Robust and Efficient WMLES Unstructured Grid Generation with HeldenMesh

Mesh generation for wall-modeled large eddy simulations (WMLES) based CFD simulations represents a critical area of research as there are significant challenges which must be overcome before this technology can be adopted for widespread use. Two critical challenges associated with these scale-resolving simulations is mesh size and mesh quality. Mesh size represents a critical challenge as WMLES simulations require at least an order of magnitude increase in mesh size compared to current Reynolds-averaged Navier-Stokes (RANS) based simulations. This means required mesh sizes are measured in billions of nodes (exascale) rather than tens or hundreds of millions. Existing commercial mesh generators can take several days just to generate these large meshes. Mesh quality also represents a critical challenge as the WMLES solver is much more sensitive to element regularity, edge alignment, element type (hex, prism, pyramid, tet), maximum aspect ratio, and surface spacing than typical RANS simulations. The objective of our Phase II effort is to solve these significant challenges by developing an automated, scalable, and high-quality mesh generation capability for next generation CFD based WMLES applications. Our approach develops enhancements to our industry leading time-to-mesh HeldenMesh grid generator to improve its support for WMLES applications while also reducing current Reynolds-averaged Navier-Stokes (RANS) based mesh generation times. It also develops a new tool which rapidly generates the billions of nodes meshes needed for WMLES simulations using a robust and automated mesh refinement approach reducing WMLES mesh generation times from days to seconds. Finally, it also proves the production readiness of these tools on several real-world WMLES applications while also establishing the best practices needed to ensure solution accuracy. Our program represents a key enabler for widespread adoption of WMLES. A primary shortcoming identified during the NASA-sponsored CFD Vision 2030 Study was that the generation of Navier-Stokes based CFD meshes constitutes a principal bottleneck in the simulation process. This bottleneck comes from the significant human intervention needed to generate meshes.  In addition, a more recent NASA study entitled “A Guide for Aircraft Certification by Analysis” identified increased confidence in the prediction capability of the computational tools as a key challenge for enabling certification by analysis and accelerated configuration and technology maturation.  Crucial to addressing both challenges is the development of automated, scalable, and high-quality mesh generation capabilities for next generation CFD based wall-modeled large eddy simulations (WMLES).  Our program solves these challenges by developing new capabilities and automated tools that reduce current WMLES mesh generation times from days to seconds while meeting the stringent mesh quality requirements needed for these simulations. This represents a key enabler for widespread adoption of WMLES. The three primary technical objectives of our effort are:  1) Develop Enhancements to HeldenMesh for WMLES Applications.  2) Development of HeldenRefinement.  3) Testing, Demonstration, and Support.  HeldenMesh is our industry leading time-to-mesh unstructured grid generator.  Objective 1 incorporates enhancements to it to improve its support for WMLES applications while also reducing current Reynolds-averaged Navier-Stokes (RANS) based mesh generation times.  HeldenRefinement is a newly developed tool which rapidly generates the billions of nodes meshes needed for WMLES simulations using a robust and automated mesh refinement approach.  It is fully developed under objective 2.  Objective 3 proves the production readiness of these tools on several real-world WMLES applications while also establishing the best practices needed to ensure solution accuracy.  The specific deliverables are:  1) An enhanced HeldenMesh production software release.  2) Beta HeldenRefinement software release.  3) Software manuals and training materials.  4) Meshes for NASA evaluation with FUN3D.

The successful completion of this Phase I effort supports all NASA programs and projects that use CFD for advanced aircraft concept design, launch vehicle design, and planetary entry vehicles. The technology developed under this project will enable design decisions by Aeronautics Research Mission Directorate (ARMD) and Human Exploration Operations Mission Directorate (HEOMD). Helden Aerospace has already successfully transitioned its existing HeldenMesh commercial grid generator to industry where it is widespread use. This Phase II effort further improves this CFD toolset by reducing its already industry leading mesh generation times and incorporating new WMLES mesh generation capabilities.  It results in a product with strong commercial near and far term viability. 

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