基于超临界流体传热弱化机理的湍流模型开发

Heat transfer deterioration (HTD) in supercritical fluids became concerned in the field of heat transfer due to the start of research and development of the supercritical water-cooled reactor in many countries. The past studies have been mainly based on the integral heat transfer data, while the understanding of local phenomena is very little. Even though it is a useful tool to acquire the local phenomena in the flow, computational fluid dynamics (CFD) is still suffering from shortage of competent turbulent models. With the recognition of the above challenges this project combines experimental study and theoretical derivation in the process of turbulence model development. In the experiment study the integral heat transfer measurement and the flow visulization measurement are applied at the same time in order to investigate the relation between HTD and local flow features. The HTD mechanism can then be generalized based on the relation. Accounting for the HTD mechanism a new turbulence model is proposed with the aid of the direct numerical simulation (DNS) data already available in the literature. The proposed model is further optimized and validated with the assitance of the experiment data obtained in this project. The performance of proposed model is judged in the viewpoint of its prediction performance for both local and integral phenomena. This model can be utilized in the future CFD analysis for HTD in supercritical fluids and make CFD a more popular and reliable tool in this field.

超临界流体的传热弱化现象因超临界水冷堆的研发而受到广泛关注。目前对传热弱化现象的研究仍以宏观传热数据为基础，缺乏对传热弱化局部流动机理的认识。而计算流体力学（CFD）作为流动传热局部现象的重要研究手段，其在超临界流体传热弱化研究中的应用仍苦于没有适当的湍流模型。从以上两个基本问题出发，本课题采用宏观传热测量与局部可视化流场测量相结合的方法研究超临界氟利昂中的传热弱化，建立传热弱化的宏观传热与可视化流场实验数据库。基于实验数据，研究传热弱化所伴随的流场特征,归纳宏观传热弱化现象与局部流动现象之间的联系规律。以所得到的机理认识为基础，利用文献中的传热弱化直接模拟数据，开发能准确预测传热弱化现象的湍流模型；并利用所建立的实验数据库，从局部流场和宏观传热两个方面来验证并优化湍流模型。所提出的湍流模型将为CFD在超临界流体传热弱化研究中的应用夯实基础。

超临界流体的传热弱化现象因超临界水冷堆的研发而受到广泛关注。目前对传热弱化现象的研究仍以宏观传热数据为基础，缺乏对传热弱化局部流动机理的认识。计算流体力学（CFD）作为流动传热的重要研究手段，其在传热弱化研究中的应用仍苦于没有适当的湍流模型。为了开发适用的湍流模型并加深对传热弱化机理的认识，本项目从最基本的Favre平均的动量方程出发，分析超临界条件下湍流的产生与耗散，并通过合理假设焓导致的湍动能产生项的闭合问题转化成湍流热流密度的闭合问题。本项目选用常规流动传热计算中性能优异的k-ε-ζ-f模型作为基本模型，以OpenFOAM为平台，在基本模型上添加了多种湍流热流密度的闭合模型。为了更好地描述各向异性特征，利用文献中的传热弱化直接模拟数据及试验数据，研究评价了湍流热流密度的简单梯度模型、泛梯度模型、代数热流模型、椭圆混合代数热流模型等闭合模型对传热弱化的预测影响。为了更充分地验证该湍流模型，本课题还开展了宏观传热试验。在湍流模型验证及优化过程中，将充分利用实验得到的宏观传热试验数据，从局部流场及宏观传热的角度来综合评判湍流模型的性能。通过评估证明，本项目开发的湍流模型改善了超临界流体传热弱化的预测结果。研究结果能够用于以后的超临界流动传热的CFD模拟。本基金项目共发表SCI论文2篇，国际会议论文3篇，作基金研究相关的特邀报告2次。