【正文】 中文 4400 字 外文翻譯 學(xué)生姓名 學(xué)院名稱 機(jī)電工程學(xué)院 專業(yè)名稱 指導(dǎo)教師 2020 年 05 月 27 日 Research on low cavitation in water hydraulic twostage throttle poppet valve Abstract: Cavitation has important effects on the performances and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Twostage throttle valve is a practicable configuration to mitigate cavitation, which is extensively used in water hydraulic pressure relief valves and throttle valves. The pressure distribution inside a medium chamber located between two throttles of a twostage throttle valve is investigated through numerical simulations. The effects of the passage area ratio of the two throttles and the inlet and outlet pressures on the pressure inside the medium chamber are examined. The simulation results indicate that (a) the pressure inside the medium chamber is not constant, (b) the locations of maximum and minimum pressures inside the medium chamber are both fixed, which will not vary with the passage area ratio or the inlet and outlet pressures, and (c) the ratio of the pressure drop across the front throttle to the total pressure drop across the twostage throttle valve is nearly constant. The critical cavitation index of the twostage throttle valve is then established. A semiempirical design criterion is obtained for the water hydraulic twostage throttle valve. The correlation between the critical cavitation index and the passage area ratio of the two throttles is investigated. Relevant validation experiments are conducted at a custommanufactured testing apparatus. The experimental results are consistent with the simulated ones. Further analyses indicate that (a) the large backpressure can improve not only the anticavitation capability but also the total load rigidity of the water hydraulic twostage throttle valve, (b) an appropriate passage area ratio will be beneficial for improving the anticavitation capability of the water hydraulic twostage throttle valve, and (c) the water hydraulic twostage throttle valve with a passage area ratio of would have the best anticavitation performance with the lowest risk of cavitation. Keywords: putational fluid dynamics simulation cavitation load rigidity passage area ratio twostage throttle valve water hydraulics 1 INTRODUCTION Water hydraulic systems are operated with raw water (pure tap water) substituting for mineral oil. They have advantages in terms of durability, reliability, safety, and cleanness. Such sys tems are being more and more popular, especially in fields of steel and glass production, coal and gold mining, food and medicine processing, nuclear power generation, ocean exploration, and underwater robotics [1–5]. Because the opening of a water hydraulic control valve is very small pared with that of oil valve, the water flow velocity through the water hydraulic control valve is larger under the same pressure condition。 thus cavitation erosion may occur due to the high vapour pressure of water. Cavitation has an important effect on the performance and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Previously, a number of studies on the relationships between cavitation and discharge coefficient, thrust force and pressure distributions in the valves, and mitigation of cavitation damage were carried out through increasing outlet pressure of valves, modifying shapes of throttles, adding stages of valves, selecting anticorrosion materials for parts, and controlling maximum fluid temperature and flow velocity. Tsukiji et al. [6] investigated cavitation by flow visualization in hydraulic poppettype holding valves to reduce cavitation. Some measures were employed to diminish noise and cavitation through controlling flowrate, upstream pressure, downstream pressure, and valve lift in case of converging flow. Aoyama et al. [7] studied experimentally the unsteady cavitation performance in an oil hydraulic poppet valve. It was found that, as absolute values of the variation rates of inlet and outlet pressure increased, the incipient cavitation index exhibited a tendency to decrease, whereas the final cavitation index a tendency to increase under all geometrical parameters. As the absolute values of the variation rates of inlet and outlet pressure further increased, the hysteresis between the incipient and final cavitation indices would bee larger than ever for each bination of the valve and valve seat. Ishihara et al. [8] studied oil flow unsteadiness effect on cavitation phenomena at sharpedged orifices. The rate of pressure drop across the orifice was kept constant, and cavitation incipience and finale were recorded by using scattered laser beams showing that (a) there existed two types of cavitation, namely, gaseous cavitation and vapourous