Impact Of Chemical Pollution On Cavitation Performance Of Hydraulic Machinery In Large Reservoirs

Waterpower source is an important part of the avilible energy in China. With a large number of giant hydropower stations planning to launch in southwest and many large-scale pumping stations also having been built in the South-to-North Water Transfer Project, security and stability of large-scale hydraulic machinery have become particularly important. In addition, good cavitation performance of hydraulic machinery is one of the key factors of keeing the operation of the whole hyeraulic units safe and reliable.In China, construction of hydropower projects is in full swing. At the same time, a problem is coming out which cannot be ignored, That is, many rivers and lakes where hydropower project locted are facing a severe situation of water pollution. The major pollutants are total phosphorus, total nitrogen and heavy metal complex. Prior design, testing and simulation of hydraulic machine are on the basis for most of the references that water is clean. When the working water suffers chemical pollution referring to changes in the nature, there is a problem should be attracted attention. That is, whether the cavitation performance of hydraulic machinery is affected and what the impact it is. This article focused on the cavitation pressure characteristics of polluted water and the impact of chemical pollution on cavitation performance of hyedraulic machinery. Take the reservoirs which suffering TP pollution on the Wujiang River Basin as an example. The study results successfully applied to numerical simulation of cavitation flow, and better results were achived.In order to understand the situation of total phosphorus pollution in Wujiang River Basin, field sampling of water and sediment were collected within cascade hydropower stations, contamination of total phosphorus in the watershed and tributaries were investigated. The results showed that total phosphorus pollution was serious in Wujiang River watershed and water quality worse than Grade V class. In addition, there was a high content of heavy metals in sediment.In order to study the impacet of chemical pollution on hydraulic mechanical properties, cavitation statements both in conditions of clean water and were compared in the jet test apparatus. High-speed photography observed that phosphogypsum suspension was more prone to cavitation, and in the same condition, bubble cloud volume was significantly larger than in clean water. Meanwhile, cavitation pressure characteristics of polluting water showed that the incipient cavitation pressure and the critical cavitation pressure were significantly increased, and in the saturation concentration, cavitation pressure became larger with total phosphorus concentration increasing.Over the years, many books about cavitation and cavitation erosion of hydraulic machinery confused cavitation and vaporization of water. When cavitation occurred, the vapor pressure or the saturated vapor pressure was identified as the cavitation pressure the water, and the mistaken pressure was applied to the calculation of cavitation in hydraulic machinery. Based on the above test results, main factors affecting cavitation of hydraulic mechanical were corrected, such as the cavitation number, turbine cavitation coefficient, and turbine sunction head. The corrected values were applied to evaluate the cavitation performance of the Goupitan and Three Gorges power station which suffering total phosphorus pollution.An object such as a turbine blade or vane pump runner, when attack angle of flow is small, hydrofoil cavitation may occur on the suction side of the airfoil. In this article, cavitation process was observed and the relationship between the cavitation pressure and the number and size of the bubbles in the unit volume. Experiments confirmed that the internal cavity is a mixed body of water containing many bubbles, rather than gas; the shape and siz of cavity are directly related to the size and number of bubbles. The size and number of bubbles depend on the cavitation pressure characteristics of water and the pressure distribution on suction surface. Therefore, in the paper the cavitation pressure characteristics of water and 3D numerical simulation were combined to simulate the internal cavitating flow, which more consistent with the actual situation.