This guest contribution on Innovation Intelligence is written by Milos Stanic, Product Manager and CFD Developer at FluiDyna. nanoFluidX is available through the Altair Partner Alliance and for purchase through Altair exclusively.
nanoFluidX (nFX) is a state-of-the-art SPH solver for ultra-fast, weakly-compressible, multi-phase flow simulations of complex geometries. Oil distribution in an engine spinning at 9000 rpm? No problem. Gearbox or a differential at several thousand rpm? Not an issue. Planetary gearbox? Sure. Ah, yes, you would say, but only for 3 revolutions. What if we told you that with nFX you can simulate a few to several seconds of physical time, spinning at thousands of rpm in a matter of a week or so?
The Essence of Smoothed Particle Hydrodynamics
The Smoothed Particle Hydrodynamics (SPH) CFD method was developed by Lucy, Gingold and Monaghan back in the late 70’s for purposes of simulating astrophysical flows. Since then, SPH has come a very long way. Initially thought of as inferior to its “finite” (finite element (FE) and finite volume (FV)) counterparts due to performance issues and initially non-elegant numerical tweaks, SPH has matured into a well-established numerical method used in a number of industrial and scientific fields. SPH has particularly blossomed with the rise of the Graphical Processing Units (GPU) in the area of scientific computing, as the main algorithm of the SPH method is extremely well-suited for parallelization.
First thing to know about SPH is that it is a Lagrangian numerical approach, which stands in contrast to the more common Eulerian approach. The Eulerian approach is used in FE and FV methods where we choose a control volume/element and we track the changes of flow parameters in that control volume as a function of time. By doing so, from a purely mathematical reasoning, we introduce the convection term in the governing equations which is known to be troublesome in terms of numerical handling. On the other hand, the Lagrangian approach chooses to discretize a finite amount of the fluid itself, essentially creating a particle which has its own mass, volume, and thus density, and also it has its pressure and velocity fields. In the Lagrangian approach, we ride along with the particle and track its instantaneous properties in time (e.g. velocity, pressure…). By doing so, we get rid of the convection term in the governing equations, making coding quite a bit easier. Another, and probably more important consequence of the Lagrangian approach, is that it is a meshless approach, implying extremely reduced pre-processing time.
nanoFluidX and Oiling Simulations
nanoFluidX (nFX) is a state-of-the-art SPH solver for ultra-fast, weakly-compressible, multi-phase flow simulations of complex geometries, developed by FluiDyna GmbH. The weakly-compressible formulation implies that all incompressible fluids are approximated to be able to compress by a specified margin (usually 1%). This makes the solver fully explicit, while maintaining reasonable time steps and stability. Because of the fully explicit solver and limited range of the kernel function (smoothing length), the code is able to harvest the vast GPU power with extraordinary efficiency.
Which brings us to the point – when it comes to complex moving geometries, such as the ones encountered in common powertrain assemblies, there are few, if any, simulation tools on the market that can compete with the speed and simplicity of nanoFluidX.
Oil distribution in an engine spinning at 9000 rpm? No problem. Gearbox or a differential at several thousand rpm? Not an issue. Planetary gearbox? Sure. Ah, yes, you would say, but only for 3 revolutions. What if we told you that with nFX you can simulate a few to several seconds of physical time, spinning at thousands of rpm in a matter of a week or so?
On top of that, remember that nFX is an SPH code, so there is no mesh. In our official training for the nFX code, we cover entire pre-processing in a single morning. Since nFX is meshless and there are no refinement zones, all you essentially do during the pre-processing is select the CAD elements and click “generate particles”. That is how easy it gets.
A commonly asked question is “can nFX do lubrication?”, as in resolve thin (sub-millimeter) oil films during the simulations. In theory, this is possible, however in practice it requires unreasonably high particle resolution. On the other hand, you could resolve the thin films if you would zoom-in on a certain detail within the geometry and simulate it separately (sub-modelling). We therefore like to emphasize that nFX is meant for simulation of macroscopic oil flow in powertrain components, rather than use the buzz-word “lubrication”.
Oil distribution and flow structure resolving is just one of the results nFX is able to output. What nFX also generates are the torques and forces exerted on the solid components by the present fluid (oil) during operation. This is particularly useful for analyzing oil churning losses and optimizing the level of oil in the sump.
As it is not enough, nFX also includes heat-transfer capabilities and the upcoming v1.04 (end of Q1 2016) will furthermore include temperature-viscosity coupling models for the accurate representation of oil in temperature-dynamic environments.
Where can you purchase or inform yourself further on nanoFluidX?
Altair is the exclusive distributor of nanoFluidX. nFX can be accessed either through the Altair Partner Alliance (APA) program, or purchased as a feature-based license independent from the APA program. Contact your closest Altair office for more information.
If you have more technical questions about nFX please visit www.nanofluidx.com.
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