Drag Reduction on Freight Trucks
Research by: Dr. Roy Harfield, Dr .Anwar Ahmed
The Aerospace Engineering Department at Auburn University is currently collaborating with Digital Fusion out of Huntsville, AL to develop a framework to reduce the aerodynamic drag and increase the highway safety of tractor trailers. The project is being funded under a research grant from the U.S. Department of Transportation. The efforts involved include CFD simulations, experimental wind tunnel testing, and aerodynamic optimization. These activities are taking a unique step forward for tractor trailer design by coupling performance evaluation using Computational Fluid Dynamics (CFD) with a genetic algorithm (GA). Genetic Algorithms are population based evolutionary algorithms in which individual members (designs) of a population of designs are tested for fitness (minimum drag in this case). Successive generations of candidate designs are produced from preceding generations using probabilistic reproduction rules.
To illustrate the focus of this activity, a minimum drag two-dimensional mirror has been designed using the tournament based GA along coupled to FLUENT® for drag prediction. A schematic showing the mirror hardware and the optimized flow solution for this design exercise are shown in the figures below.
 "Flow Around Mirror")
 "Pressure Differential Around Mirror")
Schematic of mirror setup and flow solution around optimized mirror shape
In a related effort, Dr. Roy and a group of his students are being supported by the U.S. Department of Energy in the investigation of the structure of the turbulent wake developed behind tractor-trailers. An unsteady turbulence simulation is shown below where the larger, more energetic turbulent structures in the wake are simulated, while the smaller, more homogeneous structures are modeled. This figure gives the z-component of vorticity which provides a measure of the rotation of the flow about the z-axis (blue denotes clockwise rotation while red denotes counter-clockwise rotation).
 "Turbulent Truck Wake")
Unsteady Turbulence simulation of a Truck Wake
