissipative and do a poor job preserving turbulent structures and acoustic waves. To maximize the strengths of both approaches, hybrid methods utilize …

Investigation Of Grid Adaptation To Reduce Computational Efforts For A 2-D Hydrogen-Fueled Dual-Mode Scramjet, Kam Keong Foo

Doctoral Dissertations and Master's Theses

A two-dimensional dual-mode scramjet flowpath is developed and evaluated using the ANSYS Fluent density-based flow solver with various computational grids. Results are obtained for fuel-off, fuel-on non-reacting, and fuel-on reacting cases at different equivalence ratios. A one-step global chemical kinetics hydrogen-air model is used in conjunction with the eddy-dissipation model. Coarse, medium and fine computational grids are used to evaluate grid sensitivity and to investigate a lack of grid independence. Different grid adaptation strategies are performed on the coarse grid in an attempt to emulate the solutions obtained from the finer grids. The goal of this study is to investigate …