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
1. Determining the drag effects of different trailer models.

2. Decreasing the CO2 production rate when towing a trailer.

3. Improving fuel economy when towing a trailer.

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

Specifications



The National Highway Traffic Safety Administration (NHTSA) specifies certain regulations that tractor trailers must meet, such as the emissions produced from towing various tractor trailers. The equation below calculates the emission rate (gCO2¬/ton-mile) from towing a tractor trailer of various specifications:

e_CO2=(C_1+C_2*TRRL+C_3*〖ΔC〗_d A+C_4*WR)*C_5

Our emphasis of this project is focusing on the ΔCdA term (m2), which is a change in drag coefficient multiplied by cross-sectional area (change in drag area). A table of expected changes in drag can be seen below.

The emission rate needs to be minimized so that the fuel consumption rate (galdiesel/1000 ton-mile) is also minimized when towing tractor trailers. The conversion can be seen in the following equation:

FC(〖gal〗_diesel/(1000 ton-mile))=(e_CO2 (g_CO2/(ton-mile)))/10,180(g_CO2/〖gal〗_diesel ) *1000

If the change in drag area is reduced significantly, emission rates will decrease as well as fuel consumption rates. We are only focusing on the external trailer designs. Any extra weight that would be added with an increase in internal volume of the trailer will be ignored.



Concept Development









Project 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.