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To: Mr. D. O’Notknow, Chief Design Engineer Hydrogen Power Vans, 5170 Rotunda Circle, Dearborn, MI 48060 From: J. Chen, M. Killingsworth, and F. Vitale, Test Engineers, Group 5 Date: December 10, 2002 RE: HPV Body Shape DIST: Ms. V. E. Hicle, Manager, Advanced Testing Group FOREWORD Hydrogen Power Vans (HPV) has developed and refined a revolutionary hydrogen fueled combustion system to incorporate in a new class of vehicles that is a cross between a minivan and an SUV. However, HPV has no knowledge of the effects of the vehicle’s shape on fuel efficiency and overall performance. Thus, HPV has asked us to perform tests and recommend the vehicle shape that best minimizes the wind resistance while maximizing the volume. The purpose of this report is to present the requested information, as well as other pertinent results, conclusions, recommendations, and supporting documentation. SUMMARY We have completed a series of performance tests on balsa wood models that we designed and manufactured to resemble a mix between a minivan and an SUV. During testing we measured wind velocity (V), lift force (FL), and drag force (FD). We then scaled the results from our small-scale model to a full-sized vehicle. The requested full-sized vehicle predictions for the vehicle shape that maximized the volume/drag ratio () were determined and are given in Table 1 below. Table 1: Full-Sized Vehicle Performance Results Velocity: V (mph) Forward FL (N) Forward FD (N) Backward FD (N) Coast Down Time (seconds) Coast Down Distance (miles) Sideward FD (N) Volume/Drag Ratio: (m3/N) 40.0 0.2 79 9 360 50 420 50 N/A N/A 1300 50 0.045 0.006 60.0 0.2 180 20 800 110 940 110 N/A N/A N/A 0.020 0.003 60 to 5 N/A N/A N/A 126 15 0.52 0.05 N/A N/A Using a conservative approach, we determined that the drag and lift coefficients (CD and CL) remain constant when scaled from the small-scale model to the full-sized vehicle. Thus, there will be no peculiarities when scaling the forces acting on the model to the vehicle since all the variables, except velocity (V), remain constant as well. PROCEDURE To quickly determine a reasonable vehicle body shape that minimizes wind resistance and maximizes passenger spaciousness, we first designed and manufactured small-scale models from the provided balsa wood blocks. We then tested these models in an 8 x 8 inch cross-section wind tunnel (Model N4D17FK10A) that was designed to produce a uniform flow in the testing area. The wind speed simulates the vehicle velocity and was measured by a pressure gauge. We followed the standard operating procedure outlined in the ME 395 Coursepack (WTT 5)1 to calibrate the wind tunnel and test our models. Design and Manufacturing of Balsa Wood Models: HPV supplied us with three balsa wood blocks with a length, width, and height of 4, 2, and 2 inches, respectively. These blocks were approximately 1/42 the size of a full-sized vehicle. Maintaining maximum dimensions of 4 x 2 x 2 inches, we aerodynamically shaped two of the blocks to resemble a mix between a minivan and an SUV. We began shaping our blocks by drawing a profile of a large and spacious minivan on one block and a profile of a sleek and sporty SUV on the other block. These shapes were then cutout of the block using a box cutter, smoothed over with a drummel tool, and finished with 100 grain sandpaper. Over the course of testing we refined our shapes to create a sleeker design by rounding edges with the sandpaper to further reduce wind resistance. Wind Tunnel Testing: We first calculated the blockage ratio of the unshaped balsa wood block in the wind tunnel to ensure that the incoming flow would be uniform (must be less than 15%). Then, we calibrated the wind tunnel according to the SOP, which is described further in the performance results of model results section. The wind speed was calibrated by setting it to a positive value close to zero (1.5 0.2 mph or 0.67 0.09 m/s). We tested the 4 x 2 x 2 inch unshaped balsa wood block in the wind tunnel with a front, then back, and then side wind of speeds from 15.0 0.2 to 60.0 0.2 mph (6.71 0.09 to 26.82 0.09 m/s) in increments of 5.0 0.2 mph (2.24 0.09 m/s). In addition, we tested the support on which the balsa wood models were mounted (the sting). The forces associated with the sting were subtracted from the forces recorded for each model to accurately determine the forces on the models only. We then tested the two shaped blocks in the wind tunnel using the same method that was applied to the unshaped block. Error: All Errors reported were determined using the error combination method described by the standard operating procedures outlined in ME 395 Coursepack (EA 7-10)1.
Approximate Word count = 3220
Approximate Pages = 12.9
(250 words per page double spaced)
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