Based on the direct simulation Monte Carlo method, we have simulated a flow of rarefied gas into vacuum through a channel with sudden contraction or expansion in cross section. The nonequilibrium effects at the input and output of the channel have been taken into account by including certain pre- and post-channel regions into the geometry under consideration. In a wide range of gas rarefaction, the mass flow rate through the channel and the flow field both inside the channel and in the upstream and downstream regions have been calculated. The results have been compared with the characteristics of a channel with the constant cross section. A significant effect of the channel geometry has been established. The Knudsen minimum has been found in the mass flow rate as a function of gas rarefaction, while a compression zone and a circulation zone have been discovered in the flow field.

在直接模拟蒙特卡洛方法的基础上，我们模拟了稀有气体通过横截面突然收缩或膨胀的通道进入真空的过程。通过将某些前和后通道区域包括在所考虑的几何图形中，已考虑到通道输入和输出处的非平衡效应。在广泛的气体稀化中，已经计算了通过通道的质量流量以及通道内部以及上游和下游区域的流场。将结果与具有恒定横截面的通道的特性进行了比较。已经确定了通道几何形状的重大影响。已发现质量流量中的克努森最小值与气体稀薄度有关，