Difference between the verbs 轮 and 轮流 (meaning to take turns)
When 轮(rotate/ to take turn) is acting as a verb, most of the time it would include the result complement 到 - e.g "轮到你了" [it rotates to you (it is your turn)] 

or followed by a word particle 着 (indicate continuous state)  as in 轮着做 (taking turns to work)

or incorporated into a compound words along with a noun, like 轮米(getting in line for or queuing for rice handouts), 轮班 (in rotation; in shift) 

轮 is also a noun for 'wheel' and 'turn'

轮流 (to take turns/ to alternate/to rotate) is also a verb, but it is only use as an auxiliary verb. For example, "轮流拜访他" - (take turns visiting him); 轮流看火 (take turns watching the fire). In other words, whenever you see 轮流, another verb must follow it directly. Meaning it can never be placed directly before the object