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Steady behavior prediction from unsteady data !!

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Old   November 18, 2005, 15:44
Default Steady behavior prediction from unsteady data !!
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Mamun
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I heard that quasi-steady analysis could lead to the prediction of the unsteady flow behavior. But is it possible to predict the steady-state behavior from the unsteady analysis ? How ? Thanks a lot for your attention.
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Old   November 18, 2005, 17:19
Default Re: Steady behavior prediction from unsteady data
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Mani
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Sure. If there is a stable steady-state solution to the physical problem, even an unsteady simulation will settle on that steady-state allowing for sufficient time. Some simple steady-state computations are nothing but accelerated unsteady computations to get quickly to infinite time.
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Old   November 19, 2005, 08:44
Default Re: Steady behavior prediction from unsteady data
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Mamun
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Thanks a lot for your comments. I have the computational results of the unsteady analysis for a wind turbine (although I computed the steady behavior about a couple of points before going for the unsteady analysis) but I don't have sufficient time to do the complete steady state analysis. So I want to predict it from the unsteady data.

Would you explain briefly the methodology to predict the steady behavior from unstedy analysis or provide me with some good links to the related articles or papers ?

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Old   November 21, 2005, 01:46
Default Re: Steady behavior prediction from unsteady data
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Mani
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Well, first you have to specify what you mean by "unsteady"? What is the unsteady nature of the flow you are studying (apart from the obvious unsteadiness through rotation)? If the unsteadiness is periodic, you can easily extract time-average data (which is not really "steady-state"). If it's not periodic but asymptotic, you could estimate a steady-state by extrapolation (getting into dangerous terrain).

It seems unusual to me that you wouldn't have time for a steady-state analysis but spent probably one or two orders of magnitude more time on an unsteady analysis, without even knowing the steady-state... ?
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Old   November 23, 2005, 03:09
Default Re: Steady behavior prediction from unsteady data
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Mamun
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First of all, I would like to express my sincerest gratitude to you for paying attention to my case.

Well, I am studying an axial flow air turbine (the Wells turbine for extracting wave energy) which is usually subjected to an oscillating airflow (from an air chamber through the turbine to the atmosphere and from the atmosphere through the turbine to the air chamber). So the flow through the turbine is best described by a unsteady sinusoidal axial flow.

Until recently, I calculated the steady behavior for several points i.e., several rotational speed (determined by the desired flow coefficient within the operating range of the turbine)and then I calculated the unsteady behavior.

Recently, some modifications have been made to the turbine geometry supposedly to improve its operating characteristics. And I have to validate the geometry as soon as possible. I heard that steady behavior can be predicted by the unsteady data (you also supported the statement). So I decided to complete the unsteady calculations so that I can predict both the steady and unsteady behavior. Of course, I calculated a few points for the steady state but it is not complete. I have to predict both the steady and the unsteady behavior. Usually in my case, the complete steady state calcualtions involves more time than the unsteady analysis since it consists of a number of individual points (rotational speed).

I don't know how to get the time-average data or do extrapolation. Would you please explain me the methodologies or give me some references. You can also send me emails.

Best Regards.
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