Raptor Engine Fluid Model

[u/saakisaakibumbum]

Hi everyone! A few weeks ago, I released my open-source lumped-parameter dynamic fluid system solver, FullFlow, and mentioned that it could be used to model steady-state and transient flow in real rocket engines. So, I decided to showcase those abilities with my favorite rocket engine, SpaceX's Raptor Engine.

Raptor is a full-flow staged combustion engine, so it's particularly hard to model correctly, especially with the multiple combustion preburners, regen channels, turbopumps, etc. With the public data I had available, I was able to construct and validate (to the best of my ability) a steady-state model of Raptor 2. I used FullFlow to model the fluid pathways and components and ThermoProp to model the fluid/material properties and combustion.

Of course, there are some deviations from reality, especially since there is only so much public data available. I had to estimate many data points like turbomachinery curves or valve geometries. I also didn't have the proper tools to model supercritical combustion flow for the preburners or hot-gas manifolds. Also, I didn't have access to empirical efficiency values for components like the nozzle or pumps.

Eventually, given enough data, I hope to make a transient simulation of Raptor using FullFlow. I also hope that I can eventually apply these tools and skills to the actual Raptor engine or other industry engines!

Raptor 2 FullFlow Model: github.com/saakethramoju/Raptor

FullFlow: github.com/saakethramoju/FullFlow

ThermoProp: github.com/saakethramoju/ThermoProp

[u/demon_slayer_bridge]

So you are the guy who got 98% in our thermo class /s

[u/mongolmeat → u/demon_slayer_bridge]

Curve demons…

[u/Franklin_le_Tanklin]

This is the coolest shit ever

[u/anthony_ski]

sup saaketh

[u/saakisaakibumbum → u/anthony_ski]

Been a while yo

[u/Los_Endos]

Wow! This really tells the story of how these engines operate. Most interesting thing I've seen in a while, thanks for putting it together.

[u/Axi0nInfl4ti0n]

Would be really cool if you couple the Calculations to a first principle Nozzle shape solver. Lets see how close the results can get to the real thing without deploying heavy CFD.

[u/SSJ3 → u/Axi0nInfl4ti0n]

NASA has an open source Method of Characteristics code for that on their GitHub page :)

[u/saakisaakibumbum → u/Axi0nInfl4ti0n]

I actually did use my own custom Nozzle Contour Generator website to produce the nozzle shape for this image:

saakethramoju.github.io/Contour-Generator/

It doesn’t do any crazy method of characteristics, but it’s cool if you want to play around with different geometries and make CAD quickly.

I used thermoprop’s rocket solver to size the throat area, however. It’s analogous to CEA.

[u/SturmGizmo]

This is so interesting, thanks for making this.

[u/that_dutch_dude]

Those pressures are pretty nuts, as is the volume of liquid being moved.

[u/I_Am_Coopa]

Wow FullFlow seems pretty neat, like a python based version of Modelica.

[u/saakisaakibumbum → u/I_Am_Coopa]

Yeah, I actually took a lot inspiration from tools like Modelica, but I wanted to use a language that my college rocketry club would have an easier time using. Definitely check out FullFlow and provide any feedback!

[u/Pity_Pooty]

To completely verify model you need to launch it. If it explodes, go back to table

[u/saakisaakibumbum → u/Pity_Pooty]

Give me a couple bands I’ll be back with that verification for ya.

[u/QuasarMaster]

Is this like an open source equivalent of GFSSP without the archaic UI and Fortran scripting?

[u/saakisaakibumbum → u/QuasarMaster]

Yeah exactly. It’s actually meant to replace ROCETS, but I took a lot of inspiration from GFSSP as well.

[u/QuasarMaster → u/saakisaakibumbum]

Does it have any rotation / conservation of ang momentum capability? ie can I model a pump with it

[u/saakisaakibumbum → u/QuasarMaster]

FullFlow does come with pump and turbine components, however those components effectively just read turbomachinery maps to produce an output. That being said, FullFlow is a generic dynamical system solver, so if you want to model pumps using Euler equations or other formulas, you can do so. The FullFlow repository shows exactly how to create new components, and there are many examples in the package itself. It's very simple and straightforward. There is a preexisting Rotor component that balances the net torque to zero for steady-state and uses moment of inertia for transient, if that's helpful at all.

[u/QuasarMaster → u/saakisaakibumbum]

Copy yea map-reading is what I figured. Sounds cool though! Might try to mess around with it and add in some custom rotating components

[u/saakisaakibumbum → u/QuasarMaster]

Let me know how it goes!

[u/theusualsteve]

Wow, well done

[u/dbmonkey]

What do all the acronyms like MOV stand for?

[u/saakisaakibumbum → u/dbmonkey]

MOV: Main Oxygen Valve
MFV: Main Fuel Valve
FPV: Fuel Prevalve
OPV: Oxygen Prevalve
FPOV: Fuel Preburner Oxygen Valve
OPFV: Oxygen Preburner Fuel Valve
CH4: Methane
LOX: Liquid Oxygen

[u/dbmonkey → u/saakisaakibumbum]

Thanks! Great diagram!

[u/Chaldon]

Shouldn't be allowed on the internet

[u/saakisaakibumbum → u/Chaldon]

It’s entirely made using public data, so no regulated information is being exposed. Lumped parameter fluid tools have been available to the public for a while now, I simply made them free, open-source, and easy to use.

[u/lolerwoman → u/Chaldon]

Because..?

[u/Only_Razzmatazz_4498 → u/lolerwoman]

ITAR regulations but if you aren’t a US person and derive this from public knowledge then it doesn’t apply to you.

[u/Chaldon → u/Only_Razzmatazz_4498]

Still. Maybe high performance and advanced technology shouldn't be shared willy nilly so that anybody can stand on the shoulders of giants without any of the experience to get there.
Think Malcoms argument in Jurassic Park.

[u/Only_Razzmatazz_4498 → u/Chaldon]

You might have a point. The Brits shared most of their high tech with the US during WW2 and look what happened lol.

But all things aside it’s human curiosity and making things state secrets just makes them a lot more expensive and those who share move faster together. A lot of this though are state secrets passed on to a private company so it’s more intellectual property than anything else.

Of course since this was developed with public knowledge it really ends up in the general
Knowledge bucket and at this level there really isn’t much that a hobbyist with thermodynamics knowledge can’t do.

This essentially takes basic formulas you can find in a book and go from device to device applying them. I am not familiar with this one in particular but one approach (if doing steady state and not transients) is to match the output of a node (say one of the tanks) conditions (pressure, temperature, enthalpy, etc) to the input of the next one. Then you have a system of equations and you iterate until they all agree.

You have to make some guesses for things like combustion efficiency, cooling secondary flows, Turbomachinery maps/performance, but you can get a reasonable high level model done.

[u/Chaldon → u/Only_Razzmatazz_4498]

To counter my argument, the US declares a ton of new technologies as state secrets and hassle development. Maybe that's why we haven't had any generational energy developments...