I know that by designing an airplane or a car close to a teardrop, we can reduce the drag. My question has to do with the surface friction treatment. Some torpedoes glide in water more efficiently when wrapped in bubble cloaks.
Some feathers have textures to reduce friction. Some modern bathing suits textures help reduce friction.
Are there studies on surface treatments, such as texture, special paint, grooves, or perforations, to reduce drag?
Implied in my question is: If there are any results that do reduce skin friction, where have they been applied?