The study was done using three different grid topologies: 1) Structured O-grid, 2) Structured C-H grid, 3) Unstructured T-Rex grid. comparison to experimental data) of the NACA 0012 airfoil was conducted at various angles of attack (alpha). The simulations were executed in ANSYS Fluent 2019.A validation study (i.e. The production of vortices appeared to have been the source of higher efficiency at lower Reynolds numbers instead of bubble formation. Upstream bubble formation on the modified airfoils appeared to negatively affect lift performance compared to the unmodified NACA 0009, likely due to a reduction of maximum suction pressure over the first 15% of the chord length. This facilitated the onset of Kelvin-Helmholtz instability mechanism and transition to turbulence, promoting early boundary layer reattachment. Sharp leading edges were found to consistently act as locations of enforced boundary layer separation by displacing the latter into the free stream. NACA 0009-05 experienced its highest efficiency at Re = 1 x 10^4, where vortex-mediated reattachment occurred. Peak efficiencies achieved by NACA 0009-03 corresponded to angles of attack for which a vortex cascade developed over its suction surface. Vortices were not present on the unmodified NACA 0009 at any time, making it a unique consequence of sharp leading edge modification. It appeared that the formation of vortices on the suction surface of the sharp leading edge airfoils played a role in either boundary layer reattachment or viscous drag mitigation. Below Re = 3 x 10^4, however, peak efficiency was attained by the modified airfoils, with NACA 0009-03 having the highest peak at Re = 2 x 10^4 and NACA 0009-05 having the highest peak at Re = 1 x 10^4. The unmodified NACA 0009 offered the highest lift and the least drag compared to the modified airfoils at Reynolds numbers between 3 x 10^4 and 5 x 10^4, which caused it to also have the highest efficiency peak within that range. A sharp leading edge in this study is defined as a leading edge where the radius of curvature is zero. Modifications were made to the NACA 0009 airfoil according to the NACA Modified 4-Digit algorithm developed by Stack and von Doenhoff, with one version having a sharp leading edge (NACA 0009-03) and another having a sharp leading edge with the location of maximum thickness moved to its mid chord (NACA 0009-05). The Langtry-Menter 4-equation Transition SST model was employed to solve the flow field. In this numerical study, a 2D method of simulating the behavior of such flows over a symmetric NACA 0009 airfoil was demonstrated at low ( 2 x 10^4 ≤ Re ≤ 5 x 10^4) Reynolds numbers and compared against experimental data. This gives rise to flow phenomena that deviate significantly from those at higher Reynolds numbers. A consequence of shorter chord length wings, lower flight speeds, and lower density atmospheres is that such flows experience a dominance of viscous forces over inertial forces, producing lower chord-based Reynolds numbers. The rise of microelectronics has paved the way for the development of small-scale unmanned aerial vehicles (UAVs) that can be employed for a number of military and scientific applications.
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