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Drag coefficient comparisons are made for two half-size truck models with variable length, grain-haul height, closed trailers, and with identical frontal areas and length/volume distributions. One, a simple block model, with sharp edges, but characterized by correct overall dimensions, was designed to simulate only the major physical features of the truck, such as wheels, fenders, hood, cab and trailer. The second model accurately replicated body shape and hardware exposed to external and cooling air streams. Testing was conducted in the 9m x 9m NRCC, solid- wall wind tunnel of the National Research Council Canada (NRCC) over a velocity range of 48 to 193 kph (30 to 120 mph). Both models were yawed through ±14° with full-length and truncated trailer bodies. The measured coefficient data were corrected by adjusting the tunnel dynamic pressure, yaw angle, and the horizontal buoyancy effect using a simple modified pressure-signature correction method.

A critical assessment is made of tunnel wall interference corrections, indicated testing limits, and the data correlations for yawed truck models inside a solid-wall test section, using a modified pressure-signature method. Two models, a full-size tractor-trailer and a similar half-scale model, were tested in the 9 x 9 meter wind tunnel of the National Research Council of Canada (NRCC). Both models were yawed through ±14° with full length and truncated trailer bodies for the purpose of determining wind-averaged drag and exploring the real aerodynamic testing limits due to tunnel interference. The correction method employed an algorithm to perform an iterative solution to determine the strengths of potential sources, sinks, and horseshoe vortices for given inputs (measured ceiling pressures, side force, yaw and roll moments, as well as dimensional data). The output comprised corrections to tunnel dynamic pressure and yaw angle, and a horizontal buoyancy effect.

This paper outlines the techniques used to install both a full scale and a half scale tractor-trailer model in the 9×9 meter National Research Council of Canada wind tunnel in Ottawa, Canada. The objectives were to measure the cooling drag of an active cooling system and to investigate the aerodynamic testing limits of long, yawed models inside a solid wall wind tunnel. The tunnel interference problem is discussed as it pertains to the upstream boundary, test section floor, downstream boundary, ceiling and side walls and tractor-trailer surface pressure measurements. A potential solution to the problem, however, is the subject of a follow-up paper.