Illangasekare’s primary area of research is in modeling of flow and transport in permeable and fractured media. His research encompasses many areas that include numerical modeling of saturated and unsaturated flow in soils, surface-subsurface interaction, arid-zone hydrology, integrated hydrologic modeling, flow in subfreezing snow, transport of dissolved and multiphase wastes, wireless sensor networking for environmental monitoring and intelligent remediation and environmental impacts of energy development. His research combines basic theories describing fundamental processes, numerical models and experiments that are conducted at a hierarchy of scales from small laboratory cells to intermediate scale test systems that includes a coupled porous media/ low velocity boundary layer environmental wind tunnel.