  The number of studies related to unmanned air vehicles (UAV), micro air
vehicles (MAV), wind turbines, birds and insects which operate at low Reynolds
(Re) numbers have rapidly increased, recently. In this thesis, unsteady
aerodynamics of low Reynolds number flows (Re=25000, 50000 and 75000) on
NACA4412 airfoil shaped wing which is mainly used in wind turbines and micro
air vehicles and operates at low Reynolds numbers and has aspect ratio of 1
(AR=1) was investigated by means of numerous experimental analyses at various
angles of attack changing from 0{\deg} to 45{\deg}. Due to the obtained force
measurement results, maximum lift coefficients and stall angles were determined
as 1.19, 1.21, 1.24 and 39{\deg}, 38{\deg}, 37{\deg} for Re=25000, 50000 and
75000, respectively. Flow visualization with smoke-wire and oil, velocity
distribution experiments were conducted at different planes (z/s= +0.4, +0.2,
+0.1, 0, -0.1, -0.2) on the wing. Furthermore, the effects of tip vortices on
the wing were determined. The tip vortices were observed at the tip of the wing
at low angles of attack and developed through the wake region moved on the wing
horizontally with increasing angle of attack and effect of these vortices on
the wing increased. It was seen that the tip vortices caused to pressure
differences in the wake region and moved to the spanwise direction and this
situation led to decrease separation bubble, which is occurred at low Re
numbers, and increase stall angle. Additionally, flow condition became steadier
due to the tip vortices.
