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The boundary interference of high blockage models inside open jet test section is studied in three phases. First, a wind tunnel test was performed using a high blockage automotive model inside the 1/15th scale Langley Full Scale Wind tunnel. Second, a CFD simulation was done using CFL3D code (developed by NASA Langley Research Center). Finally, a panel method was used to assess the boundary interference and to study the effect of the collector. The objective of the study is to highlight the challenges in assessing the boundary interference for high blockage models. A secondary object is to present a model to integrate all the available information from the wind tunnel test and the CFD simulation to solve the problem using a panel method.

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.

The CFD tools in aerodynamic design process have been commonly used in aerospace industry in last three decades. Although there are many CFD software algorithms developed for aerodynamic applications, the nature of a complex, three-dimensional geometry in incompressible highly separated, viscous flow made computational simulation of ground vehicle aerodynamics more difficult than aerospace applications. However, recent developments in computational hardware and software industry enabled many new engineering applications on computational environment. Traditional production process has largely influenced by computational design, analysis, manufacturing and visualization. Different aspects of linking advanced computational tools and aerodynamic vehicle design challenges are discussed in the present work. Key technologies like parallel computation, turbulence modeling and CFD/wind tunnel compatibility issues are presented.

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.

An objective considered in designing the new generation of heavy trucks is fuel efficiency. This can be significantly improved by reducing the overall drag force on the truck when it is in motion. With this impetus, the external aerodynamics of a heavy truck was simulated using computational fluid dynamics and the external flow was presented using computer visualization. Initially, a thorough validation study was conducted on the Ahmed body. Consequently, the model and the method were selected to be the time-dependent, three dimensional, Reynolds-averaged Navier Stokes equations that are solved using a finite volume method. The RNG k-ε model was elected for closure of the turbulent quantities. Finally, to help the estimation of the error due to two commonly practiced engineering simplifications, a parametric study was conducted. The external flow around the truck was computed with and without the tires (-6% drag error), then with or without ground plane motion (+9% drag error).