# Calculate velocity over the airfoil.

Pressure coefficient at a certain point on an airfoil is -4.2.Calculate velocity at this point assuming the flow over the airfoil to be inviscid and incompressible is (a) 50 ft/s and (b) 200 ft/s.

Asked on 1st January 2019 in

(a) For inviscid and incompressible flow coefficient of pressure is given as ${C_p} = 1 – {\left( {\frac{v}{{{v_\infty }}}} \right)^2}$$v = \sqrt {v_\infty ^2\left( {1 – {C_p}} \right)}$$= \sqrt {{{\left( {50} \right)}^2}\left( {1 – \left( { – 3.84} \right)} \right)}$$= \sqrt {2500\left( {1 + 3.84} \right)}$$= 110\,{\rm{ft/sec}}$also (b) for $${{v_\infty }}$$ = 200 ft/sec ${C_p} = 1 – {\left( {\frac{v}{{{v_\infty }}}} \right)^2}$$v = \sqrt {v_\infty ^2\left( {1 – {C_p}} \right)}$$= \sqrt {{{\left( {200} \right)}^2}\left( {1 – \left( { – 3.84} \right)} \right)}$$= \sqrt {40000\left( {1 + 3.84} \right)}$$= 440\,{\rm{ft/sec}}$