FluidSimCpp/verification/SAAB_GT17.md

Saab B205 with GT17 and ECU boost control

The desktop Saab menu entry and --scenario b205 now select an estimated GT1752 turbo configuration. --turbo gt17 makes that choice explicit; --turbo none selects the previous naturally aspirated baseline. CLI and WAV capture follow the same defaults. SaabB205Scenario preserves its baseline API; SaabTurboScenario is the boosted convenience class.

The GT17 calibration uses a 26 mm compressor tip radius, 19 mm effective turbine radius, 2e-5 kg m² rotor inertia, 420/350 mm² effective compressor/turbine areas, 70% efficiencies, 100 cc housing volumes and a 24 mm wastegate. These are model estimates, not a measured Saab map or verified rotor inertia. The Garrett catalog identifies the Saab GT1752 application: https://www.turbomaster.info/eng/downloads/catalog_garrett.pdf

The ECU requests up to 45 kPa gauge boost, ramping with pedal and RPM. A PI controller uses manifold pressure filtered over 50 ms, conditional integration, and bounded pneumatic bleed duty (0–85%). Duty reduces the pressure signal to the existing spring/diaphragm actuator. Actual valve travel remains damped and boost emerges from the physical rotor, restrictions and conserved gas transfers. Zero duty restores the mechanical pressure-can response; it does not forcibly open the valve or impose a manifold pressure. Targets below spring boost cannot be achieved by wastegate bleed alone.

Lift-off, fuel cut and invalid sensor data request zero duty and clear the PI integral. Invalid boost sensors cut fuel. Manifold or charge pressure above 75 kPa gauge triggers fuel cut, recovering below 55 kPa gauge. This is a basic estimated safety calibration, not a reproduction of Saab Trionic software. No intercooler, compressor surge/BOV model or knock model has been added; charge heating and exhaust backpressure remain present.

The regression holds the engine at 3,500 RPM, applies full pedal for six seconds, then releases for three. It checks boost settling within 8 kPa of the 45 kPa target, shaft spool-up/down, finite audio, no pipe positivity repairs, no housing donor limiting, and gas/rotor energy residual below 0.1 J. Controller checks cover overboost, recovery, pedal release and an invalid sensor. The HUD shows target gauge boost, actuator bleed duty, turbo RPM and absolute gas pressures.

cmake --build build-desktop --target fluidsim_desktop -j4
./build-desktop/fluidsim_desktop --scenario b205 --turbo gt17
./build-audit/fluidsim_scenario_benchmark 6 loaded b205-gt17

All ten CTest suites pass, including the new ten-second Saab turbo regression. The GT17 benchmark holds 5,500 RPM, below the Saab's 6,500 RPM limiter.