[Roh]

Guys,
I'm trying to do an RDE simulation based on this article:



http://proceedings.asmedigitalcollec...icleid=1775897


But I don't know why it doesn't work. Everyhting's going very well and working correctly but don't realize why cannot create the detonation. I can initiate the zone using "Patch" and the solution is working properly after triggering the "calculate" button but this damn detonation does not create. look What I've gotton:

[whitet86]

Roh,

Sorry for not responding to your last couple of messages. Did you create the user defined function that tracks the inlet boundary condition? This is what propagates the detonation properties around the chamber. I also believe I had to patch it with a starting temp, pressure, and velocity to get it traveling in the proper direction. From your static pressure contour, it looks like you have 2 deflagrations traveling in opposite directions instead of a detonation wave while your temp looks like the combustion never started. Check your activation energies in your material models depending on the species used.

[Roh]

Originally Posted by whitet86

Roh,

Sorry for not responding to your last couple of messages. Did you create the user defined function that tracks the inlet boundary condition? This is what propagates the detonation properties around the chamber. I also believe I had to patch it with a starting temp, pressure, and velocity to get it traveling in the proper direction. From your static pressure contour, it looks like you have 2 deflagrations traveling in opposite directions instead of a detonation wave.

No problem, Thank you for your answer.
Yes, created and compiled it and it works fine.
The above screenshoots are for a detonation with 0 velocity and that's why you see two deflagration. I've used the velocity that you've meantioned in your project as x velocity in my project. so just one deflegration created. just like above. Here is some other setting of my project:


































Do you see any other problem? What do think about this problem?

[whitet86]

What sizes are the mesh and time step set to?

[Roh]

Originally Posted by whitet86

What sizes are the mesh and time step set to?

Minimum lenght of the edge of cell is around 0.0005m


Domain is 298*75


The timestep is 5e-08


And the quality:

Minimum Orthogonal Quality = 1.00000e+00 cell 0 on zone 2 at location ( 2.97748e-01 2.50183e-04) (To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,
where Inverse Orthogonal Quality = 1 - Orthogonal Quality)


Maximum Aspect Ratio = 1.47485e+00 cell 82048 on zone 2 at location ( 1.84156e-03 7.42496e-02)

[whitet86]

It looks like it should be working. Maybe try increasing the face mesh to 0.005m. I had trouble patching in the zones when I ran it some times and it would get similar results. Try increasing the temp, pressure, and velocity of the detonation patch to see if it initiates.

Tim

[Roh]

Originally Posted by whitet86

It looks like it should be working. Maybe try increasing the face mesh to 0.005m. I had trouble patching in the zones when I ran it some times and it would get similar results. Try increasing the temp, pressure, and velocity of the detonation patch to see if it initiates.

Tim

Sometimes in calculation I get excess temperature. Did you get excess temperature (in some cells or faces) when the calculation was running?



Another question, Why do you think that changing the face mesh would help?



I'll try with more pressure.

[whitet86]

Usually my solves didn't initiate or they were close to theoretical temps. The only time they were high was when my standard enthalpy and activation energies were modified and then the whole model showed increased temps.

I recommended going to a face mesh with a bigger grid because there was a correlation between grid size and activation energy needed. This probably won't help in the long term because the larger grid will produce less accurate results, but was just an idea to try and get it started.

[Roh]

Originally Posted by whitet86

... there was a correlation between grid size and activation energy needed...

Thank you for your reply,
Could you please provide any source or formula for this part of your remark?


Didn't aware of such correlation.

[whitet86]

It was just something I noticed as I did my grid size study in the paper I sent you. The 0.5mm grid and 0.1mm grid needed different activation energies in Table 4 to get similar results.

Tim

[machao]

how did you get the activation energy? I also need the data.Is the number correct?

[Roh]

Originally Posted by whitet86

It was just something I noticed as I did my grid size study in the paper I sent you. The 0.5mm grid and 0.1mm grid needed different activation energies in Table 4 to get similar results.

Tim

Thank you, Tim,
Due to your paper, I'm going to change the activation energy and try with my mesh. Hope to get a promising result. I'll be in touch with you.


Thanks

Originally Posted by machao

how did you get the activation energy? I also need the data.Is the number correct?

Currently, trying to get a promising result as I said to Tim. But there are some articles on the net that you can see the activation energy in them.