基于OpenFOAM的真实流体模型库及均相求解器开发

Development of Real-Fluid Model Libraries and Homogeneous Solver Based on OpenFOAM

关键词:  真实流体  热物理性质  超临界环境  低温射流  流动特性  均相求解器

Key words:  Real-fluid  Thermo-physical properties  Supercritical conditions  Cryogenic jet  Flow characteristic  Homogeneous solver

摘要:

为了正确认识高压环境下的流体非理想性特征，及其对于低温射流喷雾过程的影响作用，将多种不同真实流体模型写入到开源CFD程序OpenFOAM仿真平台中，编译形成具有广泛通用性的真实流体热物理模型库；并将高压下真实流体特征的影响引入到压力修正算法中；开发出适用于描述超临界环境下低温流体流动过程的均相求解器。对高压下流体热物理性质的非理想性，以及超临界环境下的低温液氮射流喷注过程进行研究。结果表明：高压下的真实流体效应主要体现在低温区域，本文所建立的模型库可以在任意热力学状态范围内正确预测流体热物性；基于此模型库所开发的均相求解器可正确预测超临界环境下低温射流的详细流动特征和结构，而理想气体模型则会大幅低估射流核心区密度分布，中心线上误差高达68.9%；综合考虑计算精度和效率，PR EoS及相关模型更适合于这类超临界流动问题的求解；低温射流跨临界喷注中局部区域所发生的虚假沸腾现象会导致射流温升速率降低、体积膨胀速率加快；射流核心区压缩因子明显<1，在数值仿真时必须考虑高压环境下的真实流体效应。

Abstract:

In order to understand the non-ideality of fluid under high-pressure conditions and their effects on spray process of cryogenic jet, several different real-fluid models were implemented into open source CFD toolbox OpenFOAM, which was then compiled to form generalized real-fluid thermo-physical model libraries. In addition, the effects of non-linearity of these models were introduced to pressure-corrector algorithm. Thus, a homogeneous solver which was appropriate to characterize flow of cryogenic fluid at supercritical condition was developed. Non-ideality of thermo-physical properties under high-pressure conditions and injection of cryogenic liquid nitrogen jet under supercritical condition were investigated. The results indicated that the effects of real-fluid characteristics are primarily exhibited in the high-pressure, low-temperature regions, and the model libraries developed in this study could correctly predict thermo-physical properties under any thermodynamic conditions. The newly developed solver based on these libraries could correctly reveal the flow characteristic and structures of cryogenic jet under supercritical condition, whereas the ideal gas model would largely underestimate the density in core region of jet, the error on centerline is up to 68.9%. The PR EoS together with the dependent models behave relatively superior to other model packages based on the comprehensive comparison of the computational accuracy and efficiency. The pseudo-boiling phenomenon in local region during trans-critical injection of cryogenic jet would result in decrease of temperature raising rate and increase of volume expansion rate, and the compressibility factor in core region of jet is remarkably less than 1, consequently, the real-fluid effects under high-pressure conditions must be considered during simulation.