Computational Mechanics Research and Support for Aerodynamics ...

For each level, the figures below show the particle trajectories at different times in the simulation. In
addition, velocity isosurfaces are shown on each of the figures to provide a look at the motion of the air
as the truck passes through the underpass. Figure 3.6 shows trajectories of the particles at the level of
the wheel axles. Most of the particles stay at this level except for the ones being trapped behind the
cabin. These trapped particles can be lifted up and dragged by the vehicles for long distances.
In Figure 3.7, the trajectories of the particles at the engine hood level are shown. The particles that are
along the mid-width of the vehicle are lifted up from the hood level to the trailer-top level and are
dragged along with the vehicle. The particles away from the mid-width of the vehicle are pushed to the
sides of it and are not lifted higher.
In Figure 3.8, the trajectories of the particles located at the windshield level are shown. These particles
are also smoothly pushed up to the top surface of the trailer. Once the particles get to the back of the
trailer, they become part of the developing vortex wake. This causes the particles to move down rapidly
and follow the back of the trailer – i.e., the particles are entrapped in the trailer’s vortex wake.
Eventually, some of the particles exit from the wake and appear to move into the space between the
bridge beams. The particles at the trailer’s top-surface-level behave in a similar way (see Figure 3.9);
they also appear to find their way into the space between the bridge beams.
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