04 Jan 5 tips to improve your CFD simulation accuracy
As CFD softwares are getting easier and easier to use, people still find difficult to get accurate results from them. This because any simulation output depends not only on the software quality, but also on the human factor: experience is fundamental.
How can CFD experts get good results then? There are many things to look at, many settings to choose carefully, but in this post you can find 5 tips that surely will improve your CFD experience and capabilities.
The easiest tip ever, it is also the most difficult to achieve. Most of the time, input geometry files have to be simplified in order to ignore small details that, beside having little effect on the CFD simulation results, may force your mesh cell to assume a very small size.
Keep in mind our suggestion in this wiki page.
Meshing is not only a technical capability. It is very close to being an art. Every user has to remember that choices made at this level may influence CFD results he obtain later on during the simulation phase.
It is very important to use the correct cell size in order to accurately resolve every gradient that may occur in flows. For this reason CFD experts suggest to refer to the Yplus value, a coefficient calculated after the CFD simulation has been completed. This value takes into account the local cell size and the physics of the fluid – such as dynamic viscosity and density – and tells us whether the mesh size has been chosen correctly compared to the fluid properties. The selection of a correct Yplus value may depend on turbulence models, but it is possible to state that a value between 30 and 300 is commonly considered the most suitable for most simulations.
So get back to your results, and remesh the geometry if you did not get Yplus in the correct range!
When it gets to models things usually are very complicated to solve. Compressible flows, turbulence, heat exchange, mixture … these are just examples of models every CFD user is required to pick his own from.
First of all, we need to think about the main goal of our simulation: do we have to measure heat flows? Are we interested into friction coefficients? When answering to these questions, we obtain every information we need to provide to our CFD simulation set-up.
Keep in mind that CONSELF Cloud CFD solution offers every user a guided procedure that allows to easily find your way. Subscribe to our FREE WELCOME PLAN and start your simulations right now!
Often we forget one of the basic rule of CFD: check the simulation convergence to the appropriate residual level.
What are residuals? They are a set of parameters that tells the user whether the current solution represents the final physical solution of the problem defined with the given mesh and boundary conditions. They specify how far we are from considering the current iteration as the final one of our process or if we need to proceed a little bit more.
In general a residual level of E-04 is suggested, but higher (or actually lower) values are required in high accurate solutions such as in validation cases.
Most of the time we forget that we can’t have good results if we can not analyze them. After any CFD simulation, a huge amount of data is generated. These data must be processed in order to extract the most important info we need in order to understand the details of the physical phenomena we reproduced. In many case we are looking for forces, friction, heat exchange, gas concentration, fluid-wall interaction, temperature, … there are so many parameters that it is difficult to fit them into a little category.
With CONSELF you have complete control over these results by using our post-processing tool (based on the well known ParaView). With this advanced tool it is possible to extract slices, contours and get any information from your results dataset.
CONSELF wants to make state of the art, cutting edge technology, available to every professional in the globe.
CFD & FEM simulation software is a very powerful tool, with its adoption optimization and innovation can be achieved in every field. To make this instrument accessible to everyone means lowering costs, but mainly to develop an infrastructure that favours a super-easy adoption by market new entrants.
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Ruggero Poletto – firstname.lastname@example.org