The Civil War Soldiers and Sailors system at http://www.itd.nps.gov/cwss/soldiers.htm lists no fewer than 1161 men named WOODRUFF who served in the Civil War--Union and Confederate. By comparison, the total for CARNELL is a relatively modest 51. Unless you have a little more to go on than last names (e.g., which side, state, or regiment), your task is a bit daunting.

Hope this helps a little.