The determination of fluid viscosities from measured falling-needle velocities depends upon accurate prediction of the drag forces acting on a thin cylinder translating axisymmetrically and axially down a tube. Without a complete hydrodynamic theory of the device, the manufacturer’s calibrations must rely on certain empirical estimates to take account of the shape and finite length of the needle. Here, the advantages of slender-body theory are exploited to calculate drag coefficients in the presence of the tube wall, for shapes varying from spheroidal toward cylindrical. Our results suggest an alternative means of calibration.
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Davis et al. (2001) studied this question.