<p> The purpose of this research is to examine methods by which quantification of inlet flow distortion may be improved upon. Specifically, this research investigates how data interpolation effects results, optimizing sampling locations of the flow, and determining the sensitivity related to how many sample locations there are. The main parameters that are indicative of a "good" design are total pressure recovery, mass flow capture, and distortion. This work focuses on the total pressure distortion, which describes the amount of non-uniformity that exists in the flow as it enters the engine. All engines must tolerate some level of distortion, however too much distortion can cause the engine to stall or the inlet to unstart. Flow distortion is measured at the interface between the inlet and the engine.</p><p> To determine inlet flow distortion, a combination of computational and experimental pressure data is generated and then collapsed into an index that indicates the amount of distortion. Computational simulations generate continuous contour maps, but experimental data is discrete. Researchers require continuous contour maps to evaluate the overall distortion pattern. There is no guidance on how to best manipulate discrete points into a continuous pattern. Using one experimental, 320 probe data set and one, 320 point computational data set with three test runs each, this work compares the pressure results obtained using all 320 points of data from the original sets, both quantitatively and qualitatively, with results derived from selecting 40 grid point subsets and interpolating to 320 grid points. Each of the two, 40 point sets were interpolated to 320 grid points using four different interpolation methods in an attempt to establish the best method for interpolating small sets of data into an accurate, continuous contour map. Interpolation methods investigated are bilinear, spline, and Kriging in Cartesian space, as well as angular in polar space. Spline interpolation methods should be used as they result in the most accurate, precise, and visually correct predictions when compared results achieved from the full data sets.</p><p> Researchers were interested if fewer than the recommended 40 probes could be used &ndash; especially when placed in areas of high interest - but still obtain equivalent or better results. For this investigation, the computational results from a two-dimensional inlet and experimental results of an axisymmetric inlet were used. To find the areas of interest, a uniform sampling of all possible locations was run through a Monte Carlo simulation with a varying number of probes. A probability density function of the resultant distortion index was plotted. Certain probes are required to come within the desired accuracy level of the distortion index based on the full data set. For the experimental results, all three test cases could be characterized with 20 probes. For the axisymmetric inlet, placing 40 probes in select locations could get the results for parameters of interest within less than 10% of the exact solution for almost all cases. For the two dimensional inlet, the results were not as clear. 80 probes were required to get within 10% of the exact solution for all run numbers, although this is largely due to the small value of the exact result.</p><p> The sensitivity of each probe added to the experiment was analyzed. Instead of looking at the overall pattern established by optimizing probe placements, the focus is on varying the number of sampled probes from 20 to 40. The number of points falling within a 1\% tolerance band of the exact solution were counted as good points. The results were normalized for each data set and a general sensitivity function was found to determine the sensitivity of the results. A linear regression was used to generalize the results for all data sets used in this work. However, they can be used by directly comparing the number of good points obtained with various numbers of probes as well. The sensitivity in the results is higher when fewer probes are used and gradually tapers off near 40 probes. There is a bigger gain in good points when the number of probes is increased from 20 to 21 probes than from 39 to 40 probes.</p>

This thesis explores the fidelity of the ground based simulator used at USNTPS during the Advanced Flight Controls Design exercise. A Simulink model is developed as a test platform and used to compare the longitudinal flight characteristics of the simulator. The model is also compared to the same characteristics of a Learjet in the approach configuration. The Simulink model is modified with the aim of yielding a better training aid for the students as well as providing a means of comparison between the simulator flight data and the actual Learjet flight data. Open loop and closed loop trials are completed to gather data for analysis and improvement of the Simulink model. Regression analysis is also performed on the flight data as a means of comparing the longitudinal stability coefficients.

<p> It is well known that the composition of the planet's atmosphere is changing at an unprecedented rate. Tremendous and well-documented amounts of man-made carbon are being released into the atmosphere, but is not clear where that extra carbon is going and how it interacts with the environment. The influence of human activities on the carbon cycle is of particular concern to scientists and policymakers. To clarify this important issue, in-situ measurements must be taken to improve our understanding of the mechanism that drives the exchange of CO2 within the atmosphere, which is dominated by turbulence. As such, there is great interest in the measurement of CO2 concentration and CO2 flux within the atmosphere. </p><p> A wide variety of platforms, in both mobile and fixed configurations, are being used to study closely the flux of CO2 within the atmosphere's boundary layer. Most of these platforms tend to be expensive and complex to operate. Recent developments of technologies such as microelectromechanical devices, GPS, and batteries have enabled the use of unmanned aerial vehicles as a viable method for performing atmospheric studies. Parallel to the studies of carbon exchange, field measurements of buoyancy flux are valuable. This variable helps to understand the mechanisms of turbulence production. It can be assessed with the use of a sonic anemometer, which has the ability of measuring wind speed fluctuations, alongside with virtual temperature. This has motivated the creation of an instrumented UAV the measurement of in situ variables such as CO2 flux, virtual temperature, wind speed, and turbulence. </p><p> An unmanned aerial system, nicknamed UAV Esperanza, was designed, constructed and tested with the purpose of measuring turbulent flux. The novelty of this system was the incorporation of an onboard sonic anemometer, an inexpensive inertial measurement unit/GPS navigation system, and a relatively low-cost gas analyzer. Field experiments demonstrated the capability of the system to resolve vertical profiles of average wind speed, virtual potential temperature, turbulent kinetic energy, CO2 concentration, and turbulent fluxes of buoyancy and CO2. The UAV system has the ability to obtain average CO2 flux values comparable to existing manned aircraft-based systems. Moreover, this is accomplished with a fraction of the operational costs of manned airplanes. </p><p> Error analysis of different scenarios demonstrated that the developed UAV system is appropriate for measuring plumes of power plants, daytime fluxes of crops, and forests. However, limitations of the onboard gas analyzer, range, and endurance of the aircraft render the system unsuitable for spectrum analysis </p>

<p> Reusable Launch Vehicles (RLVs) present a more environmentally-friendly and cost-effective approach to accessing space when compared to traditional launch vehicles that are discarded after each flight. This paper studies the recyclable nature of RLVs by presenting a solution method for determining minimal-fuel optimal trajectories using principles from optimal control theory and Particle Swarm Optimization (PSO). The problem is formulated as a minimum-fuel, minimum-landing error powered descent problem where it is desired to move the RLV from a fixed set of initial conditions to three different sets of terminal conditions: an unspecified downrange landing, a specified downrange landing, and a return-to-launch-site landing. However, unlike other powered descent studies, this paper considers the highly nonlinear effects caused by atmospheric drag, which are often ignored for similar powered descent studies on the Moon or Mars. Rather than optimize the controls directly, the throttle control is assumed to be bang-off-bang with a predetermined thrust direction for each phase of flight. An overview of optimal control theory and particle swarm optimization is first presented. The PSO method is presented and verified in a one-dimensional comparison study, and is then applied to the two-dimensional cases, the results of which are illustrated.</p>

<p> The efficiency of fixed wing Micro Aerial Vehicles can be improved if their endurance can be increased by thermal soaring. This requires development of a soaring strategy that can detect, map, and utilize thermals based on the temperature characteristics and implementation of that strategy on a UAV equipped with two different temperature sensors.</p><p> In this thesis, a simulation model is developed for the thermal soaring method. A climate model with velocity and temperature characteristics is developed to validate the soaring method in the simulation. A Small Unmanned Aerial System with two different temperature sensors is developed for a fixed wing UAV. Finally, a Hardware in the Loop simulation setup is developed that can validate the working of the unmanned system. The results of simulation show that if the UAV is able to detect thermals using two different temperature sensors, it can utilize the updraft to remain airborne for longer duration. </p>

The effects of structural motion on the aerodynamics of the X-56A airfoil are investigated experimentally. An oscillatory plunging mechanism provides a sinusoidal plunging motion. The static aerodynamic characteristics of the X-56A airfoil model are verified against computational results from XFLR5 and thin airfoil theory. The plunging experiments are carried out at a Reynolds number of 200,000 to be comparable to CFD simulations and future 1/2 scale flight test experiments. Two nominal angles of attack were used in the plunging experiments: 10 degrees and 12 degrees. At both angles, the oscillation parameters used (k = 0.61 and 0.70, h = 0.030 - 0.048) provide effective angles of attack that extend up to and past the region associated with static stall. For the case of a nominal angle of 10 degrees, the phase-averaged lift cycles are seen to oscillate symmetrically about the static CL value and increasing the oscillation amplitude increases the magnitude of the CL variation. A comparison with CFD and Theodorsen's theory shows fair agreement, but the comparison to theory worsens as the oscillation amplitude increases. This is due to limitations in Theodorsen's theory and uncertainty in the experimental CL. An FFT of the lift shows the primary frequency to be the same as the plunging frequency for all cases. For the case of a nominal angle of 12 degrees, the phase-averaged lift cycle is no longer symmetric about the static lift value. A comparison of CL between the experimental data and CFD simulations shows reasonable agreement. Observing the pressure distribution around the airfoil at this higher angle reveals a growth-reduction cycle experienced by the laminar separation bubble which is not seen to occur in the 10 degree case. An FFT of the lift at this angle again shows the primary frequency to be equivalent to the plunging frequency. Additionally, the first harmonic is more prominent at this angle. Hot wire measurements behind the airfoil show an oscillation about the free stream value for the 10 degree cases and a drastic periodic drop in velocity for the 12 degree cases. This drop in velocity is thought to be associated with the passage of a vortex which can also be seen in CFD visualizations.

<p> Saturn&rsquo;s moon, Titan, has been a scientific marvel since Cassini&rsquo;s flyby discovered methane-ethane lakes in the northern hemisphere. Several science missions to explore these lakes have been proposed, but none have been launched. Using these previous mission designs, as well as the success of the Huygens probe, this paper will discuss the development of a deployable multi-buoy system with the intent of studying the methane-ethane lakes. The buoys will study the chemical makeup of the lakes, determine meteorology of Titan atmosphere, and map the depth and floor of the targeted lakes. This thesis is a concept study on the multi-buoy system that reviews briefly the concept and design.</p>

<p> An experimental investigation was performed to study the fundamental interaction between a static and dynamic vortex generator with a laminar boundary layer. The effectiveness of static vortex generators (<i>VG</i>s) on delaying boundary layer separation is well established. However, as a passive flow control device, static <i>VG</i>s are associated with a drag penalty since they are always present in the flow. In the current study a piezoelectric-based dynamic vortex generator (D<i>VG</i>) was developed with the goal of mitigating the drag experienced when using a <i>VG</i> as a flow control device and exploring whether or not a D<i>VG</i> was more effective in flow mixing within the boundary layer. Experiments were conducted in a small wind tunnel, where the <i>VG</i> was flush mounted to the floor. The <i>VG</i> was rectangular in shape and erected into the flow with a mean height of the local boundary layer thickness, &delta;, or <i>h_m</i> = 3 mm. The skew angle of the <i>VG </i> was &thetas; = 18&deg; with respect to the incoming flow, oscillated at a driving frequency of <i>f</i> = 40 Hz with a peak to peak displacement (or amplitude) of 0.5&middot;&delta;, or <i>h_a</i> = 1.5 mm. During the experiments, the free stream velocity was held constant at <i>U</i>_&infin; = 10 m/s. This corresponded to a Reynolds number of <i>Re</i>_&delta; &ap; 2000, which was based on the local boundary layer thickness at the center of the <i>VG.</i> Surface oil flow visualization experiments were performed to obtain qualitative information on the structures present in the flow, while Stereoscopic particle image velocimetry (<i>SPIV</i>) was used to provide quantitative measurements of the 3-D flow field at multiple spanwise planes downstream of the <i>VG</i> under both static and dynamic conditions. Several flow features were detected in the oil flow visualization experiments, including two vortical structures&mdash;the main vortex and primary horseshoe vortex&mdash;which were confirmed in the <i>SPIV</i> results. The time-averaged flow field showed similar results, though the strength of the vortices appeared less when the <i>VG</i> was actuated. However, phase-averaged data revealed the size, strength, and location of the vortices varied as a function of the actuation cycle, with peaks of vorticity magnitude being greater at certain phases as compared to the static case. The varying flow field associated with the dynamic motion of the <i>DVG</i> showed higher levels of turbulent kinetic energy, therefore confirming enhanced mixing in contrast to the static case.</p>

An experimental investigation was conducted to study compressibility effects on dynamic stall for an airfoil pitching at a constant rate. Instantaneous, whole field velocity data was acquired using an on-line, video-based particle image velocimetry (PIV) system, which incorporated a passive, optical, displacement bias technique to eliminate the sign ambiguity inherent in PIV measurements of reversed flows. Vorticity data were subsequently computed from the corresponding velocity field. Free stream Mach numbers were 0.23 and 0.45, and corresponding Reynolds numbers were 280,000 and 620,000, respectively. Non-dimensional pitch rates were 0.010, 0.030, and 0.060. Although the flow was near sonic in the high speed case, no shocks were observed. The sequence of events at high speed was remarkably similar to that at both low speed and to that observed in water tank experiments. The dynamic stall process is initiated with formation and convection aft of a single, discrete, vortex. Formation and initial release of the structure is probably initiated by a van Dommelen-Shen unsteady separation. A region of closed vorticity forms over the forward portion of the airfoil, caused by periodic reattachment and shedding of discrete vortical structures of positive sign from the leading edge. These structures and the adverse pressure gradient then induce production of negative vorticity near the airfoil surface, which is convected forward and accumulates near the quarter chord. Subsequently, coherent negative vorticity is ejected into the outer flow, isolating the initial structures from the leading edge. Subsequent interaction induces separation from the surface of the dynamic stall vortex, which is composed of several small, interacting structures rather than a single, large structure. / The data complement Schlieren and surface pressure investigations, which are useful but provide no information about local flow direction. The data also demonstrate the utility of PIV for investigating highly unsteady, reversed flows with dynamic boundary conditions at compressible or transonic speeds. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6318. / Major Professor: Anjaneyulu Krothapalli. / Thesis (Ph.D.)--The Florida State University, 1993.

abstract: There are a large group of amputees living in the country and the number of them is supposed to increase a lot in the following years. Among them, lower-limb amputees are the majority. In order to improve the locomotion of lower-limb amputees, many prostheses have been developed. Most commercially available prostheses are passive. They can not actively provide pure torque as an intact human could do. Powered prostheses have been the focus during the past decades. Some advanced prostheses have been successful in walking on level ground as well as on inclined surface and climbing stairs. However, not much work has been done regarding walking on compliant surfaces. My preliminary studies on myoelectric signals of the lower limbs during walking showed that there exists difference in muscle activation when walking on compliant surfaces. However, the mapping of muscle activities to joint torques for a prosthesis that will be capable of providing the required control to walk on compliant surfaces is not straightforward. In order to explore the effects of surface compliance on leg joint torque, a dynamic model of the lower limb was built using Simscape. The simulated walker (android) was commanded to track the same kinematics data of intact human walking on solid surface. Multiple simulations were done while varying ground stiffness in order to see how the torque at the leg joints would change as a function of the ground compliance. The results of this study could be used for the control of powered prostheses for robust walking on compliant surfaces. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2019