Consider an airfoil (a wing) in an airflow. When angle of attack increases, at some point the flow start to separate from trailing edge. By increasing the angle of attack more, this separation area
Effect of Gurney flap on flow separation and aerodynamic
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Boundary Layer Separation and Pressure Drag
aerodynamics - Why does lift decrease and drag increase when
Why does center pressure of an aerofoil locate at 30% to 40% of
Aerodynamic Lift, Drag and Moment Coefficients
Effect of Gurney flap on flow separation and aerodynamic
Pressure coefficient distribution for the baseline airfoil
Wind-tunnel tests of synthetic jet control effects on airfoil flow
Digital mapping of surface turbulence status and aerodynamic stall