Abstract The use of splitter blade as a passive flow control mechanism in the design of separation free aggressive annular diffuser is explored through computational fluid dynamics simulations. The fundamental working principle of a splitter blade in case of a two-dimensional rectangular diffuser and an annular diffuser is discussed. The effects of splitter blade configuration on the end-wall adverse pressure gradients are discussed. An aggressive diffuser design space is identified with ducts of maximum slope of 50 deg and maximum divergence angle between the outer and inner walls of 10 deg for axial-length to inlet height ratio ranging from 1.25 to 2.5. One or more splitter blades are employed in the duct to eliminate flow separation for all the ducts in the aggressive design space considered. Requirement of number of splitter blades in the aggressive design space is demarcated. Performance charts for the ducts in this aggressive design space are also established.