Fidelity CFD Technology Update Part I – Aerospace Design

There are always a few tricks and tips for an easy yet effective solution to a design problem. For aerospace applications, this is no different! The complexity of subsonic to supersonic aircraft design and wind tunnel testing can be replicated and resolved using computational fluid dynamics (CFD) tools. Since meshing is an important step in CFD solutions, tools capable of clearly capturing fine details, treating hanging nodes, optimizing the mesh quality, and automating mesh generation can ease the next step in a CFD workflow. Integrating a range of solvers that can cater to application-specific accuracy and resource constraints adds value to the CFD platform. This blog post will delve into the meshing tools and solvers integrated within the Cadence Fidelity CFD platform that can ease your next aerospace design.

Mesh Your Next Aerospace Geometry with the Fidelity CFD Platform

Fidelity Hexpress

Unstructured meshing is usually the best meshing option for complex aerospace geometries, such as subsonic or supersonic aircraft. The Fidelity Hexpress meshing tool offers two approaches for unstructured meshing: unstructured volume-to-surface (V2S) and unstructured surface-to-volume (S2V) meshing. These approaches can generate full-tet, full-hexa with hanging nodes, or hexa-dominant meshes. Surface capturing, boundary layer generation, and mesh optimization are automated in Hexpress meshing.

  

This tool supports both solid-fluid conformal and non-conformal meshing. It also offers solver-specific mesh optimization, export, and parallel mesh generation from a single CPU to cluster nodes.

Fidelity Flashpoint

The Flashpoint tool (from Pointwise) has recently been integrated into the Fidelity CFD platform for surface meshes. It includes brand-new features such as pinch point defeaturing (a must-have for high-lift aircraft). Here, meshing can be directly carried out on the CAD file, thereby minimizing deviations from the geometry. This tool can generate surface mesh for an industrial aircraft geometry in less than 15 minutes. Moreover, users have the flexibility to automate the Flashpoint meshing using Python scripting.

NASA CRM aircraft meshed with Fidelity Flashpoint (left); store geometry meshed with Fidelity Flashpoint (right).

Solve the Flow Physics of Your Aerospace Design with the Fidelity CFD Platform

Free Air Simulations

Free air simulations are commonly used for studying external aerodynamics in aerospace and defense applications. In free air simulation, the aircraft is set in a large domain with far-field boundary conditions on the sides. In this case, changing the angle of attack (AoA) of the aircraft can be done by changing the orientation of the far field ("freestream") velocity without the need to re-mesh the aircraft.

Fidelity Flow yields fast convergence and numerical robustness for free air simulations, i.e., for incompressible to supersonic flow regimes. High-speed external flows can be challenging, especially at transonic or supersonic to hypersonic speed. With the Fidelity Flow solver and its density-based formulation, even flows that reach Mach numbers up to 20 (vehicle reentry) can be modeled. For low-speed aerodynamics, the pressure-based solver has proven invaluable for simulating the flow in many applications, such as low-speed aircraft, drones, gliders, etc.

 

NASA CRM high lift configuration (left); NASA Concept 25D supersonic aircraft (right).

For supersonic flows, a simulation process speed-up of up to 14X  is possible with the best-in-class meshing and solver technology. The solver's robustness at supersonic speeds allows the simulation of off-design conditions such as supersonic engine intake buzz or unstart regimes. Advanced automation and streamlined workflows increase engineering efficiency. Customization options are also available for boundary condition ramping and quasi-unsteady simulation runs.

Hermeus reaches Mach 5 with the Cadence Fidelity CFD ( Image source: https://www.hermeus.com/press-release-series-b)

“Fidelity set itself apart with its convergence acceleration technology. We saw a 10X decrease in our run times on fewer CPUs. This really brought down the cost of running our analysis and got us answers we trust in a fraction of the time.” 

James Shields  - Senior Aerodynamics Engineer, Hermeus Corporation

In-Tunnel simulations

RUAG wind tunnel (Image source: https://www.hbm.com/fr/9242/ruag-relies-on-hbm-solutions-in-wind-tunnel-testing/)

In-tunnel simulations are highly complex due to wind tunnel structured meshing and aircraft displacement during alpha or beta-sweep studies. In tunnel testing, the aircraft is secured to a sting and other contraptions to measure pressure and alter the aircraft's position. When adjusting the angle of attack or sideslip, the aircraft is physically shifted in the tunnel, resulting in a change in its geometry that necessitates re-meshing.   

When re-meshing is unavoidable, there are two approaches:

• Full remeshing of the new geometry
• Only remesh the moved parts of the wind tunnel and keep the mesh around the aircraft. This requires the domain to be split into several parts connected with non-matching connections. When a part is moved in a specific domain, only that domain is remeshed and the non-matching connections are recomputed.                                                                 

Specific approaches for easing in-tunnel simulations using the Fidelity CFD platform- 

• Aircraft displacement parametrization with Fidelity Design Choice and Location functionalities
• Local wind tunnel re-meshing with non-matching connections
• Subsonic computations in the pressure-based solver for fully steady (non-oscillatory) RANS solution
• Turbulence model tuning with model constants in the pressure-based solver

Computational fluid dynamics (CFD) tools have revolutionized the aerospace industry by replicating and resolving complex design problems. The Cadence Fidelity CFD platform stands out in the market with its advanced meshing tools and a range of solvers that cater to application-specific accuracy and resource constraints. The platform eases the next step in a CFD workflow by automating mesh generation and optimizing mesh quality. With the help of these tools, aerospace engineers can design more efficient and effective aircraft that push the boundaries of modern technology.

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To take your aerospace design to the next level with Cadence Fidelity CFD, request a demo today!

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Also, watch how Hermeus is Reaching for Mach 5 with the Cadence Fidelity CFD Solutions.