TAGGED: #fluent-#cfd-#ansys
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April 15, 2024 at 9:15 amalrifaiSubscriber
Hello,
My setup consists of a mass-flow inlet and a pressure outlet. I know both the inlet mass flow and inlet total pressure, while I have 0 information at the outlet. I start with an initial guess of what the outlet pressure may be and use a targeted mass-flow for my outlet. However, I never manage to achieve my desired inlet pressure. How would I go about updating my outlet pressure until I get my desired inlet pressure? Is it a UDF that I have to write? And if that's the case, I have no idea where to start from. -
April 15, 2024 at 11:15 amRobForum Moderator
Is the fluid compressible?
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April 15, 2024 at 11:17 amalrifaiSubscriber
It's incompressible
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April 15, 2024 at 12:08 pmRobForum Moderator
OK, so what do you gain from altering the outlet pressure to find the inlet pressure? You know the inlet pressure relative to outlet for a given mass flow. As an aside, for incompressible flows use a velocity inlet, it's generally more stable and can be slightly quicker.
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April 15, 2024 at 12:25 pmalrifaiSubscriber
I want to alter the outlet pressure to obtain the total inlet pressure that is calculated
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April 15, 2024 at 12:28 pmRobForum Moderator
And you can't look at the inlet pressure against a known outlet pressure and use the domain dP?
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April 15, 2024 at 12:31 pmalrifaiSubscriber
We dont have a known outlet pressure, we start off with a guess and update that value until we're somewhat close to the value we want for inlet pressure, but I dont want to do that manually, I wanna be able to specify that in fluent.
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April 15, 2024 at 12:35 pmalrifaiSubscriber
I've written the following expression:
IF(inlet_pressure < Inlet_total_pressure, Outlet_gauge_pressure + abs(inlet_pressure-Inlet_total_pressure), Outlet_gauge_pressure + abs(inlet_pressure-Inlet_total_pressure)), but I'm unsure if this is getting updated iteration for iteration -
April 15, 2024 at 12:48 pmRobForum Moderator
OK, so we start with an outlet pressure of 0 Pa. You run the model and get an inlet pressure. If I increase the outlet pressure by (for example 100,000Pa) what might I expect the inlet pressure to be? If you're not sure feel free to run the model.
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April 15, 2024 at 12:51 pmalrifaiSubscriber
I ran it with the expression and it seems to work now, I had forgotten to turn off targeted-mf and it seems to be fine now. I get the mass flow I want at the outlet and the pressure I want at the inlet
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