Method
This page summarises how Deneb Aero computes its results. The report of each project states the method used for that project (Engineering Report).
Solver
Each run is a steady, incompressible Reynolds-averaged Navier–Stokes (RANS) solution computed with OpenFOAM. The aircraft is pitched by α and yawed by β in a box several body lengths across, at the cruise speed in the project’s air.
Two set-ups are used:
Set-up |
Model and mesh |
Used for |
|---|---|---|
Wall-resolved transition |
k-ω SST with the γ–Reθ transition model (SST-LM). Body-fitted mesh with about 20 prism layers resolving the boundary layer, first-cell y⁺ below 1. For a 2.5 m aircraft about 6 million cells. |
The polar (Performance and Full flight model). Captures laminar flow and its transition. |
Wall functions |
k-ω SST, fully turbulent, with wall functions. Coarser mesh, about 2 million cells for a 2.5 m aircraft. |
Control, sideslip, rate and propeller runs, as increments from a neutral run on the same mesh. Quick look and multirotor body runs. |
The freestream turbulence is 0.25%. The mesh is generated automatically for each attitude.
Convergence
A run iterates until its loads are stationary. The loads are averaged over the final iterations of the run. The convergence check also looks at the residuals, continuity and the bounding of the turbulence fields. The outcome is the solution type of the run (Solution Types and Convergence).
Controls
Each control surface is rotated about its hinge line in the CAD geometry, and the aircraft is meshed and solved with the surface deflected. The effect of the control is the difference from the neutral run on the same mesh. Deflections of ±5° and ±10° form the response tables of the flight model.
Rate damping
The roll, pitch and yaw damping are computed in a rotating frame of reference, started from the converged α 2° run.
Propellers
Propellers are modelled as actuator disks: the cruise motor at the thrust that holds cruise, and the lift rotors holding the weight. The results are the propwash applied in the flight model and the download of the rotors on the airframe.
Unsteady runs
Past the lift peak, angles can be solved again in physical time (URANS), with the polar’s model and mesh: 20 chord transits to settle, then 40 averaged. The time mean replaces the steady value in the polar.
Flight model
The flight model interpolates the CFD tables in α and in the control deflection. Outside the sampled range, responses are held at their end values. Where the damping is semi-empirical rather than from the rate runs, the notes of the last build say so (Building the Flight Model). Motors and the battery are modelled from the motor constants and a lithium-polymer pack whose voltage falls as it empties and sags under load. The autopilot is ArduPilot SITL (ArduPlane or ArduCopter) with generated parameters.