How OpenFLUME compares to other 1-D thermo-fluid network tools
OpenFLUME is a finite-volume node-and-branch network solver for pressure, flow, and temperature in pipe systems, with lumped solid thermal networks attached. The best-known tools in this class are NASA's GFSSP and C&R Technologies' SINDA/FLUINT; several commercial 1-D system-simulation packages overlap with it.
OpenFLUME is Alpha software (version 0.3.1). The other tools have years or decades of production use behind them. OpenFLUME's case rests on access, transparency, and auditability.
What OpenFLUME is
- A finite-volume network solver: nodes store mass and energy, and branches carry mass flow governed by a momentum relation. The steady solver is Newton–Raphson; the transient solver is backward Euler with fixed or adaptive time steps.
- Real-fluid properties from CoolProp compiled to WebAssembly, plus ideal-gas, incompressible, and thermal-expansion-liquid models.
- Runs entirely in the browser, in a Web Worker; no model data is sent to a server. The same core is available from Python (
pip install openflume, see Python package). - MIT licensed. The source, tests, and the scripts that generate the verification reports are public.
Comparison matrix
Entries for third-party tools are general and publicly known. Licensing, prices, versions, and capabilities change, so check the vendor or distributor for anything that affects your decision. "Check vendor" means the point is unverified here, not that the capability is missing.
| OpenFLUME | NASA GFSSP | SINDA/FLUINT | Commercial 1-D system tools (Flowmaster, AFT Fathom/Arrow, GT-SUITE, EcosimPro, Simscape Fluids, Modelica-based tools) | |
|---|---|---|---|---|
| Origin / owner | Open-source project, single author | NASA Marshall Space Flight Center | C&R Technologies (commercial) | Commercial vendors. Modelica is an open language with both open-source and commercial tools |
| How you get it | Open a URL, or pip install openflume | NASA software release process; check NASA's software catalog for eligibility | Commercial license from C&R | Commercial license from each vendor (OpenModelica is open source) |
| Installation | None (browser) | Installed desktop software | Installed desktop software | Installed desktop software, or a toolbox inside a host platform (e.g. Simscape needs MATLAB/Simulink) |
| Source code available | Yes (MIT) | Check distributor | No (commercial) | Generally no. Modelica libraries are often readable source |
| Data locality | Runs locally in the browser; nothing leaves the machine | Local | Local | Local desktop. Check vendor for cloud options |
| Maturity / heritage | Alpha; no flight or program qualification heritage | Long NASA use in propulsion and fluid systems | Long industry use in spacecraft and aerospace thermal analysis | Long industrial use in their target sectors |
| Formulation | Node/branch finite volume, Newton–Raphson, backward Euler | Node/branch finite volume (the formulation OpenFLUME follows) | Lumped thermal network (SINDA) and fluid network (FLUINT) | Varies by product |
| Component library | 19 branch types plus user JavaScript components | Extensive; user subroutines | Extensive; user logic | Typically large, sector-specific libraries |
| Two-phase | HEM only (no Lockhart–Martinelli yet) | Check documentation | Check vendor | Varies; check vendor |
| Water hammer / acoustic waves | No. Lumped inertia only, no method of characteristics | Check documentation | Check vendor | Some vendors ship dedicated surge/waterhammer tools; check vendor |
| Shock capture | No | Check documentation | Check vendor | Varies |
| Verification evidence | Seven reports generated from live solves; tests in public CI | Published NASA reports and papers | Vendor documentation and sample problems | Vendor documentation |
| Scripting | Python package; TypeScript core library; plain-text .fn model files | Input files; check documentation | Input decks with user logic | Varies (APIs, co-simulation, FMI for some) |
| Sharing a model | Exchange plain-text .fn files; the recipient needs only a browser | Exchange input files | Exchange input files | Exchange project files; recipient needs a license |
| Support | GitHub issues; no commercial support | Check NASA | Commercial support from C&R | Commercial support from vendor |
Where OpenFLUME is weaker
The full list is §1.7 Scope Boundaries.
- Alpha. Version 0.3.1. Interfaces and file formats may change. Results have no program, flight, or certification heritage.
- No shock capture. Quasi-1-D compressible duct flow (Fanno and Rayleigh choking, converging–diverging nozzles) is supported. Normal shocks, over-expanded or separated nozzles, and supersonic-to-subsonic transitions are not. Thrust is not computed.
- No acoustic wave propagation. Lumped fluid inertia captures bulk surge, but without method-of-characteristics water hammer, wave timing and reflections cannot be simulated.
- Two-phase is HEM only. Without separated-flow (Lockhart–Martinelli) multipliers, high-void-fraction pressure drop is under-predicted.
- Cavitation only at the cavitating-venturi closure; no general inception check.
- Turbomachinery is a pump curve. No compressor or turbine maps, and no shaft-work heating.
- No general junction mixing of unlike fluids, except at CEA reacting junctions.
- Smaller component library: 19 branch types, plus user code.
- User code is trusted, not sandboxed.
- Steady closed ideal-gas loops need a pressure anchor.
- Cryogenic chilldown is validated only to a factor-of-1.6 regression band on chilldown time (§8.4).
- One author, heavy AI assistance, no commercial support.
Where OpenFLUME is stronger
- Nothing to install. Open the app and run a built-in example. No account and no license server.
- Local-first. Models and results stay on your machine.
- Open source and auditable (MIT). Every equation, closure, and tolerance is in a public repository, so each claim in the user manual can be traced to the code that implements it.
- Generated verification reports. Seven reports are written by scripts from live solves. The gate tests run in CI on every pull request, and weekly with the slow suite (overview).
- Scriptable.
pip install openflumedrives the same core from Python for sweeps, optimizers, notebooks, and CI checks on models. - Plain-text models.
.fnfiles diff cleanly in version control. - Teaching and review. Models open from a link, so a student or reviewer can rerun the exact case.