D p = ∮ p n ⋅ i d S , Y = ∮ p n ⋅ j d S . displaystyle start off aligned D_ p &=oint pmathbf n cdot mathbf i ;mathrm d S,Y&=oint pmathbf n cdot mathbf j ;mathrm d S.finish aligned By using the streamwise vector i parallel into the freestream rather than k while in the integral, we attain an expression for your force drag Dp (which inclu