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June 23, 2015, 06:39 |
Reverse Flow Pressure-Outlet
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#1 |
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Gustavo
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Hi,
I have seen in lotīs of Posts the Suggestion to extent the outlet. But actually, I donīt know what does it means and neither how to do it. Could anyone give me a hint about this? Iīm working with a laminar model. Mixture of O2 and N2. Species Transport on and Energy Equation on. The Problem consist of a gasfeed inside a chamber. So I have an inlet (5mm) to fill in gas in the gasfeed, than I have an outlet (2mm) from this gasfeed to fill in the chamber, and then I have the outlet (260mm) in the middle-top of the chamber. Iīm using mass flow inlet (1e-5 kg/s) and pressure outlet in both outlets (1Pa). I donīt know what is causing this reverse flow. Anyone has a hint? thanks in advance |
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June 23, 2015, 07:41 |
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#2 |
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"extent the outlet" = make the outlet longer.
So add some volume behind the outlet. |
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June 23, 2015, 07:59 |
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#3 |
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Gustavo
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Thank you so much for your reply. But Iīm still facing reverse flow
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June 23, 2015, 08:01 |
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#4 |
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Wait a minute... Do you mean you have reversed flow during the simulation, or do you have reversed flow in the final converged solution?
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June 23, 2015, 08:05 |
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#5 |
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Gustavo
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I have reversed flow durind the Simulation and also when the solution is converged...
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June 23, 2015, 08:09 |
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#6 |
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OK, ignore the reversed flow during the simulation, but only focus on the one in the converged solution.
If you want to know where the reversed flow comes from: just look at the result! Look at how the flow lines go, and try to understand why you have reversed flow. That is the best hint I can give: look at you solution... It is not much, but I can do no better... |
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June 23, 2015, 08:14 |
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#7 |
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Gustavo
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I will do that.
I donīt know the relationship, but when I set the operating conditions to 0Pa in the pressure Iīm not able to run the Simulation because I have Problems with mass diffusivity. When I Keep the Default pressure I can run the Simulation but reversed flow appears. Do you know something about that? once more thank you for your time |
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June 23, 2015, 08:18 |
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#8 |
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But those are two physically different problems that you are simulating.
If you set the operating pressure to atmospheric pressure, your outlet pressure is 101325 Pa + 1 Pa = 101326 Pa. If you set the operating pressure to 0 Pa, your outlet pressure is 0 Pa + 1 Pa = 1 Pa. So if you change operating pressure, you change your simulation physically! |
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June 23, 2015, 08:28 |
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#9 |
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Gustavo
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My objective is to Keep the pressure inside the chamber around 1Pa.
Making the operating pressure as 101325 Pa I could see in the countours of pressure that I achieved this objective. The pressure inside the chamber after results converged was 1Pa. So in my understanding, based on this Point of view Iīm in a good way. I just Need to understand why Iīm having reversed flow. I think my geometry is not properly defined. I have a pipe with 30mm Diameter and 1060 mm lenght inside a cubic chamber (1060x1060x1060mm). I created an inlet to provide gas for the pipe. Than I create an outlet in this pipe to provide gas inside the chamber. Than I have the outlet to remove gas from the chamber. Is this construction ok? Or do you think I Need to Change something? Iīm afraid this is the origin of my Problems. thank you so much |
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June 23, 2015, 08:48 |
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#10 | ||
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Quote:
Quote:
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June 23, 2015, 09:02 |
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#11 |
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Gustavo
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I mean the gauge pressure 1 Pa. (This is a low-pressure Simulation)
With this Simulation I would like to see the pressure difference between the pipe and the chamber. And also the behaviour of the gas from the inlet until the outlet of the chamber. |
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June 23, 2015, 09:08 |
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#12 |
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June 23, 2015, 09:10 |
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#13 |
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Gustavo
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Sorry... Iīm not so familiar with this concepts. Iīm new in fluent. So, I mean Total Pressure = 1Pa (to have a low pressure condition)
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June 23, 2015, 09:19 |
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#14 |
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What you can do is set operating pressure at 1 Pa, and set your boundary condition to 0 Pa.
(BTW: this is all probably unrelated to your reversed flow. If you want to know why you have reversed flow, look at the solution!) |
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June 23, 2015, 09:32 |
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#15 |
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Gustavo
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Thank you so much...
In my result, I didnīt got a streamline from the inlet of the pipe until the outlet of the chamber. I donīt know if it is related to the reversed flow... |
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June 23, 2015, 09:40 |
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#16 |
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Then where do the streamlines from the inlet end?
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June 23, 2015, 09:42 |
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#17 |
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Gustavo
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The end is on the top of the pipe.
The inlet is in z direction and the top of the pipe is in the plane xy. So the inlet is perpendicular to the face of the pipe. |
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June 23, 2015, 09:47 |
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#18 |
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So you have streamlines that start at the inlet and end at a wall?
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June 23, 2015, 09:52 |
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#19 |
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Gustavo
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Exactly...
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June 23, 2015, 09:56 |
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#20 |
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Then it is hard to believe that you have a converged solution. Check your mass flow balance. (Reports->Fluxes, Mass Flow Rate and select all boundaries)
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reverse flow |
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