基于对流换热的低温空化流动数值模拟研究

Numerical Study of Cryogenic Cavitation Based onConvection Heat Transfer

关键词:  低温  空化模型  热力学效应  对流换热

Key words:  Cryogenic  Cavitation model  Thermodynamic effect  Convection heat transfer

摘要:

为了考虑低温介质的热力学效应对空化发展的影响，基于气泡表面对流换热平衡建立了温降与气泡生长的关系，引入夹带理论估计了对流换热系数，并对一种输运型空化模型进行修正，将修正后的空化模型以二次开发的形式嵌入至商业软件中，同时引入能量方程源项以及物性参数随温度变化关系，对二维翼型表面空化流动进行数值仿真，通过与实验结果的对比，发现计算结果与实验结果符合较好，修正后的空化模型能够更好地预测空化区内温度的分布，最大温降偏差由62.18%降低至7.14%，平均温度偏差由0.59%降低至0.28%。考虑热效应之后，空化区主要由气液混合组成，来自主流的液体一部分经对流传递至空化区，一部分在翼型头部和气液界面处发生空化形成蒸汽，导致空化区气相体积分数显著减小，空化区与主流之间的界面变得模糊，最大温降和压降均发生在翼型头部位置。

Abstract:

In order to considering the thermodynamic effect on cryogenic cavitation, a relationship between temperature depressions and bubble growth was built based on convection type heat equilibrium, in which the convection heat transfer coefficient was estimated using the entrainment theory. Then a transport-based cavitation model was extended, and embedded in commercial CFD software, together with energy source and thermodynamic properties which were specified as the function of temperature. Numerical simulation of cavitation flow above a 2D foil surface was performed, it was found that the simulation results agreed with experiment results well, the extended cavitation model could predict the temperature distribution inside the cavity better, the max temperature depression error is reduced to 7.14% from 62.18%, the average temperature error is reduced to 0.28% from 0.59%. After taking the thermal effect into account, the cavity is mainly composed of vapor and liquid, part of liquid coming from main flow transfer into the cavity through convection, the other part vaporize near the head of foil and the interface, resulting in that vapor volume fraction decrease remarkably in the cavity, the interface between cavity and main flow become indistinct. The max temperature/pressure depression is located in the leading region of the cavity.