低温推进剂管网系统中盲支管充填过程压力演化的模拟与水击特性研究

Numerical Investigation on Pressure Evolution and Water Hammer Characteristics in Cryogenic Pipeline Filling Process of the Blind Branch

  • 摘要: 低温推进剂管路充填过程可能发生剧烈的水击破坏,其形成机制、演化规律与常温水击差异显著。建立了低温液体充填常温管路压力演化的数值仿真模型,可实现大温差传热、气液掺混、流体相变等耦合计算,得到低温充填水击两相流态分布、热质转化与管内瞬变压力,探明了低温充填水击压力峰值的形成机制。低温充填水击时存在气相压缩、冷凝水击、振荡衰减及稳定蒸发等四个阶段,导致低温充填水击压力峰值有两个因素:液体惯性截止的反流作用和气体冷凝的水击作用,其中气体冷凝作用占主导。与常温充填水击相比,低温液体气液相变导致充填管路水击压力更高,压力衰减更快。如果忽略气液相变,管内氮气在液氮惯性冲击下被压缩,液氮动能逐步释放,以较低的加速度(354 m/s2)发生液氮冲击盲管末端,冲击压力值较低;如果气体冷凝作用显著,液氮充填过程管内氮气基本液化,失去了对高速液氮流的缓冲,导致液氮发生剧烈的流动截止现象,加速度可达1 102 m/s2,冲击压力值增大。当低温液体贮箱压力为0.2 MPa时,低温充填过程盲管末端最高压力值达0.843 MPa。

     

    Abstract: The pipe filling process of cryogenic propellant pipelines could result in severe water hammer damage, and the formation mechanism and evolution exhibit significant differences compared to the water hammer in room-temperature condition. A Computational Fluid Dynamics (CFD) model for the cryogenic liquid filling a room-temperature pipeline was established, which enables coupled calculations of large temperature heat transfer, gas-liquid mixing, and phase change effects. The model provides insights into the two-phase flow patterns, heat and mass transfer, and the pressure transient variation in the cryogenic filling process. It was found that the water hammer induced by cryogenic filling could be divided into four stages, including the gas compression, the condensation induced water hammer, the oscillatory decay, and the stable evaporation. The pressure peak value in the cryogenic filling event owned to two mechanisms, involving the inertial flow cut-off of liquid flow and the condensation water hammer of cavitation, and the cavitation condensation effect played the dominant role in the cryogenic condition. Compared to the room-temperature liquid filling situation, the gas-liquid phase transition results in higher water hammer pressure amplitude and faster pressure decay during a cryogenic pipe-filling process. When the evaporation and condensation is neglected, nitrogen gas inside the pipeline is compressed under the inertial impact of liquid nitrogen, and liquid nitrogen's kinetic energy is gradually released, resulting in lower acceleration(354 m/s2) and lower pressure fluctuation. However, when gas condensation effects become significant, the nitrogen gas inside the pipeline essentially liquefies during the liquid nitrogen filling process, losing its buffering effect. This leads to a severe flow cutoff phenomenon in the liquid nitrogen, with acceleration reaching up to 1102 m/s2 and an increase in impact pressure. When the container pressure was 0.2 MPa, the maximum pressure at the end of the pipeline could reach about 0.843 MPa.

     

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