Studies on nonequilibrium phenomena in gas flows-New approach by hybrid micro-macro gasdynamics-

1.日本组(JG)和意大利组(IG)研究了稀薄气体的二维Benard问题。JG发现了无流稳定解的一个新的参数域，这在经典流体力学中是未知的。JG还研究了多辊解的稳定性，阐明了从不稳定的多辊解到稳定的多辊解的过渡过程。IG使用直接模拟蒙特卡罗(DSMC)方法展示了一个具有混沌行为的流动的例子。JG研究了由气体凝聚相组成的两个同轴圆柱体之间Couette流的分叉。首先，在只有内柱转动的情况下，通过对初值问题的DSMC方法分析，研究了分叉的结构，阐明了初始条件与稳定定常解之间的关系。接下来，在外筒也在旋转的一般情况下，系统的渐近…在钢瓶旋转较慢、气体稍显稀薄的情况下进行了进一步的分析。从而较全面地阐明了分叉的结构，发现了各种新的分叉解。JG对利用温度场诱导的稀薄气流制造真空泵的可能性进行了实验研究。结果表明，该泵的流动情况与数值模拟的结果一致，证明了该泵的实用性。JG还总结了包括本实验在内的温度场诱导稀薄气体流动的前人研究成果。联合专家小组全面、系统地总结了天然气凝析向其凝析相流动的现有结果，并向政府间专家组提供了信息。JG和IG合作研究了无限强激波的结构，并利用JG发展的有限差分方法澄清了速度分布函数中的奇异性。JG还为Boltzmann方程的含时问题发展了一种更高精度的数值格式。较少

1. The two-dimensional Benard problem for a rarefied gas was studied by both Japanese group (JG) and Italian group (IG). JG found a new bound of the parameter region for a stable solution without a flow, which has not been known in classical fluid dynamics. JG also investigated the stability of multi-roll solutions and clarified the process of transition from unstable multi-roll solutions to stable ones. IG showed an example of the flow with chaotic behavior using the direct simulation Monte Carlo (DSMC) method.2. JG studied bifurcation of the Couette flow between two coaxial circular cylinders made of the condensed phase of a gas. First, in the case where only the inner cylinder is rotating, the structure of the bifurcation was investigated by analyzing the initial-value problems by the DSMC method, and the relation between the initial conditions and the stable steady solutions was clarified. Next, in the general case, where the outer cylinder is also rotating, a systematic asymptotic … More analysis was carried out under the condition that the rotation of the cylinders is slow and the gas is slightly rarefied. As a result, the structure of the bifurcation was clarified comprehensively, and various new types of bifurcated solution were discovered.3. JG performed an experimental study of the possibility of a vacuum pump using a rarefied gas flow induced by temperature fields. As a result, a flow consistent with the flow predicted numerically was observed, and the practicality of the pump was demonstrated. JG also summarized the previous results for the rarefied gas flows induced by temperature fields, including this experiment.4. JG provided a comprehensive and systematic summary of the existing results for flows of a gas condensing onto its condensed phase and gave the information to IG.5. JG and IG cooperated to study the structure of an infinitely strong shock wave and clarified the singularity in the velocity distribution function by means of a finite-difference method developed by JG. JG also developed a numerical scheme of higher accuracy for time-dependent problems of the Boltzmann equation. Less