Meaning of wū:
wū
呜
Onomatopoeia
(onom.) for humming or whimpering
Dāng cì'ěr de jǐngbào shēng xiǎngqǐ shí, měi gè rén dōu tīng dào le yī zhèn “wū wū” shēng.
当刺耳的警报声响起时,每个人都听到了一阵“呜呜”声。
When the shrill alarm went off, everyone heard a 'woo woo' sound.