Aerodynamic Study of Bulk Commodity Tractor Trailers

Our project goal is to test aerodynamic features of four existing tractor trailers in order to reduce emissions. This will be accomplished by studying and comparing the drag coefficients of each design. Our designs will be created with either 3D printing and/or laser cutting technology.

Problem Definition
Semi-trucks are used all over the world for transporting goods. They provide easy and affordable methods to keep economies running. The downside is that semi-trucks produce a lot of carbon-dioxide pollution from their exhaust. If the trailers they tow are improved aerodynamically, that carbon-dioxide production can be minimized. Western Trailer Company, headquartered in Boise, ID, has four main tractor trailer models, which are a flat-floor trailer, drop-center trailer, hopper trailer, and pup trailer. The Trailer Park Boys are tasked with testing and simulating these models in various configurations so improvements can be made to meet new tractor trailer requirements that will be implemented in 2018.

Design Goals & Deliverables
At the end of the project, the client will receive:

•	Scale models of selected Western Trailer products suitable for testing in the ME Wind Tunnel

•	Wind Tunnel data on aerodynamic drag associated with different scale models at different wind speeds

•	Methodology for translating changes in scale model drag coefficients to changes in fuel efficiency and emissions for full-size trailers (following appropriate federal guidelines)

•	Quantify changes in trailer performance associated with changes in trailer geometry for specific trailer models

•	Final design report that documents the team’s model development and testing process

Testing Matrices
The testing matrix for the 48 foot trailer configuration is located on the left, while the testing matrix for the A-Train configuration is located on the right. Another factor that will change is the spacing of the lead trailer and the pup trailer for the A-Train configuration.

Data Processing
The data will be processed and analyzed as follows: The drag force values are acquired from the sting in the wind tunnel with LabVIEW software. The wind speeds are correlated to the frequency of the fan driver input. The density of air is assumed to be constant and evaluated at room temperature. The front cross-sectional area will be used. The emission output (grams of CO2 per ton-mile) will be calculated. The Red values are for the 48-foot trailer configuration, while the Blue values are for lead and pup trailer

The Tire Rolling Resistance Level (TRRL) and Weight Reduction (WR) was taken from an example from Cornell Law School that discussed the details of the new regulations. The front cross-sectional area will be used as the 'A' constant in question. C5 deals with specific tire pressure systems (1.0 for no system installed). Lastly, fuel consumption per 1000 ton-miles will be calculated.

Internal Design
We attached various features of the trailers through the use of magnetic internally for ease of use and quick modification. This idea greatly simplified our modeling process by reducing the number of models we needed to create.

Testing Results
Early testing showed a relatively linear relationship between CD and wind velocity past ~12.5 m/s. We will run future tests from ~12.5 m/s to ~30 m/s in 2.5 m/s increments as the coefficient of drag levels out after that interval. Each model will be run twice and we will average the voltage data to reduce error.

Wind Tunnel Learning
When testing scale models, geometric similitude is very important. The ratio of model length to actual length must be identical with model width to actual width, and so on with all other dimensions. The Buckingham-pi theorem allows dimensional analysis to simplify testing and data processing.

3-D printing models accurately and effectively has taken many unexpected modification. This is mainly due to the fact that the 3-D printer can only print and 8" x 8". The upper left hand image shows a part that needed to be printed in sections. The upper right hand image shows that tabs and inserts were needed to be designed into the part.