# PDF approach (urgent!!!)

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 September 23, 2003, 14:50 PDF approach (urgent!!!) #1 anand Guest   Posts: n/a hello, my problem is combustion (PDF approach)in a duct that contains a bluff body. At the center of the bluff body, fuel jet will enter the duct. I am using Fluent for this model. Since there is different inlets for fuel and air with different velocities, I want to know how to give the fuel inlet without using injections. Thanks in advance.. waiting for a quick reply

 September 24, 2003, 09:25 Re: PDF approach (urgent!!!) #2 Ale Guest   Posts: n/a You should be able to define two different velocity inlets for the fuel jet and the air stream (you have to do this when building your grid), so that you can define different velocities for the two inlets. Regards, Ale

 September 25, 2003, 14:30 Re: PDF approach (urgent!!!) #3 anand Guest   Posts: n/a thank you sir, i have builded the grid accordingly. but my problem is how to give fuel inlet,bcos only one fluid (air)available in the material panel.i want to use prepdf combustion modelling(without using injections). regdas anand

 September 26, 2003, 03:21 Re: PDF approach (urgent!!!) #4 Ale Guest   Posts: n/a When you use the PDF approach, you have to build the look-up table by prePDF and generate a .pdf file. When you have loaded this file, a new material (pdf-mixture) is available. Then you can set different boundary conditions for the two inlets of your domain (the air stream and the fuel jet): you have to set the different velocities and the mixture fraction and variance. Usually mixture fraction = 1 for the fuel and 0 for the oxidizer. I hope this helps. Regards, Ale

 September 26, 2003, 06:52 Re: PDF approach (urgent!!!) #5 anand Guest   Posts: n/a thank you sir, i will try this sir. in my case fuel is ch4/h2. how to give this. sir i have onemore doubt regarding the mixture variance. i understood the mixture fraction . i don't know about variance . can you plz explain me. thank you anand

 September 26, 2003, 07:30 Re: PDF approach (urgent!!!) #6 anand Guest   Posts: n/a Hi Sir, I have created the pdf lookup table. and i have activated non-premixed combustion and i read the pdf look table. than i have given mixture fraction 1 for fuel and zero for air .i have given two different velocities(fuel and air). than i iterated . solution is diverging and giving the folloeing msg. Error: divergence detected in AMG solver: enthalpy Error Object: () can you plz check and tell me sir regards anand

 September 26, 2003, 09:05 Re: PDF approach (urgent!!!) #7 Ale Guest   Posts: n/a Hi, the fuel can have any composition, you just have to define it in prePDF before computing the look-up table. What kind of table did you choose? Adiabatic or non-adiabatic? Did you receive any warning or error message during the computation of the look-up table? I think you could stard with the adiabatic table (so that you don't have to solve the energy equation). Regards, Ale

 September 26, 2003, 12:10 Re: PDF approach (urgent!!!) #8 anand Guest   Posts: n/a basically system is not adiabatic. now i will use that adabatic. and i have doubt on mean mixture fraction for fuel. how much i have to give. regards anand

 September 26, 2003, 12:32 Re: PDF approach (urgent!!!) #9 Ale Guest   Posts: n/a The b.c. for fuel mixture fraction at the fuel inlet is one, if you have defined for the fuel its real composition. Regards, Ale

 September 27, 2003, 00:29 Re: PDF approach (urgent!!!) #10 anand Guest   Posts: n/a thank you sir. regards anand

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