Conceptual problem in a airbox simulation

Lisandro Maders · February 25, 2013, 17:37

First of all, i'm Brazillian, then sorry for my English.

Well, I had simulated an airbox on Fluent, and I am a litle confused with the results.
I had, as boundary conditions, velocity at the inlet, and pressure at the outlet.
The flow is laminar, with a velocity of 0.05 m/s, and the pressure at the outlet was 900 Pa (Gauge Pressure)
I put this to solve and it converged. But the problem is that I looked at the pressure contour in the results, and the pressure at the inlet area was 900 Pa too.

How I have the same pressure value on the both inlet and outlet? Because I think these values Fluent plot are values which are integrated in the area, right?

Well, I though I was forced to find a value higher than 900 Pascal, if somebody has something to say, thank you very much.

flotus1 · February 26, 2013, 03:33

How high is the pressure drop you would expect for your setup?
And is the pressure really EXACTLY the same at the inlet?

Lisandro Maders · February 26, 2013, 08:15

Quote:

Originally Posted by flotus1

How high is the pressure drop you would expect for your setup?
And is the pressure really EXACTLY the same at the inlet?

Thank you for your reply.

I was expecting a minimun about 100 Pascal, which satisfy the term of potencial energy (I don't know if you say like this.. is the energy related with the heigh difference), and yes, the value is exactly the same (I don't want to lie, I am without the .data file here with me now, but if there is some difference, is about 10-5, 10-6, something that is not shown in the 'color legend'.. ) I you really want to know if is EXACTLY the same, I can answer you today in the afternoon.

I have done some simulations as a test with a simple pipe, and the difference of pressure is about 10-3, wich is similar with an analitic calculation using the Bernoulli Equation with frictional pressure drop.

So, the problem is occuring just in the airbox model, not with the pipe (I believe so).

flotus1 · February 26, 2013, 08:43

Unless you accidentally used the inviscid model or a fluid with (nearly) zero viscosity or free slip wall boundary conditions at the walls, I have no idea what could cause the error.

February 25, 2013, 17:37	Conceptual problem in a airbox simulation	#1
Lisandro Maders Member Lisandro Maders Join Date: Feb 2013 Posts: 98 Rep Power: 13	First of all, i'm Brazillian, then sorry for my English. Well, I had simulated an airbox on Fluent, and I am a litle confused with the results. I had, as boundary conditions, velocity at the inlet, and pressure at the outlet. The flow is laminar, with a velocity of 0.05 m/s, and the pressure at the outlet was 900 Pa (Gauge Pressure) I put this to solve and it converged. But the problem is that I looked at the pressure contour in the results, and the pressure at the inlet area was 900 Pa too. How I have the same pressure value on the both inlet and outlet? Because I think these values Fluent plot are values which are integrated in the area, right? Well, I though I was forced to find a value higher than 900 Pascal, if somebody has something to say, thank you very much.

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February 26, 2013, 03:33		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	How high is the pressure drop you would expect for your setup? And is the pressure really EXACTLY the same at the inlet?

February 26, 2013, 08:43		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Unless you accidentally used the inviscid model or a fluid with (nearly) zero viscosity or free slip wall boundary conditions at the walls, I have no idea what could cause the error.