Simulation, manufacturing and experimental investigation of surface structures to reduce clearance mass flow rates in rarefied gases

在这个项目的过程中，表面结构将被研究，以影响分子在稀薄气体流动中的散射方向。因此，例如，间隙质量流量可以降低，从而改善真空泵的运行性能。研究的重点一方面是在微米范围内的这种表面结构的生产（加工技术研究所），另一方面是通过结构表面间隙的稀薄流动的实验和理论研究（流体学主席）。在理论初步研究的基础上，制造初始结构并在真空试验台上进行测量，以确定表面结构对间隙质量流量的影响。此外，DSMC方法还开发了一种新的壁面反射模型，该模型可以映射表面结构的反射特性，而不需要在DSMC模拟的网格中解析表面结构的几何形状。为此，对表面几何进行了分析、抽象，并以几何形式存储在壁面反射模型中。然后根据测试粒子法确定壁面反射模型内的壁面反射，通过测试粒子法可以计算表面结构中分子的散射方向。为了确保有针对性和可重复性的表面制备，开发和制造具有几何定义的切削刃的工具，从而可以创建所需的表面。这些准备工作是在专用的切屑形成分析机器上进行的，该机器根据刨削原理工作。在刀具磨削前，建立了有限元切屑形成模型，研究了不同刀具微形状目标表面的制备。技术重点是防止或有针对性地调整毛刺的形成，这在模拟初步调查中被认为是一个挑战，特别是由于切屑截面小。此外，仿真还用于设计刀具形状，目的是尽量减少被动力，以便尽可能精确地制造所需的表面结构。开发的工具在内部实验室通过磨削制造后，用于制备表面结构。在对生成的结构进行微观数字化和使用DSMC方法模拟稀薄间隙流的基础上，对工具进行迭代调整以优化生成的表面。实验和模拟的间隙流动研究表明，制造的表面结构在稀薄气体流动中具有降低间隙质量流率的潜力。

In the course of this project, surface structures will be investigated in order to influence the scattering direction of molecules in rarefied gas flows. As a result, for example, clearance mass flow rates can be reduced, which improves the operating behaviour of vacuum pumps. The focus of the investigation is on the one hand the production of such surface structures in the micro meter range (Institute of Machining Technology) and on the other hand the experimental and theoretical investigation of the rarefied flows through clearances with structured surfaces (Chair of Fluidics). Based on theoretical preliminary investigations, initial structures are to be manufactured and measured in a vacuum test rig so that the influence of the surface structure on the clearance mass flow rate can be determined. Furthermore, a new wall reflection model is being developed for the DSMC method, which maps the reflection properties of the surface structures without resolving the geometry of the surface structures in the mesh of the DSMC simulation. For this purpose, the surface geometry is analysed, abstracted and geometrically stored in the wall reflection model. The determination of the wall reflection within the wall reflection model is then based on the test particle method, with which the direction of scattering of the molecules in the surface structure can be calculated. In order to ensure a targeted and reproducible preparation of the surfaces, tools with geometrically defined cutting edges are developed and manufactured with the help of which the desired surface can be created. The preparations are carried out on a special machine for chip formation analysis, which works according to the principle of planing. Prior to tool grinding, a finite element chip formation model is developed and the preparation of the target surface with varying tool micro-shapes is investigated. The technological focus is on the prevention or targeted adjustment of the burr formation, which was identified as a challenge in simulative preliminary investigations - especially due to the small chip crosssections. In addition, the simulation is used to design the tool shape with the aim of minimizing passive forces so that the desired surface structure can be manufactured as accurately as possible. After the developed tools are manufactured by grinding in the in-house laboratory, they are used to prepare the surface structure. Based on a microscopic digitization of the generated structures and the simulation of the rarefied clearance flows using the DSMC method, an iterative adjustment of the tools to optimize the resulting surfaces is carried out. The experimental and simulative clearance flow investigation of the manufactured surface structures shows their potential with regard to the reduction of clearance mass flow rates in rarefied gas flows.