A turbomachinery apparatus (10) includes: a turbine (22), including: a turbine component (36) defining at least one arcuate flowpath surface (40); an array of axial-flow turbine airfoils (46) extending from the flowpath surface, the turbine airfoils defining spaces therebetween; and a plurality of splitter airfoils (146) extending from the at least one flowpath surface, in the spaces between the turbine airfoils, each splitter airfoil having opposed pressure and suction sides extending between a leading edge and a trailing edge, wherein the splitter airfoils have a thickness ratio which is less than a thickness ratio of the turbine airfoils.