The Astros informed reliever Travis Blackley that he’ll be designated for assignment on Friday to make room for hard-throwing lefthander Kevin Chapman to come up from Class AAA Oklahoma City. “He’s been very effective and has stuff to get big league hitters out, and we really want to put him in the bullpen,” Astros general manager Jeff Luhnow said of Chapman. “This (Blackley decision) is a move that facilities that.” Chapman, 25, had 61 strikeouts over 50 2/3 innings while going 1-2 with a 3.20 ERA and two saves over 45 appearances for the RedHawks. Blackley, who was acquired from Oakland via trade on April 4 after he had been [.]