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Old   March 13, 2022, 14:09
Exclamation Unphysical wall heat transfer outputs
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Guillaume Beardsell
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I am puzzled by some outputs from the boundary monitor files (bound*_wall.out) during an IC engine simulation:
- Instantaneous Wall Heat Transfer (column HT_xfer_Rate)
https://postimg.cc/z3H34FMj
- Integrated Wall Heat Transfer (column Tot_HT_xfer)
https://postimg.cc/1nn5hyWt

However, I don't see these unphysical spikes in both:
- the average near-wall temperature (column Near_Wall_Avg_T)
https://postimg.cc/0zDB4Fds
- the average heat transfer coefficient (column Avg_HTC)
https://postimg.cc/Mc0gnNvD

What is going on?

I will be happy to provide all relevant details!
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Old   March 14, 2022, 08:42
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John Etcheverry
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Quote:
Originally Posted by magicbretzel View Post
I am puzzled by some outputs from the boundary monitor files (bound*_wall.out) during an IC engine simulation:
- Instantaneous Wall Heat Transfer (column HT_xfer_Rate)
https://postimg.cc/z3H34FMj
- Integrated Wall Heat Transfer (column Tot_HT_xfer)
https://postimg.cc/1nn5hyWt

However, I don't see these unphysical spikes in both:
- the average near-wall temperature (column Near_Wall_Avg_T)
https://postimg.cc/0zDB4Fds
- the average heat transfer coefficient (column Avg_HTC)
https://postimg.cc/Mc0gnNvD

What is going on?

I will be happy to provide all relevant details!
Hi, Guillaume.
The plots, for the most part, look OK to me. The change in instantaneous heat transfer is a question mark but integrated is doing what I would expect and summing the change in instantaneous change into the integral.

Looking at instantaneous heat transfer for a moment, a couple of possibilities come to mind. Is it possible some engine event is occuring near this time? Is a spray causing piston wetting to occur and, in turn, cause a drop in heat transfer? Second, have you checked for recoveries around this time? I could see a recovery causing a change in variables.

Let me know what you find.

- John
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Old   March 28, 2022, 18:46
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Hi John,

Thank you for the suggestions. I looked at the log file to see if there had been a recovery at that time, and it doesn't seem to be the case:

[0m[1m[ 37.20%] [0m[32mncyc 3826; Crank -414.194 (deg); dt= 1.136448270e-05 (dt_cfl by region 2)[0m[0m
[0m[1m[ 37.22%] [0m[32mncyc 3827; Crank -414.072 (deg); dt= 5.076327947e-06 (dt_cfld)[0m[0m
[0m[1m[ 37.23%] [0m[32mncyc 3828; Crank -414.017 (deg); dt= 6.345409934e-06 (dt_grow)[0m[0m
[0m[35mWriting post file output/post000022_-4.13948e+02.h5 .........[0m
[35mWriting post file output/post000022_-4.13948e+02.h5 complete[0m
[1m[ 37.24%] [0m[32mncyc 3829; Crank -413.948 (deg); dt= 7.931762418e-06 (dt_grow)[0m[0m
[0m[1m[ 37.26%] [0m[32mncyc 3830; Crank -413.863 (deg); dt= 9.914703022e-06 (dt_grow)[0m[0m

At Crank -414.072 is when the instantaneous heat transfer spikes, as can be seen in the boundary monitor file that I attached.

There are no special events occurring around that crank angle. This is very puzzling.
Attached Files
File Type: txt bound3-wall_spikeout.txt (4.3 KB, 1 views)
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