vortex shedding frequency
i am working on flow around a circular cylinder of diameter 2m using OpenFOAM 1.4.1 and 1.5 versions past 1 month. I am getting pressure and velocity contours correctly in both the versions.I am facing difficult to get the vortex shedding frequency in OpenFOAM.
Can you please suggest me how to get the strouhal number and vortex shedding frequency in OpenFOAM 1.5.
Flow conditions (laminar flow):
Reynolds number---------> 150 (based on cylinder diameter)
viscosity------>0.01333 m2/sec(based on cylinder diameter)
diameter of cylinder--------> 2 meters
OpenFOAM version-------->1.4.1, 1.5
can you please give me a suggestion how to get these values using the probes function and FFT.
waiting for your response
Please correct me if I am wrong.
You can catch the time series data for Cd or Cl and use FFT to get the spectra to identify the St.
vortex shedding frequency
Thanks for your reply..........
I have successfully completed that work 1 month back using OpenFOAM...anyway thanks for your kind response...
FFT for a sound spectrum
I read you are talking about FFT from probes. I would need this for my case.
How do we proceed FFT in OpenFOAM, or is there any documentation I could find on this?
hi all of foamers,
can any one tell me how to calculate strouhal number or shedding frequency?
( OF 1.5-dev)
waiting for your response...
You could proceed as described in the following paper:
Bohorquez, P., Sanmiguel-Rojas, E., Sevilla, A., Jiménez-González, J., Martínez-Bazán, C. Stability and dynamics of the laminar wake past a slender blunt-based axisymmetric body. Journal of Fluid Mechanics (in press)
hi dear pbohorquez
thanks for your paper atachment, i think that it is very helpful for me but :
i am working on flow around a circular cylinder of diameter 0.025 & Re=150 using OpenFOAM 1.5-dev versions & get pressure and velocity contours correctly,
i have two question:
1) when i want to calculate Drag and lift coeff with add a related code to controlDict, the answer of this work not validate. why??:(( answer of drag is very low, while drag in Re=150 must be nearly 1)
2) how can i calculate vortex shedding frequency
3)if have another related refrence for my work, i am very glad that atached link for me
i chose this parameter for calculate cd & cl =>
liftDir=(0 1 0)
dragDir=(1 0 0)
tank a lot
To compute the St number you should include in the controlDict the 'sets' and generate during the numerical simulations the samples of the velocity field at the point you are interested in. Then read the information you generated with some software. I employed Matlab to read the data and ezfft to compute the Fourier transform.
I did not calculate the Drag and Lift, so I can not help.
flow around cylinder..
i m also new in dis CFD area...
i m working on flow over two side by side cylinders... @ Re= 100 and 200..
i got good results..
but i want to find out Strouhal number for all cases...
i came to know by finding shedding frequency with help of FFT, using cofficient of lift data, in fluent 13.0 we can calculate Strouhal number...
but i m getting helpess..
how to use FFT to find shedding frequency....????? :mad::confused:
Hi dear all,
Rishitosh, did you find how to compute the St nmbr ?
any one find the answer? Provide me please. How to add ''sets'' in controlDict file and using fft?
Any answer will be appreciated.
Based on my experience in sampling the wake to get the Strouhal number in OpenFOAM, the best way to do it is to compute the velocity spectra at certain points in the wake. I prefer to use points in the separated shear layer (the regimes I've studied are Re > 10K) but it depends on your case. I've tried using Cd and Cl but these methods seem a bit less optimal in finding all of the relevant frequencies.
1. Use the controlDict 'probes' feature to get a time history of your instantaneous velocity. You'll want to sample at every timestep.
2. Subtract the mean from your instantaneous to get U'.
3. Feed your U' history into a program like MATLAB. I find that the plomb() function gives best results, but there are others.
4. The result gives you a spectra in wave number space, which you will have to convert into frequencies.
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