Dusuk Reynolds Sayili akislarda kanat uzerinde kararsiz aerodinamigin incelenmesi

TL;DR

This study investigates unsteady aerodynamics of low Reynolds number flows on a NACA4412 wing, analyzing effects of tip vortices, flow visualization, and force measurements to understand stall behavior and flow stability.

Contribution

It provides experimental insights into low Reynolds number aerodynamics, focusing on tip vortex effects and flow stability for wind turbine and MAV wings.

Findings

Maximum lift coefficients around 1.19 to 1.24 at Re=25000 to 75000

Tip vortices increase stall angle and stabilize flow

Flow becomes steadier with vortex development

Abstract

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.