Payload fairing v34 — CFD report

Uploaded STL payload_fairing_205x92mm_v34.stl, same pipeline as other Ø92×205 fairing cases on this site.

Mesh and geometry checks

Watertight. Current upload: trimesh.is_watertight is True (1888 triangles). surfaceCheck on the scaled STL: Surface is closed. All edges connected to two faces. The CFD below was re-run with full remesh on this STL.

Bounding box (mm, before centering in the case): X ∈ [−51.86, 51.86], Y ∈ [−51.86, 51.86], Z ∈ [−118.72, 311.48]. After import, the case uses the usual centering and scaling to metres from simulate.sh.

Simulation setup

OpenFOAM Foundation 13, steady incompressible RANS, SST k–ω
Freestream along −Z, 41.6667 m/s (150 km/h), ρ = 1.225 kg/m³
300 pseudo-time iterations; forceCoeffs on wingGroup
Aref, lRef from bounding-box estimate in simulate.sh

Results (150 km/h)

Quantity	Value
Cd	0.0105
Cl	≈ 0
Drag	0.4969 N
Aref (OpenFOAM / `simulate.sh`)	0.044618 m² — bounding-box Y × Z (not frontal; see below)
lRef	0.430207 m
Mesh cells	242 412
Case folder	`payload_fairing_205x92mm_v34_sim`

Cd/Cl averaged over last 50 time steps; drag = Cd × ½ρU²Aref with the script’s Aref.

Reference area for freestream along −Z

For flow along −Z, the usual reference for drag coefficient is the frontal (projected) area in the X–Y plane. The pipeline’s simulate.sh instead sets Aref = (Y_bbox) × (Z_bbox), which is not that frontal area.

Computed from this STL (vertex projections; convex hull in XY unless noted):

Definition	Area (m²)
Frontal, convex hull of XY vertices (recommended for axisymmetric-like bodies)	0.008233
Frontal, bounding rectangle X × Y	0.010756
Frontal, disk π(D/2)² with D = max(X span, Y span)	0.008448
`simulate.sh` (Y × Z bbox)	0.044618

Same measured drag with Cd_sim = 0.0105 implies Cd on the frontal hull area Cd_hull ≈ Cd_sim × Aref_sim / A_{frontal hull} ≈ 0.0569 (drag force unchanged; only the reference area in the denominator changes).

Reproduce: scripts/compute_frontal_aref_xy.py payload_fairing_205x92mm_v34.stl

Pressure (VTK time 300)

Surface

Slice Y = 0

Geometry (STL, Z height)

Side

Oblique

Download

payload_fairing_205x92mm_v34.stl

Machine-readable row: fairing_results.json (key "34").