Turbine frequency tuning, fluid dynamic efficiency, and performance can be improved using a particular profile for a turn of a cooling passage in an airfoil. By blending aspects of baseline and bulb contours into a blended turn with a non-uniform profile, mechanical and/or thermal stress can be reduced in the turn and in an airfoil including the turn, particularly on an outflow side of the turn. Stresses on the airfoil can be reduced using a turn profile that is a blend of a baseline profile and a bulb profile and that can be described by the airfoil core profile.