This study was performed to assess the aerodynamics of the outer skin of the vehicle, and to improve upon the most simple and effective solution to gain efficiency during a drag race. This was accomplished by analyzing the original surfaces after modeling the jet car in SolidWorks. It should be noted that the model was generated via pictures from the internet, and estimates of actual geometry.
Once the initial analysis was performed, various parameters for identifying trouble spots, or 'hot spots' were analyzed using graphical representations to locate surfaces that required improvement. Pressure and density distributions were used, along with velocity plots over the surface. Once the surfaces were identified, FloWorks can evaluate the aerodynamic forces on specific surfaces generated by the dynamic pressure exhibited by the air on the current jet car configuration. These speeds are approximately 260 mph in the 1/4-mile.
When the jet car surfaces impede the incoming airflow, this increases the air pressure in localalized regions. By re-shaping these offending surfaces, the high pressure areas are reduced and allow for the air to pass by regions at a lower pressure. The red shapes in the leading edges of the jet car indicate these regions, and their relative contribution to air drag of the vehicle.
From this front view of a velocity distribution, the blue areas indicate slow flow, and can be correlated to the areas of high pressure. The dynamic force of this airflow produces approximately 540 lbs (@260 mph) of resistance to the jet car, reducing its acceleration down the track.
Shown above is the comparison of before and after. On the left is the pressure distribution, and on the right is the velocity distribution. Integrated across the surface areas the overall reduction in aerodynamic drag force is approximately 160 lbs. (from 540 lbs.). The means that 30% of the drag was removed by this surface modification. Drag force is related to the velocity squared (among other parameters), so this decrease is substantial.
Below is the finite element analysis (FEA) done for a circular window under vacuum.
The first image is a simply supported case (worst case, idealized), and the second is the clamped case which better represents the boundary condition in the real application. Notice the center of the window shows roughly a 50% reduction in Von Mises stress, indicative of a clamped window design. Although the stresses at the interface are shown as high stress regions, they are localized and result in compressive stresses. Therefore, the glass window's structure was in compression and far below the fracture strength of the material, so was deemed of sufficient thickness for this application.
The clamp and frame displacement plots are shown below...
The side bars are under vacuum loading as well, but were relatively stiff as indicated by the small displacement shown below.
Although some of these studies did not include contact stresses at the time the images were saved, assembly analysis was used to complete the analysis margins including effective joint stiffness and hertzian stresses.
This is a high voltage, high vacuum assembly I designed and tested with success. Many design and assembly features were improved, tested and found to be superior to its predecessors. Although the original designers were skeptical of the new design concepts, after testing they have accepted the new design and incorporated the new features into other programs.
My brother's rear fenders before I helped him redesign them...
And the new the bars, although in the picture it is difficult to discern their improved appearance...I will put the finite element analysis results up later.