Measurement of fluid force on a bluff body in a quasi-steady free surface flow

Experiments have been carried out to study the dynamic response of a bluff body in a quasi-steady free surface flow in a horizontal short flume. Flow features were obtained by using of several flowmeter equipments, current meter and acoustic doppler velocimeter, in order to select different measurement control volumes and, thus, different velocity scale. The obstacle was a sphere placed in the middle cross section of the flume. Measurements were performed in the flume at Reynolds number from 10, 000 up to 60,000, based on the sphere diameter. The drag and lift forces were measured directly at the fixed end of the pivot supporting the sphere by the use of a set of strain gauges. Drag and lift coefficients were derived comparing the steady longitudinal and transverse measured force to the time average velocity data, while the inertial coefficient was proposed versus Strouhal and Reynolds numbers. Finally a comparison between forces and velocity spectrum was performed to ensure possible resonance effect.