Lift and Drag

MECH 3720L – Fluid Dynamics Laboratory Pressure Distribution Lift and Drag Measurements on a Circular Cylinder in Cross Flow Object:

To measure pressures around the circumference of a circular cylinder submerged in a fluid flow. The pressure distribution around the 2-dimensional cylinder will be used to evaluate the lift and drag forces exerted on the cylinder by the fluid flow.

Procedure:

For a specific air-speed (control position #2) in the wind tunnel, read the height, hi , of the liquid column in the manometer for the surface pressure port angles of  i  0  , 10  ,  , 350 .

 pi  p   gh where  pi  p   is the pressure difference between surface pressure, pi , and freestream pressure, p , at  i and  is the density of manometer fluid. Enter the data in a table. The drag force, D , per unit length of the cylinder is calculated from: D

2

 ( p  p ) cos( )r d  0

2r n  ( pi  p ) cos i n i 1

The lift force, L , per unit length of the cylinder is: L

2

 ( p  p ) sin( )r d  0

2r n  ( pi  p ) sin  i n i 1

The drag and lift coefficients, C D and C L , are to be determined using: CD 

CL 

1 2r

2

1 2r

2

 C p cos( )r d  0

 C p sin( )r d  0

 n  C p cos i n i 1 i

 n  C p sin  i n i 1 i

where C pi is the coefficient of pressure at  i . C pi is calculated as follows: p  p  pi  p  hi Cp  i   1 p1  p  h1 2 V  2 i

where p1  p  is the difference in pressure at  i  0  . Repeat the experiment for the rough cylinder. Results:

Plot C p verses  i for the two cylinders on the same graph. Compare the pressure distribution with published results. Calculate the Reynolds number, Re D , for the flow around the cylinder and compare the calculated Re D and the drag coefficients, C D , with the published data (refer to handouts). Discuss briefly why there is a difference in pressure distribution between that obtained by inviscid theory and that obtained experimentally. If your results deviate from the published data explain why. Discuss any other pertinent observation.

Report:

Turn in the report following the instructions outlined in “Laboratory Report Writing”.

References:

White, F.M., Fluid Mechanics; McGraw-Hill, 1979.

i

Fox, R.W., and McDonald, H.T.; Introduction to Fluid Mechanics; John Wiley & Sons, 1985.