# Translational Boundary Conditions along with Rotational Periodic Boundary Conditions

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 July 27, 2016, 14:25 Translational Boundary Conditions along with Rotational Periodic Boundary Conditions #1 New Member   ishan Join Date: Mar 2016 Posts: 1 Rep Power: 0 I have made an parametric finned tube CAD model in ANSYS Design Modeler. My goal is to study the pressure drop in the tube for different combination of number of fins, fin height and fin width. The internal fins have a certain helix angle and there are a number of fins. The tube has one inlet and one outlet. Since the fins are arranged in a helical pattern, a single helical strip of one helix pitch length is to be modeled. I can understand that a transnational periodic boundary condition can be applied between the inlet and outlet of one strip of the fin, but I am not sure as to how would the sides of the fin can be modeled. I have one reference where he applies rotational periodicity to the sides of that one single strip.I went ahead with the reference, but I got absolutely wrong results. The pressure drop was of the -10^4 order,which is not even close to the reference measurements. The residuals were close to 10^-6 for all the equations.I am using 4 mesh interfaces;2 for connecting inlet and outlet and 2 for connecting the side faces of the helical strip. I applied the periodic conditions through "Mesh Interfaces" option in Fluent,however I got a bit confused when a started to input the "mass flow rate" in periodic operating conditions.There was only periodic operating conditions input, so for which PBC I was entering the mass flow rate-rotation and translational ? The model being used is RANS SST k-omega. I also went through the "periodic repeats " option thinking that I have two periodic zones adjacent to each other, but it's usage was for something completely different. Also,since I have gone into a considerable detail, I also want to know whether it's possible to have mixed type boundary conditions ,for example, can I have translational and rotational boundary conditions on two faces of an hellical geometry, such as this pipe?

 March 6, 2017, 02:30 #2 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 227 Rep Power: 11 Dear Bluemans I hope you must be doing good. Exactly, exactly, I am also facing the same problem . I got two boundary conditions (in fact 4) two inlet and outlet and two rotational. Upon a number of posts sent on CFD-online I got now reply. So I just modled one strip with rot. periodic only and with whole pipe length. So i put velo.inlet and pr_outlet. Of cousre, this increased the mesh size a lot but I had no other option. Right now, my PC can handle upto 3.5 million successfully. Have you come up with a solution for this yet?

 Tags fluent, parameterization, periodic conditions

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