Question

(10 marks) An aerofoil is being tested in a wind tunnel using smoke to visualise the flow as shown in the figure below. The aerofoil is very long into the page so that the flow does not vary along the span and no fluctuation is seen over time. i. Is this flow one-, two-, or three-dimensional? ii. Is this flow steady or unsteady? iii. Is this flow uniform or non-uniform? iv. Do the smoke lines mark streamlines? Explain your answer in one sentence. V. Sketch a suitable control volume in your script book that could be used to find the forces exerted on the aerofoil.

Answer 1

i. The flow is two-dimensional, as it is given that variations in the span-wise direction are not present.

ii. The flow is steady, as it is given that fluctuations over time are not present.

iii. The flow is non-uniform, as the velocity, in this case, varies in space.

iv. Actually the smoke lines represent Streaklines, but in case of steady flow, the streaklines and streamlines are the same therefore, here the smokes lines represent streamlines also.

v.
Control volume Fcu Fou = Force on Controle volume by acrofoil.