Excitation of Plates and Hydrofoils by Trailing Edge Flows

The flow-induced vibration of lifting surfaces is discussed from the perspective of the properties of the various flow regimes that exist on the surfaces. Depending on the Reynolds number and the geometry of the foil, the flow excitation may be tonal (generated by periodic vortex shedding) or random (generated by turbulent flow on the surface). Conditions will be cited for the existence of vortex shedding excitation, and relationships will be given for estimating the levels of flow-induced vibration to be expected from each flow source. The governing parameters for feedback between vibration and vortex shedding, which are necessary to produce singing, are quantified through measurements of surface pressures generated by wakes which are forced with oscillating trailing edges. Criteria will be given for estimating the upper bound of singing vibration amplitudes of hydrofoils and merchant marine propellers as a function of structural parameters.