An Immersed Boundary Geometric Preprocessor for Arbitrarily Complex Terrain and Geometry

Abstract

There is a growing interest to apply the immersed boundary method to compute wind fields over arbitrarily complex terrain. The computer implementation of an immersed boundary module into an existing flow solver can be accomplished with minor modifications to the rest of the computer program. However, a versatile preprocessor is needed at the first place to extract the essential geometric information pertinent to the immersion of an arbitrarily complex terrain inside a 3D Cartesian mesh. Errors in the geometric information can negatively impact the correct implementation of the immersed boundary method as part of the solution algorithm. Additionally, the distance field from the terrain is needed to implement various subgrid-scale turbulence models and to initialize wind fields over complex terrain. Despite the popularity of the immersed boundary method, procedures used in the geometric preprocessing stage have received less attention. The present study found that concave and convex regions of complex terrain are particularly challenging to process with existing procedures discussed in the literature. To address this issue, a geometric preprocessor with a distance field solver was presented, and the solver demonstrated its versatility for arbitrarily complex geometry, terrain, and urban environments. The distance field solver uses the initial distance field at the immersed boundaries and propagates it to the rest of the domain by solving the Eikonal equation with the fast sweeping method.

Direct Numerical Simulation of Turbulent Katabatic Slope Flows with an Immersed-Boundary Method

“…where RHS i includes advective, diffusive, and pressure gradient terms. If the velocity at the boundary can be prescribed as (Senocak et al, 2015). In the GIN3D solver, the velocity reconstruction scheme for laminar conditions follows a linear approach in the direction normal to the surface, similar to the works of Gilmanov et al 2003, Gilmanov and Sotiropoulos (2005) and Gilmanov and Acharya (2008).…”

Dynamic rating of overhead transmission lines over complex terrain using a large-eddy simulation paradigm

“…The first step of this IB method is to identify the Cartesian grid cells cut by the surface, which can be challenging with arbitrarily complex terrain. The details of the geometric pre-processing can be found in [43]. Once the geometric information is known, the values in near-surface grid cells cut by the immersed surface can be reconstructed each simulation time step by interpolating between the known boundary condition at the immersed surface, e.g.…”

Wind Farm Power Prediction in Complex Terrain

“…The IB method has proven successful in resolving terrain and complex geometry. It can also be implemented in existing flow solvers without modifications to the core flow solver [57].…”

“…We developed an IB preprocessor to generate the geometric data to implement the IB method [57]. The preprocessor is used to tag nodes, calculate the distance from an IB node to the surface for use in reconstruction, and bind an IB node with a surface element.…”

“…As part of this research, an article detailing our immersed boundary preprocessor for complex terrain was published in 2015 [57]. Another article detailing the methods we use to simulate winds over complex terrain and showing some of the associated sensitivities has been submitted for publication [16].…”