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Aerodynamics of Trucks in Wind Tunnels: The Importance of Replicating Model Form, Model Detail, Cooling System and Test Conditions
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Abstract
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. This method was previously shown to result in correlating the wind-averaged drag coefficient data of the half-scale detailed model and actual full-scale vehicle within a 1% to 2% margin for the 7 mph wind speed and 55 mph road speed (7 and 55 mph) and 7 and 30 mph conditions, respectively.
The half-scale model, representing a 2.2% frontal-area blockage in the wind tunnel was observed to be independent of Reynolds number effects inside the range of 2.2 x 106 to 4.4 x 106. Increasing trailer body length increased drag significantly. Engine cooling airflow was found to be the source of 3.8% of the total wind-averaged drag coefficient at a Reynolds number of 2.2 x 106, the ram and fan airflow contributions being 66% and 34% respectively. The difference in the wind-averaged drag due to model form and detail was inversely proportional to body length: a minimum of 2% for the full-length model and up to 11% for a 38% shortened model with the block model having the higher drag.
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Olson, M. and Schaub, U., "Aerodynamics of Trucks in Wind Tunnels: The Importance of Replicating Model Form, Model Detail, Cooling System and Test Conditions," SAE Technical Paper 920345, 1992, https://doi.org/10.4271/920345.Also In
Vehicle Aerodynamics: Wake Flows, Computational Fluid Dynamics, and Aerodynamic Testing
Number: SP-0908; Published: 1992-02-01
Number: SP-0908; Published: 1992-02-01
References
- Hackett, J.E. Wilsden, D.J. Lilley, D.E. “Estimation of Tunnel Blockage from Wall Pressure Signatures: A Review and Data Correlation.” N.A.S.A. CR-152 241 March 1979
- Schaub, U.W. Olson, M.E. Raimondo, S. “Correction of Wind Tunnel Force Data for Yawed Full and Half-Scale Truck Models Using a Modified Pressure-Signature Method.” SAE 900187 February 1990
- “SAE Wind Tunnel Test Procedure for Trucks and Buses.” SAE Recommended Practice. J1252 1979
- Waudby-Smith, P.M. Rainbird, W.J. “Some Principles of Automotive Aerodynamic Testing in Wind Tunnels with Examples from Slotted Wall Test Section Facilities.- SAE 850284 February 1985
- Schaub, U.W. Nishimura, Y. Olson, M.E. Creswick, G.E. “A Full Scale Class 8 Conventional Tractor-Trailer in the 9X9m Wind Tunnel.” SAE 881876 November 1988
- Hucho, Wolf-Heinrich Vogel-Verlag 1981 4 156 157
- Götz, Hans “Commercial Vehicles” Chapter 8 of Aerodynamics of Road Vehicles Butterworths 1987 Hucho, Wolf-Heinrich