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Old   May 6, 2002, 15:27
Default Transient Problem
  #1
Sundar
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Hi People, I am trying to solve a Transient Problem in Fluent Version 6 and I am having convergence problems. I was able to obtain convergence in Steady state model. Well the problem is to see whether flow reaches at the same time in eight reactors mounted in series. Flow comes from an inlet duct and branches before it reaches the inlet of the reactors. The design is done so as to reach the reactor inlets at the same time. well the time it takes for flow to reach the inlets of the reactors is 0.13 seconds. The flow is turbulent and I am taking advantage of enhanced wall functions in vesrion 6. The turbulent model I am applying right now is the realizable K-e Model. Well any suggestions how to be successfull in transient problems will be greatly appreciated.

Thanks Sundar
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Old   May 6, 2002, 16:42
Default Re: Transient Problem
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Thomas P. Abraham
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Hello Sundar,

While doing unsteady simulation with RANS approach, you would be trying to capture the unsteadiness of the gross mean flow, leaving the turbulence model to account for the turbulent fluctuations which occur over very small time scales.

So, the time scale you would choose should be larger than the time scale of the turbulent flucutations and smaller than the time scale of the large eddy.

Thomas
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Old   May 7, 2002, 10:20
Default Re: Transient Problem
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bala
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well that is a problem if you don't have turbulent data. moreover if you are using a model to predict something you won't have much information because if you knew you 'd not have to predict.

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