If you look underneath a lot of New cars you'll see dimples all over the bottom. The most recent one that I've seen is the MKV Jetta. Apparently they've got the airflow under that car figured out pretty well, because there is an automatic transmission cooler mounted horizontally level with the rest of the underside of the car.

And I didn't see any Turd Swirlers anywhere near there.
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a bodyboard manufacturer came out with boards years ago with a dimpled bottom surface.