Thank you for the opportunity to help you with your question!
The alliterative moments of these lines occur with the e of Grendel/greet/heat, with "great" a variation upon the e-emphasis; with gallant/battle, and with sword/foe (albeit unevenly to our ear). These, it might be said, form the horizontal pattern of alliteration. However, there is also a vertical, which lends extra coherence to the lines. There is Grendel/greet/heat/unsheathed and--more roughly--warrior/hero/sword/foe. Simile refers to a metaphoric use of language as indicated by "like" or "as." There is as such no simile in these lines. However, the lines are highly figurative. To greet is to engage or confront (not welcome). The "heat" warrior is presumably less hot than formidable or toiling. There is also a slight figurative touch in the notion of unsheathing a sword against someone. One removes a sword from the scabbard, but this does not involve any suggestion of being "against" this person or that. I can raise my fist, but to do so against someone is something else entirely.
Please let me know if you need any clarification. I'm always happy to answer your questions.
Oct 1st, 2015
Studypool's Notebank makes it easy to buy and sell old notes, study guides, reviews, etc.