The evaluation of the force acting on bluff body in unsteady flow

The in-line and transverse forces acting on a sphere immersed in a unsteady free surface flow in a horizontal short flume have been measured through a set of strain gauges. The flow field around the obstacle has been obtained using different flowmeter, current meter and laser doppler anemometer, in order to select different measurement control volumes and, thus, different velocity scale. Measurements have been performed in the range of sphere Reynolds numbers Re =DUm/v lying between 10^4 and 6x10^4 ( D sphere radius, Um mean velocity of flow,  fluid kinematic viscosity), and for Froude numbers Fr= Um/(ghm^)0.5 (g acceleration of gravity) ranging from 0.5 to 3.0. Drag and lift coefficients have been derived through the steady longitudinal and transverse measured force while the inertial coefficient have determined through the use of Fourier analysis.