MODELLING AND SIMULATION
Changing CFD
GEMMA CHURCH INVESTIGATES HOW CFD IS PROVIDERS ARE LOWERING THE BARRIER FOR SIMULATION
Computational Fluid Dynamics (CFD) is a staple fluid mechanics technology, where numerical
analysis and data structures are used to analyse and solve a host of fluid flow problems. This established solution is now branching out, tackling everything from environmental issues to heart conditions and aeroacoustics. This diversity of applications has
affected the design and functionality of traditional CFD software, where engineers can now take on diverse problem sets with simulation and modelling. Andy Fine, Altair’s vice president for CFD solutions, EMEA, said: ‘We are dealing with increasingly complex physics when looking at CFD problems. While most CFD technology is extremely mature, it’s very expensive and requires a lot of specialist knowledge. We are trying to lower these barriers to entry by providing increasingly accessible, cheaper solutions.’ The accuracy versus performance
trade-off is another major challenge to democratise CFD, where some applications require large computational resources to meet user expectations. Ed Fontes, CTO at Comsol, explained: ‘Here, you often find a conflict between the user’s expectation and the software’s ability to deliver accurate results to a small computational cost. Unfortunately, there are no free lunches: Accuracy costs.’ Fontes added: ‘It is easy to get colourful plots at low computational costs by adding lots of artificial diffusion, but this yields inaccurate results. We invest a substantial portion of our development time in numerical methods and solvers, in order to solve problems accurately and on desktop computers.’ Multiphysics coupling is another
30 Scientific Computing World Autumn 2020
increasingly important consideration in CFD, where tools must address usability issues. Fontes explained: ‘It should be straightforward to couple CFD to other types of analysis, for example structural mechanics (fluid-structure interaction), chemical reactions, heat transfer, electromagnetic fields, equation-based modeling, etc. The solver settings for CFD should work together with the solution for other numerical equations added by other phenomena, either fully coupled or using a segregated solution strategy.’ Comsol’s Application Builder is
addressing these usability concerns. Fontes said: ‘It allows CFD experts to build dedicated graphical user interfaces on top of specific CFD problems defined in Comsol. These experts can build applications that can be used by a larger community of engineers and scientists that are domain experts, but may not be CFD experts.’ Comsol has also optimised many of its
existing tools for CFD over the last few years, including its meshing tool, iterative solvers and tools for results evaluation. ‘The mesh and solver projects have been very important for CFD and are still large projects, so we are in no way done. We are proud of the ability to visualise and evaluate results,’ Fontes explained. Altair has recently increased its focus on CFD, targeting specific and specialist applications across multiple industries
Mixing and free surface shape in a chemical reactor. The impeller is placed at the bottom and two heat exchanger tubes are placed around the impeller. The model can be used to compute the shape of the free surface, flow field, composition, and temperature field in the reactor
using a suite of software solutions. Fine explained: ‘One size does not fit all in the CFD space. We make a decision for each client, based on their application, to find the best solution.’ Altair runs a unique licensing system
called Altair Units. The company’s full suite of software solutions is available via Altair Units from its marketplace Altair One, where engineers can also get access to specialist support teams, including a CFD division, and third-party solutions from the Altair Partner Alliance. Altair’s CFD simulation suite includes Altair AcuSolve, which allows engineers to tackle several general purpose CFD problems, including flow, heat transfer, turbulence, and non- Newtonian material analysis, for example. Altair ultraFluidX and Altair nanoFluidX
Model of the CFD around a prehistoric animal. The optimal position of the feeding organ (sort of mouth) would be in the recirculation zone behind the arms of the anchor-shaped structure, where solid nutrients would settle on the surface of the animal. (Model reproduced from Darroch et al,
https://royalsocietypublishing.org/doi/ full/10.1098/rsbl.2017.0033)
are application-specific CFD solutions. Altair ultraFluidX was developed specifically for ultra-fast prediction of aerodynamic properties for a variety of vehicles, whereas Altair nanoFluidX is a particle-based hydrodynamics (SPH) tool to predict fluid flow around complex geometries under complicated motion. ‘These tools allow us to tackle problems that are practically impossible to work with using traditional CFD,’ Fine said. One of these emerging areas is
aeroacoustics, where the noises and vibrations created by an object in motion are investigated and reduced. These sounds are now more noticeable than
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