Ground-Effect Racing Diffuser Downforce and Pressure Recovery

Motorsport Aerodynamics (CFD)PASS · 2.13%

Aerodynamic downforce and underbody Venturi diffuser pressure recovery for a ground-effect racing chassis with rear wing, verified against ground-effect wind-tunnel benchmark data.

Tolerance:: 5%

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Problem statement

Geometry: Racing chassis undertray with front splitter, Venturi throat (ground clearance h = 24 mm), upswept rear diffuser (expansion angle 16°), and inverted rear wing in wind tunnel 800 × 340 × 260 mm.
Material: Air at 20 °C (rho = 1.204 kg/m³, mu = 1.825e-5 Pa·s).
Boundary conditions: Inlet velocity U = 40 m/s along +X (intensity 5%), outlet gauge pressure 0 Pa, ground plane symmetry / slip, car body and wing no-slip viscous walls.
Measured quantity: Aerodynamic downforce coefficient -CL (target 4.300) and diffuser static pressure recovery Delta_p from throat minimum pressure to duct exit.

WebCAE Terminal

Paste these commands into the Terminal panel inside WebCAE. They use the same text DSL as the application; run one command per line:

units mm
import path="cfd_motorsport_diffuser.step" format=step
mesh tet size=28
cfd fluid air
cfd set mode=steady speed=40 turbulence=sst iterations=180 tol=1e-4 threads=8 intensity=5
cfd inlet surface number 1 speed=40 intensity=0.05
cfd outlet surface number 6 pressure=0
cfd symmetry surface number 2
cfd symmetry surface number 3
cfd symmetry surface number 4
cfd symmetry surface number 5
cfd wall surface number 7 monitor=on
cfd wall surface number 8 monitor=on
cfd wall surface number 9 monitor=on
cfd wall surface number 10 monitor=on
cfd wall surface number 11 monitor=on
cfd wall surface number 12 monitor=on
cfd wall surface number 13 monitor=on
cfd wall surface number 14 monitor=on
cfd wall surface number 15 monitor=on
cfd wall surface number 16 monitor=on
cfd wall surface number 17 monitor=on
cfd wall surface number 18 monitor=on
cfd wall surface number 19 monitor=on
cfd wall surface number 20 monitor=on
cfd wall surface number 21 monitor=on
cfd wall surface number 22 monitor=on
solve cfd

Results comparison

Reference value	4.300 (-CL)
Our result	4.208 (-CL)
Deviation	2.13%
Tolerance	5%
Status	PASS · 2.13%
Element family	Finite-volume CFD
Mesh details	4176 узлов, 18570 тет (Netgen P1 tet mesh, Venturi undertray + диффузор)

Updated: 2026-10-19 · WebCAE solver