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 rashmi October 14, 2008 07:09

Urgent!!!!!

hi everybody, could any one tell me the method to calculate the boundary layer thickness for pipe model.

Thanks

With regards, Rashmi.R

 Prasad Dudhgaonkar October 14, 2008 07:27

Re: Urgent!!!!!

Do you mean inviscid Poiseulle flow in a pipe? If yes, for raduis R, displacement thickness = R/4 and momemtum thickness = R/12.

 dev.... October 14, 2008 07:29

Re: Urgent!!!!!

Hi, could you give more detail about the problem, like laminar/turbulent flow ?,r u considering Uniform inlet.

 rashmi October 14, 2008 23:15

Re: Urgent!!!!!

I have 3d rectangular pipe with an length 10m, width 7m and height 5m, in that air is flowing at 10,000 m/s, so its an turbulent condition. So pls now can u tell me how to calcuate the boundary layer thickness for my problem, so that i have to give this in Gambit software.

With regards, Rashmi

 Prasad Dudhgaonkar October 15, 2008 02:15

Re: Urgent!!!!!

Create a fine volume mesh for 10x7x5 brick. Mesh=>BL=>CreateSelect respective edges and directions.You'll have to play with b/a (1.2)and number of rows.(8) You may set depth of BL to 0.5 (turbulent flow has shallower BL). You don't need to have BL along the flow direction. Please keep number of mesh elements restricted to the economy of solution. I tried with the values I have given in the bracket, I could get a nice mesh with 51200 hex elements. You may need a finer grid.

Well, for your case the air flows through a big pipe at 3600 km/h... Mach No. = 30+! Very interesting. Anyway, Gambit doesn't worry about it! At least I guess so. I hope the above advice will help.

 rashmi October 15, 2008 02:38

Re: Urgent!!!!!

First thanks a lot for ur valuable time to me, actually dear friend i need to know how u calculated number of rows and growth factor(b/a) for my analysis. Could u pls tell me that one.

 devesh October 15, 2008 03:30

Re: Urgent!!!!!

Hi,

I think prasad is absolutly right. you have to play with Groth Factor & No. of rows. There is no exact method to calculate these factor, I guess!!!. It depends on your mesh requirement.

you put 1.2 in b/a pannel, then by guess put any value in No. of Rows box. Now select that face on which you want to BL mesh. you'ill find the idea how BL mesh works.Play with that & get the required mesh.

Is this a real case Problem, where Air Duct Flow with Ma>30, you are going to solve???

 Prasad Dudhgaonkar October 15, 2008 06:05

Re: Urgent!!!!!

Rashmi, you can refer to Modeling Guide=>Meshing the model=>Create boundary layer. Remember not to input 'First row'(a) while feeding other three parameter, I've mentioned earlier. With a little application of logic you'll realize that feeding all the four parameters will invite an error. Essentially it's about providing sufficient resolution of mesh in the area where boundary layer is supposed to be present. Large number of mesh elements will make the solution slower. And I am not aware where is focus your analysis going to lie during the computations, although my curiosity about it is infinitely aroused! :)Thanks Devesh for your comment.Best luckPrasad

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