Research Blog 3
Conclusion
The results supported the original hypothesis as the fifteen degree panel trials yielded the lowest drag force, which was followed by the thirty degree panels, and finally the zero degree panels possessed the highest drag force. This indicates that in a real world scenario involving the use of trailer panels to reduce wind drag on tractor-trailers, panels placed at an angle of fifteen degrees would be ideal in efficient travel when compared to angles of zero and thirty degrees. While panels placed at fifteen degrees could be the optimum placement for panels, it is possible that a most exact, different angle exists which could be pinpointed using further research by narrowing down the range progressively. Discovering this angle is highly pertinent to reducing fuel consumption by tractor-trailers as semi-trucks are the highest fuel-consuming vehicles on the road. Thus, decreasing fuel consumption by even a marginal value per truck could result in substantial profit increases for trucking companies, fuel price decreases, and decreased air pollution.
Data Analysis
The sample means for each of the panels were 0.285 Newtons, 0.256 Newtons, and 0.270 Newtons for 0°, 15°, and 30°, respectively. While these means indicated a trend which supported the original hypothesis, descriptive analysis was used in the form of box plots, shown left, to further analyze the data. The most drastic difference between the box plots was shown with the 0° box plot as the first quartile was higher than the maximum of the 15° box plot and was equal to the third quartile of the 30° box-plot. These indicated that the 0° box plot was clearly higher in magnitude than the 15° and 30° box plots. However, there was reasonable overlap between the 15° and 30° box plots; this overlap was enough to warrant the need for a statistical test. A two sample t-test was conducted between these groups to compare whether the fifteen degree mean drag force was significantly lower than that of the thirty degree mean. The results of the t-test provided further support for the hypothesis as the p-value was approximately zero, indicating that the difference in sample means was significant at the alpha level of 0.05. therefore, the combination of evidence from descriptive statistics and the two sample t-test provided sufficient evidence to support the hypothesis.
Scientific Analysis
The figure to the left shows how a trailer panel can reduce the vortexes that create drag. By redirecting the airstream at a different angle than the ninety degree edge that a bar tractor trailer gives, a smooth streamlined flow can result. The air redirection removes some energy from the truck's motion, but it, in turn, reduces drag at a greater magnitude. The resulting laminar flow eliminates a majority of the drag that occurred under the turbulent flow conditions without trailer panels.
The air friction on the sides of the semi truck appears to be the same in both diagrams, so turbulence in the back is the only factor mitigated by the trailer panels. The laminar flow resulting from the trailer panels do not allow for turbulence to be created behind the tractor trailer. Turbulence removes mechanical energy from the semi truck and reduces fuel efficiency. Since the trailer panels lessen the effects of drag, mechanical energy and thus fuel are saved.
The best time for usage of this panel angle is while the tractor-trailer is traveling via highway as the higher wind velocity on the structure results in a higher overall wind drag. This corresponds to a larger quantity of mechanical energy saved as more wind is redirected around the vortexes.
Advice/Improvements
The dynamics of the experiment could be improved in several aspects. The first improvement would be to use more panel angles groups with smaller ranges. This would allow for more accuracy in pinpointing the ideal panel angle as it is not necessarily 15°. The purpose of this experiment was to identify the ideal panel angle of attachment; however, only the first step has been completed. Now that the range has been narrowed, the search for the optimum angle must continue. In addition, the effects of other factors in conjunction with the panel angles could be tested as trailer panels are usually not the only form of drag reduction used. For example, varying trailer panel angles could be tested in differing combinations with trailer skirts. Finally, in a repeated experiment similar to this one, a fan capable of producing a higher velocity than this one, more than five meters per second, should be used unless a smaller tractor-trailer model is used. This will allow for a tilt on the tunnel to not be required.