XX The two vortices tend to drag the surrounding air with them, and this secondary movment induces a small component is called downwash(下洗) X The downwash velocity combines with the freestream velocity to produce a loca/relative wind which is canted downward in the vicinity of each airfoil section of the wing X definition of induced angle of attack
※ The two vortices tend to drag the surrounding air with them, and this secondary movment induces a small component is called downwash(下洗）. ※ The downwash velocity combines with the freestream velocity to produce a local relative wind which is canted downward in the vicinity of each airfoil section of the wing. ※ definition of induced angle of attack
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XX TWo important effects due to the downwash 1 the angle of attack actually seen(or feel) by the local section is the angle between the chord line and the local relative wind. This angle is defined by a a cc =a-al 2 The local lift vector is in the direction perpendicular to the local relative wind. As a subsequence there is a drag created by the presence of downwash
※ Two important effects due to the downwash. 1 the angle of attack actually seen(or feel) by the local section is the angle between the chord line and the local relative wind. This angle is defined by aeff eff = −i 2 The local lift vector is in the direction perpendicular to the local relative wind. As a subsequence, there is a drag created by the presence of downwash
Geometric angle of attack induced angle of attack feff effective angle of attack Chord line Local airfoil section of finite wing rela e Ind