Wind-Tunnel Modelling off Commercial Vehicle Drag-Reducing Devices: Three Case Studies

Road and wind-tunnel tests are presented which examine the drag coefficient reductions from aerodynamic devices fitted to three trucks.

A modified SAE Type II procedure utilising an instrumented chase car, evaluated on-road, constant-speed drag reductions as a function of yaw angle. At 100 km/h, turbulence intensities of 1% - 4% were measured.

The wind-tunnel results generally overestimated drag savings, particularly at high yaw angles. This was greater for cabin deflectors than for solid fairings. Simulating higher turbulence intensities gave improved agreement and it is argued that turbulence is a dominant modelling parameter.