# periodic boundary conditions setup

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 October 18, 2007, 06:31 periodic boundary conditions setup #1 studentcfd Guest   Posts: n/a dear all, i want to solve flow through axial flow propeller,with six no of blades.I am using bladegen for blade geometry,turbogrid/icem mesh tools are available. Previously i was modelling a full 360 degree case with rot domain size extended by 5 mm both towards in and out,which have a fr rot interface in between for the furher stationary domains. But it is very time consuming process.Thats why i would like to know abt how should i set my b.c.for a periodic setup.i am trying with following condns,are they right? 1.mesh in t grid with periodics size of default 2.extended in and out with(1/6 volume of a pipe)icem mesh. 3.1/6 mass fow at out 4.1/6 tot pre at inlet 5.per interface both in stationary as well as rot dom. Whether default size choosen by bladegen for periodics and inflow,outflow of a rot domain should be kept or we should modify them and how? Anyone who have tried periodic conditions,pls help?

 October 18, 2007, 06:45 Re: periodic boundary conditions setup #2 Anantha Guest   Posts: n/a Hello, You can take one blade sector for the propeller. In your case it will be 360/6 = 60 degree sector. 6 here is the number of blades. You can apply interface between the propeller and the rest of the stationary domain. Apply periodicity BC to the periodic faces of propeller. This is a straight forward job in CFX. For the rest of your stationary components, you can either choose to go for the sector or full model depending up on the geometry. If it is simple pipe, you can take sector for that too and even you can take a sector any small values like 1 degree sector. Make sure that you have maximum overlap of area between the interface regions. For the boundary conditions: If you are using mass flow BC, you have to scale down to the correct value for the sector. But for pressure never scale down. Pressure is always same on a boundary and does not change according to the boundary area. Hope this helps. Regards Anantha

 October 18, 2007, 08:46 Re: periodic boundary conditions setup #3 studentcfd Guest   Posts: n/a Thanks Anantha. its right we must have same pressure and sector mass flow. Now with the size of rotating domain,how should we choose it? is there any experience based/thumb rule to decide its size,both with periodic and and a 360 degree case? Really a confusing issue for me untill now. Thanks in advance.

 October 18, 2007, 09:38 Re: periodic boundary conditions setup #4 Anantha Guest   Posts: n/a Are you mentioning about the number of blade passages to be modeled? About what selection are you refering to? Anantha

 October 25, 2007, 01:38 Re: periodic boundary conditions setup #5 studentcfd Guest   Posts: n/a Hello anantha! I was asking about the size of rotating domain. This is a axial flow propeller case,so if I goes with ICEM mesh,I will have a pipe with its dia +2 mm of tip dia. But what about width of that pipe which i m going to define as a rot domain?What should be its extension length from leading as well as trailing edge (i.e in upstream and downstream direction)? Thanks in advance.

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