In Depth Cd/Fuel Economy Study Comparing SAE Type Ⅱ Results with Scale Model Rolling Road and Non-rolling Road Wind Tunnel Results

摘要

The trucking industry is moving into a new era of development brought on by governmental concerns over energy independence as well as the realities of increasing fuel costs. This has renewed interest in optimizing the aerodynamics of Class 8 tractor-trailer trucks. However, many of the large aerodynamic gains have already been developed, for example trailer skirts and boat tails that give fuel economy improvements of approximately 5 %. Research continues in order to better understand the aerodynamics of these vehicles and further improve their efficiency. Scale model rolling road testing has been around for several decades. In fact, the earliest rolling road wind tunnel test of a Class-8 truck that the authors are aware of occurred in the late 1980s. In order to define the performance of a heavy duty truck, it has been well established that the use of wind averaged drag coefficients are required. To achieve wind averaged drag coefficients, it is necessary to measure data with a model in yaw for either a static floor or rolling road tunnel. The authors previously published results comparing a generic truck model tested using both a moving ground plane and a static ground plane. This paper builds on the work using a more detailed and modern truck model. The improvements in aerodynamic drag by fitting trailer skirts are discussed. These drag reductions are converted into fuel efficiency improvements and are compared to SAE type Ⅱ testing. The reader will be able to appreciate the difficulty associated with attempting to correlate wind tunnel results to SAE Type Ⅱ results. Some of the issues related to scale model rolling road testing such as Reynolds number dependency and yaw over a rolling road will be explored. Due to the size and nature of heavy duty trucks, cross winds must be taken into account. In addition to track or on-road testing, static tunnels have been the primary experimental tool for developing heavy duty trucks. Using the static floor tunnel method, heavy duty truck models have fixed (non-rotating tires) and are yawed via a turn table mounted in the floor of a tunnel. Multiple studies have been published which illustrate the necessity for rotating the tires in order to achieve improved correlation to real-world results, for examples see.