Accuracy
Checked against the textbooks, and clear about its limits.
WindCanvas is a real flow solver, not an animation. Here is how its numbers compare with published results, and where you should not rely on them.
The short version
On the standard 2D benchmarks, WindCanvas lands within a few percent of the textbook values, including the shedding frequency of the vortex street.
In 3D, a grid that fits a laptop’s graphics memory puts only about 17 cells across a car. That is enough to show the flow and compare designs, but the absolute drag of a real vehicle reads about 2.5 times high.
| Benchmark | Measured | Reference |
|---|---|---|
| Cylinder, Re = 100, 2D, 20 cells across | Cd 1.383, St 0.168 | Cd 1.353, St 0.166–0.168 |
| Same cylinder at 10 cells with the 2× refinement patch | Cd 1.368 | Cd 1.353 |
| Cylinder, Re = 1000, 2D | Cd 1.548, St 0.243 | Cd ≈ 1.55, St 0.241–0.25 |
| NACA 0012 at 4°, Re = 1000, 2D | Cl 0.207, Cd 0.127 | Cl ≈ 0.20, Cd ≈ 0.125 |
| Channel flow, peak velocity ratio | 1.498 | 1.5 exact |
| Sphere, Re = 100, 3D, 16 cells across | Cd 1.17 | ≈ 1.13 in this tunnel |
| Default sedan, 3D, about 17 cells across | Cd 0.73 | ≈ 0.3 for a real car |
How it works
What is under the hood.
Lattice-Boltzmann method. Instead of solving the Navier–Stokes equations directly, WindCanvas tracks how populations of fluid particles stream and collide on a grid (D2Q9 in 2D, D3Q19 in 3D). It is well suited to graphics chips, which is why it runs live.
Cumulant collisions and LES. A cumulant collision model keeps the solver stable at high Reynolds numbers, and a Smagorinsky large-eddy model represents turbulence smaller than a grid cell.
Curved walls. Walls are placed where the surface really is between grid points (interpolated bounce-back), so a cylinder is round rather than a staircase. In 2D, a patch at twice the resolution can follow the body to sharpen the boundary layer and wake.
Effective Reynolds number. A laptop grid cannot resolve a full-size car at motorway speed, so WindCanvas runs the flow at the highest Reynolds number the grid supports and shows you that effective value beside every result.
Fidelity grade
Every result says how far to trust it.
The Analysis tab grades each run from the cells across the body, the effective Reynolds number and how settled the flow is, and explains in plain words what limits the result. Compare designs at the same grade, and treat a difference smaller than the stated uncertainty as no difference.
- Grid studies show how the drag changes as the grid is refined.
- The validation suite (Pro) reruns the benchmarks above on your own computer.
- The user guide’s chapter on physics and accuracy explains every assumption.