Wind-tunnel studies of the shape of charged and uncharged water drops in the absence or presence of an electric field

Experimental results on the shape of charged and uncharged water drops suspended above the test section of a vertical wind tunnel and subjected to a vertical or horizontal electric field, are reported. The equivalent spherical radii, a0, of uncharged water drops ranged from 1.75 to 3.30 mm, and that of the charged water drops from 1.50 to 3.20 mm. Our results show that the external vertical or horizontal electric fields up to 5 kV cm-1 and 3.5 kV cm-1, respectively, do not significantly affect the shape of uncharged drops. Also the shape of charged drops carrying charges of up to half of Rayleigh's limit and falling in the absence of an electric field, does not show any significant changes. However, when charged drops of a0 = 2.0 and 2.5 mm carrying electric charges of 2.5·10-10 C and 5.0·10-10 C, respectively (about one fifth and one seventh of Rayleigh's limit for the respective sizes), fall in the presence of a vertical electric field, a significant increase in distortion ratio is observed as the electric field is increased from zero to 4 kV cm-1. The significance of the results in the evolution of precipitation in electrical environments of thunderstorms is discussed