The Chicago Blues Festival, Friday to Sunday from noon to 9:30 PM in Grant Park, is a day shorter this year than in previous years but still features a near overwhelming amount of music. And it’s still 100 percent free. Blues scholars and Reader contributors Bill Dahl and David Whiteis have rounded up the festival’s most notable acts (broken down by day), including Shirley Johnson and Eddie C. Campbell on Friday, Lil’ Ed & the Blues Imperials, Lurrie Bell, John Primer, and Bettye LaVette on Saturday, and Lee Boys, Ralph “Soul” Jackson (at the Rabbit Factory Soul Revue), Big Jack Johnson, and Sharon Jones & the Dap-Kings on Sunday.