Computer implementation of an immersed boundary (IB) module inside a flow solver can be accomplished non-intrusively. However a versatile preprocessor is needed at the first place to extract the geometric information pertinent to the immersion of an arbitrarily complex geometry inside a Cartesian mesh. Geometric errors can negatively impact the correct implementation of the IB method as part of the solution algorithm. Additionally, the distance field from the geometry is needed to implement various turbulence models or flow initialization. Geometric processing stage for complex geometry have received less attention despite the popularity of the IB method. Our experience has shown that some of the procedures described in the literature have difficulties processing highly complex geometry or can be inflexible to implement reconstruction schemes for turbulent flows. To address these issues, we present a geometric preprocessor with a distance field solver. We constructed our procedure from computational geometry algorithms such as point-in-triangle and point-in-edge. 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. We demonstrate the versatility of our preprocessor for challenging test geometries from the computer graphics field, complex terrain and urban environments.

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