EXPERIMENTAL INVESTIGATIONS CONCERNING THE INFLUENCE OF LIQUID PROPERTY AND SPEED OF ROTATION ON THE INCEPTION OF BLADE CAVITATION IN PUMPS WITH DIFFERENT SPECIFIC SPEEDS

摘要

The presented experimental results obtained on pumps with different specific speeds n{sub}s installed in various test facilities demonstrate the significant influence of liquid property (tensile strength and local gas content) as well as speed of rotation on the inception of impeller blade cavitation. According to the approaches of A. Keller, both influences can be taken into account and qualified by using modified, respectively-extended, computation formulas for the cavitation number σ{sub}u. By the aid of systematically performed cavitation tests, 1. Awad et. al. verified the described method for a small standard centrifugal pump with n{sub}s = 24min{sup}(-1) (1290 rpm in US-units). In order to verify the measured results and the applicability of the approach to other configurations, additional tests were carried out on rotodynamic pumps with a n{sub}s of 44 min{sup}(-1) (2270 rpm in US-units) and 180 min{sup}(-1) (9300 rpm in US-units). The application of the described method is based on the capability to measure the actual tensile strength of the test fluid within the test section. This was realized with a special device called "Vortex Venturi" located in the suction pipe directly upstream of the impeller blading. The comparison of the measured data obtained at the investigated pumps and test installations leads to the conclusion, that the method described by A. Keller enables the transformation of cavitation numbers measured at different speeds of rotation as well as test installations, which finally corresponds to the various conditions of liquid property by using a simple formula.