SOURCE SIZE EFFECTS ON CAVITATION DAMAGE M. A. Hosien † and S. M. Selim

Cavitation is important as a consequence of its effects. Uncontrolled cavitation can produce serious erosion to all materials. In the light of the current world wide interest in the problem of cavitation damage prediction and scaling, it was decided to evaluate the effects of source size on the cavitation damage. For this purpose, an experimental study of the effect of source size on the weight loss rate in the steady–state zone of pure aluminum test specimens was conducted using three different shapes of cavitation inducer to represent the types of cavitation normally occur in practice. For each source shape seven sizes from 15 mm to 27 mm were used. The tests were performed in two separate groups, one at constant cavitation number and various flow velocities (24-42.5 m/s) and the other at constant flow velocity and different cavitation numbers (0.017-0.15)for each source size. The results showed that, for all flow conditions and source shapes and sizes, the weight loss rate ( ) increased up to blockage ratio (B) of about 0.5 and then decreased with increasing blockage ratio. Also the results indicated that the weight loss rate was proportional to the source size raised to two characteristic powers: , with positive index ( ) and , with negative index . The values of and were varied quite widely depending on the flow conditions, source shape and size and place of erosion. The magnitudes of and were varied from 1.88 to 5.09 and from -1.92 to -11.3, respectively. In addition, the results illustrated that the size exponent’s e1 and e2 were varied approximately exponentially with both the flow velocity and cavitation number. The values of flow velocity and cavitation number exponents were varied widely between cavitation source shape and place of erosion measurements. The results presented herein have proved that the effect of source size on cavitation damage is extremely complex and no general scaling laws can be established at present. Undoubtedly, further systematic studies should be carried out