Treatment of solid objects in the Pencil Code using an immersed boundary method and overset grids

ABSTRACT

Two methods for solid body representation in flow simulations available in the Pencil Code are the immersed boundary method and overset grids. These methods are quite different in terms of computational cost, flexibility and numerical accuracy. We present here an investigation of the use of the different methods with the purpose of assessing their strengths and weaknesses. At present, the overset grid method in the Pencil Code can only be used for representing cylinders in the flow. For this task, it surpasses the immersed boundary method in yielding highly accurate solutions at moderate computational costs. This is partly due to local grid stretching and a body-conformal grid, and partly due to the possibility of working with local time step restrictions on different grids. The immersed boundary method makes up the lack of computational efficiency with flexibility in regard to application to complex geometries, due to a recent extension of the method that allows our implementation of it to represent arbitrarily shaped objects in the flow.

KEYWORDS:

• Pencil code
• immersed boundary method
• overset grids
• compressible fluid dynamics
• complex geometries

ORCID

Jørgen R. Aarnes  http://orcid.org/0000-0002-5899-2597

Additional information

Funding

We would like to acknowledge that this research is funded by the Research Council of Norway (Norges Forskingsråd) under the FRINATEK Grant [grant number 231444] and by the National Natural Science Foundation of China [No. 51576176]. The research is supported in part by the GrateCFD project [grant 267957/E20], which is funded by LOGE AB, Statkraft Varme AS, EGE Oslo, Vattenfall AB, Hitachi Zosen Inova AG and Returkraft AS together with the Research Council of Norway through the ENERGIX program. Computational resources were provided by UNINETT Sigma2 AS [project numbers NN9405K, NN2649K].