The effect of the ground on a rotor wake in forward flight has been investigated experimentally in the working section of an 8ft x Oft straight-through wind tunnel. A three bladed fully articulated rotor with a solidity ratio of 0.07 and diameter of 1.06m, powered by a hydraulic motor, has been tested at a height of 0.47 rotor diameter above a solid ground board which has an elliptical leading edge. Tests have been run at various low advance ratios (<0.1) with two collective pitch settings. A three-element hot wire anemometer probe has been used to measure the average value of the three components of velocity simultaneously in the forward half (advancing side) of the rotor wake and in the main stream surrounding it. The rotor wake and the ground vortices have been visualized by smoke. Surface flow patterns on the ground board have located the interaction region between the rotor wake and the oncoming flow on the ground board. Theoretical estimates of the flowfield based on Heyson's vortex cylinder model (Ref. 2) are compared with the experimental results. Both experimental results and theoretical estimates show that the ground-induced interference is an upwash and a decrease in forward velocity. The upwash interference' opposes the vertical flow through the rotor, and have large effects on the rotor performance in producing thrust. The streamwise interference decelerates the mainstream and becomes more noticeable as the wake boundary is approached.

The Texas A&M Flight Research Laboratory (FRL) recently received delivery of its newest aircraft, the Velocity XL-5 RG. The Velocity can fly faster than the other aircraft owned by the FRL and does not have a propeller in the front of the aircraft to disrupt the air flow. These are definite advantages that make the Velocity an attractive addition to the FRL inventory to be used in boundary-layer stability and transition control. Possible mounting locations built into the aircraft for future projects include hard points in the wings and roof of the fuselage. One of the drawbacks of the aircraft is that it has a canard ahead of the main wing that could disrupt the incoming flow for a wing glove or research requiring test pieces mounted to the hard point in the wing. Therefore, it is necessary to understand the influence the canard and the impact of its wake on the wing of the aircraft before any in-depth aerodynamic research could be completed on the aircraft. A combination of in-flight measurements of the canard wake and Computational Fluid Dynamics (CFD) were used to provide a clear picture of the flowfield around the aircraft. The first step of the project consisted of making a 3-D CAD model of the aircraft. This model was then used for the CFD simulations in Fluent. 2-D, 3-D, inviscid, and viscous simulations were preformed on the aircraft. A pressure rake was designed to house a 5-hole probe and 18 Pitot probes that extended forward of the main wing to measure the location and strength of the canard wake at various flight conditions. There were five primary test points that were recorded at multiple times over the course of three flights. Once all of the data were collected from the flights, the freestream conditions became the inputs into the final, 3-D CFD simulations on the aircraft. The good agreement between the CFD results and the in-flight measurements provided the necessary verification of the CFD model of the aircraft. These results can be used in the future planning and execution of experiments involving the Velocity XL-5 RG.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22416号 / 工博第4677号 / 新制||工||1730(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 八木 知己, 教授 清野 純史, 教授 高橋 良和 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Computational Fluid Dynamics (CFD) can play an important role in building design. For all aspects and stages of building design, CFD can be used to provide more accurate and rapid predictions of building performance with regard to air flow, pressure, temperature, and similar parameters. Generally, the process involved in conducting CFD analyses is relatively complex and requires a good understanding of how best to utilize computational numerical methods. Moreover, the level of skill required to perform an accurate CFD analysis remains a challenge for many professionals particularly architects. In addition, the user needs to input a number of different items of information and parameters into the CFD program in order to obtain a successful and credible solution. This research seeks to improve the general understanding of how CFD can best be used as a design assistance tool. While there have been a number of quantitative studies suggesting CFD may be a useful tool for building related airflow assessment, few researchers have explored the more qualitative aspects of CFD, in particular developing a better understanding of the procedures required for the proper application of CFD to whole building analysis. This study therefore adopted a combined qualitative and quantitative methodology, with the researcher immersing himself into a case study approach and defining several lessons-learned that are documented and shared. This research will assist practicing architects and architecture students to better understand the application of CFD to building analysis and design. / Ph. D.

<p>Highly loaded aerodynamic devices for propulsion and power generation are emerging to increase power output in a more compact machine are emerging. These devices can experience increased losses due to separation, as in the low-pressure turbine, which arise due to the operation at conditions that increases the adverse pressure gradients ore decrease the Reynolds number of the flow through the device. Therefore, flow control strategies become appealing to reduce losses at these conditions. This work aims to validate flow injection as an effective flow control strategy in the transonic regime.</p> <p>A test facility which was used to study boundary layer separation in a quasi-2d test article was modified to include flow injection and conditions were modified so that the facility was operated in the transonic regime. Valves were chosen which could achieve a wide range of excitation frequencies and the flow control ports were designed to accommodate their nominal flow rate. A preliminary test matrix was built while considering the limitations of the test facility.</p> <p>A numerical study was conducted to identify flow structures of interest and determine a preliminary understanding of the test article. The flow control was then added to the numerical study to guide the experimental set points for injected flow. The response of the flow to continuous slot blowing was characterized, and a 3D simulation with discrete injection ports was done to ensure the set-points determined from the 2D study were viable for discrete injection.</p> <p>Blow-down experiments were then conducted to study the behavior of bulk separation in a transonic regime for a quasi-2D geometry. Once behavior of the separation was understood, steady injection and then pulsated injection were applied in attempts to mitigate the separation. Steady injection was utilized to find the required pressure of injection relative to the total pressure at the inlet of the test article, while the pulsated injection served to identify a frequency at which the time averaged mitigation of separation was greatest.</p> <p>The experiments show that both steady and pulsated flow injection are viable techniques in flow control. It is also shown that pulsation does not allow for a lower pressure injection, but instead allows for the same effect with a lower mass flow requirement. Two-dimensional computational simulations are shown to be effective in determining injection frequencies but not the extent of separation or required injection pressures.</p>

Experimental methods for the investigation of trailing vortex strengths, total lift, and lift distributions for three-dimensional wings in close proximity flight were developed. With these experiments we model compound aircraft flight either docked tip-to-tip, or flying in formation. There is a distinct lack of experimental formation flight data using three-dimensional wing models for tests. The absence of fixed walls on either end of the wing permits the development of the asymmetric shedding of vortices, and the determination of the asymmetric circulation distribution induced by the proximity of the leading wing. The pair consisted of a swept NACA-0012 non-cambered wing simulating one half of a leading aircraft and a rectangular cambered NACA 63-420 wing simulating the trailing aircraft. Important aspects of the work included theoretical development, experimental setup, data acquisition and processing, and results validation. Experimentally determining the lift for formation flight, in addition to the local flow behavior for a pair of wings, can provide valuable insight for the proposition of flying actual aircraft in formation to increase mission efficiency. To eliminate the need for bulky mounting stings and direct load measurement devices that can potentially interfere with the local flowfield, a minimally invasive velocity probe method is developed. A series of experiments were performed to assist with the development of the method. Velocity and vorticity distributions obtained along a near-field plane were processed to calculate wingtip vortex strengths. Additionally, vortex position instabilities and the shedding of vorticity inboard of the wingtips were observed. To determine the circulation distributions for the trailing wing, the initial method is modified. By processing velocity information acquired in a near-field plane, both the lift and induced drag were calculated for the trailing airfoil. Comparisons are made to directly measured loads and to results reported earlier. Directly measured lift and drag coefficients were found to agree with existing literature. / Master of Science

<p> Efficiency is an essential metric for assessing turbine performance. Modern turbines rely heavily on numerical computational fluid dynamic (CFD) tools for design improvement. With more compact turbines leading to lower aspect ratio airfoils, the influence of secondary flows is significant on performance. Secondary flows and detached flows, in general, remain a challenge for commercial CFD solvers; hence, there is a need for high fidelity experimental data to tune these solvers used by turbine designers. Efficiency measurements in engine-representative test rigs are challenging for multiple reasons; an inherent problem to any experiment is to remove the effects specific to the turbine rig. This problem is compounded by the narrow uncertainty band required, ideally less than 0.5% uncertainty, to detect the incremental improvements achieved by turbine designers.  Efficiency measurements carried out in engine-representative turbine rigs have traditionally relied upon strong assumptions, such as neglecting heat transfer effects. Furthermore, prior to this research there was no framework to compute uncertainty propagation that combines both inputs from experiments and computational tools. </p> <p>This dissertation presents a comprehensive methodology to obtain high-fidelity adiabatic efficiency data in engine-representative turbine facilities. This dissertation presents probabilistic sampling techniques to allow for uncertainty propagation. The effect of rig-specific effects such as heat transfer and gas properties, on efficiency is demonstrated. Sources of uncertainty are identified, and a framework is presented which divides the sources into bias and stochastic. The framework allows the combination of experimental and numerical uncertainty. The accuracy of temperature and aerodynamic pressure probes, used for efficiency determination, is quantified. Corrections for those effects are presented that rely on hybrid numerical and experimental methods. Uncertainty is propagated through these methods using numerical sampling. </p> <p>Finally, two test cases are presented, a stator vane in an annular cascade and a two-stage turbine in a rotating rig. The performance is analyzed using the methods and corrections developed. The uncertainty on the measured efficiency is similar to literature but the uncertainty framework allows an uncertainty estimate on the adiabatic efficiency. </p>