RSM simulation
Hello everyone. I am using ANSYS CFX to do the simulations of the air flow in a simplified combustor geometry. I know that RSM is good for this simulation, but as you know, in ANSYS CFX, there are several types of RSM, like, LES, BSL, SSG. Could anyone tell me which one is most suitable for my case, i.e, which one is most accurate to get the results similar with the experimental results. Thanks very much for your help.
Eric 
Re: RSM simulation
Can anyone help me with this, please?

Re: RSM simulation
Hi Eric,
The RSM models you mentioned (RSMSSG and RSMLRR) differ in the closure approximations used in the reynolds stress transport equations. LRR uses a linear relation for the pressurestrain correlation, which is only valid for small turbulence anisotropy. SSG uses a nonlinear relation and is more accurate (especially for higher anisotropy). Therefore RSMSSG should be your standard choice when considerin a RSMmodel. LES is a different story altogether as it is not a RANSmethod (reynolds averaged NavierStokes), but a filtering of the NS equations. Basically the eddies down to the size of the grid spacing are resolved directly, while smaller eddies are modeled. Employing this method requires an approach specific to LES (finer grids, smaller timesteps compared to RANS). Hope this helps. 
Re: RSM simulation
I'd like to add that RSMBSL might offer some advantages when flow separation is of major importance. RSMBSL is an SSTlike version of the stressomega RSM model (omegaequation based as opposed to epsilonequation based as the other models are), which is better suited to walltreatment.
As turbulence anisotropy is probably of more importance in a combustor geometry, I think SSG should still be your first pick, but you can always play around a bit to see the impact of the specific models. 
Re: RSM simulation
Hi Timon. Thanks very much for your kind reply.
I tried RSM SSG model, but the results do not converge, while if I use Kepsilon model, the results will become converged. As kepsilon is not very accurate and not good for the large recirculation areas prediciton, I cannot use kepsilon for my project. Can you help with me with this? Could you please give me your email address so that I could you write something more detaily and send you some files I have done. Many thanks Eric 
Re: RSM simulation
Hi Eric,
Convergence is always a bit more troublesome with RSM, as it is far more sensitive to the grid than 2equation models. A few tips:  make sure you have a very good grid (good quality elements)  restart from a converged SST solution  use local timestepping (gradually increase the timescale factor, from 1 up to about 5 more or less)  use first order discretization first and switch to second order when residuals become more smooth. 
All times are GMT 4. The time now is 09:23. 