Question

1. Measuring Drag on a Cylinder Pre-Lab Analysis: You will test two free-stream velocities of 10 and 20 m/s and two cylinder diameters of 19 mm and 38 mm, depending on which wind tunnel you use. In preparation for the lab calculate the following: a. The expected dynamic pressure values in units of inH20 that you would expect to measure for air moving at 10 m/s and 20 m/s, respectively. Write the calculated values into the "Predicted Pdyn (inH20) from pre-lab" fields on the first page of your data collection sheet- you will use these values during lab. Assume an air density of 1.17 kg/m3. (1inH20 249 Pa) b. The maximum and minimum gauge pressures (i.e, relative to atmospheric) in inches of H20 which you expect to see for flow around each cylinder at 20 m/s. For this problem, you can assume that the stagnation pressure in the test section of the wind tunnel is approximately atmospheric pressure. When consulting the Cp distribution in the lab handout, assume a laminar boundary layer for these predictions. References: [1] Munson, Young, and Okishi (2006).

Answer 1

2 n s g.ven thad sdagnation Pessure Ptot Patm Pa 2Pv Patm Also P Pao Cp 2 Gage pressore P Patm Peo tp(Paot fv) P-Patm Cp-1) 2. Ne Can see tha this ewpression is Inde pen dent aff the Size o the cynder we Can read Also fom the chart tor larna boundary laye, that minimum p 3 and maximum Cp- t-1.202 Hence minimum gage presure C-1-3-1) 2 2.16 tn H20 -538.22y9 tn H2o -S 38.2Pa 202 Mavimum qage Pressure 2 oinH20

Theoretical and Acal Soface Pressore distribulion for flow Past a cytinde is shoon tn the plot below: o.0 Turbulent laminar O -2.0- -3.0 180 135