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Aerodynamic testing of heavy commercial vehicles is of increasing interest as demands for dramatically improved fuel economy take hold. Various challenges which compromise the fidelity of wind tunnel simulations must be overcome in order for the full potential of sophisticated aerodynamic treatments to be realized; three are addressed herein. First, a limited number of wind tunnels are available for testing of this class of vehicle at large scales. The authors suggest that facilities developed for large or full-scale testing of race cars may be an important resource. Second, ground simulation in wind tunnels has led to the development of Moving Ground Plane (MGP, aka Rolling Road (RR)) systems of various types. Questions arise as to the behavior of MGP/RR systems with vehicles at large yaw angles. It can actually be deduced that complete simulation of crosswind conditions on an open road in a wind tunnel may be impractical.

The issue of ground simulation in wind tunnels has led to the development of Moving Ground Plane (MGP, aka rolling road) systems of various types. Motorsports aerodynamics has perhaps been the primary application to date, where the range of vehicle yaw angles tends to be quite limited. In fact, since yaw angles are typically developed as result of vehicle slip in cornering, or asymmetric set-up in the case of stock cars, they are limited to a few degrees. Further, since in both cases the vehicle centerline typically rotates with respect to the relative velocity vector (i.e. simulating vehicle slip in cornering), it seems clear that yawing the vehicle in the wind tunnel above a fixed (non-rotated) MGP is a valid simulation option. In the case of vehicles operating in strong crosswind conditions, for example commercial vehicles (heavy trucks) on interstate highways, the situation is more complex.

Aerodynamics plays an important role in marketing vehicles especially with the recent increases in gas prices. The aerodynamics of one of the widely used vehicle classes (pickup trucks) is examined. The focus is to investigate the effect of the pickup truck configuration on the structure of the airflow around the vehicle and ultimately on the generated aerodynamic drag. The study includes CFD simulations performed using STAR CCM+ developed by CD-Adapco Inc. and full-scale wind tunnel testing conducted in the Langley Full Scale Tunnel (LFST) located at the NASA Langley Research Center but operated by Old Dominion University. The studied pickup truck configurations include a simplified model (no sidewalls or tailgate) and tailgate-off, tailgate-down, and tailgate-up. In all the CFD simulations a generic geometry of an extended cab pickup truck is used. The results indicate that there is a large separation region downstream of the cab and that it controls the aerodynamic drag.

A numerical study of a racecar front wing is presented. The focus of the study is to investigate the aerodynamics characteristics of a wing operating in a small ground clearance. A finite-span wing with a symmetric airfoil section is used. It was found that as the wing gets closer to the ground it generates more downforce and more drag. As the wing gets very close to the ground, the downforce reaches a maximum value and after that the wing generated less downforce as it gets closer to the ground. The drag force follows a similar trend of dependency on the ground clearance. The lower surface of the wing and the ground form a convergent-divergent-nozzle shape that is responsible of all the changes in the generated forces. For very small ground clearances, the boundary layers developed on the wing lower surface and the ground get closer to each other, decrease the airflow below the wing and ultimately decrease the generated downforce significantly.

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.

The aerodynamics of a finite-span rectangular wing is investigated using a numerical method. A high-lift single element airfoil section is used. The study focuses on the effect of the ground clearance (the vertical distance between the leading edge of the wing and the ground). The study includes the effect on the overall characteristics of the flow around the wing and the generated aerodynamic forces (down force and drag). Two wings are used in the study with and without end plates. The CFD code “STAR CCM+” is used in the study. The study showed that there is a range of ground clearance where it has a strong effect on the wing behavior. That effective range was the same for wings with and without end plates. At a small ground clearance, the down force can be easily doubled by small change in the clearance. However, the use of a high lift airfoil section increases the interaction with the ground boundary layer and may cause a decrease in the generated down force.

A numerical study is presented for high-lift airfoils suitable for racecar applications. The study includes the effect of ground clearance (distance between the airfoil and the ground), angle of attack and Reynolds number based on airfoil chord length. The finite volume code CFL3D, developed by NASA Langley Research Center, is used in the study. Four airfoils are used to represent different airfoil families. The study shows that Reynolds number has a very small effect on the downforce and the drag. Medium and large ground clearance are studied. For medium ground clearance the downforce and the drag increase, as airfoil gets closer to the ground. A considerable increase in the downforce can be gained by even small changes in the ground clearance. As the angle of attack increases both the drag and the downforce increase as expected. For large ground clearance the airfoil performance is close to the freestream case.

This paper reports on an exploratory automotive test which was undertaken in the NASA Langley Research Center 14 by 22 wind tunnel in the Fall of 2003. The test was collaboration between Old Dominion University, who supplied the automotive balance, NASA, who provided wind tunnel time, and Penske Racing South, who provided an instrumented test vehicle. The test generated a rather unique data set, encompassing whole body forces, surface pressures, and floor boundary layer profiles, measured on the same test article, with both an open jet and closed jet test section, utilizing the variable configuration of the 14 by 22. The nominal test velocity was 60 m/s, the nominal blockage was 7.4%, and the yaw angle ranged from −6 to +6 degrees. Results indicate substantial interference effects, as expected, with around 19% higher drag (uncorrected) in the closed configuration, relative to open. The corresponding front and rear downforce values were 14% and 13% higher respectively.