الفهرس 
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Abstract
In this work the effect of pressure gradient on the lateral wake shape and drag coefficient behind an isolated airfoil is investigated.
A wind tunnel was designed and constructed to achieve a two dimensional flow with zero, positive and negative pressure gradients at different undisturbed velocities.
The resulted velocity distribution shows that at the positive pressure gradients, the distributions are flatter with respect to zero pressure gradient, while for negative pressure gradient, the distribution are sharper. Also as the undisturbed velocity increases, the wake decay increases.
The parameters which affect on the wake shape were studied. These parameters are :-
1-The wake width.
2-The wake depth.
3-The momentum thikness.4-The displacement thickness.
5-The shape factor ( displacement thickness / momentum thickness) .
The wake width and wake depth increase as the positive pressure gradient increases and vice versa.
The wake depth increases tell the angle of diffuser equals 12 to 14 ,and then it slightly decreases with further increasing of the positive pressure gradient. For all pressure gradients, the wake width increases and the wake depth decreases as the distance downstream of the trailing edge increases. The momentum thickness and the displacement thickness increase as the positive pressure gradient increases. The shape factor decreases with the increasing of the distance downstream of the trailing edge, and approaches to the value one after a long distance from the trailing edge. The shape factor slightly increases ( or decreases ) as the positive ( or the negative ) pressure gradient increases.
The experimental results show that, as the positive pressure gradient increases, the drag coefficient slightly decreases, but as the negative pressure increases, the drag coefficient increases sharply with respect to zero pressure gradient.