The Cavermod device: Force measurements

The Cavermod device, as described in the companion paper (Filali et al., 19 99), allows us to produce the axial collapse of a cavitating vortex at high velocities. From a global point of view we can consider that it produces a high momentum in the axial direction. Large forces, concentrated on a smal l area and able to produce erosion pits on hard materials, result from the sudden momentum stopping against a solid wall. In this paper the results of the forces measurements are given. Four different measurements devices are used to analyze the Cavermod performance in both cases of long and short v ortex: dislocations in MgO (Magnesium Oxide) single crystal, Two special pi ezoelectric ceramic transducers and a PVDF film transducer. Special attenti on is given to the PVDF film response which is found twice the response of other devices. In addition, an attempt is made to interpret the temporal fo rce signal given by a ceramic transducer in terms of local erosive pressure .