# Unsteady Boundary Profile with data file

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 January 23, 2009, 10:32 Unsteady Boundary Profile with data file #1 Arianna Guest   Posts: n/a Hi there, I'm working with an unsteady case and I need to set some boundary conditions by using a file data, every line of this file should contain the flow time value and the linked boundary value. Is it available a function to load this file with somethingh like DEFINE_PROFILE, or I have to write some code on my own.. Any help will be really appreciated!!! Thanks in advance, Arianna

 November 4, 2009, 02:32 Unsteady Boundary Profile with data file #3 New Member   Join Date: Jul 2009 Posts: 7 Rep Power: 16 Hi, I have a similar problem. I am trying to solve a pipe flow problem in fluent 6.3.26. I have a transient pressure data which I read through file>>read-transient-table command. My question is, Does fluent read the time data according to the order of data given or does it read it according to the timestep I give? Ex: ------------- pre 2 5 0 time pressure 2 20 4 25 6 30 8 35 10 40 ------------- It is normal to give time step size (s) = 2 for this configuration, yet I start my iterations giving time step size (s) = 1, and it solves something. How does it solve it, does it interpolate? And finally, if I give time step size (s) = 4 will it take 25 Pa for the first time step? Thanks. akjha likes this.

 November 4, 2009, 06:53 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 If the transient table works like the profile, then fluent just makes linear interpolation. Since you don't give any value at time 0, I assume fluent will start at time 0 with a pressure of 0. Then between time 2 and 4, fluent rises the pressure from 20 to 25 (linear) So as you understand, it is not time step. There are just reference points. __________________ In memory of my friend Hervé: CFD engineer & freerider

 November 5, 2009, 03:52 Unsteady Boundary Profile with data file #5 New Member   Join Date: Jul 2009 Posts: 7 Rep Power: 16 Hi Max, Thanks a lot for your answer. It sounds very reasonable. It is probably the right answer to it yet, I wonder if there are any user manual/tutorial references to it. Btw, I crop my data according to the timestep I use, adding the zeroth timestep value of pressure to the beginning and solve my problems. But it is a long and clumsy way.

 November 6, 2009, 00:56 #6 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 Check Help Chapter 7.26.2 "Boundary Profile File Format". If the pressure doen't change non-linearly with the time step, you don't have to describe the profile with your time-step increment. If it is a long way, as you mentionned, you may try a udf for desribing your inlet BC (Chapter 8.2.1 Boundary Conditions from UDF Help) __________________ In memory of my friend Hervé: CFD engineer & freerider

 October 11, 2010, 12:10 setup local axis rotation for blades? #7 New Member   Dave Smith Join Date: Jul 2010 Posts: 27 Rep Power: 15 Hi I am trying to write a transient data file for rotation of helicopter blades (4 blades) inclined at a plane. The rotation needs to take place around an inclined planed so I have created a local axis in gambit at 25deg (with rotation about the z axis, so the y and x axis have moved out of poisition compared to global axis). So it has all been setup in gambit and the active axis is the local axis. But when I put this in fluent and install a udf for rotation about x axis it starts to rotate the blades around the global x axis rather than the local x axis which is what it should be using. I dont understand how to set in fluent that rotation needs to be around the local x axis? If I write a transient data file then I want to write something like this sampledata 10 1 time thetax thetay thetaz 0 0 0 0 1 4 25 0 2 8 25 0 and so on I have only selected 25 for theta y as the inclined plane is 25deg to the vertical axis, is this the correct way for writing this file? Please advise Any advice regarding this would be helpful Dave

 October 12, 2010, 02:01 #8 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 if you only need the local axis, then translate and rotate your domain untill local axis reach global one. For instace if your local axis has a translation vector (1 0 0) and a 45°-rotation about (0 0 1), then move all your domain with translation vector (-1 0 0) and a 45°-rotation about (0 0 -1). Just check that origine (0 0 0) match origin from your "previous" local axis __________________ In memory of my friend Hervé: CFD engineer & freerider

 October 12, 2010, 05:01 #10 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 post a sketch because it's hard to imagine... Fluent recognizes (as far as I know) only the global axis in gambit. So if you only needs the local axis, move your domain untill the top-level axis (global) matches your local one. In other words, if you need 2 differents local axis, then I don't know. But maybe there are workarounds, like moving your domain during post-processing. (compute force with global axis, then translate/rotate your grid and re-compute force on your other body) __________________ In memory of my friend Hervé: CFD engineer & freerider

 October 20, 2010, 10:04 rotation about local axis #11 New Member   Dave Smith Join Date: Jul 2010 Posts: 27 Rep Power: 15 Hi Max Sorry I have replied late. I have tried rotating the grid in fluent but unfortunately by rotating the grid the global axis remains constant and any rotation you chosse about the x axis will be performed around the global x axis. What I want is that a local axis is created at an inclined plane(rotate global z axis by 30deg) and a local axis is now created. This does not happen by rotating the grid using fluent options. I have attached a picture, what I want is to rotate the helicopter blade around the X1 axis (red axis, as this is the inclined plane). The first image(left side) shows all the blades on the x axis, the second image is more clear as it just shows one blade, now this blade needs to be rotated around the local X1 axis only, and it will then be rotating like a helicopter blade but at an inclined plane. My question is how can I create this in fluent as everytime I incline the plane to create a local axis this does not work, thus I can try and use the global axis which fluent works in and have a transient boundary profile like that shown below. But I need to have components of theta_x , theta_y and theta_z. For global axis sampletransient 2 4 1 time theata_x theta_y theta_z 0 0 0.01 0.5 30 0 0.02 1 30 0 0.03 1.5 30 0 etc (theta_y has 30deg so that the plane can be continuosuly inclined at 30deg) Can a transient boundary profile be setup like this? Or if the local axis can be setup I can have something like this, shown below (but the transient boundary profile may not be written in the correct format as I do not know how to introduce variable theta _x, theta_y and theta_z. For local axis sampletransient 2 4 1 time theata_x theta_y theta_z 0 0 0.01 0.5 0 0 0.02 1 0 0 0.03 1.5 0 0 etc Can something like this be written, how can I put the theta values in a transient profile, an example is given for crank angle but how can you display the theta values in the transient boundary profile? Can anyone offer any help aswell?

October 20, 2010, 10:07
#12
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Dave Smith
Join Date: Jul 2010
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P.S I am sorry about the very long message above I wanted to be as clear as possible pictures are attached to this post
Attached Images
 rotor blade.JPG (29.9 KB, 88 views)

 October 22, 2010, 02:15 #13 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 I never did that, and maybe there is a trick (which I ignore) But I would split your calculations in 2 phasis. First you compute with blades rotating around x-axis (end of first calculation) Read case and data at latetest Timestep, and rotate the grid as I mentionned earlier (don't know where is the problem). So you go in Grid/rotate, and set the rotation around z-axis (according to your sketch). Now your axis is (O x1 y1 z) Second you compute with blades rotation around the new x-axis (x1 in your sketch). __________________ In memory of my friend Hervé: CFD engineer & freerider

 November 10, 2010, 13:41 #14 New Member   Dave Smith Join Date: Jul 2010 Posts: 27 Rep Power: 15 Hi Max I have left the other problem for now as it is taking a long time to solve. I have another question. I am using dynamic meshing for my rotor blade, can I use dynamic meshing in Fluent for a structured grid? If yes, what type of structured grid would work? Also is layering and remeshing required if I use a structured grid? The mesh will have to remesh is this even possible in fluent to remesh a structured grid? In addition does it matter which software I use to grid my model, I usually use Gambit or Turbo grid? And as a questions for CFD physics, what are the actual advantages of using a structured grid compared to an unstructured grid? Thanks Dave

 November 11, 2010, 01:43 #15 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 smoothing and remeshing can only be used with tetra. You can use Layering with hexa (or wedge) ... advantage of hexa: more accurate, and generally hexa-grid will ask less cells in comparison with tetra disadvantage: will ask more time to generate the grid __________________ In memory of my friend Hervé: CFD engineer & freerider

 November 11, 2010, 09:53 #16 New Member   Dave Smith Join Date: Jul 2010 Posts: 27 Rep Power: 15 Hi Max I have another question. I can write a UDF for the 4 blade rotor motion which is fine and the forces produced are good, but there is also methods for transient table or profile that can be used. When I put a column for time and another for theta_x (as rotation is about the x axis), the forces produced for this simulation are not good at all. Thus the forces produced for the UDF simulation are good and using the same parameters and settings, the forces produced whilst using transient table or profile are not good at all, they actually look completely wrong. Have you ever encountered this? Please advise what I can try, and what I may be doing wrong. Thanks Dave

 November 12, 2010, 01:14 #17 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 no idea since I don't have your data. You need to investigate. are your pressure distributions on blades ok? compare your wrong values, with the right ones (but computed in the global axis) etc... this is debugging and it's a part a CFD __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 27, 2012, 22:06 Please help me #18 Member   Join Date: Jan 2012 Posts: 58 Rep Power: 14 hello, i am working on fluent 6.3.26 , i am trying to solve the unsteady problem of train moving in tunnel. i am not able to solve that . can any body help me . my email is sheikhnasir39@gmail.com thanks

August 6, 2012, 21:09
Requesting help in Fluent
#19
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MINNESOTA
Join Date: Aug 2012
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Hi Max

I have a data set in excel and I would like to have this data as a boundary condition of one of walls as a input flux. I'm a beginner in Fluent and I don't know ho to rite a UDF or create profile, Could you help me with this problem,Thank you so much.

Quote:
 Originally Posted by -mAx- post a sketch because it's hard to imagine... Fluent recognizes (as far as I know) only the global axis in gambit. So if you only needs the local axis, move your domain untill the top-level axis (global) matches your local one. In other words, if you need 2 differents local axis, then I don't know. But maybe there are workarounds, like moving your domain during post-processing. (compute force with global axis, then translate/rotate your grid and re-compute force on your other body)

 August 7, 2012, 01:25 #20 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41 check online help http://aerojet.engr.ucdavis.edu/flue...ug/node303.htm __________________ In memory of my friend Hervé: CFD engineer & freerider