球群の低レイノルズ数での運動 : 第2報,中心線に沿って運動する等しい2球

The velocities and drag forces experienced by two equal-sized spheres freely-falling along their line of centers are measured using the 'falling-sphere' technique at low Reynolds numbers. The width of the test tank with square cross-section used was 100 times as large as the diameter of the used sphere. The measurements, with an estimated uncertainty of ±1.2%, show that the lower sphere experiences the Oseen drag and that the upper sphere experiences the Stokes drag, which is predicted by Stimson & Jeffery. The flow visualization using a naturally occurring phenomenon in glycerol illustrates the difference of the hydrodynamic drag force between the lower sphere and the upper sphere. The numerical calculations of Stimson-Jeffery's solution reveal in detail the occurrence of vortex flows within a closed separating region between the two spheres.