Better knowledge in the areas of aerodynamics and optimization has allowed designers to develop efficient wingtip structures in recent years. However, the requirements faced by wingtip devices can be considerably different amongst an aircraft’s flight regimes. Traditional static wingtip devices are then a compromise between conflicting requirements, resulting in less than optimal performance within each regime. Alternatively, a morphing wingtip can reconfigure leading to improved performance over a range of dissimilar flight conditions. Developed within this thesis, is a modular morphing wingtip concept that centers on the use of variable geometry truss mechanisms to permit morphing. A conceptual design framework is established to aid in the development of the concept. The framework uses a metaheuristic optimization procedure to determine optimal continuous wingtip configurations. The configurations are then discretized for the modular concept. The functionality of the framework is demonstrated through a design study on a hypothetical wing/winglet within the thesis.

Better knowledge in the areas of aerodynamics and optimization has allowed designers to develop efficient wingtip structures in recent years. However, the requirements faced by wingtip devices can be considerably different amongst an aircraft’s flight regimes. Traditional static wingtip devices are then a compromise between conflicting requirements, resulting in less than optimal performance within each regime. Alternatively, a morphing wingtip can reconfigure leading to improved performance over a range of dissimilar flight conditions. Developed within this thesis, is a modular morphing wingtip concept that centers on the use of variable geometry truss mechanisms to permit morphing. A conceptual design framework is established to aid in the development of the concept. The framework uses a metaheuristic optimization procedure to determine optimal continuous wingtip configurations. The configurations are then discretized for the modular concept. The functionality of the framework is demonstrated through a design study on a hypothetical wing/winglet within the thesis.

Wingtip vortices, created as a byproduct of lift, are both a hazard and a significant limiting factor in the increase of air traffic. In order to reduce separation distances between airplanes and increase safety, active flow control solutions are considered, however, more research is required to better understand the behavior of wingtip vortices. Therefore, this research focuses on the modification of the flow structure downstream using pulsed jets, visualization of the behavior of wingtip vortices using two dimensional particle image velocimetry, as well as measurements of the forces and moments affected by the pulsed jets using an aerodynamic balance. A NACA 0012 wing model equipped with two slots was mounted in a wind tunnel at approximately 150,000 Reynolds number. A valve system was designed to create jets of air at the wing tip in a steady or pulsed pattern from a slot placed either on the pressure side or the suction side. Particle image velocimetry measurements were taken at various distances downstream, and post-processed for the characterization of the vortex : position, angle, distance, vorticity contour, and circulation. Results indicate that the vortex can be forced into a cyclic pattern constrained between the baseline (no jet) vortex core position, and the position when the jet is permanently activated (steady blowing cases). Depending on the slot used, the vortex trajectory can be forced into an inclination angle. Steady blowing cases show near-sinusoidal oscillations, while pulsed blowing cases exhibit a steady rise in angle, with a slight oscillating pattern in displacement distance values. The circulation values are significantly changed, with a significantly higher dispersion than for the baseline case. Furthermore, the vortex core size is consistently larger as it is displaced away from the baseline case. Additionally, lift, drag and pitching moment were measured in a wind tunnel using an aerodynamic balance. Results showed that lift/drag coefficients consistent with published results, and that activating the jets on the pressure or suction side decreased lift. As instability grows, the destruction of the wingtip vortices occurs past the maximum downstream distance studied, therefore, additional PIV measurements should be taken further downstream. Moreover, supplementary PIV measurements at the slot themselves should be considered to better understand how the perturbed flow structure interacts with the pulsed jets.

Wind tunnel experiments have been conducted on six different wingtip configurations to determine their wake vortex characteristics. The trailing wingtip vortex was probed by a 1/8 inch diameter five hole yawhead pressure probe in the VPI & SU Stability Wind Tunnel. The vortex tangential and axial velocity profiles are compared at five and twenty chord lengths downstream. Primary focus is placed on the Whitcomb winglet and its individual components, the upper winglet alone and the lower winglet alone. It is shown that the Whitcomb winglet and the upper winglet configuration both produce two distinct vortices of the same rotation. The maximum tangential velocity in each vortex is about 64 percent less than that produced by a conventional wingtip configuration. The axial velocity profiles exhibit strong velocity deficits throughout the vortex core. Aerodynamic force tests were conducted to compare the lift and drag characteristics of the wingtip configurations. Both the Whitcomb winglet and the upper winglet configuration have a remarkable ability to increase the lift-drag ratio and reduce the drag coefficient. / Ph. D.

Previous applications have shown that a wingtip treatment on a commercial airliner will reduce drag and increase fuel efficiency and the most common types of treatment are blended winglets and raked wingtips. With Boeing currently investigating novel designs for its next generation of airliners, a variable geometry raked wingtip novel control effector (VGRWT/NCE) was studied to determine the aerodynamic performance benefits over an untreated wingtip. The Boeing SUGAR design employing a truss-braced wing was selected as the baseline. Vortex lattice method (VLM) and computational fluid dynamics (CFD) software was implemented to analyze the aerodynamic performance of such a configuration applied to a next-generation, transonic, mid-range transport aircraft. Several models were created to simulate various sweep positions for the VGRWT/NCE tip, as well as a baseline model with an untreated wingtip. The majority of investigation was conducted using the VLM software, with CFD used largely as a validation of the VLM analysis. The VGRWT/NCE tip was shown to increase the lift of the wing while also decreasing the drag. As expected, the unswept VGRWT/NCE tip increases the amount of lift available over the untreated wingtip, which will be very beneficial for take-off and landing. Similarly, the swept VGRWT/NCE tip reduced the drag of the wing during cruise compared to the unmodified tip, which will favorably impact the fuel efficiency of the aircraft. Also, the swept VGRWT/NCE tip showed an increase in moment compared to the unmodified wingtip, implying an increase in stability, as well providing an avenue for roll control and gust alleviation for flexible wings. CFD analysis validated VLM as a useful low fidelity tool that yielded quite accurate results. The main results of this study are tabulated "deltas" in the forces and moments on the VGRWT/NCE tip as a function of sweep angle and aileron deflection compared to the baseline wing. A side study of the effects of the joint between the main wing and the movable tip showed that the drag impact can be kept small by careful design. / Master of Science

Compound Aircraft Transport (CAT) flight involves two or more aircraft using the resources of each other; a symbiotic relationship exists consisting of a host, the mothership aircraft and a parasite, the hitchhiker aircraft. Wingtip-docked flight is just as its name implies; the two aircraft are connected wingtip-to-wingtip. Formation flight describes multiple aircraft or flying objects that maintain a pattern or shape in the air. There are large aerodynamic advantages in CAT flight. The aforementioned wingtip-docked flight increases total span of the aircraft system, and formation flight utilizes the upwash from the trailing wingtip vortex of the lead aircraft (mothership) to reduce the energy necessary to achieve and/or maintain a specific flight goal for the hitchhiker and the system. The Stability Wind Tunnel (6 X 6 X 24 foot test section) at Virginia Tech, computational aerodynamic analysis with the vortex lattice method (VLM), and a desktop aircraft model were used to answer questions of the best location for a hitchhiker aircraft and analyze stability of the CAT system. Wind tunnel tests implemented a 1/32 scale F-84E model (hitchhiker) and an outboard wing portion representing a B-36 (mothership). These models were chosen to simulate flight tests of an actual wingtip-docked project, Tom Tom, in the 1950s. That project was terminated after a devastating accident that demonstrated a possible "flapping" motion instability. The wind tunnel test included a broad range of hitchhiker locations: varying spanwise gap distance, longitudinal or streamwise distance, and vertical location (above or below wing) with respect to a B-36-like wing. The data showed very little change in the aerodynamic forces of the mothership, and possibilities of large benefits in lift and drag for the hitchhiker when located slightly aft and inboard with respect to the mothership. Three CAT flight configurations were highlighted: wingtip-docked, close formation, and towed formation. The wingtip-docked configuration had a 20-40 percent performance benefit for the hitchhiker compared to solo flight. The close formation configuration had performance benefits for the hitchhiker approximately 10 times that of solo flight, and the towed formation was approximately 8 times better than solo flight. The VLM analysis completed and reenforced the experimental wind tunnel data. A modified VLM program (VLM CAT) incorporated multiple aircraft in various locations as well as additional calculations for induced drag. VLM CAT results clearly followed the trends seen in the wind tunnel data, but since VLM did not model the fuselage, has assumptions like a flat wake, and is an inviscid computation it did not predict the large benefits or excursions as seen in the wind tunnel data. Increases in performance for the hitchhiker in VLM CAT were on the order of 3 to 4 times that of the hitchhiker in solo flight, while the wind tunnel study saw up to 10 times that of solo flight. VLM CAT is a valuable tool in supplying quick analysis of position and planform effects in CAT flight. Modifications to a desktop F-16 dynamic simulation have been developed to investigate the stability of wingtip-docked flight. These modifications analyze the stability issues linked with sideslip angle as seen by the Tom Tom Project test pilot, when he entered docking maneuvers with 5 degrees yaw to simulate a ``tired pilot". The wingtip-docked system was determined to have an unstable aperiodic mode for sideslip angle greater than 0.0 degrees and an unstable oscillatory mode for sideslip angle greater than 2.0 degrees. There is a small range of sideslip angle that is a stable oscillatory mode, sideslip angle between 0.0 and 2.0 degrees. The variables, altitude and speed, yield little effect on the stability of the system. The sensitivity analysis was indeterminate in distinguishing a state driving the instability, but the analysis was conclusive in verifying the lateral-longitudinal (roll-pitch) coupled motion observed by test pilots in wingtip-docked flight experiments. The parameter with the largest influence on the instability was the change in pitch angular acceleration with respect to roll angle. The aerodynamic results presented in this study have determined some important parameters in the location of a hitchhiker with respect to a mothership. The largest aerodynamic benefits are seen when the hitchhiker wingtip is slightly aft, inboard and below the wingtip of the mothership. In addition, the stability analysis has identified an instability in the CAT system in terms of sideslip angle, and that the wingtip-docked hitchhiker is coupled in lateral and longitudinal motion, which does concur with the divergent "flapping" motion about the hinged rotational axis experienced by the Tom Tom Project test pilot. / Ph. D.

No description available.

An experiment was performed in the Cal Poly Mechanical Engineering 2x2 ft wind tunnel to quantify the effect of spanwise synthetic jet actuation (SJA) on the drag of a NACA 0015 semispan wing. The wing, which was designed and manufactured for this experiment, has an aspect ratio of 4.20, a span of 0.427 m (16.813”), and is built around an internal array of piezoelectric actuators, which work in series to create a synthetic jet that emanates from the wingtip in the spanwise direction. Direct lift and drag measurements were taken at a Reynolds Number of 100,000 and 200,000 using a load cell/slider mechanism to quantify the effect of actuation on the lift and drag. It was found that the piezoelectric disks used in the synthetic jet actuators cause structural vibrations that have a significant effect on the aerodynamics of the NACA 0015 model. The experiment was performed in a way as to isolate the effect of vibration from the effect of the synthetic jet on the lift and drag. Lift and drag data was supported with pressure readings from 60 pressure ports distributed in rows along the span of the wing. Oil droplet flow visualization was also performed to understand the effect of SJA near the wingtip. The synthetic jet and vibration had effects on the drag. The synthetic jet with vibration decreased the drag only slightly while vibration alone could decrease drag significantly from 11.3% at α = 4° to 23.4% at α = 10° and Re = 100,000. The lift was slightly increased with a slight increase due to the jet and showed a slight increase due to vibration. Two complete rows of pressure ports at 2y/b = 37.5% and 85.1% showed changes in lift due to actuation as well. The synthetic jet increased the lift near the wingtip at 2y/b = 85.1% and had little to no effect inboard at the 37.5% location, hence, the synthetic jet changes the lift distribution on the wing. Oil flow visualization was used to support this claim. Without actuation, the footprint of the tip vortex was present on the upper surface of the wing. With actuation on, the footprint disappeared suggesting the vortex was pushed off the wingtip by the jet. It is possible that the increased lift with actuation can be caused by the vortex being pushed outboard.

A numerical technique is developed to simulate the vortices associated with stationary and flapping wings. The Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are used over an unstructured grid. The present work assesses the locations of the origins of vortex generation, models those locations and develops a systematic mesh refinement strategy to simulate vortices more accurately using the URANS model. The vortex center plays a key role in the analysis of the simulation data. A novel approach to locating a vortex center is also developed referred to as the Max-Max criterion. Experimental validation of the simulated vortex from a stationary NACA0012 wing is achieved. The tangential velocity along the core of the vortex falls within five percent of the experimental data in the case of the stationary NACA0012 simulation. The wing surface pressure coefficient also matches with the experimental data. The refinement techniques are then focused on unsteady simulations of pitching and dual-mode wing flapping. Tip vortex strength, location, and wing surface pressure are analyzed. Links to vortex behavior and wing motion are inferred.

No description available.