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Fluid dynamics, CFD, science, HPC and industry views

Categories of CFD Software

There's a brief article on Engineering.com highlighting the Pros and Cons of 5 CFD Software Categories that makes interesting, if a little light, reading. The 5 categories are Open Source, through Open Source plus Wrapper, CAD-integrated, Specialised and Complete. There's quite a lot going on here, and worth digging a little deeper (and also worth having a look at that article first)….

The open source category, our particular favourite, is free at the point of use, assuming you have some hardware (or maybe just access to a web browser, which is all you need to use
SimScale, more of that later). It's not really free at the point of delivering some useful analysis, as you need to invest some time to learn it, or hire someone who knows how it works - of course assuming that you have chosen which software to use, which given the capability and complexity of some of the tool sets out there is not straight forward. Nevertheless, the lack of license costs is a clear advantage, although these can be offset by the cost of finding folk skilled in the art. For us one of the real value adds of open source is access to the source code and the availability of people skilled in its use and development (like us). This suits niche applications well where you can have some specific development performed for your particular application much faster and cheaper than through the other categories, which would almost always involve the software company doing the development, and prioritising it against their own roadmap - for SME's or bespoke requirements it's going to have to work hard to make it to the top of their list. The examples are CFD (finite volume: OpenFOAM and SU2) and also Lattice Boltzmann (LBM) based (Palabos). There's a lot of open source tools out there, so you can't mention them all, but the FEA open source equivalent to Comsol, Elmer, definitely deserves a mention. It could be labelled as "multi-physics" solvers as it can do fluids, solids, electromagnetics and a bunch of other stuff too, so maybe omitted for those reasons (although technically OpenFOAM is "multi physics" too).

We're not too sure about the interpretation of "wrapped" open source in the article, certainly in terms of suggesting support is poor. Taking the widely known and used finite volume differential equation solving toolset OpenFOAM as an example (it's
not just CFD), there are some GUI front ends such as HelyxOS from Engys that are very much do it yourself, but the commercial Helyx offering and Caedium from Symscape are provided by people who absolutely know their onions, and are able and willing to help you with yours. There's a subtlety here too: there's a lot of not wrapped, i.e. no GUI, developed flavours such as that from Caelus and the specific application versions from CFDSupport. Maybe OpenFOAM is a bit of a special case here, as it's had some good work for some time from a number of areas. It's interesting though that the examples provided are Caedium (already mentioned), SimScale, and Visual-CFD (from ESI). A particular mention here is deserved for SimScale which combines OpenFOAM, SU2 (a CFD specific, compressible flow and adjoint optimisation focussed delivery) and Calculix (a solid mechanics specific FEA solver with good contact modelling capability). All of these are open source, and SimScale "wraps" them up into a web browser. The SimScale guys also know their stuff, so maybe these examples are a bit off point.

CAD Integrated CFD gets a fair description in terms of pro's and con's, and very much on point with regards it not been the route of choice for analysts. There's another blog's worth of material on the topic of whether you need a designer, engineer or analyst to do your CFD for you - the subject of "Democratisation" of CFD - we'll get on to this in another blog.

The Specialised CFD category is a tricky one, which tries to identify a subset of what we would describe as commercial analyst level CFD. If there is a line it's certainly blurred; the Complete CFD category is described as being standard in the aerospace and auto industry, but Exa
PowerFlow is heavily used by Jaguar Land Rover in the UK, and that software is in the Specialised CFD grouping. Volkswagen and Audi are heavy users of OpenFOAM, too. The Commercial Analyst Level CFD certainly feels a better catch all description - granted within that you have tools that only offer specific functionality rather than the "everything you could need" level from the well know big players, but the only real disadvantage for the specific functionality offerers is just that. This category is worthy of some further detail, but any sub-categorisation doesn't really add much to the open source versus commercial benefits and limitations conversation, so we'll leave it there for now.

A finer point worth dropping in at the end is the use of "CFD Software" as a description, with some later mention of pre- and post-processing capability. The landscape across open source and commercial looks a little different when you start to think about pre- and post-processing tools - we'll be discussing these two other parts of the CFD process with regards open and commercial tools in another blog, coming soon….
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