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 K.L.Huang March 25, 2000 07:04

question

Hi.

Sorry for my poor English,at first.

I have some question about CFD.

1.I have built a model with Tet mesh, but I find it's very difficult to converge, even I solve it by SIMPISO method. But when I reduce the relax factor of velocity(0.125) ,pressure(0.1) ,TE(0.25) , and temperature(0.8), I find it converge slowly.So my question is what is the function of relax factor? and such a low relax factor will affect the solution or not?

2.In the issued news of Star-CD, they say that they have solved the Coal combustion problem. How do they treat the fine coal particle. According to the tutour 9.5 and 9.6, the two phase lagrange method were introduced in case of C7H8, but in case of C, I think there is no such a evaporate pressure and the liquid phase, how do you solve such a question in droplet method?

3.Continue question 2. If I try to solve coal combustion in Euler method. That is, I treat the Coal as scalar(fine coal particle is conveyed by air), how do I set up the boundry condition.

K.L.Huang

 Peter Stephenson March 29, 2000 04:57

Re: question

I have had some successes with coal combustion in v 3.050 but I haven't yet had any success with v 3.100A. CD staff are helping me with this. The particle initial sizes are specified as part of the 'droplet parcels' initial conditions. The theory is in chapter 10 of the v 3.10 Methodology manual.

I have also written a very simple Euler coal combustion model (also in v 3050) and got it to work (by using some user-supplied subroutines). The coal appears as a scalar, so you just specify its inlet value in the usual way for scalar boundaries. If I remember correctly, I had to write my own subroutine for the density, to make sure that I had got an 'effective' density (ie allowing for coal and air or gas in each cell). That way, you also get the correct inlet mass flow rates for air and fuel.

I hope that helps

Peter Stephenson

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