One of the topics I find interesting on this forum is car mods, specifically those that improve fuel consumption through areodynamic improvements. In researching here and eslewhere, the general rule is that there's not much you can do up front besides block air infiltration, but you can get big drag reduction in the rear. I wanted to see what airflow looled like over the back end, and what sort of changes might be beneficial.
I had also noticed that the hatch lid didn't meet well with the roofline.
Roofline.JPG 69.5KB 10 downloads
I laid out ~4" tufts of yarn and string in a 5" grid pattern over the back half of the car.
TT layout done.JPG 147.95KB 9 downloads
The idea is to drive at speed and look at the patterns the tufts take on the car. I took video, but need the right SW to pull snippets. Here are a couple stills.
Capture.JPG 130.1KB 9 downloads
Capture1.JPG 118.68KB 8 downloads
Laminar flow is everywhere
- roof all the way back to the lip; that little step does nothing
- windows sweeping up toward the roof, right to the hatch glass
- door panels above rear wheel well, but ending under lights
Turbulent flow dominates the tailgate (lots of blurry tufts)
- lip under the glass down to the top of the bumper
- flanks under rear lights sweeping forward to wheel wells
The big surprise is the rear window - near calm
- strings lay flat and don't move much
- pattern is downward with slight outward flare
- pattern extends to L/R edges of the glass, right next to high-speed laminar flow
... evidence of clean separation from rear lights, up across upper hatch edge - a calm rear window.
... evidence of turbulent separation along the flanks, below the lights - a turbulent hatch panel below the window.
Take a look and let me know what you think. I'll note that I'm looking at video as well for my descriptions.