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

TL;DR

This paper compares immersed boundary and overset grid methods in the Pencil Code for solid object flow simulations, highlighting their respective strengths in accuracy, flexibility, and computational cost.

Contribution

It introduces a new implementation of the immersed boundary method for arbitrarily shaped objects and assesses the performance of both methods in flow simulations.

Findings

Overset grids provide highly accurate solutions for cylinders with moderate computational cost.

Immersed boundary method offers greater flexibility for complex geometries.

Overset grids outperform immersed boundary in accuracy for simple shapes like cylinders.

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 regards 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.