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Motorsport Underbody Venturi Diffuser & Rear Wing: Ground Effect (CFD)
3D RANS (k-ω SST) ground-effect aerodynamics of a racecar body with front splitter, low-clearance undertray throat, 16° rear diffuser ramp, and rear wing element at 40 m/s (144 km/h), generating 106.1 N of aerodynamic downforce.
In modern motorsport aerodynamics, over 60% of total downforce is generated by the underbody floor and rear diffuser operating in close ground proximity. This 3D CFD case models a half-car aerodynamic body with a low-clearance undertray Venturi throat above the ground plane, an upswept rear diffuser expansion ramp, and an upper rear wing element inside a 900 × 260 × 320 mm wind tunnel at U_∞ = 40 m/s (144 km/h). The constriction between the undertray and the ground accelerates the airflow, creating a strong low-pressure suction zone (p_min = −1,942.4 Pa) that pulls the vehicle downward with F_Z = −106.12 N of net aerodynamic downforce while the diffuser ramp recovers pressure into the wake.
1. Geometry & FEA Mesh
- •Single B-Rep fluid domain (D_fluid = Tunnel − CarBodyAndWing): 900 mm length (X ∈ [-200, 700] mm), 260 mm width (Y ∈ [0, 260] mm), and 320 mm height (Z ∈ [0, 320] mm).
- •Underbody Venturi channel with low ground clearance, upswept rear diffuser ramp, and rear wing element generating coupled undertray + upper-element downforce.
- •Unstructured tetrahedral mesh: 18,570 tetrahedra and 4,176 nodes (volume error 0.00%).
- •Working fluid: air (ρ = 1.225 kg/m³, μ = 1.81×10⁻⁵ Pa·s) with Menter k-ω SST turbulence model.
2. Loads & Boundary Conditions
- •Wind tunnel inlet face (surface number 1): uniform velocity U_in = 40.0 m/s (144 km/h) along +X ([1, 0, 0]).
- •Downstream outlet face (surface number 25): static gauge pressure p_out = 0 Pa.
- •Centerline symmetry plane, moving-ground floor plane, and tunnel ceiling/side wall (surfaces 2, 3, 6, 9): slip / symmetry boundary conditions.
- •All car body, undertray throat, diffuser ramp, and rear wing surfaces (19 wet faces): viscous no-slip wall (u = 0).
3. Simulation Results & Findings
- ✓Venturi constriction under the floor accelerates flow up to |U|_max = 113.38 m/s (2.83× freestream) and drops static pressure to p_min = −1,942.4 Pa.
- ✓Total vertical aerodynamic force is strongly negative (downforce): F_Z = −106.12 N (C_L = −4.2083) with aerodynamic drag F_D = 109.29 N.
- ✓Trailing edge of the diffuser and rear wing sheds a strong counter-rotating vortex pair with peak vorticity |ω|_max = 2,102.4 s⁻¹ and Q_max = 8.48×10⁵ s⁻²; mass imbalance is 0.00%.
WebCAE allows automotive and motorsport aero engineers to iterate on ride height, diffuser ramp angle, and splitter balance directly in the browser or desktop app with immediate downforce and streamline feedback.
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