Experimental investigation on forces due to vortex cavitation collapse for different materials

Tests are conducted in a Vortex Cavitation Generator (VCG) to evaluate the erosion characteristics of different materials under similar conditions. Accelerations due to vortex cavitation collapses are measured and the corresponding forces are inferred for each material by means of transmissibility functions obtained using an instrumented hammer. Pits due to cavitation are determined using a new image processing method from pictures of the sample's surface taken before and after the tests. A short-term (about 2 h) test allows to establish a direct correlation between the impact forces and the pit counting on a reference material (REF), and to estimate a damaging threshold, force value above which the material suffers the first damage. Long-term (60 h) tests permit to investigate the consequences of intense erosion on the hydrodynamic response of the cavitation collapses, and to estimate the aptitude of different materials and coatings to sustain prolonged cavitation erosion. Analysis of the results shows that the maximum amplitude of the accelerations increases with time, and therefore with material removal, and that the value of the cumulated forces correlate linearly with the initial roughness of the tested samples. (C) 1999 Elsevier Science S.A. All rights reserved.