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The flow conditions in a closed test section wind tunnel are not the same as in freestream due in part to the constraints imposed by the wind tunnel walls. Boundary correction methods can be applied to wind tunnel results to estimate the effects of wind tunnel wall constraints. One such scheme, the two-variable method, which is a measurement based scheme used to estimate a particular class of wind tunnel wall constraints known as solid and wake blockage, is described herein. The Glenn L. Martin Wind Tunnel (GLMWT) has implemented the two-variable method and has applied it previously for large models in a variety of applications, primarily in the evaluation of yacht’s offwind sail performance. This paper describes the application of the two-variable method to simplified fastback style three-dimensional automobile shapes at zero yaw angle. Models ranged in size from 2.75% to 5.53% of the tunnel’s cross-sectional area.

The Ford P2000 prototype vehicle represents Ford Motor Company's commitment towards environmental stewardship through high fuel efficiency and low tailpipe emission. Low aerodynamic drag coefficient (Cd), weight reduction, and power train efficiency improvements are required in order to accomplish the overall fuel economy target. The objective of this study is to establish an aerodynamic efficient body shape (Cd = .20) that meets the cost, weight, styling, package and fuel economy targets. Furthermore, this vehicle must be able to be operated and manufactured. A new computational fluid dynamics (CFD) method based on a lattice gas approach was piloted for developing and evaluating body shape design alternatives in support of the P2000 PRODIGY aerodynamic objective. Wind tunnel tests were performed to further explore the aerodynamic opportunities that are beyond the capability of the computational method as well as validate the CFD prediction.

The work presented here is a further step in a continuing effort by the authors to study and document the aerodynamic effect of varying aspect ratio, ground clearance, and underbody roughness for basic rectangular shapes with radiused edges in ground effect. Previous papers by the authors have presented extensive wake data for a range of aspect ratios and underbody roughness conditions. Force and moment data have been published for various aspect ratios, underbody roughness, and ground clearance. In this paper, additional wake data showing the effects of variation in ground clearance is presented. The focus of this paper is on analyses to make progress toward a rational correlation between body characteristics, the forces, and the measured wake properties. A parametric analysis is presented linking the effects of the parameters varied in the study to the changes in the aerodynamic forces and moments. Results show correlations between the wake flows and the force results.

There is little information in the technical literature about the dependence of drag coefficient, CD, on aspect ratio (height/width) for car and truck aerodynamics. Some of the information suggests that CD should increase with aspect ratio as the flow over the body becomes more two dimensional. Recent tests of candidate shapes for a commercial van with various roof heights suggested the opposite is true; the taller vans had lower drag coefficients. This report discusses the results of several experimental investigations to examine this relationship. Scale model and production drag measurements of commercial vans are presented along with drag measurements of simple shapes. The shapes consisted of eight radiused rectangular boxes of constant length and frontal area, but with different height/width ratios. The effects of underbody roughness and bumper presence were evaluated and are discussed.

Almost all published results of wake measurements for ground vehicles or similar shapes have included very limited information on streamwise development of wake structures. This is typically a result of the fact that the wake measurements have been conducted as parts of particular vehicle development efforts. So the focus has been on the incremental changes in the wakes associated with alternative geometries or buildup of various parts. The objectives are typically reached by limiting the surveys to a single streamwise plane. The present study, by contrast, is a study of wake development for a series of relatively simple rectangular shapes with radiused edges with a systematic variation in the ratio of height to width or “Aspect Ratio”.

A critical aspect of the performance of the front wing of a Formula One or Indy race car is studied by idealizing it as a negatively cambered two-dimensional airfoil operating in ground effect and determining the fiowfield at various heights. When the airfoil operates at heights roughly equal to the airfoil thickness, significant negative lift is generated. As the height is decreased, there is an expected downforce reduction. The primary objective of this work is to elucidate the force reduction phenomena for the specific case of an inverted NACA 4412 airfoil traveling at high Reynolds number above ground in still air. This is the road condition. The secondary objective is to compare and contrast the fiowfield about this airfoil in road conditions and when operating in the wind tunnel environment, i.e. when the airfoil and the ground are not moving relative to each other.

A critical aspect of the performance of the front wing of a Formula One or Indy race car is studied by idealizing them as a symmetric two-dimensional airfoil operating in ground effect. When such an airfoil operates at heights roughly equal to the airfoil thickness and lower, measurable amounts of negative force are generated. As the height continues to decrease, there is an expected force reversal. There are two objectives of the study reported in this paper. The first is the adequate verification of the Finite-Analytic Navier-Stokes computational approach by comparing computational results for the case of a stationary airfoil at various heights above ground to experimental results. The second is to elucidate the force reversal phenomena for the specific case of a NACA 0015 airfoil traveling at high Reynolds number above stationary ground in still air by utilizing the validated code.