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A heavy truck wind tunnel test program is currently underway at the Langley Full Scale Tunnel (LFST). Seven passive drag reducing device configurations have been evaluated on a heavy truck model with the objective of understanding the practical limits to drag reduction achievable on a modern tractor trailer through add-on devices. The configurations tested include side skirts of varying length, a full gap seal, and tapered rear panels. All configurations were evaluated over a nominal 15 degree yaw sweep to establish wind averaged drag coefficients over a broad speed range using SAE J1252. The tests were conducted by first quantifying the benefit of each individual treatment and finally looking at the combined benefit of an ideal fully treated vehicle. Results show a maximum achievable gain in wind averaged drag coefficient (65 mph) of about 31 percent for the modern conventional-cab tractor-trailer.

A wind tunnel test program was conducted at the Langley Full Scale Tunnel (LFST) to evaluate the performance of five passive drag reduction configurations on a modern straight truck at full scale. Configurations were tested in a build-up fashion with results representing a cumulative effect. Tested configurations include a front valance, a front box fairing, a boat-tail, an ideal side-skirt, and a practical side-skirt. Configurations were evaluated over a nominal 9 degree yaw sweep to establish wind averaged drag coefficients using SAE J1252. Genuine replicate yaw sweeps were used in an uncertainty analysis. Results show up to 28% improvement in wind-averaged drag coefficient and that significant gains can be made in straight truck fuel economy, even at non-highway speeds.

A computer simulation was developed to investigate the effect of wind on test track estimation of heavy truck fuel efficiency. Monte Carlo simulations were run for various wind conditions, both with and without gusts, and for two different vehicle aerodynamic configurations. The vehicle configurations chosen for this study are representative of typical Class 8 tractor trailers and use wind tunnel measured drag polars for performance computations. The baseline (control) case is representative of a modern streamlined tractor and conventional trailer. The comparison (test) case is the baseline case with the addition of a trailer drag reduction device (trailer skirt). The integrated drag coefficient, overall required power, total fuel consumption, and average rate of fuel consumption were calculated for a heavy truck on an oval test track to show the effect of wind on test results.

External aerodynamics remains one of the major concerns in designing a new generation road vehicle. In the present study, the external aerodynamics of an Ahmed body at a scale and Reynolds number, that are representative of a car or light truck at highway speeds, is explored. An experimental model test was compared with a computational model using various back angles. In addition, the experiment allowed lift and drag to be measured at yaw angles up to ±15 degrees. Reynolds number effect on drag and lift coefficients was studied and wind averaged drag coefficients were calculated. The numerical calculations used a Reynolds-averaged, unsteady Navier-Stokes formulation. Both experimental and computational results are presented for back angles of 0-, 12.5-, and 25-degrees, then compared with each other and the data available in the literature.

Commercial heavy trucks are characterized as bluffbodies and have unsteady wake flows and high base drag. Base drag has been studied for many years as a primary target for aerodynamic drag reduction. Many aftend devices have been created for active or passive reduction of base drag. Base flaps are one type of device that have shown promise for drag reduction. They consist of 3 or 4 panels joined at their edges to form an open box structure. Although base flaps have been shown to reduce drag, they have not been adopted by the trucking industry because they are inconvenient to deploy on a commercial scale. A practical refinement to base flaps is the two-panel wake board (WB). It is a commercially viable solution, with easy deployment and significant drag reduction. This paper presents experimental data for two-panel wake boards with varying width and inset on an Ahmed body at yaw angles up to 12 degrees.

Aerodynamic drag, lift, and side forces have a profound influence on fuel efficiency, vehicle speed, stability, acceleration and performance. All of these areas benefit from drag reduction and changing the lift force in favor of the operating conditions. The present study simulates the external flow field around a heavy truck with three prototype add-on drag reduction devices using a computational method. The model and the method are selected to be three dimensional and time-dependent. The Reynolds-averaged Navier Stokes equations are solved using a finite volume method. The Renormalization Group (RNG) k-ε model was elected for closure of the turbulent quantities. The run cases were chosen so that the influence of each drag reduction device could be established using a regression model from a Design of Experiments (DOEX) derived test matrix.