The application of smart materials to control the flight dynamics of a Micro Air Vehicle (MAV) has numerous benefits over traditional servomechanisms. Under study is wing morphing achieved through the use of piezoelectric Macro Fiber Composites (MFCs). These devices exhibit low power draw but excellent bandwidth characteristics. This thesis provides a background in the 2D analytical and computer modeling tools and methods needed to design and characterize an MFC-actuated airfoil. A composite airfoil is designed with embedded MFCs in a bimorph configuration. The deflection capabilities under actuation are predicted with the commercial finite element package NX Nastran. Placement of the piezoelectric actuator is studied for optimal effectiveness. A thermal analogy is used to represent piezoelectric strain. Lift and drag coefficients in low Reynolds number flow are explored with XFOIL. Predictions are made on static aeroelastic effects. The thin, cambered Generic Micro Aerial Vehicle (GenMAV) airfoil is fabricated with a bimorph actuator. Experimental data are taken with and without aerodynamic loading to validate the computer model. This is accomplished with in-house 2D wind tunnel testing. / Master of Science

Separated flows about single and multi-element airfoils are featured in many scenarios of practical interest, including: stall of fixed wing aircraft, dynamic stall of rotorcraft blades, and stall of compressor and turbine elements within jet engines. In each case, static and/or dynamic stall can lead to losses in performance. More importantly, modeling and analysis tools for stalled flows are relatively poorly evolved and designs must completely avoid stall due to a lack of understanding. The underlying argument is that advancements are necessary to facilitate understanding of and applications involving static and dynamic stall. The state-of-the-art in modeling stall involves numerical solutions to the governing equations of fluids. These tools often either lack fidelity or are prohibitively expensive. Ever-increasing computational power will likely lead to increased application of numerical solutions. The focus of this thesis is improvements in numerical modeling of stall, the need of which arises from poorly evolved analysis tools and the spread of numerical approaches. Technical barriers have included ensuring unsteady flow field and vorticity reproduction, transition modeling, non-linear effects such as viscosity, and convergence of predictions. Contributions to static and dynamic stall analysis have been been made. A hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy-Simulation turbulence technique was demonstrated to predict the unsteadiness and acoustics within a cavity with accuracy approaching Large-Eddy-Simulation. Practices to model separated flows were developed and applied to stalled airfoils. Convergence was characterized to allow computational resources to be focused only as needed. Techniques were established for estimation of integrated coefficients, onset of stall, and reattachment from unconverged data. Separation and stall onset were governed by turbulent transport, while the location of reattachment depended on the mean flow. Application of these methodologies to oscillating flapped airfoils revealed flow through the gap was dominated by the flap angle for low angles of attack. Lag between the aerodynamic response and input flap scheduling was associated with increased oscillation frequency and airfoil/flap gap size. Massively separated flow structures were also examined.

No description available.

Fully morphing wings allow the active change of the wing surface contours/wing configuration in flight enabling the optimum wing design for various flight regimes. These wing shape deformations are obtained by using smart actuators, which requires that the wing structure be flexible enough to morph under applied actuator loads and at the same time be fully capable of holding the aerodynamic loads. The study of such wing surface deformation requires an aeroelastic analysis since there is an active structural deformation under an applied aerodynamic field. Herein, a 2-D wing section, that is, an airfoil is considered. Modeling a variable geometry airfoil is performed using B-spline expansions. B-spline representation is also favorable towards optimization and provides a methodology to design curves based on discrete polygon points. The energy required for deforming the airfoil contour needs to be minimized. One of the methodologies adopted to minimize this actuation energy is to use the aerodynamic load itself for wing deformation. Another approach is to treat the airfoil deformation as a Multi Disciplinary Optimization (MDO) problem wherein the actuation energy needs to be minimized subject to certain constraints. The structural analysis is performed using commercial finite element software. The aerodynamic model is initiated from viscous-inviscid interaction codes and later developed from commercial Computational Fluid Dynamics (CFD) codes. Various modeling levels are investigated to determine the design requirements on morphing airfoils for enhanced aircraft maneuverability. / Singapore-MIT Alliance (SMA)

The goal of this thesis work has been to develop and manufacture an ice layer which was to be mounted on the tip of a scaled down wing model. The iced wing should be tested in a wind tunnel and aerodynamic comparisons should be made to the same wing without ice.The development of the ice was carried out as a modified product development process. The main differences are that there is no costumer and that the actual shape and functions of the product are more or less predetermined. The challenge was to find the best way to create the ice layer and how to mount it to the wing without damaging it or covering any pressure sensors. Product development methods such as pros and cons lists and prototypes were used to solve problems before printing the plastic ice layer in a rapid prototyping machine.Wind tunnel experiments were then conducted on the wing with and without the manufactured ice. Raw data from the wind tunnel were processed and lift and drag coefficients were calculated using mathematical equations. Finally, conclusions were drawn by comparing the results from the wind tunnel tests with theory, other works as well as CFD simulations.The ice layer was successfully manufactured and it met the target specifications. The aerodynamic performance of an iced aircraft wing proved to be considerably worse compared to a blank wing. The maximum achievable lift force decreased by 22% and an increased drag force will require more thrust from the airplane.

Experimental aeroacoustic research was conducted on a wind turbine specific airfoil at low Reynolds numbers. The goal of this thesis was to study trailing edge noise generation from the airfoil and investigate correlations between the noise and the flow field. Before experiments were performed the current wind tunnel had to be modified in order to make it more suitable for aeroacoustic tests. Sound absorbing foam was added to the inside of the tunnel to lower the background noise levels and turbulence reduction screens were added which lowered the turbulence. An S822 airfoil was chosen because it is designed for low Reynolds flows attainable in the wind tunnel which are on the order of 104. Smoke wire flow visualization was used to gain insight into the airfoil wake development and oil film flow visualization was used to qualitatively assess the boundary layer development. Laser Doppler anemometry (LDA) was used to measure two components of velocity at high data rates in the airfoil wake. Wake profiles were measured in addition to single point measurements to determine the velocity spectrum. A microphone was mounted inside the test section in order to measure the trailing edge noise. Initial plans included measuring the trailing edge noise with a microphone array capable of quantifying and locating noise sources. Although an array was built and beamforming code was written it was only used in preliminary monopole source tests. Oil film results showed the behaviour of the boundary layer to be consistent with previous low Reynolds number experiments. LDA results revealed sharp peaks in the velocity spectra at 1100 Hz from U0 = 15–24 m/s, and 3100 and 3800 Hz, from U0 = 25–35 m/s, which were inconsistent with vortex shedding results of previous researchers. Also present were a series of broad peaks in the spectra that increase from 1200–1700 Hz in the U0 = 25–35 m/s range. The shedding frequency from the smoke wire flow visualization was calculated to be 1250 Hz at U0 = 26 m/s. These sharp peaks were also present in the acoustic spectrum. It was reasoned that these peaks are due to wind tunnel resonance which is a common occurrence in hard wall wind tunnels. In particular the tone at 1100 Hz is due to a standing wave with a wavelength equal to half the tunnel width. The shedding frequency from the smoke wire flow visualization was calculated to be 1100 Hz at U0 = 20 m/s. These tones exhibited a “ladder-like” relationship with freestream velocity, another aspect indicative of wind tunnel resonance. It was reasoned that the wind tunnel resonance was forcing the shedding frequency of the airfoil in the U0 = 15–24 m/s range, and in the U0 = 25–35 m/s range, the shedding frequency corresponded to the broad peaks in the LDA spectra.

The heat transfer characteristics of airflows in serpentine cooling channels in stator vanes of gas turbines and the novel QuTech® Heat Pipe (QTHP) for electronic cooling applications were studied. The cooling channels are modeled as smooth and roughened two-pass trapezoidal channels with a 180° turn over a range of Reynolds numbers between about 10,000 and 60,000. The naphthalene sublimation technique and the heat and mass transfer analogy were applied. The results showed that there was a very large variation of the local heat (mass) transfer distribution in the turn and downstream of the turn. The local heat (mass) transfer was high near the end wall and the downstream outer wall in the turn and was relatively low in two regions near the upstream outer wall and the downstream edge at the tip of the divider wall in the turn. The variation of the local heat (mass) transfer was larger with ribs on two opposite walls than with smooth walls. The regional average heat (mass) transfer was lower in the turn and higher in the entire channel with the flow entering the channel through the larger straight section than when the flow was reversed. The pressure drop across the turn was higher with the flow entering the channel through the larger channel than when the flow was reversed. Thermal performance of the QuTech® Heat Pipe was identified over a range of inclination angles between 90° and -90° and thermal mechanism of the QTHP was studied with GC-MS, ICP-OES, XRD, XPS, and DSC. This study resulted in the following findings: the performance of the QTHP was severely dependent on gravity; the QTHP utilizes water as working fluid; there were inorganic components such as Na, K, P, S, and Cr, etc.; and the vaporization temperature of the working fluid (mostly water) was lower than the boiling temperature of pure water. This was due to the presence of inorganic salt hydrates in the QTHP. It may be concluded that thermal performance of heat pipes increases with additional latent heat of fusion energy and energy required to release water molecules from salt hydrates.

This thesis investigates the effects of camber change on the mission adaptive wing of a structurally designed unmanned aerial vehicle (UAV). The commercial computational fluid dynamics (CFD) software ANSYS/FLUENT is employed for the aerodynamic analyses. Several cambered airfoils are compared in terms of their aerodynamic coefficients and the effects of the camber change formed in specific sections of the wing on the spanwise pressure distribution are investigated. The mission adaptive wing is modeled structurally to observe the effect of spanwise pressure distribution on the wing structure. For the structural design and analysis of the UAV under this study, commercial software MSC/PATRAN and MSC/NASTRAN are used. The structural static and dynamic analyses of the unmanned aerial vehicle are also performed under specified flight conditions. The results of these analyses show that the designed structure is safe within the flight envelope. Having completed aero-structural design and analysis, the designed unmanned aerial vehicle is manufactured by TUSAS Aerospace Industries (TAI).

No description available.

No description available.