We meassure lift and drag for 2D and 3D wing case,we use same airfoil at same AoA and same airflow speed for both case. Wind tunnel can change test section walls width.
2D wing test:
So first we put airfoil in wind tunnel so walls touch arifoil tips(2D wing),at AoA=15degrees and airflow speed=20m/s and meassure lift and drag..
3D wing test:
Now we increase walls width so airflow "act" like 3D wing in test section.We use same AoA=15 and same airflow speed (20m/s) over airfoil like in 2D wing- test. note: AoA=15 is angle between chord line and freestream airflow not angle between chord line and effective airflow at 3D wing
Question is,what will be drag of 3D wing-test compare to 2D wing-test,smaller ,equal or larger?
My logic is that 3D airflow leakage on tips will decrease overall pressure difference at wing ,so lift will be smaller than in 2D wing-test but drag will be also smaller than in 2D-test,because when you integrate smaller pressure difference over airfoil surface you will get smaller drag as well.
(BUT if we must have SAME LIFT IN BOTH TEST,than 3D wing test will have larger drag,because then we must increase AoA at 3D wing to compensate lift reduction caused by airflow leakage,so now when we have increased AoA we also have larger drag..)
3D wing will have less drag,drag decrease when AoA decrease,3D wing "feel" effective AoA,so it fly at smaller "AoA" than 2D wing.
how blue-lift can be larger than red-lift,wing at AoA=10 can not produce larger lift than wing at AoA=20 ??