ggBleed

Project Overview

Aircraft ECS design is the work I know best, and I wanted something I could actually show. So this is built only from public data: published papers, theses and government reports, with every value cited. The models run in OpenModelica, which is open source, so nothing here depends on a paid tool.

ggBleed models how an airliner’s engines supply bleed air to the aircraft: hot, high-pressure air taken from the engine compressor, regulated, and cooled before it goes to air conditioning, anti-ice and pressurization. It feeds directly into ggPack, the air conditioning pack model.

Roadmap & Development Phases

The model progresses through the following milestones:

What It Models

• Compressible gas dynamics: ideal-gas properties, isentropic and choked/unchoked orifice flow, and the standard atmosphere.
• Precooler: ε-NTU crossflow heat exchanger with a lumped core thermal mass. The core time constant comes from an identified precooler model,¹ and the conductance is solved from two published flight-test cases.²
• Valves and control: high-stage valve, a pressure-regulating shutoff valve (PRSOV) holding a gauge setpoint, and a fan air valve driven by an outlet thermostat. The setpoint, control band, temperature limit and overheat trip come from an incident investigation report,³ and the sensor and valve lags from a laboratory bleed rig.⁴
• Flight mission: ground, takeoff, climb, cruise with a wing anti-ice step, idle descent and approach, rebuilt from published engine port states,⁵⁶ a published cruise point⁷ and the standard atmosphere.

Technical Approach

The same system is built twice: a causal Python model and an acausal OpenModelica model, so the two paradigms can be compared side by side. The OpenModelica cruise experiment closes the plant with boundary sources and sinks and runs at the same published cruise point as the Python mission.⁷

Validation

So far the model is checked against published limits, not fitted to measured data:

• Through climb and cruise, the sensed precooler outlet stays inside the published control band,³ the intermediate stage supplies cruise, the high stage takes over in descent, and nothing trips.
• The PRSOV regulates to the published setpoint, and the temperature limit and trip act at the published values.³
• The precooler’s conductance is solved so the two flight-test cases land in that band.²

The OpenModelica cruise experiment settles on the same setpoint and band. Measured-data validation cases are catalogued in the research library and are the next phase.

Results

The sensed outlet temperature holds the published 390–440 °F band through climb and cruise³ and dips below it at idle power in descent. It never reaches the temperature limit or the overheat trip.

Research

The parameters and validation cases come from a curated library of 28 public papers, reports and theses on aircraft bleed and air conditioning systems, each read and filed with a short summary and notes on where its data sits. Progress notes and research findings are posted below as the work goes on.

Sources & Disclaimer

This is an independent educational project. It is a 737-800-class reference architecture built only from public sources: peer-reviewed papers, a doctoral dissertation, an FAA technical report and a government incident report. No manufacturer, maintenance, training or other proprietary documents were used, and it is not a replica of any manufacturer’s hardware. It is not affiliated with or endorsed by Boeing, Airbus, or any equipment supplier.

Every model value in the code is tagged to one of the references below, to a derivation written out from them, to textbook physics, or to a labelled generic modelling assumption. A provenance checker runs with the test suite and fails the build on any untagged value.

References