I came across these terms in Ansys !
Hi all!I am working on my BSc thesis in computer science. It may sound strange, but the main topic is vehicle platooning. In the thesis, I also need to investigate the aerodynamic forces of vehicles in platoons; the drag force (and coefficient), especially. My physics background is really limited (just a 6 ECTS basic course); my math knowledge is basic too (Calculus 1).
I have been studying OpenFOAM, a popular CFD suite that allows to do so. OpenFOAM includes a tutorial that investigates the aerodynamic forces of a motorbike, which uses the k-omega SST turbulence model. It requires to set some parameters, such as k and omega. Fortunately, the OpenFOAM guide provides a method for their estimation. I used this setup as a starting point in "learning" CFD.
My geometry consists of of a platoon with two trucks and three cars with an inter-vehicle gap of 5 meters. The resulting mesh should be "enough" accurate. My primary computational resource is server with 8 cores and 100 Gb of memory. The mesh consists of 24 Millions of cells.This is an image of the geometry and resulting flow. This is a close view of the mesh (truck), and this is the added layer.
However, my results look a bit bad, or at least that's how I think they are.This is a logscale plot of the residuals (convergence process), and in my opinion they are high...Moreover, the force coefficients of the first car (third vehicle of the convoy) exhibit strange behaviors; whereas those of the second car look "smoother", just like those of the third one. I am not sure if this is due to the higher or lower turbulence that a vehicle suffers. In any case, shouldn't these coefficients "converge" in a "smoother" way?
During these CFD experiments, I had to google most of the things, because my field of expertise is computer science, and not fluid dynamics. As a result, sometimes I used some blind faith in setting the parameters, and it could really well be that this has affected the results :(To overcome this, I think that I need to acquire more knowledge of the various parameters involved. For example, everyone seems to agree that the Y+ values sho
... keep reading on reddit β‘I am currently working on a 2D RANS simulation with the k-epsilon turbulence model for wind turbine wake simulation. I implemented the transport equations for k and epsilon but stability for k and epsilon seems to be a problem. Are there any good resources for easy implementation on an evenly spaced grid using finite difference methods?
https://preview.redd.it/840x0k2s6f871.jpg?width=708&format=pjpg&auto=webp&s=be1ea0d478a360a1b16a5439cec5d9b41fc2840e
Hey guys! I'm trying find an explanation on why the turbulence damping parameter is by default set to 10! For what fluids is this correct? What happens if I increase it? Does anybody have any more information about this? Fluent's theory manual just states that the factor is by default set to 10, and nothing more! Cheers!
Plus is it possible to perform such modeling on Matlab rather than on Fortran/C++?
Hey there,
this might be a bit of a noob question concerning eddy viscosity RANS models.
A few months ago I heard someone talk about (unfortunately I can only recall from memory) talk about the theoretical differences between two- and one-equation turbulence models. While I am quite familiar with practical differences, e.g., between k-e and k-w SST or/and Spalart-Allmaras, and do understand that a two-equation model is typically better suited for (e.g.) adverse pressure gradients - I do not understand why.
That person said (freely quoted), that one equation models are inherently worse in modelling (the effect) of turbulence due to only one additional transport equation, and that at least two transport equations are required to actually model turbulence. I.e. one equation models are a bit of a botched job, which work in reality but are inherently worse suited.
Now, I'm trying to understand (if it's even correctly remembered by me) why two-transport equations are at least necessary and how that can be shown.
Thanks for your help!
I'm trying to simulate a turbulent flow via k-omega SST model. As a result, I got minimum value of yPlus at the wall equal to 24.7. As far as I know, this model could be implemented for yPlus in a range of [30, 300]. Will it be a correct solution to make the mesh at the wall finer, so that my first cell lies in the boundary layer and restart the simulation? Will the yPlus values increase then? If not, is it still OK to use this model?
Title. Why does changing the variable from energy to frequency have such an effect? Or it's just an empirical thing?
Thanks.
What type of model is SST K-Omega? E.g. Unsteady LES or Unsteady RANS? This is for Fluent 19.1.
There are many turbulence models, does anyone one has summarized turbulence model cheat sheet.
