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-   -   Erosion modelling (http://www.cfd-online.com/Forums/fluent/105891-erosion-modelling.html)

 Ugo August 11, 2012 20:21

Erosion modelling

Hi everyone, I really need help with my erosion model.. I am using the k-omega turbulence model, and if I dnt specify a discrete phase, it converges. But once I specify a discrete phase, it never converges, and continuosly says turbulent viscosity greater than 1e+5...

secondly, i have to verify that my results are correct. can anyone help me with coefficients commonly used in ersosion models and data to prove their validity...

Thanks

Ugo

 CFD-student August 16, 2012 05:15

Hi Ugo,

Regarding your first question, are you trying to simulate the particles in a 1-way or 2-way coupled fashion? Usually turbulent viscosity limitations stems from low quality meshes or ill defined turbulent boundary conditions.

Regarding your second question I would recomend you to use one of the main erosion models for example the model proposed by DNV, det norska veritas in their report DNV RP O501 which you can obtain for free. Their model is claimed to be experimentally validated for sand impingement in hydrocarbon mixtures.

 Ugo August 16, 2012 05:43

Hi CFD-Student,
Thanks for replying. its actually a 1-way coupled erosion by fly ash in preheater tubes. I cant seem to find a way to relate the values i get in FLUENT, to an empirical formulae. I model with impatc angles and coefficients, and discovered that maximum erosion occurs at tthe 35 degree angle. but then how do I validate it with the empirical formulae.

Thanks once again.

 CFD-student August 16, 2012 05:55

Np at all,
If you are employing a 1-way coupled simulation. Then you first solve the flow field without specifying the discrete phase. Thereafter you implement the discrete phase but you dont start any iterations via the solver. You just go the report > sample and then sample the erosion. Particle trajectories are calculated on the already resolved flow field without updating the solution.

While the erosion process is highly complicated, empirical formulae often just predict the maximum erosion rate in for example en elbow but dont give any information about the location of maximum erosion. The advantage with CFD is that you can get this kind of localized information. The maximum erosion rate you obtain should be bounded by the values you get from empirical formulae. Keep in mind that erosion modeling is highly complicated and often results only with an accuracy of one order of magnitude can be obtained. Due to this correlations are often highly conservative.

 Ugo August 16, 2012 06:11

Hi
When i specified it, it just gave me "number tracked = 690, escaped = 690, aborted = 0, trapped = 0, evaporated = 0, incomplete = 0" and nothing more, I didnt get a particle trajectory data impact angle data.
Do I have to specify things like wall boundary conditions, I used coefficients from Tabakoff from a tutorial I saw online, and an injection velocity of 4m/s. I dnt really know if I am doing the right thing....If it would not be too much hassle for your, could you give me a step-by-step approach to how this is done. There are quite a number of values I have to specify, and I do not know if in the 1-coupled mode, they are required, e.g particle diameter, total flow rate etc... Thanks, I am really grateful

 Ugo August 16, 2012 06:20

Hi CFD-Student, I forgot to add my email address, ugocpu@yahoo.com. Please if you have anything that could help me out, especially in the process of 1-way coupled simulation, please do send it... How do I actually obtain the impact angles of the ash particles?

Thanks kindest regards

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