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Maxwell velocity slip and Smoluchowski temperature jump boundary condition for ANSYS CFX.

Number: 176

Author(s) : JUNEMANN T., PLESKUN P., BRÜMMER A.

Summary

Multi-dimensional numeric flow simulation is a common but non-trivial approach to simulate the operation behavior of screw machines. Current challenges of computational fluid dynamics (CFD) simulations of screw machines are especially related to turbulence modelling and meshing. An adaption of CFD simulations to screw vacuum pumps is difficult since the Navier-Stokes equations have limited validity for low pressure regimes. However, the scope of application can be extended to higher Knudsen numbers (e.g. lower pressure regimes) by the use of velocity slip and temperature jump boundary conditions at solid surfaces. Even if the complete simulation of screw vacuum pumps is still challenging, these boundary conditions can be used to examine isolated effects like clearance flows or inhomogeneous pressure distributions in working chambers. A common commercial CFD-Solver is ANSYS CFX, which also has been successfully applied to screw machines, but it does not provide a Maxwell velocity slip and a Smoluchowski temperature jump boundary condition. In the presented work these boundary conditions are implemented in Ansys CFX using user-defined expressions in a similar way as it has been implemented in the rhoCentralFOAM solver of the open source toolbox OpenFOAM. The boundary conditions are validated by comparison with stationary OpenFOAM results, DSMC results and measurements for a hypersonic plate flow. In addition, the boundary conditions are verified by experimental and DSMC results of a gas flow in a clearance between a rotational shaft and a plane counter plate.

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Pages: 10

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Details

  • Original title: Maxwell velocity slip and Smoluchowski temperature jump boundary condition for ANSYS CFX.
  • Record ID : 30028988
  • Languages: English
  • Subject: Technology
  • Source: 12th International Conference on Compressors and their Systems
  • Publication date: 2021/09
  • Document available for consultation in the library of the IIR headquarters only.

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