In fluid dynamics, vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff (as opposed to streamlined) body at certain velocities, depending on the size and shape of the body. In this flow, vortices are created at the back of the body and detach periodically from either side of the body. See Von Kármán vortex street. The fluid flow past the object creates alternating low-pressure vortices on the downstream side of the object. The object will tend to move toward the low-pressure zone.

Also another example indicating the concept of vortex shedding like speed wind flows towards these chimneys vortex shedding occurs. This is a region of very low pressure that forces the chimney towards it. If the vortices that shed off the chimney have a frequency equal to the resonance frequency of the chimney then it starts swaying out of control.

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Dear Amir,

Use velocity monitors.

I don't think you can do that in Tecplot. What you need is to perform a spectral analysis in a combined way, that is in space and time. The spectral energy content in space can give an idea of the wavelengts of the vortical structures while the spectral energy in time can address the frequencies.

Filippo Maria Denaro Thank you so much for your timely response . I would really appreciate If you could provide a link of literature related to this technique or explain a bit further yourself as I am a newbie and don't really have the idea of that .

One would presume that you are using Ansys for your simulations. Whatever may be the method, from the velocity field you can obtain the vorticity field. Once you have the vorticity field, use tecplot to draw the iso-contours. You will clearly see the tip vortices, if it is not numerically dissipated. The Fourier-Laplace transform may show you multiple peaks and you would not know which corresponds to shedding.

Tapan K. Sengupta Thank you so much for your response .

I have already extracted the iso-contours and can see the tip vertices . I want to see the behavior of these vertices with time history . How can I do that ?

Plot the vorticity time series and use Fast Fourier Transform using ready to use softwares like MATLAB. This essntially, what Filippo Maria Denaro has already suggested to you.

Aamir Sultan

If you want to get a quantitative estimation the only tool is the spectral analysis as confirmed by Tapan K. Sengupta .

Alternatively, I can suggest a rough qualitative estimation. Load in Tecplot a sequence of 3D fields at several times (along a sufficiently long period of time to contain at least some turnover time). Then exctract the vortical structures from the lambda-2 option in Tecplot, create an animation fo the evolution of the structures and from that try to evaluate qualitatively the wavelenght and frequency of the largest structures.

Hi Aamir, I guess you did a time-accurate simulation, then what Filippo Maria Denaro and Tapan K. Sengupta suggested, doing Fast Fourier Transform of a representative parameter such as velocity or pressure at one or several selected probing point in the vortex field, would be the best approach as far as I know.

The following is just for your information. In your future research, however, you may want to take a look at the Fourier-based Harmonic Balance method (also called the time-spectral method in the literature) to deal with time-periodic problems such as your case here. This approach is a reduced-order modeling in time domain. It can convert the unsteady, time-periodic problems into mathematically steady ones and compute directly the desired final periodic pattern with out going through the long initial transients as usually encountered in traditional time-accurate analysis. As a result, this approach is much more efficient. Moreover, if the frequency in the system is unknown beforehand, one can use a frequency search technique (usually an optimization approach based on the flow governing equation) to drive the frequency value to converge as a part of flow solutions. For this point, I recommend the following papers that have discussions of harmonic balance frequency search for CFD simulation:

Ekici and Huang, Conference Paper An Assessment of Frequency-Domain and Time-Domain Techniques...

Hall et al: Article Harmonic balance methods applied to computational fluid dyna...

Also works that have harmonic balance frequency search for aeroelastic problems (flutter and limit cycle oscillations):

Ekici and Hall: Article Harmonic Balance Analysis of Limit Cycle Oscillations in Tur...

and my papers with Ekici (systematical development of the above original idea of Ekici and Hall):

https://www.researchgate.net/project/Aeroelastic-Solution-Techniques-based-on-the-Harmonic-Balance-Method

Hope this is not too lengthy, Good luck!

Hang Li Thank you so much for such a detailed answer . I will definitely go through the resources that you have mentioned in your answer to get better grip of the topic . .

Aamir Sultan You are welcome! and wish all the best to your research!

In fluid dynamics, vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff (as opposed to streamlined) body at certain velocities, depending on the size and shape of the body. In this flow, vortices are created at the back of the body and detach periodically from either side of the body. See Von Kármán vortex street. The fluid flow past the object creates alternating low-pressure vortices on the downstream side of the object. The object will tend to move toward the low-pressure zone.

Also another example indicating the concept of vortex shedding like speed wind flows towards these chimneys vortex shedding occurs. This is a region of very low pressure that forces the chimney towards it. If the vortices that shed off the chimney have a frequency equal to the resonance frequency of the chimney then it starts swaying out of control.

You may refer to the following cites :

References