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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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