[Aerodynamics] Why does the drag coefficient increase after turbulence

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SUMMARY

The discussion focuses on the behavior of the drag coefficient in relation to turbulence and the Reynolds number, specifically around 5 x 10^5 for a smooth sphere. It is established that the drag coefficient decreases as the airflow remains attached to the sphere's surface, minimizing the wake size. However, as speed increases beyond this transition point, the wake enlarges, leading to an increase in the drag coefficient due to turbulence effects.

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  • Understanding of Reynolds number and its significance in fluid dynamics
  • Knowledge of drag coefficients and their relation to object shapes
  • Familiarity with the concept of wake formation in aerodynamics
  • Basic principles of turbulence and its effects on airflow
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As you can see, around Reynolds number of 5 105 the transition occurs for a smooth sphere.

However, why is it that after this transition that the drag coefficient increases at turbulence?
 
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A lot of the drag for a sphere is related to the size of the wake induced behind the sphere. The drop in the curves corresponds to the air tending to stay attached longer to the surface of the sphere, reducing the size of the induced wake, and decreasing coefficient of drag. As the speed continues to increase, the wake starts to increase in size again.
 

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