Browsing by Author "Dr. Kailash C. Misra, Committee Member"

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Analytical and Experimental Approaches to Airfoil-Aircraft Design Integration
(2002-06-07) McAvoy, Christopher William; Dr. Kailash C. Misra, Committee Member; Dr. Ndaona Chokani, Committee Member; Dr. Ashok Gopalarathnam, Committee Chair
The aerodynamic characteristics of the wing airfoil are critical to achieving desired aircraft performance. However, even with all of the advances in airfoil and aircraft design, there remains little guidance on how to tailor an airfoil to suit a particular aircraft. Typically a trial-and-error approach is used to select the most-suitable airfoil. An airfoil thus selected is optimized for only a narrow range of flight conditions. Some form of geometry change is needed to adapt the airfoil for other flight conditions and it is desirable to automate this geometry change to avoid an increase in pilot workload. To make progress in these important aeronautical needs, the research described in this thesis is the result of seeking answers to two questions: (1) how does one efficiently tailor an airfoil to suit an aircraft? and (2) how can an airfoil be adapted for a wide range of flight conditions without increased pilot workload? The first part of the thesis presents a two-pronged approach to tailoring an airfoil for an aircraft: (1) an approach in which aircraft performance simulations are used to study the effects of airfoil changes and to guide the airfoil design and (2) an analytical approach to determine expressions that provide guidance in sizing and locating the airfoil low-drag range. The analytical study shows that there is an ideal value for the lift coefficient for the lower corner of the airfoil low-drag range when the airfoil is tailored for aircraft level-flight maximum speed. Likewise there is an ideal value for the lift coefficient for the upper corner of the low-drag range when the airfoil is tailored for maximizing the aircraft range. These ideal locations are functions of the amount of laminar flow on the upper and lower surfaces of the airfoil and also depend on the geometry, drag, and power characteristics of the aircraft. Comparison of the results from the two approaches for a hypothetical general aviation aircraft are presented to validate the expressions derived in the analytical approach. The second part of the thesis examines the use of a small trailing-edge flap, often referred to as a 'cruise flap,' that can be used to extend the low-drag range of a natural-laminar-flow airfoil. Automation of such a cruise flap is likely to result in improved aircraft performance over a large speed range without an increase in the pilot work load. An approach for the automation is presented here using two pressure-based schemes for determining the optimum flap angle for any given airfoil lift coefficient. The schemes use the pressure difference between two pressure sensors on the airfoil surface close to the leading edge. In each of the schemes, for a given lift coefficient this nondimensionalized pressure difference is brought to a predetermined target value by deflecting the flap. It is shown that the drag polar is then shifted to bracket the given lift coefficient. This non-dimensional pressure difference can, therefore, be used to determine and set the optimum flap angle for a specified lift coefficient. The two schemes differ in the method used for the nondimensionalization. The effectiveness of the two schemes are verified using computational and wind-tunnel results for two NASA laminar flow airfoils. To further validate the effectiveness of the two schemes in an automatic flap system, a closed-loop control system is developed and demonstrated for an airfoil in a wind tunnel. The control system uses a continuously-running Newton iteration to adjust the airfoil angle of attack and flap deflection. Finally, the aircraft performance-simulation approach developed in the first part of the thesis is used to analyze the potential aircraft performance benefits of an automatic cruise flap system while addressing trim drag considerations.
Fabric Defect Detection using a GA Tuned Wavelet Filter
(2003-10-30) Brenzovich, Joseph Andrew; Dr. Kailash C. Misra, Committee Member; Dr. Warren J. Jasper, Committee Co-Chair; Dr. Jeffrey A. Joines, Committee Co-Chair
The purpose of this research project is to show that a computerized system based on image processing software is capable of identifying defects in woven fabrics. Current defect detection is carried out through use of visual inspection of fabric rolls after the rolls have been doffed from the production machinery, which adds a substantial lag between defect creation and detection. Existing methods for automatic defect detection rely on methods that suffer from substantial analysis time or a low percentage of detection. The method described in this thesis represents a quick and accurate approach to automatic defect detection and is capable of identifying defects such as lines, tears, and spots. Utilizing a Genetic Algorithm (GA) as the primary means of solving the wavelet filter equations with respect to a fabric image proved adequate in the construction of a wavelet filter that was capable of removing large amounts of the fabric texture from the image, thus allowing defect segmentation algorithms to run more effectively. Although a real-time system is not developed, suggestions for constructing such a system are presented. This work provides a foundation for the development of a real-time automated defect detector based on the algorithms and methodologies employed in this work.
Simulation of Transitional Flow over an Elliptic Cone at Mach 8 using a One-Equation Transition/Turbulence Model
(2002-11-20) Malechuk, Andrew Martin; Dr. Jack R. Edwards, Committee Co-Chair; Dr. Hassan A. Hassan, Committee Co-Chair; Dr. Kailash C. Misra, Committee Member
The purpose of this research has been to extend a previously developed one-equation model for transitional/turbulent flows (AIAA Journal, Vol. 39, No. 9) for use in the simulation of transitional/turbulent flows over three-dimensional bodies in conventional hypersonic tunnels. This is done computationally through the combination of the Spalart-Allmaras one-equation turbulence model and an eddy viscosity-transport equation based on that proposed by Xiao, Edwards, and Hassan for high disturbance environment (HIDE) induced transition. The blending of these two pieces of the model is achieved through the use of an intermittency function based on the work of Dhawan and Narasimha. The test case used in this research is an elliptic cone of aspect ratio 2:1 in a Mach 8 environment with Reynolds numbers between the range of 1.98x10⁶/ft and 6.09x10⁵/ft. Two separate methods are used to find the boundary layer edge flow properties under the resulting conical shock. The first of these methods uses fluid values extracted from the surface of the cone after an inviscid calculation. The second searches for the boundary layer edge by locating the largest momentum flux under the shock. The second of the two approaches is found to be the most successful in replicating transitional flow heat flux data measured experimentally by Kimmel, Poggie, and Schwoerk. Over the range of Reynolds numbers examined, the model reasonably predicts the location and extent of the transitional region, but does not effectively predict fluid properties within the transitional region.