Colloquium: Coen Holland (FPT)

This thesis investigates automotive underbody aerodynamics using an on-site 3D Lagrangian Particle Tracking (LPT) system. By utilising the Ring of Fire setup—using sub-terranean high-speed cameras and helium-filled soap bubbles as tracers—velocity fields beneath a moving car model (7.5 m/s) were reconstructed for three geometries: a flat floor, a 15° diffuser, and a diffuser equipped with a set of vortex generator fins at its leading edge. Results show a peak velocity of 1.4 times the freestream speed beneath the diffuser-equipped model, with velocity and pressure profiles aligning with literature. Vortex generators helped move high-momentum flow closer to the diffuser surface, potentially mitigating laminar separation. By combining data from multiple runs per geometry, the obtained velocity distributions converged to within 1% of the mean car velocity. The study demonstrates the feasibility of 3D LPT for on-site underbody flow measurements and its potential for larger, faster vehicles.

Supervisor: Andrea Sciacchitano