[Turbulent]

Hello,

I want to build accurate mesh for flow past a circular cylinder at low Reynolds number (about 100-200) in order to study vortex shedding.

Does anyone have good guideline to create mesh for this particular case: mesh form, required cell sizes, distribution around the cylinder etc.

thanks,
Jack

[iilw1314]

hi ,you may use concentric circle around the cylinder ,so you will get a round zone.or you can use rectangle zone ,41x31 should be ok,and put the cylinder in the rectangle,the location should be (11,10.5),and creat boudary layer mesh around the cylinder ,if your grid is structured you should do more work and if your grids are unstructured it is very easy.above is used for FVM,if you use FDM,it seems much easier.

[Turbulent]

anymore specific guidelines?

[iilw1314]

hi guy,the problem you are doing is very like mine.my RE=150,M=0.2.and in my case,the net in the boundary is about 0.01D(D means diameter)and the nets around the circle is nearly squared.and the boundary layer is about 0.5D,my case uses unstructured grids.and can you tell me what kind of grid is in your case?maybe we can contact more ,that will be helpful to each other,my email:linjiany@mail.ustc.edu.cn,

[rishitosh]

hiii..

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....?????
-Rishi

[cfdnewbie]

You have already posted your question in another thread. Please do not double-post.
Regarding your question: I suggest you read up on how to do an FFT, or you specify what exactly your problem is....if you dont trust Fluents FFt to find the Strouhal number, thenexport the file and do the FFt externally!

[rishitosh]

hiii cfdnewbie..
sorry...

i trust but.. i m not getting hw to use FFT in fluent...
i m hvng record for coefficient of lift wid time....

plzzzzzzzzz....... help me..
its urgent..
can u give tell me steps....???
hw to get frequency..???? plzzzz...

[cfdnewbie]

Sorry, I have some trouble understanding your english, maybe you can get a friend to help you with the writing?
Here is what you should do ( ifyou want to do a FFT in matlab):
Export your data at equidistant interval nodes to a textfile.
Open matlab, either paste the data into a vector, or read fom file, then use the fft command, (fft) and plot the result over the associated frequencies. The Strouhal frqueny shouldstand out as a clear spike. It shouldnt take long, it is just a couple of lines in matlab.
Hope this helps!

[rishitosh]

hii cfdnewbie...

thnx for understanding my prblm and taking interest ..

i'll try dat in matlab..

thnx again...