What are "schlieren" in English?

Solution 1:

A descriptive term for the patterns you illustrate is swirl:

A twisting or spiralling movement or pattern:
she emerged with a swirl of skirts
swirls of colour

ODO

1a : a whirling mass or motion : eddy
b : whirling confusion <a swirl of events>
2 : a twisting shape, mark, or pattern
3 : an act or instance of swirling

Merriam-Webster.com

Solution 2:

Technically speaking, the phenomenon that causes that pattern in fluids like water or smoke is turbulence, in which you'll find terms like vortex (plural vortices), which has connotations of speed or violence, or eddy, which is more or less the same as far as fluid dynamics is concerned, but in terms of literary connotations is somewhat calmer and/or slower. Both of these terms imply motion, though, so they might not work so well when talking about rock or wood.

In general, when describing that pattern I would probably go with whorl, which is also used to refer to the looping pattern in fingerprints, or maybe swirl.

Solution 3:

If you take a direct translation, the English would be streak, or streaks.

With that said, in English the different types of patterning often attract different names. 'Lines' of streaking is often referred to as grain, rounded streaking is sometimes referred to as marbling

Marbling:

having markings or coloration suggestive of marble ^source

Could apply to: paint, oil, coffee, marbled paper

Grain:

the arrangement, pattern, or direction of fibres in substances such as wood, stone, cloth, or paper ^source

Could apply to: concrete, rock

A word for the smoke like pattern is a bit more tricky, perhaps; smoky, wispy or diffuse.

Effectively, what you are seeing are patterns in nature

Patterns in nature are visible regularities of form found in the natural world. These patterns recur in different contexts and can sometimes be modelled mathematically. Natural patterns include symmetries, trees, spirals, meanders, waves, foams, arrays, cracks and stripes.^source