Thesis (M.A.)--University of North Carolina at Chapel Hill, 2002. / Includes bibliographical references (leaves [115]-121).

Master of Science

This research will investigate various swept wing models, designing the mechanism for their pitching motion and control, designing wind tunnel implementation, and performing data measurements and analysis using particle image velocimetry. A NACA0012 section with an aspect ratio of AR = 4, free stream velocity of U∞=34 m/s, and Reynolds Number is Rec=2x105. Swept airfoils of Λ=0°, 15°, and 30° will be pitched sinusoidally between an AoA of 4°and 22°, at a reduced frequency of k=πfc/U∞=0.2. Higher sweep angles developing arch-type vortices interact with wing tip flow and abrupt tip stall is observed. Lower sweep angles possessed defined leading edge vortices persist near the tip after lift has collapsed at mid span. Stall angle was delayed during dynamic motion of the wing as well as the presence of arch and ring type vortices increased with sweep angle and contributed to flow reattachment along the top surface of the wing.

This study analyzed the relationships present between grip strength, wrist flexion, arm length, partial and total, and throwing velocity. Thirty-one subjects were tested to obtain the data on these variables. A multiple linear regression equation produced a significant F ratio for the relationship between grip strength and throwing velocity. Neither wrist flexion nor arm length obtained a significant F ratio to throwing velocity. A stepwise multiple regression equation again displayed a significant F ratio for grip strength and throwing velocity. Wrist flexion and arm length did not produce a significant F ratio for their relationships to throwing velocity. This study concludes that of the variables tested, only grip strength displayed a significant relationship to throwing velocity. This study indicates that throwing velocity can be predicted at a moderate level from the measurement of grip strength.

Vertical Takeoff-and-Landing (VTOL) Micro Air Vehicles (MAVs) provide a versatile operational platform which combines the capabilities of fixed wing and rotary wing MAVs. In order to improve performance of these vehicles, a better understanding of the rapid transition between horizontal and vertical flight is required. This study examines the flow structures around the Mini-Vertigo VTOL MAV using flow visualization techniques. This will gives an understanding of the flow structures which dominate the flight dynamics of rapid pitching maneuvers. This study consists of three objectives: develop an experimental facility, use flow visualization to investigate the flow around the experimental subject during pitching, and analyze the results. The model used for testing features a low aspect ratio (AR), low Reynolds number (Re) Zimmerman planform wing with two contra-rotating propellers in a tractor configuration. The experimental facility, located at the Department of Aerospace and Mechanical Engineering at The University of Arizona, consists of: a closed loop open test section wind tunnel capable of airspeeds up to 15m/s and controlled with a variable frequency drive (VFD); a power source and wire to generate vapor from a mixture of turbine oil, petroleum jelly, and iron powder, which is placed across the wind tunnel nozzle outlet; a five axis robotic arm mounted below the test section capable of controlling the experimental subject for pitching maneuvers; and, a pair of video cameras capable of recording the flow visualization at 600 frames per second. The flow within the wind tunnel was carefully examined in order to insure that the experimental subject was placed within a region of flow unaffected by boundary effects and that there were no significant disturbances or oscillations within the flow. The flow around the experimental subject was studied in both static and dynamic testing. For the static tests, the angle of attack (AOA) of the experimental subject was varied across a range of AOA from 15 to 70 degrees. For each range of AOA, the Re was varied to 10700, 22600, and 35500, and advance ratio (J) was varied from undefined, 0.60, to 0.47. Several conclusions can be drawn from the static testing. The flow is dominated by the propeller slipstream effects. The slipstream drastically delayed leading edge (LE) separation and vortex shedding. It also causes flow to be either deflected downward into the slipstream or to deflect outward towards the wing tip before passing over the LE. The slipstream strength also increases the turbulence in the slipstream and relative velocity of the flow at the wing surface compared to freestream. The Re affects the LE (visible only without slipstream) and trailing edge (TE) vortex shedding frequencies, increased Re increases the frequency. Additionally, it appears that the non-dimensional LE and TE vortex shedding frequencies are constant at a value of 0.216, irrespective of both Re and advance ratio. This is important because it means that these observations are likely valid across a broad range of flight conditions. Dynamic testing also varied the advance ratio and the Re. It also varied the reduced frequency. Both positive and negative pitching was examined. Many of the conclusions drawn were the same as those from static testing. Increasing the Re increased the vortex shedding frequency. The slipstream delayed LE separation and caused significant deflection downward and towards the wingtip, as well as increasing turbulence and relative flow speed at the top surface prior to separation. Dynamic testing also found that in the presence of the slipstream, increased Re decreases the AOA of LE separation, while without the slipstream, increased Re increases the AOA of LE separation. In addition, the pitching rate has several effects on the flow. For positive pitching, increasing the pitch rate decreases the AOA of separation and for negative pitching; increasing the pitch rate has no apparent effect on the AOA of separation. This is contrary to expectations. Previous study1 has shown that increasing the pitching rate delays stall and nose down pitching hastens stall. Additionally, greater positive pitching rate slightly increases the TE vortex shedding frequency. In the absence of a slipstream, LE and TE vortex-shedding frequency are generally the same. Some interesting phenomena were found at the LE. In the presence of a pulsating slipstream from the propellers, the LE separation bubble oscillates in both height and length. It does so at the same frequency as the propeller rotation and is due to variation in the flow speed at the LE. During pitch down maneuvers, the flow reattaches at the LE first and then the region of attached flow moves aft, opposite of the characteristics of pitch up. With only minimal variation, the non-dimensional TE vortex shedding frequency remains constant at an average value of 0.229. However, it appears that increasing the pitching rate increases this value slightly. Re and advance ratio have no appreciable effect on this data. It is therefore possible to extend this result to a large range of flight conditions. A comparison of the static and dynamic testing resulted in several findings that correlated very well with previous research on this model. During positive, nose-up, pitching, the increase in lift found previously was due to the increased downward deflection of the flow and the delay of stall was due to the delay in LE separation. The opposite effects were found in negative, nose-down, pitching. There was disagreement in the findings based on the size of the turbulent separation wake and the increase and decrease in drag. Positive pitching was found to increase the drag on the model however positive pitching reduces the size of the turbulent separation wake which should decrease drag. The increase in downward flow deflection caused by pitching rate was significantly less than that due to the slipstream. Therefore the increase in lift due to the slipstream is greater than that due to pitching. The flow around the Mini-Vertigo VTOL MAV is dominated by the slipstream from its propellers. The slipstream delays LE separation and causes drastic deflection in the flow. While the frequency of the vortices shed from the LE and TE varies with flow speed, the non-dimensional frequency does not. It does, however, vary slightly with the pitching rate. These results are applicable across a wide range of flight conditions.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Vita. / Includes bibliographical references. / by John Shaw. / Ph.D.

A Horizontal Axis Wind Turbine (HAWT) experiences imbalanced loads when it operates under yaw loads. For each blade element of the aerodynamically imbalanced rotor, not only is the angle of attack unsteady, but also the corresponding incident velocity, a fact usually unfairly ignored. For the unsteady angle of attack, a pitch oscillating airfoil has been studied experimentally and numerically when 3.5×10⁴<Re<10⁵. For small wind tunnel airfoils, Particle Image Velocimetry (PIV) was utilized to determine the aerodynamic loads and the pressure field where other measurement techniques are either intrusive or very challenging. For dynamic airfoils in highly separated flow fields, i.e., deep dynamic stall phenomena, loads were calculated successfully based on the control-volume approach by exploring ways to reduce the level of uncertainties in particular for drag estimation. Consecutive high resolution PIV velocity fields revealed that increasing the reduced frequency was followed by an enriched vortex growth time and phase delay as well as a reduced number of vortices during upstroke motion. Moreover, the locations of the vortices after separation were influenced by each other. Laminar separation bubble height also showed a reducing trend as the reduced frequency increased. The nature of the vortex sheet vortices before stall were explored in two Reynolds numbers, with and without laminar separation bubbles, at low angles of attack. For all cases, a vortex sheet was the result of random vortex sheding while a longer vortex sheet was more favorable for lift augmentation. A wake study and averaged drag calculation at low angles of attack were also performed with Laser Doppler Anemometry (LDA) for Re=10⁵. For the unsteady incident velocity, longitudinal freestream oscillations have been studied numerically, since experimental study of an unsteady freestream is challenging. In this regard, the streamwise freestream velocity and pitch angle of incidence oscillated with the same frequency in a wide range of phase differences. Changing the phase difference caused variation of the results, including significantly augmented and dramatically damped dynamic stall loads, both increasing and decreasing trends for vortex growth time during phase increase and shifted location of the maximum loads. The results showed strong dependency on the velocity and acceleration of the freestream during dynamic stall and the dynamic stall characteristics differed significantly from those of the steady freestream states. The results also demonstrated consistent trends regardless of the airfoil shape and the Reynolds number while Re=10⁵ and 10⁶. The vortex study presented here not only provides information about the unsteady aerodynamic forces, but also knowledge regarding airfoil noise generation and distributed flow for downstream objects beyond wind turbine applications.

No description available.

Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: Thomas W. Kaminski, Dept. of Health, Nutrition, & Exercise Sciences. Includes bibliographical references.

Thesis (Ph.D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.