 Ch 9. External Flow Multimedia Engineering Fluids Drag Lift BoundaryLayer
 Chapter 1. Basics 2. Fluid Statics 3. Kinematics 4. Laws (Integral) 5. Laws (Diff.) 6. Modeling/Similitude 7. Inviscid 8. Viscous 9. External Flow 10. Open-Channel Appendix Basic Math Units Basic Equations Water/Air Tables Sections Search eBooks Dynamics Statics Mechanics Fluids Thermodynamics Math Author(s): Chean Chin Ngo Kurt Gramoll ©Kurt Gramoll FLUID MECHANICS - CASE STUDY SOLUTION Drag Force Exerted on an 18-Wheeler without Air Deflector Drag Force Exerted on an 18-Wheeler with Air Deflector The drag force is given by      D = CD ρAV2/2 where the density of air (ρ) is 0.00238 slugs/ft3 from the tables in the Appendix. It is assumed that the average speed of the 18-wheeler is 65 mph, and its frontal area is 100 ft2. The drag exerted on the 18-wheeler without the air deflector is calculated to be      D = (0.95)(0.00238)(100)(65*5,280/3,600)2/2          = 1,027 lbf The drag exerted on the 18-wheeler with the air deflector is calculated to be      D = (0.75)(0.00238)(100)(65*5,280/3,600)2/2          = 811 lbf By installing the air deflector, there is a 21% reduction in drag. Hence, the company will save money on fuel consumption cost.

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