الفهرس 
Introduction & Literature ReviewOnly 14 pages are availabe for public view
 |  | from | 134 |  |  |
| | | from | 134 | | |
Abstract
Various flow control techniques have been invented and tested through numerous researches to extend the utilization range and performance efficiency of aerodynamic models. Tubercles, the wavy perturbations on the leading edge of wing-like bodies, is one of these techniques which is inspired from pectoral flippers of the humpback whale, the most acrobatic of baleen whales. Many studies showed the highly promising aerodynamic gain that can be obtained from using these perturbations for delaying stall-phase, softening stall-degradation, and enhancing post-stall performance. The obtainable gain depends totally on the model’s design aspects, both baseline aspects (i.e., aspect ratio, taper ratio, and sweep angle) and tubercles aspects (i.e., amplitude, wavelength, phase-angle, and waviness ratio), which have to be optimally set for the different airfoils and various flow regimes. The waviness ratio, the ratio of the tubercled extent to the total model’s spanwise length, is one of the tubercles’ geometrical aspects, which is thought to be of a dominant effect; however, it is little considered in research works. The objective of the present work is to investigate the influences of varying the modified length over the leading-edge on the aerodynamic performance of highly cambered models at the low-Re Transition flow regime, which is their optimum design range. These airfoils are highly applicable in various engineering fields such as heavy cargo planes, unmanned air vehicles, and low-Re wind turbines because of their superior lift-generation with high lift-to-drag ratios. An experimental approach was employed to test four tubercled models of the high-lift S1223 airfoil with different ratios for waved-length to total one (waviness ratios of 12.5%, 20.83%, 50%, and 100%) in a subsonic wind tunnel at two values for mean-chord-based Reynolds number, 𝑅𝑅𝑅𝑅 = (0.6 − 1.0) × 105 and compare them with their counterpart unmodified-leading-edge model. The effectiveness would be assessed based on comparative evaluation for the force coefficients curves over a range of angle-of-attack from the zero-lift angle up to 30° with a fixed increment of 2 degrees. The tests were primarily performed on the infinite-span basis (2D) by excluding the tipvortices effects on flow structure, forming an imaginary pattern of mirrored sections. The acquired outcomes could be used for blades of case-enclosed applications and for blades/wings with very high total-aspect-ratios for free-tip-flow applications. Secondarily, the finite-span (3-dimensional) performance of one of the partially-tubercled models that had been selected for its performance under the infinite-span configuration was compared with that of the conventionally modified model, which has full-span tubercles’ implementation, and with that of the straight-leading-edge model. The tubercles were designed using the non-linear shearing transformation scheme, which confines the modulation to the region ahead of the max-thickness point, preserves the further profile with superficial continuity, and keeps the same leading-edge radius as the base model. The models were virtually built using the computer-aided-design packages of SOLIDWORKS and made of PLA filaments using an FDM 3D printing machine. The building technique creates a unidirectional surface texture that might be considered as microscale tubercles. Thus, the manufactured models have superimposed waviness of macroscale (tubercles) and microscale (surface lay). Consequently, another model with a smooth surface and straight leading-edge had been involved in distinguishing the effects of unintendedly created microscale tubercles. Flow visualization through CFD numerical simulations was conducted to investigate the flow features of the smooth-surface baseline model. The visualization results could be utilized to set a correlation between tubercles’ observed performance, and baseline’s revealed flow structure. The quasi-2-D results, at 𝑅𝑅𝑅𝑅 = 1.0 × 105, showed that the microscale tubercles have a great impact as it delays the stall-phase by 143% and boosts the max-lift-performance by 8%, while the full-span application of macroscale tubercles softens the performance deterioration of the stall phase. Decreasing the waviness ratio of the macroscale tubercles further delays the primary-stall attack-angle while increasing the max lift-coefficient. The 0.28-𝑅𝑅𝑤𝑤 model, which has an extended working envelope due to its primary soft-stallphase, and the 1.00-𝑅𝑅𝑤𝑤 model miss to have better performance than that of the 0.00-𝑅𝑅𝑤𝑤 model, regarding the stall attack-angle and max lift-performance. On the other hand, the lower-Re infinite-span results exhibited that the microscale tubercles still have great influences on stall onset by 186% delay and on the max-lift-performance by 40% rise. The full-span implementation of macroscale tubercles softens the performance deterioration of the stall phase that gets worse as a result of microscale tubercles. Varying the waviness ratio forms worse performance than that of the fully-tubercled model. Moreover, the 1.00-𝑅𝑅𝑤𝑤 model manages to achieve better finite-span performance than that of the micro-tubercled model, at 𝑅𝑅𝑅𝑅 = 0.6 × 105While the 0.28-𝑅𝑅𝑤𝑤 model failed to attain so. The thesis contents include five chapters; the first one gives a detailed introduction about the presented field of science, a review for the published literature that discusses the documented influences of the current flow control approach, and defines the thesis objective ultimately, the second one provides detailed information about the design approach of the study models, the third chapter describes the CFD visualization setup and exhibits its obtained results that aim to form better understanding for the baseline model’s stall problem, the fourth chapter encompasses the methodologies and prepared setups for the experimental work, and presents elaborate discussions for the obtained results for the effects of leadingedge tubercles, and the fifth chapter gives brief conclusions for the observed outcomes and recommendations for the future work.