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During the wind-tunnel development of racing vehicles, modifications are made to the vehicles in an effort to minimize lap times. The optimal configuration is usually a function of the chassis, powertrain and track; so several different aerodynamic configurations are required to maximize performance throughout a season. The results of a wind tunnel test are typically drag and lift measurements but the desired information is the change in lap time. This paper proposes a method to relate wind tunnel measurements to on-track results using a simple performance simulation. Though relatively straightforward, this technique has been observed to improve the efficiency and outcome of several wind tunnel tests.

The 9-meter wind tunnel of the National Research Council (NRC) of Canada is equipped with a boundary layer suction system, center belt and wheel rollers to simulate ground motion relative to test articles. Although these systems were originally commissioned for testing of full-scale automotive models, they are appropriately sized for ground simulation with half-scale tractor-trailer combinations. The size of the tunnel presents an opportunity to test half-scale commercial vehicles at full-scale Reynolds numbers with a model that occupies 3% of the test section cross-sectional area. This study looks at the effects of ground simulation on the force and pressure data of a half-scale model with rotating tractor wheels. A series of model changes, typical of a drag reduction program, were undertaken and each configuration was tested with both a fixed floor and with full-ground simulation to evaluate the effects of this technology on the total and incremental drag coefficients.

The National Research Council of Canada (NRC) is commencing a new round of aerodynamic development of heavy trucks in partnership with Natural Resources Canada (NRCan), the Canadian Trucking Alliance (CTA) and the US Department of Energy (DOE). The program is meant to take second-generation, add-on technology from the wind tunnel to the fleet. The purpose is to reduce fuel consumption and greenhouse gas emissions. The benefit is that the fuel reductions pay the operators to improve their vehicle emissions. 1:10-scale model tests in the NRC 2m × 3m wind tunnel, followed by full-scale tests on a Navistar 9200 Day Cab with 40-foot trailer in the NRC 9m × 9m wind tunnel, were employed to develop the add-on devices of interest. The results demonstrated significant fuel savings from a combination of longer cab extenders, trailer skirts and trailer boat-tails that reduced fuel consumption as much as the contemporary aerodynamic cab packages.

The National Research Council of Canada (NRC) has completed the second round of full-scale wind tunnel tests on Class-8 tractor-trailer combinations. The primary intent of the program is to effect a reduction in greenhouse-gas emissions by reducing the fuel consumption of trucks through aerodynamic drag reduction. Add-on aerodynamic components developed at the NRC several decades ago have become important contenders for drag reduction. This program has encouraged the commercialization of these technologies and this round of tests evaluated the first commercial products. Three primary devices have been evaluated, with the combination able to reduce fuel consumption by approximately 6,667 liters (1,761 US gal) annually, based on 130,000 km (81,000 miles) traveled per tractor at a speed of 100 km/hr (62 mi/hr).

The 9-meter wind tunnel of the National Research Council (NRC) of Canada is commonly employed in full-scale testing of class 8 tractors. In this configuration the model blocks 10 - 15% of the test section cross-sectional area, which is greater than generally advocated blockage limits. The NRC utilizes the Maskell III method to correct data for wall interference but the effectiveness of this technique at such blockage levels remained to be seen. Corrected full-scale data was compared to data acquired with a half-scale model to determine how closely the corrected high-blockage data would agree with the low-blockage baseline. The half-scale model presented an opportunity to test at full-scale Reynolds numbers, with less than 4% blockage, which falls within most recommendations of maximum allowable blockage.

The measurement of the top speed of a racecar on a test track is commonly used in the aerodynamic development of the car and as a verification of wind tunnel results. The speed differences resulting from typical drag and lift changes will be small, requiring precise (i.e. repeatable) speed measurement. Unfortunately, changing environmental conditions over one or several days of trials will make these results unreliable at the required level of accuracy. This paper discusses the errors encountered in top speed testing and suggests methods to improve accuracy.

The 9-meter wind tunnel of the National Research Council (NRC) of Canada is commonly employed in testing of class 8 tractors at full- and model-scales. In support of this work a series of tests of an identical model at full- and half-scale were performed to investigate some of the effects resulting from simulation compromises. Minimum Reynolds Number considerations drive the crucial decisions of what scale and speed to employ for testing. The full- and half-scale campaigns included Reynolds Number sweeps allowing conclusions to be reached on the minimum Reynolds number required for testing of fully-detailed commercial truck models. Furthermore the Reynolds sweeps were repeated at a variety of yaw angles to examine whether the minimum Reynolds Number was a function of yaw angle and the resulting flow regime changes. The test section of the NRC 9-meter wind tunnel is not sufficiently long to accommodate a full-scale tractor and a typical trailer length of 48′ or more.