Author(s): F. Geiger; R. Huber; P. Rutschmann
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Abstract: Over the last years the authors have conducted many experiments to investigate cavitation erosion scale effects on concrete probes. The experiments involved cavitation erosion in the wakes of differently shaped and sized cylindrical and prismatic obstacles which were mounted in differently sized cavitation tunnels at the Technical Universities of Munich and Berlin respectively. All relevant parameters like probe conditions, temperature, gas content and tensile strength of the liquid used were measured and controlled, the latter by the method developed in-house by Keller. These experiments were then compared with large scale pit count tests with metal probes conducted under identical conditions. The comparison showed: · identical positions of material erosion for identical cavitation numbers, · a cavitation number with maximum erosion rate for a given velocity, · and unexpectedly, a material dependency on the velocity scale. For a given cavitation number the pit count method with steel probes showed a dependency of the erosion rates on the sixth power of the velocity. This result coincides with the majority of pit count and mass loss tests, which due to their mechanical engineering background have been normally carried out with metal probes. Contrarily, the mass loss tests with concrete probes revealed a dependency on the ninth power of the velocity. This result implies a material-specific non-linear relationship between the energy absorbed by the cavitation phenomenon and the resulting damage. Therefore experimentally measured cavitation erosion scale effects depend not only on length and velocity scales but also on the measuring method employed. These findings must be accounted for in the development of a general cavitation erosion model.
Year: 2009