Manifold intake simulation
 

Hi,

I am trying to simulated a simple manifold intake in a transiend state simulation .My problem is that I can't find exaclty the way to do this. For example should I also need to improt some kind of .txt file with some values. If somebody can upload some kind of file to help me I will arrpesiate that. I just need the steps on the set up stage.

Thank you very much!

Define your boundary condition as a function of time (either a CEL expression or a 1D interpolation function) and use that as the boundary value.

Manifold intake
 

Thank you very much for your respond.I wondered if it is possible to send me an example of what you just explain me, because I am very struggle after one point on this software. But with an example I think I can handle it.

Thank you very much again.

I do not have time to upload an example. But the tutorial examples have examples of using CEL expressions so you should look there.

Intake Manifold
 

Ok no problem.Do you know how I can relpy by my problem to all, so If it's possible form somebody to help me further.Because still I am very struggle with that issue.

Thanks again:
rolleyes:

What input data do you have? Massflow versus time at the exhaust valve? Pressure versus time? This is step 1.

I want to apply atmospheric pressure in the inlet.And I have 2 outlets (2 runners) on which I want to apply 0.035 kg/s (on each) mass flow rate. All I need is a full example on the setup stage in the CFX.

Thanks again.

Pressure versus time Ι want to apply

Because for example, I saw some other files ,as exemples which had also some x,y,z coordinates. That is an issue for me because I don't know what kind of coordinates are those.

Thanks

I have done this type of analysis many times. It is quite straight forward. Are you interested in the transient or steady state flow? If transient are you trying to model the pressure waves?

You define the mass flow as a function of time, and if you have many cylinders with different timing you need to define multiple functions (or link them with a time offset or what ever is appropriate). This function of time will normally be applied as a 1D interpolation function that returns a mass flow rate for a time value. So you then apply the mass flow boundary condition on the valves with the mass flow rate defined as the function.

If you are trying to model the pressure waves in the system I strongly recommend you do some preliminary work first on pressure waves in a simple straight duct so you can see what is important. Shock wave propogation in a straight duct has a simple analytical solution so you should get this simple case working accurately before attempting the 3D complex version.

Ok, maybe it is better for you (and I terribly sorry that I am doing this to you, it's just I am very struggle on this point of level).

First of all lets say that we have a system (call it manifold intake) and I have 1 inlet and 2 outlets. Now on the intake as a boundary condition I apply the atmospheric pressure. At the outlet (were we have two of them) I want to apply the mass flow rate e.i. 'x' value Kg/s. Now, I want to run the simulation in transient state and by the way were a manifold intake works. I want to start with something simple on this field to understand it correctly, so after that I can carry on with something more complicated. I 've all ready have run a transient state but I don't know how to create expression by function of "something" e.i. time. I tried to understand it by the tutorials and many others ways, but still nothing.I know were to create expressions by I don't know how to define them. That's why an example where I can see what kind of commands you gave, will help me once and for all.

Thanks again for everything.

Have another look in the documentation and tutorials on 1D interpolation functions. They are quite straight forward.

Hi, I saw tha chapter about the 1D interpolation function. Now on my file I greate a user function and I applied it in the inlet(where I gave all the appropriate data).Now when I trying to run it the programm (ANSYS 12) give me the picture bellow as you can see

Attachment 10859

and the setup has question mark and down in the messages seas:
Cannot DefineRun without a valid definition file.

The only thing I did it was to create the function and put it into the inlet boundary:
Function called: pressure
In the boundary : "pressure(t)"
To be as a function of time

Thanks

You cannot name a function "pressure". That variable name is already reserved.

Can you post either a screen shot from CFX-Pre or the CCL file?

The txt file has the values where I gave by importing the file (.txt).You can see also some pitctures

Those are also from the same error

Your images are barely readable, but it seems you have mm as the input argument. It should be a unit of time (maybe seconds?).

Ok I gave time int the argument units : sec.
But the programm is still denited to run.I appload you some pictures to see again.
When I put in to the inlet boundary condition the funtion : running (I named it), in to a brackets e.i. "running".

Because When I dot that then the programma it's not accepted to run the simulation because it gives me a guestion mark at the main screen of ANSYS on the Setup step (see the photo)
Should I click to the "Suppress physics error" ?

Thanks

And also those

Your images are still hardly readable. Do not use the lossy JPG format, use a lossless format like PNG. Also do not reduce the size of the images.

You appear to have defined the argument unit as "sec". The correct unit is "s". Also your result unit is "KPa". The correct unit is "kPa". The variables format is listed in the documentation.

Ι upload the pictures as you asked me (PNG files).I hope now they will be readable. I also 've done what you told me above by the problem still the same

And take a look also to this one.I hope I help you enough.If not I am steel here, as me what ever you want

Thanks again

The image problem is that they are being shrunk somewhere.

The problem is the way you have set things up in CFX-Pre, so fix the problem there, not WB.

My last post said you used the wrong variable names. Have you fixed that?

Yes, I fixed that problem and the results are still the same.I thing by the way you see the geometry, you can just send me What would you do if you were in my shoes In a transient state and with one inlet (boundary:pressure) and two outlet (boundaries: mass flow rate).I' ve done exactly what I need to do in the function setup according to the file that I found (how to setup a function in 1D interpolation).

The solver not even start.The graph that you see from the solver int the pictures is from a steady state and simple (one inlet "100 kPa" pressure and two outlet 0.035Kg/s each).And after that I change exactly everything and here we are now.

Can you post your CCL file for the current simulation?

I am trying to upload the file,but it doesn't accepted it.Probably because of the size.Is there any other way?

I was trying to upload the file with the simulation, because I don't know exaclty which one is the CCL file where you asked me.

Thanks

The CCL file is the top section of the output file. If the output file (with the startup error) is short then just upload that.

Look I finally found some issues to solve my problem, but now duirng the running of the solver, suddenly in the middle it stop and give me the below error:

| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead. |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| ****** Notice ****** |
| A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 2.9% of the faces, 0.9% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: outlet. |
| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead. |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| ****** Notice ****** |
| A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 1.6% of the faces, 0.6% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: outlet2. |
| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead. |
+--------------------------------------------------------------------+
| H-Energy | 0.32 | 5.7E-03 | 2.5E-01 | 5.8 1.2E-03 OK|
+----------------------+------+---------+---------+------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Floating point exception: Overflow |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

Details of error:-
----------------
Error detected by routine POPDIR
CRESLT = ILEG




Any idea?

Thanks

Can you please post your entire output file?

The error is a typical one - floating point error means you simulation has diverged. You need to improve the numerical stability. Use smaller time steps, a better initial condition, lower order differencing (but switch to higher order for accuracy later), double precision numerics, check your physics in correct, improve mesh quality.... the list goes on....

I am trying to upload the file, but it doesn't me,probably because of the size.Can you gine you email (if it's possible), so I will upload the hall file and you can take from there.Because I can't see any other way. Maybe you know

I upload a foto with the content of the CFX file that is created by the software. Check which file you need exaclty so I can sended to you.

Thanks!