Advancements in Automation of Overset Structured Mesh Generation: Algorithmic Developments and Aerodynamic Applications

Grid generation continues to be an onerous task when performing flow computations using computational
fluid dynamics (CFD), especially in the case of generating structured overset meshes. However, the
use of structured overset meshes provides significant advantages over other CFD methodologies, such
as highly efficient numerical methods, ease of use of higher-order schemes, and efficient resolution of
boundary layers. Despite these advantages, minimal research effort has been invested in automating
the mesh generation prior to performing flow computations. However, in recent years, a surface domain
decomposition approach utilizing the topology of a Boundary Representation (BRep) Computer-aided
design (CAD) solid allowed for a viable starting point for automation of overset meshes. Efforts in
completely automating the overset mesh generation process is still currently underway.

The present work details relevant efforts from both an algorithmic development and applied perspective that seek to further automation of overset mesh generation. The first element introduces a new
boundary condition for hyperbolically-generated meshes that couples the mesh boundaries together as
the meshes are generated or marched away from the initial data. This boundary condition maintains
consistent and sufficient overlap (provided consistent and sufficient overlap already exists in the initial
data), which is necessary for successful generation of overset grids. Functionally, the boundary condition
is identical in concept to overset boundaries used for solving the Navier-Stokes equations in CFD but
now applied in the context of the hyperbolic mesh generation for multiple overlapping initial curves or
surfaces. As such, the process is largely automated, since existing algorithms for overset boundaries,
such as performing domain connectivity, can be easily leveraged. This type of boundary condition is
demonstrated for two-dimensional field meshes, three-dimensional surface meshes, and three-dimensional
volume meshes.

The second element of this work is investigating the usage of the automatically-generated meshes in
CFD applications for aerodynamics analyses. The meshes generated by the automation procedure are
different compared to conventional, manually-generated meshes with regards to the increased quantities
of overset boundaries. This is mainly due to the domain decomposition approach inherited from the
input BRep topology, and it is an open question pertaining to any potential adverse effects on the flow
computations. In this effort, various RANS applications are considered ranging from simple benchmark
cases to full configurations of aircraft. Special attention is given to examining the numerical accuracy
and the computational efficiency for each of the cases presented. Overall, it is found that the increased
quantity of overset boundaries appear to have a neutral effect on the resulting flow computations.