Browsing by Author "Dr. Jack Edwards, Committee Member"

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Analytical and Computational Investigations of Airfoils Undergoing High-Frequency Sinusoidal Pitch and Plunge Motions at Low Reynolds Numbers
(2008-11-10) McGowan, Gregory Zar; Dr. Harvey Charlton, Committee Member; Dr. Jack Edwards, Committee Member; Dr. Hassan Hassan, Committee Member; Dr. Ashok Gopalarathnam, Committee Chair
Current interests in Micro Air Vehicle (MAV)technologies call for the development of aerodynamic-design tools that will aid in the design of more efficient platforms that will also have adequate stability and control for flight in gusty environments. Influenced largely by nature MAVs tend to be very small, have low flight speeds, and utilize flapping motions for propulsion. For these reasons the focus is, specifically, on high-frequency motions at low Reynolds numbers. Toward the goal of developing design tools, it is of interest to explore the use of elementary flow solutions for simple motions such as pitch and plunge oscillations to predict aerodynamic performance for more complex motions. In the early part of this research, a validation effort was undertaken. Computations from the current effort were compared with experiments conducted in a parallel, collaborative effort at the Air Force Research Laboratory (AFRL). A set of pure-pitch and pure-plunge sinusoidal oscillations of the SD7003 airfoil were examined. Phase-averaged measurements using particle image velocimetry in a water tunnel were compared with computations using two flow solvers: i) an incompressible Navier-Stokes Immersed Boundary Method and ii) an unsteady compressible Reynolds-Averaged Navier-Stokes (RANS) solver. The motions were at a reduced frequency of $k = 3.93$, and pitch-angle amplitudes were chosen such that a kinematic equivalence in amplitudes of effective angle of attack (from plunge) was obtained. Plunge cases showed good qualitative agreement between computation and experiment, but in the pitch cases, the wake vorticity in the experiment was substantially different from that predicted by both computations. Further, equivalence between the pure-pitch and pure-plunge motions was not attained through matching effective angle of attack. With the failure of pitch/plunge equivalence using equivalent amplitudes of effective angle of attack, the effort shifted to include pitch-rate and wake-effect terms through the use of analytical methods including quasi-steady thin-airfoil theory (QSTAT) and Theodorsen's theory. These theories were used to develop three analytical approaches for determining pitch motions equivalent to plunge motions. A study of variation in plunge height was then examined and followed by a study of the effect of rotation point using the RANS solver. For the range of plunge heights studied, it was observed that kinematic matching between plunge and pitch using QSTAT gave outstanding similarities in flow field, while the matching performed using Theodorsen's theory gave the best equivalence in lift coefficients for all cases. The variation of rotation point revealed that, for the given plunge height, with rotation point in front of the mid-chord location, all three schemes matched flow-field vorticity well, and with rotation point aft of the mid-chord no scheme matched vorticity fields. However, for all rotation points (except for the mid-chord location), CFD prediction of lift coefficients from the Theodorsen matching scheme matched the lift time histories closely to CFD predictions for pure-pitch. Combined pitch and plunge motions were then examined using kinematic parameters obtained from the three schemes. The results showed that QSTAT nearly cancels the vortices emanating from the trailing edge. Theodorsen's matching approach was successful in generating a lift that was close to constant over the entire cycle. Additionally this approach showed the presence of the reverse Karman vortex sheet through the wake. Combined pitch/plunge motions were then analyzed, computationally and experimentally, with a non-zero mean angle of attack. All computational results compared excellently with experiments, capturing vorticity production on the airfoil's surface and through the wake. Lift coefficient through a cycle was shown to tend toward a constant using Theodorsen's parameters, with the constant being dependent on the initial angle of attack. This result points to the possibility of designing an unsteady motion to match a given flight-condition requirement.
Flow Modeling for Micro-filtration through electro-statically charged monolith filters
(2009-11-30) Lad, Ankit Raghunath; Dr. Andrey V. Kuznetsov, Committee Chair; Dr. William Roberts, Committee Member; Dr. Jack Edwards, Committee Member
LAD, ANKIT RAGHUNATH. Flow Modeling for Micro-filtration through electro-statically charged monolith filters. (Under the direction of Dr. Andrey V. Kuznetsov.) This study is a multi-physics problem which aims at modeling fluid flow through electro-statically charged monolith filters with machined micro-channels. The multi-phase fluid (air) considered has suspended micro particles which are the impurities to be filtered out. The resulting particle trajectories due to the effect of the forces exerted on the particle such as the hydrodynamic drag, the electrostatic force of attraction and repulsion and Brownian diffusion are studied. The micro-filtration process is studied under the presence of an electric field developed due to the uniform density charge distributed over the channel surface. The model is validated by comparison with the experimental result. The advantage of using repulsive electric field instead of attractive electric field for filtration is studied. The unit cell filtration system is developed for normal and cross flow and the scope for efficiency improvement is tested. The possibility of Ã¢â‚¬Ëœselective filtrationÃ¢â‚¬â„¢ is examined by using the multiple filter layer model and the role of different hole-orientation pattern is also studied. The experimental setup of the filtration system and the filter material strength for practical applications is discussed.
On the Use of Wing Adaptation and Formation for Improved Aerodynamic Efficiency
(2005-05-11) King, Rachel Marie; Dr. Ashok Gopalarathnam, Committee Chair; Dr. Hassan Hassan, Committee Member; Dr. Jack Edwards, Committee Member; Dr. Xiao-Biao Lin, Committee Member
There is a continuous effort to improve the performance and efficiency of today's aircraft, and the reduction of aircraft drag has been the primary focus of many aerodynamicists. In the current research, two different and innovative approaches for aircraft drag reduction are examined. These approaches are: (1) multiple spanwise trailing-edge flaps, and (2) formation and ground-effect flight. The main goal of this dissertation was to assess the drag benefits of the two approaches, in an effort to explore their potential for use on future aircraft. The first approach of using multiple trailing-edge flaps has the potential for application on aircraft in the near future. By using multiple trailing-edge flaps along the wing span, it is possible to redistribute the spanwise lift distribution to suit the flight condition. For this research, a numerical approach was developed for determining optimum lift distributions on a wing with multiple trailing-edge flaps for various flight conditions. The objective of the approach was to determine the flap angles that will reduce the drag at 1-g flight conditions, and constrain the wing root-bending moment at high-g conditions to not exceed a specified value. The approach uses the concept of additional and basic lift distributions, and the proper use of a trailing-edge flap for redistributing the aerodynamic loads to bring about a minimum in profile and induced drag. The results for the flap-angle distributions are presented for a planar and a nonplanar wing, along with post-design analysis and aircraft performance simulations used to validate the optimum flap-angle distributions determined using the numerical approach. It is shown that the approach is effective in determining optimum flap angles for reducing both profile and induced drag over a wide range of flight conditions. Performance benefits due to using the optimum flap angles are shown when compared to the zero-flap case. In addition, the trailing-edge flaps were found to be successful in relieving the wing root-bending moment at high-g flight conditions, which can be used to reduce wing weight. When examining formation and ground-effect flight as another approach for aircraft drag reduction, an optimum-downwash approach using a vortex-lattice implementation was used to study formations of wings loaded optimally for minimum induced drag with roll trim. An exact approach was also developed to examine the drag of elliptically-loaded wings in formation. The exact approach allows for decomposition of the benefits by considering the mutual-interference contributions from different pairs of wings in a formation. The results show that elliptically-loaded wing formations have nearly the same drag as optimally-loaded wing formations. For a formation of planar wings, in or out of ground effect, the optimum lateral separation corresponds to a 9%-span overlap of wing tips. At this optimum lateral separation, a formation of 25 elliptically-loaded wings flying out of ground effect experiences an 81% drag reduction compared to 25 wings flying in isolation. For large formations, in or out of ground effect, multiple local optima are seen for the lateral separation. Large formations experience small additional benefits due to ground effect even at relatively large ground clearances of four wing spans. The shape of vee-formations, for equipartition of drag benefits, is found to be nearly independent of flight in or out of ground effect. Overall, both approaches for aircraft drag reduction show potential for significant drag savings. It is believed that the presented research will further increase interest in such flight techniques, and thus advance their progression toward becoming viable solutions for drag reduction on future aircraft.