Abstract. A study of airfoil behaviour is undertaken using two independent non-intrusive measurement techniques, surface oil flow visualization (SOFV) and infrared thermography (IT) to quantitatively determine flow parameters such as separation and reattachment points on the airfoil. Several airfoil heating methods are described and several airfoil materials are evaluated. Results are presented here for constant Re = 4.7 × 10 4 , with the angle of attack varied from 0 • to 13 • . Innovative post processing methods are used for the IR temperature data to reveal important details of the flow. All methods provide comparable results and allow further understanding of these characteristics and the extension to large scale, dynamic and unsteady flow situations.

<div class="section abstract"><div class="htmlview paragraph">Road vehicles have been shown to experience measurable changes in aerodynamic performance when travelling in everyday safe-distance driving conditions, with a major contributor being the lower effective wind speed associated with the wakes from forward vehicles. Using a novel traffic-wake-generator system, a comprehensive test program was undertaken to examine the influence of traffic wakes on the aerodynamic performance of heavy-duty vehicles (HDVs). The experiments were conducted in a large wind tunnel with four primary variants of a high-fidelity 30%-scale tractor-trailer model. Three high-roof-tractor models (conventional North-American sleeper-cab and day-cab, and a zero-emissions-cab style) paired with a standard dry-van trailer were tested, along with a low-roof day-cab tractor paired with a flat-bed trailer. Amongst these, trailer variants provided a total of 10 HDV configurations that were tested in uniform turbulent flow over a range of freestream yaw angles between ±15°, and with wake effects over a range of yaw angles between -2° and +11°. Up to 53 specific wake-flow conditions were applied to each HDV configuration. Wind-load and surface-pressure measurements were acquired and provide indicators of the manner in which the aerodynamic performance of the HDV models are influenced by traffic wakes.</div><div class="htmlview paragraph">Drag-coefficient reductions up to 17% for individual drag-coefficient values and up to 9% for wind-averaged values were observed. Wakes from adjacent-lane vehicles were observed to have comparable, or sometimes greater, influence to those from safe-distance same-lane vehicles. The wakes influence primarily the forward-facing surfaces of the HDV, resulting in performance changes associated with tractor modifications being affected more than for trailer modifications. These results represent the first comprehensive study of traffic-wake effects on HDVs at safe inter-vehicle distances in highway-driving conditions, and highlight potential differences in real-world aerodynamic performance relative to the standard wind-averaged uniform-flow metrics used for fuel/energy-use and emissions predictions.</div></div>