Question

6 Flies Like a Brick! A brick-shaped object that is 10cm in transverse height and 50 cm in streamwise length flies through a flow of air. The flow separates at the back edge, so the entire back side is the wake. The pressure in the wake is measured at 0.9 atm. Assume stagnation exists across entire front face. Assume unit width Determine the pressure drag and the shear drag. What would the drag coefficient be? 7 Please Explain Explain in a sentence or two or three the following statements: (a) The difference between shear drag and pressure drag. (b) For a given shape, Co increases with CL (c) Lift requires an asymmetric shape. (d) Shear causes pressure drag, but pressure drag does not depend on the value of viscosity.

Answer 1

A brick shaped object A= 10m, transverse hiight ht L. 5com to Length en flow rate or the How separate the back edge The pressure in the ware merred at 0.9 atm and free stream velocity lomst - air density pa= 1.2 kg/m3 2 500m - air velocity v= 20mis valmis caring force Pia Jetta L F P, A, -PA, Pi = 1 atm ;=0.9atm [ 1 atma 101.3 kpa ] A1 = 1041 = loom? A = 10 x 10-4m? F = (1-0,4) (101.3'x103) 10 x1074 150 = 10.13 Nl We know for 12 pa v² x E G- Drag Coefficient 10.13 = x (1.2)x (le yio-4) (102) 6 10.13 = (0.6)(10-1) CD = 10.13 = 168.83 0.6 22 69 = 162.83 u Reynolds no Rizz port Re=pul for air != 1.81x10-5 Pa - Re = 1,2x10x 0.5 1.8/ X/0-5 Re = 3.31x105 <5x105 Hence flow is laminar

for laminar flow cq - 1.328 (to 1,522 = 00023 shear Drag force Fs - 1 G Pasva (fe 1,328 0.1023 / 3.3/X/05 Shear Area As = 2x50x1 = 100 cm² (both sidel Ess} X 0.0023 * 112 x 1CD X/0-4X102 = 0.00 138N