Automotive external aerodynamics (Lattice Boltzmann)

Project · Project 43

A high-fidelity aerodynamic analysis of a full-scale DrivAer vehicle using a GPU-accelerated Lattice Boltzmann Method solver (XFlow), evaluating the aerodynamic performance of multiple body configurations — fastback, notchback and estateback — under realistic operating conditions at 140 km/h.

Method

A complete CFD setup was developed including domain sensitivity analysis, a lattice refinement strategy (coarse vs fine resolutions down to 1 cm in critical regions), and time-step control based on CFL criteria, ensuring numerical stability and physical accuracy.

The simulations employed a WMLES turbulence model with advanced wall-function treatment to capture separation and wake dynamics, which is where the differences between the three rear-end shapes actually live.

Velocity field cutting plane for the three body configurations/assets/img/projects/drivaer-velocity.png

Fig. 1 — Velocity field cutting plane at z = 0 for fastback, notchback and estateback.

Results

Aerodynamic coefficients (C_d, C_l) were quantified and validated against wind tunnel and literature data, achieving errors of under 5% in refined cases.

Pressure coefficient along the vehicle centreline compared with references/assets/img/projects/drivaer-cp.png

Fig. 2 — Pressure coefficient vs longitudinal location, against experimental and reference data.

Detailed flow physics analysis followed, including pressure coefficient distributions along the vehicle centreline, surface C_p contours, velocity field slices, and wake structure visualization. This identified the key separation regions at the rear geometry and explained the drag differences between configurations, with the estateback showing the highest drag due to early separation.

The study also highlighted the sensitivity of drag prediction to mesh, identifying limitations due to insufficient refinement in separation regions and open geometry manifolds — worth stating, because a 5% agreement in refined cases is not the same as 5% everywhere.