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采用流体体积(volume of fluid，VOF)模型，对0.1、2.03、5.07、10.13 MPa环境压力下垂直管内水蒸汽-水逆向流动过程进行数值模拟。研究垂直管内汽液两相逆流流动过程中，环境压力对淹没开始点、全部携带点、流向反转点及淹没消失点的影响。提出了淹没开始点与淹没消失点对应的无量纲汽速、液速间的经验关系式。常压环境下淹没开始点对应的无量纲汽速、液速呈线性分布，但在高压环境下呈二次函数分布，且分布方式与环境压力无关。与常压环境相同，高压环境下的淹没消失也存在滞后现象，且滞后现象的发生范围随环境压力的增大而扩大。有滞后现象的淹没消失点对应的无量纲汽速、液速呈线性关系，直线斜率随压力的升高而增大。高压环境下全部携带点和流向反转点对应的无量纲汽速，均随环境压力的增大而降低，两者均不受液速变化的影响，流向反转点受环境压力的影响相对较小。相同压力条件下，流向反转点所需的汽速低于全部携带点。根据汽液两相流动特性，分析了发生以上现象的原因。“,”The volume of fluid (VOF) method was used to conduct numerical simulation to investigate the flooding process in vertical tube under different pressure of 0.1 MPa, 2.03 MPa, 5.07 MPa and 10.13 MPa. The effects of pressure on flooding, complete carry up, flow reverse and deflooding of vapor-liquid two phase flow in vertical tube were studied. The relationship of flooding and deflooding between dimensionless quantity of vapor velocity and liquid velocity were presented. The pressure has no influence on flooding, and the distribution of flooding is a quadratic function instead of fitting with Wallis’s linear relationship. The hysteresis effect of deflooding under high pressure becomes more apparent with the increase of pressure. The distribution of deflooding is linear in the dimensionless quantity of vapor velocity and liquid velocity coordinate system. Its slope decreases with the increase of pressure. The complete carry up and flow reverse are not affected by liquid velocity but decrease with the increase of pressure, while the influence of pressure on flow reverse is small. The dimensionless quantity of vapor velocity of flow reverse is smaller than complete carry up in the same case. Basing on the characters of vapor-liquid two phase flow, reasons of the phenomenon appeared were analyzed.