A Wind Tunnel Investigation of the Effect of an External, Vertical Electric Field on the Shape of Electrically Uncharged Rain Drops

R. Rasmussen National Center for Atmospheric Research , Boulder, CO 80302

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C. Walcek National Center for Atmospheric Research , Boulder, CO 80302

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H.R. Pruppacher Department of Atmospheric Sciences, University of California, Los Angeles, CA 90024

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S.K. Mitra Department of Atmospheric Sciences, University of California, Los Angeles, CA 90024

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J. Lew Department of Atmospheric Sciences, University of California, Los Angeles, CA 90024

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V. Levizzani Department of Atmospheric Sciences, University of California, Los Angeles, CA 90024

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P.K. Wang Department of Meteorology, university of Wisconsin, Madison, WI 53076
Department of Meteorology, university of Wisconsin, Madison, WI 53076

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U. Barth Meteorologisches Institut, Johannes Gutenberg-Universität, Mainz, F.R.G.

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Abstract

Results are presented of a recent wind tunnel experiment in which electrically unchanged water drops of 1000–3000 μm equivalent radius were freely suspended in the vertical air stream of the UCLA Cloud Tunnel. During their suspension, the drops were exposed to external, vertical electric fields of 0–90 volts cm-1. The change in the drop shape with drop size and with electric field strength was noted and is discussed in the light of theoretical work cited in literature which does not take into account the feedback effects between the electric forces of an external electric field and the hydrodynamic forms due to the flow past the drop. In contrast, the present wind tunnel study, documented by photographs from a 16 mm motion picture film, recorded the shape of the water drop in response to both hydrodynamic as well as electric forces.

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

*Present affiliation: Meteorologisches Institut, Johannes Gutenberg-Universität, Mainz, F.R.G.

**State University of New York, Purchase, N.Y.

Abstract

Results are presented of a recent wind tunnel experiment in which electrically unchanged water drops of 1000–3000 μm equivalent radius were freely suspended in the vertical air stream of the UCLA Cloud Tunnel. During their suspension, the drops were exposed to external, vertical electric fields of 0–90 volts cm-1. The change in the drop shape with drop size and with electric field strength was noted and is discussed in the light of theoretical work cited in literature which does not take into account the feedback effects between the electric forces of an external electric field and the hydrodynamic forms due to the flow past the drop. In contrast, the present wind tunnel study, documented by photographs from a 16 mm motion picture film, recorded the shape of the water drop in response to both hydrodynamic as well as electric forces.

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

*Present affiliation: Meteorologisches Institut, Johannes Gutenberg-Universität, Mainz, F.R.G.

**State University of New York, Purchase, N.Y.

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