black, dark | permanent

wear | give sb | be set in
His face was set in a permanent scowl.

deepen

in a ~
Her brows drew together in a scowl.

with a ~
He looked up at me with a scowl.

have a scowl on your face

darkly, fiercely, heavily
She scowled darkly and muttered something under her breath.

down

at
His eyes scowled down at her.