What literary device is illustrated by the phrase Eddie lowered the lap bar and clack-clack-clack up they went. And what purpose does the device serve?

The literary device illustrated in the phrase is onomatopoeia, as "clack-clack-clack" imitates the sound of the rollercoaster moving up. This device serves to create a vivid and sensory image for the reader, enhancing the overall reading experience by engaging the sense of hearing.