Instrument needs circular aperture — then air can get circulated (7)
I believe the answer is:
ocarina
'instrument' is the definition.
(ocarina is a kind of instrument)
'circular aperture then air can get circulated' is the wordplay.
I cannot quite understand how this works, but
'circular' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
an anagram of 'air' is 'ari' which is within the answer.
an anagram of 'can' is 'cna' which is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
'needs' acts as a link.
(Other definitions for ocarina that I've seen before include "Terracotta wind instrument" , "Toy-like wind instrument" , "toy instrument" , "Primitive wind instrument" , "source of music" .)