[Delk]

くるくる (usually romanized as 'kurukuru') does seem to mean going round and round: https://jisho.org/search/kurukuru

Japanese isn't generally considered to have the equivalent of the 'l' sound from most other languages, and it rather has a sound that's perhaps somewhere between 'l' and a rolling 'r'. In romanized text it's generally written as 'r'. Transliteration isn't really unambiguous in the end, though, and there are multiple ways of romanizing Japanese, so while romanizing くるくる as 'kulukulu' doesn't sound like a very common transliteration, it may be possible.

Also, 'kuru' means 'to come', but I don't know if that's related.

[jonhohle]

It’s amusing that the characters even look like a conveyor belt.

[frereubu]

Thanks for the explanation. I'd heard about the r / l issues with romanizing Japanese but hadn't made the link.

[juped]

it's best explained to anglophones as a voiced 'd', not anything to do with 'r' or 'l'