1. Results Summary and Images Data Analysis The control school bus model had a higher C D than theoretically expected; 1.223 compared to a theoretical 0.6-0.8. This could be due to two reasons: the model made in Autodesk Simulation CFD was fairly coarse to reduce the mesh complexity and sharp edges tend to cause more flow separation and higher pressures than smoother ones found on a real bus. Secondly, CFD comes with inherent error that was made worse with the relatively low mesh resolutions(~100-150k elements) due to limited computing power. Despite this, it is still viable to make comparisons between the control and the three designs. The rear spoiler, even though it decreased the size of the wake, added an extra 1.267m^2 to the cross sectional area and increased overall drag force. A cost analysis was not done for it because the design did not reduce drag. All the frontal fairing designs reduced F d by a considerable amount. The worst performing, as expected, was the flat design. All the other designs were fairly similar in their %DeltaC d /Volume scores, showing that they were fairly close in efficiency. The most efficient design with the 175cm arc radius reduced F d and C d by 14.427% and had a materials payback period of 3.461 years if made with 0.5cm polycarbonate and 1.458 years if made with 0.5cm polypropylene, both reinforced with 30% glass fiber. The back plates were all fairly effective in reducing F d and C d. From the first optimization, The efficiency, measured through negative %DeltaC d /Volume, constantly increased as length decreases. 0.3m was the smallest plate size for practical reasons. In the 2nd round of optimization, the most efficient yaw angle was 30 degrees, with the efficiency decreasing as angle increased or decreased. The back plate design was also successful, with a payback period of 1.062 years for the aluminum design and 0.532 years for the steel. Fd(N)Cd%Delta CdFyCl Volume Device(cm^3)%DeltaCd/Volume Rear Spoiler42811.0695.48128.0500.007Not FeasibleNA Fd(N)Cd%Delta CdFyCl Control Bus40591.2230.000-339.573-0.102 Fd(N)Cd%Delta CdFyCl Volume Device(cm^3) %DeltaCd/Volum e Bus Back Plates – Default35921.083-11.499-339.643-0.10250142.870-229.316 Bus Back Plates - Extra horizontal flat plate36381.097-10.35264.7550.02073307.250-141.212 Bus Back Plate - Curved Boat-Tail34711.046-14.480277.7850.08461096.190-236.999 Design and Optimization of a Drag-Reduction Add-On Device for a School Bus Back Plates Fd(N)Cd%Delta CdFyCl Volume Device(cm^3) %DeltaCd/Volume (m^3) Straight37111.118-8.572-448.227-0.13560885.645-140.791 Arc radius 12535011.055-13.737245.0000.07465928.575-208.356 Arc radius 15034961.054-13.860169.6340.05164392.940-215.238 Arc radius 17534731.047-14.427-41.000-0.01263581.838-226.897 Arc radius 25035161.060-13.374119.3000.03662472.902-214.083 Control Spoiler Fairing Volume Mesh Cross Section Mesh Frontal Pressure: Fairing vs. Control Control Fairing Rear Pressure: Control vs. Plates Control Back Plates Velocity Distribution Control Back Plates Fairing Recirculation Control Fairing Back Plates Jiedong Duan Niles North High School