1、 中文 4400 字 外文翻译 学生姓名 学院名称 机电工程学院 专业名称 指导教师 2011 年 05 月 27 日 Research on low cavitation in water hydraulic two-stage 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 sev
2、ere vibration. Two-stage 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 two-stage throttle valve is inv
3、estigated 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 loca
4、tions 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 two-stage throttle valve is nearl
5、y constant. The critical cavitation index of the two-stage throttle valve is then established. A semiempirical design criterion is obtained for the water hydraulic two-stage throttle valve. The correlation between the critical cavitation index and the passage area ratio of the two throttles is inves
6、tigated. Relevant validation experiments are conducted at a custom-manufactured testing apparatus. The experimental results are consistent with the simulated ones. Further analyses indicate that (a) the large backpressure can improve not only the anti-cavitation capability but also the total load ri
7、gidity of the water hydraulic two-stage throttle valve, (b) an appropriate passage area ratio will be beneficial for improving the anti-cavitation capability of the water hydraulic two-stage throttle valve, and (c) the water hydraulic two-stage throttle valve with a passage area ratio of 0.6 would h
8、ave the best anti-cavitation performance with the lowest risk of cavitation. Keywords: computational fluid dynamics simulation cavitation load rigidity passage area ratio two-stage throttle valve water hydraulics 1 INTRODUCTION Water hydraulic systems are operated with raw water (pure tap water) sub
9、stituting for mineral oil. They have advantages in terms of durability, reliability, safety, and cleanness. Such systems are becoming more and more popular, especially in fields of steel and glass production, coal and gold mining, food and medicine processing, nuclear power generation, ocean explora
10、tion, and underwater robotics 15. Because the opening of a water hydraulic control valve is very small compared 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 vap
11、our 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 for
12、ce 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 anti-corrosion materials for parts, and controlling maximum fluid temperature and flow vel
13、ocity. Tsukiji et al. 6 investigated cavitation by flow visualization in hydraulic poppet-type 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
14、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 c
15、avitation 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 become larger than ever for each combination of the valve and
16、 valve seat. Ishihara et al. 8 studied oil flow unsteadiness effect on cavitation phenomena at sharp-edged 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 ty
17、pes of cavitation, namely, gaseous cavitation and vapourous cavitation, and (b) cavitation incipience and finale varied with the initial condition, the temperature of hydraulic oil, and the rate of pressure drop. Johnston et al. 9 carried out an experimental investigation of flow and force character
18、istics of hydraulic poppet and disc valves using water as the working fluid. The axisymmetric valve housing was constructed from clear perspex to facilitate flow visualization； tests were performed on a range of different poppet and disc valves operating under steady and non-cavitating conditions, f
19、or Reynolds numbers greater than 2500. Measured flow coefficients and force characteristics showed obvious differences depending on valve geometry and opening. Vaughan et al. 10 conducted computational fluid dynamics (CFD) analysis on flow through poppet valves. Simulations were compared with experi
20、mental measurements and visualized flow patterns. A qualitative agreement between simulated and visualized flow patterns was identified. However, errors in the prediction of jet separation and reattachment resulted in quantitative inaccuracies. These errors were due to the limitations of the upwind
21、differencing scheme employed and the representation of turbulence by the k 1 model, which was known to be inaccurate when applied to recirculating flow. Ueno et al. 11 investigated experimentally and numerically the oil flow in a pressure control valve under an assumption of non-cavitating conditions for various configurations of the valves on
