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-   -   urgent! amplitude and frequency (http://www.cfd-online.com/Forums/fluent/41449-urgent-amplitude-frequency.html)

Sheila June 20, 2006 08:00

urgent! amplitude and frequency
 
Hi! My name is sheila. I'm simulating unsteady vortex flow over circular cylinder. I want to variate the amplitude of sinusoidal movement. Does FLUENT automaticly generate sinusoidal function or I can define it externally? Is there any other way to variate the amplitude? Can somebody tell me about the vortex flow characteristics related to frequency and amplitude of vortex shedding variation? For example, when the frequency increases whether Cl also increases or decreases?

thank you very much I really appreciate your help

ROOZBEH June 21, 2006 03:54

Re: urgent! amplitude and frequency
 
Dear Sheila; With "dynamic mesh" model of FLUENT6.1, you can simulate the unsteady flow field around and oscilating cylinder. You can vary the amplitude and frequency of cylinder oscilation. But if you want to simulate the unsteady flow field around a fixed cylinder (including the vortex shedding), you can vary the amplitude and frequency of this shedding by varing the Reynolds number. I think that increse of vortex shedding frequency, leads to increase of amplitude of variable lift coefficient. Hope this help you,

ROOZBEH.

Sheila June 22, 2006 03:29

Re: urgent! amplitude and frequency
 
Dear Roozbeh, thank you for your answers I have some other questions, I hope you can help me. I'm simulating unsteady flow field around fixed cylinder (vortex shedding). I follow the steps from studentfluent journal and I get a sinusoidal graph between Cl and time. How FLUENT generate this graph? Where can I see the formula that FLUENT use until the graph generated? can you tell me some great papers to read so I can understand more about vortex shedding. I'll have a presentation on Tuesday next week. Thank you

ROOZBEH June 22, 2006 11:23

Re: urgent! amplitude and frequency
 
Hi; Unfortunately FLUENT can not draw a curve that shows variation of a parameter vs. time. You have to read the value in each time and finaly draw the curve by another software like Excel. Vortex shedding phenomenon is usually describe in fluid mechanics books. You can search about this phenomenon in the web. This phenomenon is an unstability that occurs in the flow field as a result of even a very very little asymmetry in the flow pattern. In several Reynolds numbers, this asymmetry can not lead to unstability but in several another Reynolds numbers, this can do it. In the numerical simulations, this asymmetry can occur as a result of round off error and you should wait until this error becomes high enough to cause unstability. Hope these help you,

ROOZBEH


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