Abstract
The instantaneous fluid forces on a circular cylinder oscillating sinusoidally in viscous liquid were measured. Data were reduced by the method of Fourier analysis to obtain the average values of the added mass and drag coefficients over a cycle of oscillation and their relations to ocsillatory conditions were studied experimentally.
1) The drag coefficient was correlated with the Reynolds number of oscillation, aωd/ν, and the amplitude ratio, a/d, where a is amplitude, ω is angular frequency, d is diameter of cylinder and ν is kinematic viscosity. An empirical equation for the drag coefficient was deduced in a range of Reynolds number of oscillation from 1 to 20.
2) The added mass coefficient was correlated with the modified Reynolds number dd2ω/ν and a/d. when modified Reynolds number dd2ω/ν was comparatively small, experimental values for the added mass coefficient agreed well with the theory given by Stokes. The value of modified Reynolds number, where added mass coefficient began to deviate from theory, varied with a/d and had a minimum value around a/d=2.
3) When aωd/ν was large enough, the added mass and drag coefficients had a minimum and maximum, respectively, around a/d=2. For smaller a/d, the added mass coefficient had values of about unity as predicted by potential flow theory. At a larger value of aωd/ν and a smaller a/d, quasi-steady state theory was applicable to the estimation of fluid force at each phase of oscillation, because inertial force due to added mass becomes larger than the drag force.
