PARTICLE MOTION AND FLUCTUATING FORCES APPLIED ON A SPHERICAL PARTICLE IN TURBULENT SHEAR FLOWS WITH LINEAR VELOCITY GRADIENT

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(1) The time-mean pressure distributions on the surfaces of test spheres fixed in the two-dimensional vertical duct whose flows were turbulent linear shear flows were measured, and time-mean lift and drag were computed by surface integration of the pressure distributions. The results are summarized as;(a) The lift is applied on a sphere in the direction from the higher velocity side to the lower velocity side of the duct flow. (b) The lift increased nearly proportionally with increasing the velocity gradient of the shear flow. (c) The value of drag is scarcely dependent on the velocity gradient. Whereas the test range of non-dimensional velocity gradient was 0 to 0.6, and the test range of sphere Reynolds number was 16900 to 35000.(2) The drop tests of a sphere with the diameter 5 or 10mm were carried out in the vertical duct. The photographs of the trajectories of a dropping sphere were taken. The good agreements were found between the trajectories by experiments and those by numerical simulations. It was reconfirmed that the lift application agrees well with the results as described above. Whereas the test range of sphere Reynolds number was 4000 to 7000.(3) The fluctuating pressure distributions on sphere surfaces was measured with a high sensitive pressure transducer. A new phase averaging method was applied to the measurement of the fluctuating lift and drag. It was found that the values of the fluctuating parts of lift and drag were negligibly small in comparison with their steady parts. It may be said that the reason is because the turbulence intensity of the main duct flows was not so great and the shedding eddy induced fluctuating forces applied on a sphere were small.