How to apply velocity profile at inlet
 

Hi everyone,

I have done some measurement for velocity profile at the diffuser inlet and I would like to put the experimental data as the inlet boundary condition. Can you please advise me of how to do it quickly? I found similar example in the tutorial but it used the 1/7 power law formula rather than the experimental data. Can I input the values rather than the formula for the inlet velocity profile?

Thanks a lot, Sam.

Re: How to apply velocity profile at inlet
 

Yes, create a profile boundary condition file and use that. The file format is pretty easy to create, it's a CSV file with a header.

Neale

Re: How to apply velocity profile at inlet
 

Hi Neale,

Thanks for your answer. Is there any example in the user manual? Shall be obliged if you can give me some quick references. I look at the Master Index but can't find the term CSV in there. Can I insert this file directly to the Pre? I'm using 5.7 now.

Thank you, Sam.

Re: How to apply velocity profile at inlet
 

Look in Solver Modelling -> Boundary Conditions -> Profile Boundary Conditions, I think. If not there should be a link to it in the CFX-Pre documentation.

You can load a CSV file for 2D and 3D profiles. If your data is just a 1D profile setup a 1D CEL interpolation function and just type in the data or load it from a file.

Neale.

Re: How to apply velocity profile at inlet
 

Hi Neale,

Thanks for your help. I'm almost there. Just one more question please.

I now specify the inlet axial velocity at the circular inlet cross section. Tangential & radial components are zero. Will that be okay if I only put two columns of data in the CSV file? ie. r[m] velocity w [ms^-1]

I don't need to include the theta in this case right?

Thanks again for your help.

Sam.

Re: How to apply velocity profile at inlet
 

Hi Neale,

May be I should be a bit more specified about my question here.

I assume the velocity profile will only vary with r at the moment. The two column CSV file should work right? Will CFX apply the same velocity at different theta automatically if I don't write any theta value in CSV file (I have this doubt because inlet cross section is 2D rather than 1D)?

This is the data structure that I'm going to use here: [Data] r [ m ], Velocity w [ m s^-1 ]

Once I have the velocity data with different angle, I will include theta in my CSV file. May I know what's the unit of theta in CFX5.7?

Thanks a lot for your advice. Cheers,Sam

Re: How to apply velocity profile at inlet
 

hey Sam the simple way is just ask CFX5.7 to write out a profile file at the section you want, and just used it to create your profile file. let say, you want to put it at a region called "inlet",

1. click file, export and under the type option select BC profile instead of generic or what have you.

2.select the parameters you want to appear inside your profile file.

3.then click okay.

Open the profilefile.csv to the format and the unit. You can then create the profile file .csv from your data using profilefile.csv as your template!!

regards

Re: How to apply velocity profile at inlet
 

You can use 1-D linear interpolation as you were trying, with extended minima and maxima. Two values of r and v(axial) should suffice.

R P

Can we import data in cyclindrical cord?
 

Hi all,

Thank you for your help. I can now import the profile data in cartesian coord. I have one more question about the profile bc:

If I have organised the data in 2D cyclindrical coord (i.e. r & theta(deg)). Is there any straight forward way to tell CFX about the angle? I use "theta []" as the variable name but CFX seems not able to recognise this variable. Is that because I didn't plut the unit for theta? How can CFX know the column "theta" is one of the coord for 2D velocity contour?

Please kindly give me some clue. Thank you, Sam.

Re: Can we import data in cyclindrical cord?
 

Should be possible, but you might need to set the domain up to be rotating. If it's not rotating but you just need access to cylindrical co-ords then omega = 0 is valid.

Re: Can we import data in cyclindrical cord?
 

Sorry, just checked and you don't need to create a rotating domain. Cylindrical velocity components are available as an inlet BC in a non-rotating case.

Hi,
My velocity profile changes with both time and r (=sqrt(x^2+y^2))
in other words, my inlet velocity is a function of r and t , u(r,t)
how can i define this profile that has two variables in CFX?
U = u(t) * (1-r^2)
thank you for your help.
Regards,
Hesam

This function should work fine as a CEL expression. Yes, an expression can have more than one input variable.