No abstract

SUMMARYThree-dimensional incompressible laminar flow around a cube is investigated using the vorticity-vector potential formulation of the equations of motion. Numerical solutions to a semi-implicit finite difference approximation to the vorticity transport equation coupled to discrete Poisson equations for the scalar and vector potentials are obtained using an eight-colour SOR algorithm. Calculations are done at a range of Reynolds numbers from 10 to 100. The predicted drag and other flow characteristics are found to agree well with experimental results, including those from a cube drop experiment performed for the present study.

No abstract

No abstract

A 9347 km (5809 mi) cross-country fuel economy experiment was conducted to demonstrate typical fuel savings that can be obtained using drag-reducing devices on tractor-trailer trucks, and to ascertain the degree of correlation of the experimentally determined fuel savings with the fuel savings that could be predicted using data from drag reduction experiments on models in a wind-tunnel. Three trucks were used in the experiment. One truck was equipped with a commerically available wind deflector/vortex stabilizer system, another was equipped with a prototype streamline fairing/gap seal system developed at the University of Maryland, and the remaining vehicle was operated without any drag-reducing devices in order to obtain a basis from which to determine the fuel savings. The fuel savings per unit distance that resulted from use of the commerical drag reducing system was 0.029±.006 liter/km (0.012±.002 gal/mi), while that realized with the University-of-Maryland-developed prototype system was 0.057±.003 liter/km (0.024±.001 gal/mi). An analysis of the conditions under which these results were obtained indicated that they were conservative estimates of the fuel savings that would be realized with long-term operating of the vehicles and devices used in the experiment. Fuel savings predictions were performed using wind-tunnel drag reduction data, and relative airspeed and yaw angle data continuously measured in the fuel economy experiments. The measured fuel savings due to the commercial system was 75 ± 15% of the predicted value, and that due to the University of Maryland system was 78 ±4% of the predicted value. The differences obtained appear related to the nonsimulation of wind turbulence in the wind-tunnel experiments. Nomenclature A-aerodynamic drag reference area (product of height of trailer above ground and its width) BSFC = brake specific fuel consumption of engine C D = body-axis aerodynamic drag coefficient CF = relative fuel consumption calibration factor D A = body-axis aerodynamic drag force DR = rolling resistance drag force d = distance traveled by vehicle FC = volumetric fuel consumption FCD = volumetric fuel consumption per unit distance FR = fuel consumption rate on a mass basis FS = volumetric fuel savings P(I,J) = frequency of occurrence of wind condition (/,/) A/z -change in elevation / = index for wind angle band J = index for wind speed band P a = power required by accessories A/ = rolling time V = vehicle speed V r = speed of air relative to vehicle V w = wind speed W ~ vehicle weight d = slope angle of road surface j f = specific weight of fuel n D =driveline efficiency 0 = wind angle relative to vehicle heading \l/ = yaw angle p = air density