OpenFOAM

tahanson43206 · 2025-12-03 21:41:38

The run to 6 seconds from 3 seconds is underway, with finish estimated at 3 AM local time.

ChatGPT5 and I collaborated to generate graphs from the log data we are building up. The two graphs below show:

1) The decline of something called sumE
file.php?id=10
2) the more modest decline of average temperature
file.php?id=9

What I find interesting in the temperature plot is that the trendline appears to be toward the same 299 Kelvin temperature we saw with the 2 kg/s run.

I have no idea why this might be, but I assume and hope that GW Johnson will be able to explain it.

I don't know what sumE represents, so I can't comment other than to note it is decreasing more rapidly than the average temperature.

(th)

tahanson43206 · 2025-12-04 10:41:30

The run to 6 seconds of extendedMerlin with intake set at 20 kg/s is complete.

Here is a link to a plot of thrust that appears to support GW Johnson's prediction of nearly 5 tons-force.

file.php?id=12

Additional plots will be added later today. The entire log of the run is ready for input to the utility to extract a set of data for three data items: sumE, Average T and sum(rho).

The image at the link below shows the sum of rho - it closely matches thrust:
file.php?id=13

The image at the link below shows how temperature fluctuates during the startup phase, when we are exhausting the 1 bar fill and ramping up intake flow:
file.php?id=14

(th)

tahanson43206 · 2025-12-04 19:51:23

A run to 7 seconds is under way...

The reason for ** this ** run is to collect pressure data. Pressure data is available from previous runs, but it is buried in the mass of data collected by the software. A function was added to display pressure directly, and it shows the pressure inside the intake to be consistently above 9 bar. That reading is consistent with the thrust readings we are seeing for the test run with 20 kg/s of hydrogen at the intake.

In another topic i have reported on the (to me surprising) performance of the system with the gas temperature readings not above 300 Kelvin.

I hope the CFD performance stands up to scrutiny.

Here is a snapshot of performance data reported periodically in the run log:

volFieldValue heatBoxStats write:
sum(heaterCells) of e = 4.52211e+08
volFieldValue T_avg write:
volAverage(heaterCells) of T = 300.0018 << 300 Kelvin throughout the intake/heater
volFieldValue p_avg write:
volAverage(heaterCells) of p = 911545.3 << 9 bar throughout the intake/heater
volFieldValue rho_sum write:
sum(heaterCells) of rho = 17681.61 << not sure what this is
Courant Number mean: 0.04045834 max: 0.6999997
deltaT = 3.59979e-06
Time = 6.6960156s << we are well along toward the run goal of 7 seconds

(th)

tahanson43206 · 2025-12-05 07:26:37

The run to 7 seconds by the extendedMerlin model with flow set to 20 kg/s ended normally early this morning local time.
Here is what a normal end looks like:

ExecutionTime = 34485.89 s ClockTime = 34626 s << a bit over 9 hours
volFieldValue heatBoxStats write:
sum(heaterCells) of e = 4.514843e+08
volFieldValue T_avg write:
volAverage(heaterCells) of T = 299.9988 << Average temperature settled at a whisker under 300 Kelvin
volFieldValue p_avg write:
volAverage(heaterCells) of p = 911583.2 << Pressure remains steady at 9 bar
volFieldValue rho_sum write:
sum(heaterCells) of rho = 17682.52
End

Images planned for later today include: thrust and at least three items from the log

Thrust plot holding steady at 49.5 kN
file.php?id=15

Heater Sum(e) for one second from 6 to 7
file.php?id=17

Heater Sum(rho) for one second from 6 to 7
file.php?id=16

Heater Average Temperature vs Time from 6 to 7
file.php?id=18

This next set of images are from ParaView, looking at the engine compartment after 7 seconds

file.php?id=19
Pressure
file.php?id=20
Temperature
file.php?id=21
Velocity

This last section shows plots for the full seven seconds:

Tracks thrust but shows heating
file.php?id=22
Heater Sume(e) ... shows fluctuations at startup
file.php?id=23

(th)

tahanson43206 · Today 07:35:19

The Google Meeting discussion 2025/12/14 included evaluation of recent OpenFOAM work.

GW Johnson agreed with kbd512 that the next phase should be to implement the "washer" concept for a constricted throat.

However, of greater significance is the heating reports from the model. Both the 2 kg/s run to 7 seconds and the 20 kg/s run show the same temperature of 300 degrees Kelvin... GW asked me to investigate the heating system. Readers of this topic may recall that we changed to "volume" heating from convective heating, and we are now getting reasonable thrust performance but the temperatures reported are both close to 300 Kelvin.

Specifically GW suggested investigating to see what should happen to 2 kg of hydrogen in one second if it is heated with 40 MW of thermal energy. The new heating system distributes 40 MW evenly over all 24,000 cells in the intake/heater. What I think ** should ** happen is that the cold 20 Kelvin hydrogen fed in at the intake should warm as it travels the length of the heater. I don't see that happening in the animation of the model. Further more, the heating of 20 kg/s should result in a lower temperature at the nozzle, because there is more gas to be heated with the same heating energy, and we are not seeing that.

In short, I think it is too early to start work on the throat constriction.

Here is a post in which ChatGPT5 attempted to estimate the heating we should be seeing:
https://newmars.com/forums/viewtopic.ph … 08#p235708

We are seeing 300 Kelvin but ChatGPT5 thought we should be seeing something closer to 1000 Kelvin.

(th)

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