CFD Tutorial no. 1 — Propeller CFD simulation

The full path, just once

This first propeller CFD simulation tutorial covers the entire chain: BEM model, meshing, Phase 1, reading the pressure field.

Propeller CFD simulation: tutorial for your first complete calculation

CFD Tutorial no. 1 of 20. The actions described here are those of the HELICIEL CFD tool window, opened from Heliciel: they assume the PRO CFD/BEM extension is active. The preset values quoted are those of the catalogue shipped with the software; the numerical results depend on your geometry and your operating point, and should be read in the software.

A propeller CFD simulation is impressive when you look at it from a distance: mesh, solver, turbulence, convergence. This tutorial shows that in practice, in Heliciel PRO CFD/BEM, it comes down to five steps. We start from a propeller already designed by the BEM method in Heliciel, and go all the way to the pressure map on the blades.

The working case: a seven-blade aircraft propeller, free rotor (non-ducted), in air. Any propeller from your library will do — the workflow is identical. What matters here is the sequence, not the machine.

Prerequisites: a propeller or wing completed in Heliciel, and the PRO CFD/BEM extension active (the menu flags it in the main menu bar);
Duration: allow about twenty minutes with the mesh preset recommended below;
What you get: thrust and torque from a fluid mechanics calculation, and the pressure map that BEM cannot produce.

Tutorial outline:

Open the CFD bench from your project
Check the fluid and the operating point
Choose the mesh preset
Mesh the fluid
Run Phase 1 and read the forces
Display the pressure on the blades
What you can do now

1: Open the CFD bench from your project

The CFD bench does not open on a blank page: it is born from your project. In Heliciel, Prototyping menu, CFD module entry, then in the HELICIEL CFD tool window, button File > New CFD case (from current model). Heliciel exports the blade and hub geometry as STL, builds the case folder, and displays the model in the 3D view.

One detail worth knowing right away: Heliciel has already decided the case type for you. A wing becomes a "wing/airfoil" case, a propeller a "rotor" case, and if your project carries a duct, a ducted case. The type label appears at the top of the window. You have nothing to declare.

Heliciel CFD bench open on a three-blade propeller with the axes reference
The HELICIEL CFD tool window when opening a new case: the geometry is there, the fluid is not yet meshed

2: Check the fluid and the operating point

Flow tab. Here you find what your BEM project already contains: the flow speed in m/s, the fluid and its parameters. The Select fluid button lets you change it, but in a validation propeller CFD simulation you obviously keep the project's fluid — otherwise the two calculations would no longer describe the same machine.

Look for the blue arrow in the 3D view: it is the X axis, and it shows the flow direction. For a propeller, it points toward −X — the flow arrives from the front face and leaves toward the wake. For a wing, it points toward +X. The rotor's rotation axis, however, stays +X in both cases.

3: Choose the mesh preset

Parameters tab, Mesh frame. The drop-down menu offers eight presets for a free or ducted propeller, from Free Level 1 — Express to Free Level 8 — Reference. Each carries its relative cost: Level 1 is worth ×1, Level 8 is worth ×117.

For a first calculation, take Free Level 3 — Balanced (×3). It is the compromise: surface refinement 4/5, 2 boundary layers, and a mesh that takes minutes — just one on a small propeller, nine on the one in this tutorial, which carries seven 1.80 m blades. Do not start with Level 7 or 8: you would wait hours to discover a geometry error that a Level 1 would have flagged in a minute.

One thing to know about the fastest presets: a blade is 2 to 5 % of the chord in thickness. At low refinement levels, the cell is thicker than the blade, and the blade becomes invisible to the mesh. The Express and Trend levels are for diagnosis and trend only; quantitative forces start at Free Level 5 — Study.

Parameters tab of the CFD bench with the list of propeller mesh presets
The Parameters tab: the mesh preset menu, with the relative cost of each level

4: Mesh the fluid

Mesh button in the toolbar. Heliciel then runs, without any intervention on your part, the background grid construction, the extraction of the blade's sharp edges, the domain decomposition across your processor cores, the adaptive meshing around the geometry, then the quality check.

Follow the progress in the Logs tab. The status bar at the bottom shows the memory and processor in use — useful for knowing whether your machine can handle the chosen preset.

When it is done, toolbar Show menu: check CFD mesh (Cyan) and uncheck 3D model. You now see the fluid, plus the blade. This is the moment to check that the mesh hugs the leading edge and the blade tip closely.

5: Run Phase 1 and read the forces

If the Run steady Phase 1 after meshing checkbox is ticked — the default setting on the Parameters tab — the solver starts on its own. Otherwise, use the CFD calculation button.

Phase 1 is a steady calculation in a rotating frame: the mesh does not move, rotation is represented by Coriolis and centrifugal terms. It is the fast phase, and its results are directly usable. The convergence monitor watches the forces on the blades and cleanly stops the calculation once they stop moving.

Phase 2, unsteady, actually rotates the mesh. It costs roughly ten times Phase 1 — the checkbox that controls it says so explicitly. Leave it aside for this first tutorial; tutorial no. 5 is dedicated to it.

Logs tab during MRF Phase 1 with the force convergence line
When Phase 1 starts: the Logs tab lists the boundary conditions actually applied, the MRF configuration, then announces the start of the force convergence monitor — which compares them every fifteen seconds

6: Display the pressure on the blades

Results tab, Show results: frame. Check Surface pressure. The blade takes on colour: low pressure on the suction side, high pressure on the pressure side, a tight gradient at the leading edge.

This is precisely what the BEM method cannot show. BEM works by blade elements and 2D polars; it gives you forces, not a field. The propeller CFD simulation gives you the field, and reading it is how you understand why a blade delivers what it delivers.

Now check Flow lines: the fluid trajectories appear, and with them the helical wake. The Matrix Me! button opens the numerical table of quantities: thrust, torque, and their breakdown.

pressure map on a propeller's blades in the Heliciel PRO CFD 3D viewer
The result of a propeller CFD simulation: the pressure map on the blades, readable at a glance

7: What you can do now

You have run a complete propeller CFD simulation. The following tutorials each take one link of this chain and go deeper into it:

what Heliciel writes for OpenFOAM, and why you do not have to write it yourself;
choosing your mesh preset by comparing three levels on the same geometry;
seeing the MRF zone, that invisible cylinder which spins the propeller without moving the mesh;
moving on to Phase 2 sliding mesh and comparing the two sets of forces;
comparing BEM and CFD results on the same propeller.

The first-calculation trap. A result that comes out is not a result that holds. Before quoting a thrust value, check three things: that convergence was genuinely reached (not that the calculation stopped on an iteration limit), that the mesh preset was at least Study, and that the mesh quality check flagged nothing. Tutorial no. 7 teaches how to read these three signals.

The collection of twenty CFD tutorials

Next: Reading the OpenFOAM case folder »

This series complements the Heliciel design tutorials, which cover the BEM side: blade design, choosing the operating regime, performance curves. CFD comes after them, to verify and to see.