Drag crisis

In fluid dynamics, drag crisis (also Eiffel paradox or Lukyanov–Eiffel paradox) is a phenomenon in which drag coefficient drops off suddenly as Reynolds number increases. This has been well studied for round bodies like spheres and cylinders. The drag coefficient of a sphere will change rapidly from about 0.5 to 0.2 at a Reynolds number in the range of 300000. This corresponds to the point where the flow pattern changes, leaving a narrower turbulent wake. The behavior is highly dependent on small differences in the condition of the surface of the sphere. In fluid dynamics, drag crisis (also Eiffel paradox or Lukyanov–Eiffel paradox) is a phenomenon in which drag coefficient drops off suddenly as Reynolds number increases. This has been well studied for round bodies like spheres and cylinders. The drag coefficient of a sphere will change rapidly from about 0.5 to 0.2 at a Reynolds number in the range of 300000. This corresponds to the point where the flow pattern changes, leaving a narrower turbulent wake. The behavior is highly dependent on small differences in the condition of the surface of the sphere. The drag crisis was first identified in 1905 by a Russian student G.I.Lukyanov in experiments on wind tunnel of Moscow University. The supervisor of the experiments, Zhukovsky correctly guessed that this paradox can be explained by ``detachment of streamlines at different points of the sphere at different velocities``. Later the paradox was independently discovered in experiments by G.Eiffel and Maurain.Gustave Eiffel is known as a man who designed and built the Eiffel Tower, and the Statue of Liberty. Upon his retirement, he built the first wind tunnel in a lab located at the basis of the Eiffel Tower, to investigate wind loads on structures and early aircraft. In a series of test he found that the force loading experienced an abrupt decline at a critical Reynolds number. A clear explanation of the paradox from the point of view of boundary-layer theory is due to German fluid dynamicist L.Prandtl.