The experimental and numerical study of aerodynamic characteristics over an elliptic airfoil with 16% thickness at low Reynolds numbers is presented. The purpose of research is to study the nonlinearities of the lift curve and the unsteady characteristics of the laminar separation at the range of small angle of attack for low Reynolds numbers. Tests are conducted in a low-turbulence low-speed wind tunnel. The Reynolds number based on the chord of the airfoil is from 140,000 to 300,000. Surface pressure distributions, lift and drag curves over the airfoil are investigated. To explain how the laminar separation affects the aerodynamics over the airfoil, the impact of the boundary layer trip strip is explored and the surface oil-flow measurement is made. In order to depict the unsteady flow performance of trailing-edge LSB at Reynolds number 140,000, numerical simulation used by FLUENT is carried out Results show that (1) the laminar separation bubble (LSB) originally forms at the trailing edge of airfoil and then moves to the leading edge of airfoil with increased angle of attack. (2) The LSB can drive the flow transform from laminar flow to turbulent flow. (3) The existence of LSB leads to the non-linearity of lift curve at low Reynolds numbers. The trailing-edge LSB can offer extra lift. On the contrary, the leading-edge LSB prevents the increase of lift coefficient. (4) The boundary layer trip can postpone the flow separation, eliminate the trailing-edge LSB and influence the size of leading-edge LSB. (5) The numerical simulation results demonstrate that the laminar separation is unsteady and the movement of separation vortex can explain the periodic fluctuation of lift coefficient. The increase and decrease of lift coefficient accompany by the shedding and generation of separation vortex over trailing-edge airfoil surface.
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