112 lines
6.3 KiB
Markdown
112 lines
6.3 KiB
Markdown
# VZ21-size turbo prototype
|
|
|
|
Linux Release, 2026-10-23. Core is ready for an early interactive test. Further
|
|
map fitting, acoustic work and performance tuning are deferred at the user's
|
|
request so testing can start. No blade-passing whistle has been implemented yet.
|
|
|
|
## Model
|
|
|
|
Four finite 0-D gas volumes connect compressor inlet/outlet and turbine
|
|
inlet/outlet to existing `BoundarySystem` pipe orifices. Register the turbo once
|
|
with `Solver`; do not separately register its internal volumes. Internal flows
|
|
are bidirectional and choked where appropriate. Donor budgets preserve positive
|
|
mass/energy. Compensated 0-D volume accumulation prevents sub-ulp mass drift.
|
|
|
|
The compressor's estimated Euler head is psi*(omega*R)^2. Efficiency maps this
|
|
to a virtual stagnation pressure; a compressible restriction determines actual
|
|
flow against the downstream pressure. The turbine flow follows an effective
|
|
nozzle. Its torque uses a mean-line speed-ratio efficiency parabola, with finite
|
|
starting torque. Reverse flow is passive; deep surge/reverse-wheel aerodynamics
|
|
are not validated. These correlations are not a measured compressor/turbine map.
|
|
|
|
A rigid shaft obeys I*domega/dt = turbine torque - compressor torque - bearing
|
|
and windage torque. Implicit midpoint work balances the exact change in rotor
|
|
kinetic energy, including starting from rest. Adaptive shaft steps prevent
|
|
large timesteps from reversing the rotor numerically. Turbine work is removed
|
|
from gas enthalpy; compressor work is added to charge enthalpy. Bearing loss is
|
|
tracked as heat outside the gas circuits. No shaft-speed or boost clamp is used.
|
|
|
|
Estimated default parameters: inertia 4e-6 kg m^2, compressor effective radius
|
|
18 mm, turbine mean effective radius 13.5 mm, efficiencies .65, compressor head
|
|
coefficient .6, effective compressor/turbine flow areas 110/100 mm^2. Housing
|
|
volumes are 20/30/30/20 cc. Connection bores are 24/24/25/26 mm. Viscous bearing
|
|
coefficient is 1e-7 Nm/(rad/s), windage coefficient 2e-11 Nm/(rad/s)^2.
|
|
|
|
The estimated wastegate has an 800 mm^2 pressure diaphragm, 40 N preload,
|
|
6000 N/m spring, 120 Ns/m overdamped linkage, 14 mm valve and 4 mm maximum lift.
|
|
Compressor delivery gauge pressure drives its opening. Bypass gas transfers
|
|
enthalpy without delivering turbine shaft work. The actuator is an idealized
|
|
external pressure-control linkage; its mechanical/thermal energy is outside the
|
|
audited gas/rotor system. There is no intercooler, blow-off valve, oil-temperature
|
|
model, knock model or thermal/wheel failure model.
|
|
|
|
## Reference basis
|
|
|
|
[Ecotrons VZ21 specification](https://ecotrons.com/files/ECOTRONS%20Turbo%20VZ21%20technical%20specl.pdf)
|
|
provides rough applications and casing dimensions; its performance illustrations
|
|
explicitly refer to a similar IHI family rather than measured VZ21 maps. Those
|
|
figures cannot validate the coefficients used here. A
|
|
[supplier's VZ21 listing](https://www.maxpeedingrods.nl/en/products/rhb31-vz21-turbocharger-junta-100ps-for-motor-pequeno-rhino-motocicleta-at-vz21-npvl)
|
|
lists 24.2/37.1 mm compressor and 35/26.7 mm turbine inducer/exducer diameters.
|
|
The model's effective radii remain estimates.
|
|
[NASA compressor/turbine work relations](https://www.grc.nasa.gov/WWW/K-12/BGP/ctmatch.html)
|
|
provide the ideal-gas thermodynamic basis. Conservation checks establish
|
|
numerical consistency, not predictive accuracy for a real VZ21.
|
|
|
|
## Verification
|
|
|
|
All nine CTest suites passed after the changes. New checks cover stationary
|
|
equilibrium, startup, closed mass/energy balance, a pre-spun rotor, large shaft
|
|
timestep passivity, reverse flow, choking, subcritical backpressure response,
|
|
wastegate bypass, hot pulsing pipe coupling and twin throttle/limiter/release.
|
|
|
|
Closed 10 ms runs: measured mass drift zero; energy error -0.16 microjoule from
|
|
rest and -0.71 microjoule with an initially 120000 RPM shaft. Energy totals
|
|
include all gas, rotor and bearing heat. A hot 80 Hz pulsing pipe bench reached
|
|
189122 RPM, delivered .03067 kg/s charge at 376 K, and retained turbine power
|
|
pulses of 1189..4022 W. No internal transfer limiting or pipe repairs occurred.
|
|
|
|
The seven-second twin transient reached 236218 RPM, peak charge pressure
|
|
181.46 kPa absolute, peak instantaneous turbine-inlet pressure 674.10 kPa and
|
|
2.78 mm gate lift. It coasted down to 151755 RPM after release. Audio peak was
|
|
.02933 full scale, with no clipping; accumulated turbo energy residual was
|
|
-8.8 microjoules. High shaft speeds are model output, not validated operating
|
|
limits or evidence that a real VZ21 would survive them.
|
|
|
|
Same-engine-speed dyno comparison, .7 pedal, averaging the last half-second of
|
|
each two-second run:
|
|
|
|
| RPM | Turbo | MAP kPa | Exhaust collector kPa | Shaft kW | Charge K | Shaft turbo RPM |
|
|
| ---: | :---: | ---: | ---: | ---: | ---: | ---: |
|
|
| 4000 | no | 93.30 | 110.00 | 23.54 | — | — |
|
|
| 4000 | yes | 151.31 | 172.99 | 24.01 | 387.58 | 194130 |
|
|
| 7000 | no | 84.56 | 115.02 | 40.64 | — | — |
|
|
| 7000 | yes | 147.13 | 226.09 | 39.69 | 397.86 | 214361 |
|
|
|
|
Pressure and temperature costs are retained: boost does not guarantee more
|
|
shaft power. There is no forced power gain. Effective area/efficiency, gas
|
|
properties and the base engine's approximate combustion/overlap affect these
|
|
numbers strongly. They are prototype comparisons, not real engine predictions.
|
|
|
|
The original benchmark used four solver substeps per output frame. The turbo cost .81
|
|
CPU seconds per simulated second at 4000 RPM and 1.28 at 7000 RPM, versus .53
|
|
for the unboosted twin. Sustained high-load real-time playback is an open issue;
|
|
monitor underruns. The mixed transient cost .84 wall seconds per simulated
|
|
second. The subsequent [optimization audit](OPTIMIZATION.md) resolves the
|
|
subnormal-tracer slowdown and measures about .65 seconds per simulated second
|
|
in its 7,000-RPM workload. Tests run headlessly; latest Windows runtime is unverified.
|
|
|
|
## Run
|
|
|
|
```sh
|
|
cmake --build build-desktop --target fluidsim_desktop -j 4
|
|
./build-desktop/fluidsim_desktop --scenario twin --turbo vz21 --scene field
|
|
cmake --build build-audit --target fluidsim_turbo_benchmark -j 4
|
|
./build-audit/fluidsim_turbo_benchmark
|
|
```
|
|
|
|
The startup menu also offers the turbo twin. WAV capture accepts
|
|
`--scenario twin --turbo vz21`. Blade-passing acoustics are the next requested
|
|
part: they must follow rotor geometry/loading and be filtered before 44.1 kHz
|
|
sampling, rather than adding an arbitrary sound or aliased pressure ripple.
|