2.18. Velocity profiles are measured at the upstream end (surface 1) and at the downstream end (surface 2) of a rectangular control volume, as shown in Fig. P2.18. If the flow is incompress- ible, two dimensional, and steady, what is the drag coefficient for the airfoil? The verticle di- mension H is 0.025c and d Cd pooUc The pressure is poo (a constant) over the entire surface of the control volume. (This problem is an extension of Problem 2.7.) u =UⓇ (Answer: Ca=1/60=0.0167) x 3 H =0.025c u = U₁(y/H) 上 4 Figure P2.18 u = U₂(-y/H)