中文摘要：

本文提出一种能够体现流体物性变化的格子Boltzmann模型。首先，通过模拟常压下空腔内的自然对流，检验了模型的可靠性。其次，模拟了超临界压力下CO2的自然对流，讨论了伪临界温度附近急剧的物性变化对流动及传热的影响。模型的提出为深入探讨CO2的流动和传热特性提供了有力工具。本文结果为有效利用超临界CO2提高换热系统的性能提供了理论依据。

英文摘要：

A lattice Boltzmann model which considers fluid property variations is proposed in the present paper. Firstly, the model is validated through simulating the natural convection in a square cavity at normal pressure. Then, the model is used to simulate the CO2 natural convection at supercritical pressure. Effects of the dramatic variation in fluid properties around the pseudo-critical temperature on flow and heat transfer processes are discussed. The newly-proposed model is a powerful tool for the deep exploration about the flow and heat transfer characteristics of CO2. The present results provide theoretical foundation for the efficient utilization of supercritical CO2 to enhance the performance of heat transfer systems.