Adverbial - modifies a verb to mean 'doing X in shifts/waves'.
轮 ('to take turns/rotate') +
番 ('a turn, a round'). Compare
轮流 (take turns, more about orderly rotation) and
轮番 (more about repeated waves/rounds, often in pressure or attack contexts). News register favors
轮番轰炸 (round-after-round bombing),
轮番上阵 (sending in waves).
