hai, i am doing research on vortex shedding on cylinders,I want to find STROUHAL NUMBER using FFT in fluent.In literature St.no is 0.17-0.18. But my computation result shows 1.4-1.6. i attach my boundary conditions, Kindly take look at my work.if any mistake please correct the mistake.
Hi
this question is asked by me .
and i got this answer. i hope it will resolve your query.
Go to Plots>FFT
In y-axis function, select option MAGNITUDE
In x-axis function, select STROUHAL number
click on LOAD INPUT FILE,
by default the directory will be open, change the FILES OF TYPE option from INPUT SIGNAL FILES to ALL FILES,
then select Cl files (which is saved as cl-1-history by default)
Now simply click on PLOT FFT....
BEST OF LUCK
How to calculate strouhal number in flow behind square cylinder? - ResearchGate. Available from: https://www.researchgate.net/post/how_to_calculate_strouhal_number_in_flow_behind_square_cylinder#5619fd696225ff40e78b456e [accessed Oct 13, 2015].
Use the following deafult values in your analysis and try... you will get thye correct St..
density = 1.225000004381 kg/m3
viscosity = 1.71 × 10-5 Pa -s ------- you have used asDynamic Viscosity 0.000179 Pa·s
Kinematic Viscosity = 1.33 × 10-5m2/s
temp = 287 K
Cp = 1000
Cv =716
gamma = 1.40
Hello,
The enclosed file does not show you FFT procedure. The numerical part seems to work well; but, this difference may be occurred to signal definition of FFT procedure. Please describe better how you define signals and FFT in Fluent.
Hello,
I recall that the St is dimensionless, and it uses the cyclic frequency (not the angular frequency -- there is a factor of 2pi) . Make sure the 1.4-1.6 are as compatible.
In my point of view one of the main source of error is the use of Spalart–Allmaras (S–A) turbulence model (one equation). The flow structure for this problem is complicated and you need to use DES or LES. In addition, you should have y+ of nearly 1 and enough number of layers in the boundary layer around the cylinder.
Thank You sir @ Yasser ahamed.. Sir i have one more doubt in ansys work bench fluent. In Workbench Standalone Fluent LES and DES options are not available it available only in V6 version. But i had 14.5 Ansys. If there any options in 14.5 please let me know if any possibilities.Looking forward.
LES and DES will be available with transient simulations only ) in any version of Fluent). Simply, switch from steady to transient simulation and the turbulence models will appear.
OK Sir, But my doubt is when i using this conditions
Type :Pressure based
Time :Transient
Model :viscous laminar
This is LES or DES.. Please clarify me sir.Looking Forward thank you.
i go through your ppt. i found that you use actual value of density, cp and other fluid parameters. Instead of going through that you select density=1, velocity=1, dia=1 and dynamic viscosity=1/Re than it is very easy to simulate and do same in other problem. i don't know why you didn't get strouhal number correctly. You can use tecplot or matlab inbuilt function to calculate it.
Dear Rajasekarababu
Could I ask you how did you get the Strouhal number and frequancy of shedding as monitors for convergence history in your simulation?
Kindly could you tell me how can I get the FFT in fluent?
Thank you in advance for your help and good luck with your work.
Regards
Oula
Hi
this question is asked by me .
and i got this answer. i hope it will resolve your query.
Go to Plots>FFT
In y-axis function, select option MAGNITUDE
In x-axis function, select STROUHAL number
click on LOAD INPUT FILE,
by default the directory will be open, change the FILES OF TYPE option from INPUT SIGNAL FILES to ALL FILES,
then select Cl files (which is saved as cl-1-history by default)
Now simply click on PLOT FFT....
BEST OF LUCK
How to calculate strouhal number in flow behind square cylinder? - ResearchGate. Available from: https://www.researchgate.net/post/how_to_calculate_strouhal_number_in_flow_behind_square_cylinder#5619fd696225ff40e78b456e [accessed Oct 13, 2015].
Dear @ Chirag Patel
I can't thank you enough, I am really grateful. Your answer was very helpful.
I had one small mistake which is I forgot to tick the WRITE option when setting up the Cl monitors and in turn I couldn't get the " cl-1 history". But now everything is fine.
Thanks again I wish you all the best
Regards
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