Rayleigh-Bénard热对流中non-Boussinesq效应的数值研究

采用变物性格子Boltzmann通量求解器（VPLBFS）研究了Rayleigh-Bénard热对流.以超临界流体为例,采用VPLBFS的简化形式和标准形式分别得到了通常关注的基于Boussinesq假设的常物性解,只考虑部分物性变化的基于partial Boussinesq假设的PBA解,以及考虑流体全部物性变化的变物性解,分析了non-Boussinesq效应对Rayleigh-Bénard热对流的影响,讨论了不同温差条件下的non-Boussinesq效应.研究结果表明:non-Boussinesq效应对超临界流体的Rayleigh-Bénard热对流有非常显著的抑制作用,论证了在研究热对流时考虑流体全部物性变化的必要性.      

Compressibility Effects in Turbulent Boundary Layers

Local cascade （LC） scheme and space-time correlations are used to study turbulent structures and their convection behaviour in the near-wall region of compressible boundaxy layers at Ma = 0.8 and 1.3. The convection velocities of fluctuating velocity components u （streamwise） and v （vertical） are investigated by statistically analysing scale-dependent ensembles of LC structures. The results suggest that u is convected with entropy perturbations while v with an isentropic process. An abnormal thin layer distinct from the conventional viscous sub-layer is discovered in the immediate vicinity of the wall （y^＋ ≤ 1） in supersonic flows. While in the region 1 〈 y^＋ 〈 30, streamwise streaks dominate velocity, density and temperature fluctuations, the abnormal thin layer is dominated by spanwise streaks in vertical velocity and density fluctuations, where pressure and density fluctuations are strongly correlated. The LC scheme is proven to be effective in studying the nature of supersonic flows and compressibility effects on wall-bounded motions.     

格子Boltzmann方法用于模拟超临界CO2自然对流的研究

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...