On the Acceleration of Large Water Drops to Terminal Velocity

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  • 1 Laboratory for Atmospheric Research, University of Illinois at Urbana-Champaign, and Illinois Slate Water Survey, Urbana 61801
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Abstract

A theory based on the distortion of large water drops is used to calculate the drag and acceleration ofdrops in the laboratory from rest to terminal velocity. The results show that the drag coefficient curve foreach drop size lies between the curves for a sphere and for water drops at terminal velocity. A comparisonwith experimental acceleration data at sea level shows an improvement over the more approximate theoryof Wang and Pruppacher. The calculations of drops accelerating at reduced air density provide a very goodfit to the data of Davies at the reported fall distance of 11m. This new interpretation of Davies' experimentis consistent with the formula of Beard for the terminal velocity of large drops aloft.

Abstract

A theory based on the distortion of large water drops is used to calculate the drag and acceleration ofdrops in the laboratory from rest to terminal velocity. The results show that the drag coefficient curve foreach drop size lies between the curves for a sphere and for water drops at terminal velocity. A comparisonwith experimental acceleration data at sea level shows an improvement over the more approximate theoryof Wang and Pruppacher. The calculations of drops accelerating at reduced air density provide a very goodfit to the data of Davies at the reported fall distance of 11m. This new interpretation of Davies' experimentis consistent with the formula of Beard for the terminal velocity of large drops aloft.

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