BladeCC

C port of CCBlade.jl (Andrew Ning's blade element momentum solver for propellers/fans and wind turbines).

Credits and license

This project is a derivative work of two Julia packages by Andrew Ning (BYU FLOW Lab):

• CCBlade.jl — the BEM solver ported here in full (src/ccblade.c, src/airfoils.c)
• FLOWMath.jl — the numerical routines CCBlade depends on, ported as needed (src/interp.c and the Brent solver in src/ccblade.c): Akima splines, recursive 2D/3D interpolation, trapezoidal integration, and Brent root finding

Both upstream packages are MIT licensed. This port retains the same MIT license (see LICENSE.md) with the original copyright notice.

Build & test

make          # builds libbladecc.a
make test     # builds and runs the test suite (from tests/)
make check    # static analysis with cppcheck
make analyze  # static analysis with scan-build (clang)
make format   # clang-format all sources (Google style)
make format-check  # verify formatting without modifying files

Dependencies: a C99 compiler and libm. No external libraries. make check needs cppcheck; make analyze needs clang's scan-build make format/format-check need clang-format

Layout

• include/ccblade.h — public API
• src/ccblade.c — BEM core: residual, quadrant-aware bracketing, Brent root solve, simple_op/windturbine_op, thrust/torque integration (incl. azimuth-averaged), nondim
• src/airfoils.c — airfoil data: file parsing/writing, AlphaAF/ AlphaReAF/AlphaMachAF/AlphaReMachAF/SimpleAF/function callbacks, Prandtl–Glauert / skin-friction / DuSelig–Eggers corrections, Prandtl tip/hub loss, Viterna extrapolation, linear lift-curve extraction
• src/interp.c — Akima spline, recursive 2D/3D interpolation, trapezoid rule
• tests/runtests.c — port of the Julia test suite
• tests/gen_reference.jl, tests/reference_data.h — Julia-generated reference values for functions the Julia suite does not cover (viterna, Re/Mach airfoil evaluators, Akima extrapolation)
• tests/extract_arrays.jl, tests/test_arrays.h — test data transcribed programmatically from runtests.jl
• tests/compare_julia.jl, tests/compare_c.c — end-to-end C-vs-Julia sweep comparison
• tests/airfoils/ — polar data files (copied from the Julia repo)

Port fidelity

• The Akima spline is a direct port of FLOWMath's implementation (endpoint slope estimation, clamped-index extrapolation, n=2 behavior)
• All quadrant/branch logic in solve (hover, reversed flow, windmill, empirical high-induction region) is ported verbatim.
• Verification: the three portable Julia testsets pass (normal operation 157, qualitative check 338, correction methods — expanded per-element), plus ~530 checks against Julia-generated reference data, plus an independent 42-point thrust/torque sweep (hover to 55 m/s, 0–12000 RPM) agreeing with Julia to a max relative error of ~2e-11. Clean under ASan/UBSan/LeakSanitizer.

Not ported (Julia-specific)

• Automatic differentiation (ImplicitAD / ForwardDiff glue) — the solver always evaluates numerically; call cc_solve for values only.
• StructArrays broadcasting, OffsetArrays/FillArrays interop — in C you loop over CCSection/CCOperatingPoint arrays yourself.
• The Julia Rotor corrections are struct fields instead of dispatched types; see CCRotor in ccblade.h.

Notes

• cc_solve prints a warning and returns zero loads when no bracket is found, mirroring Julia's @warn behavior; use cc_solve_ex(..., &success) to detect this programmatically (relevant for batch LUT generation).