Experimental investigation on cavitation bubble precipitation characteristics in sand-laden water

Abstract

The cavitation bubble precipitation refers to the formation process of the spherical cavities, known as cavitation bubbles, as the ambient pressure of water decreases. In the fields of hydraulic machinery, the saturated vapor pressure of clean water is often used as the pressure threshold for cavitation occurrence. However, the engineering practice has demonstrated that, the incipient cavitation pressure may be significantly higher than the saturated vapor pressure, especially in sand-laden water conditions. Therefore, to determine a reasonable cavitation pressure threshold and ensure the accurate cavitation flow simulations and effective assessment of cavitation risks for hydraulic machinery operating in sand-laden water conditions, an experimental investigation is conducted. First, a high-precision experimental setup based on the vacuum pump, high-frequency pressure sensor and high-speed camera is constructed. This setup allows for the continuous pressure reduction in water, acquisition of high-precision pressure data and tracking of the entire cavitation bubble precipitation process. Second, based on the experiments in clean water conditions, the relationship between the cavitation bubble precipitation degree and pressure is established, and two key states of incipient cavitation and boiling cavitation are defined. Third, based on the experiments in sand-laden water conditions, it is observed that the numerous cavitation nuclei on sand surfaces make both the incipient and boiling cavitation pressure in sand-laden water higher than those in clean water. The quantitative relationship between the sand concentration and diameter, and the cavitation pressure is established, providing a more reasonable cavitation pressure threshold. This investigation enhances the understanding of cavitation bubble precipitation in sand-laden water and supports the development of more accurate cavitation models for hydraulic machinery operating in sand-laden water conditions.