The Tesla bladeless turbine or disk turbine is a type of gas turbine which has smooth disks for rotors, rather than bladed fans. The rotors are arranged in a coaxial stack with narrow spacing between, and have cutouts near the center. The working fluid (typically steam or combustion products) is injected perpendicular to the main axis and nearly tangential to the disks. Because of the narrow separation between the disks, the interaction between fluid and rotor is governed entirely by boundary layer effects. Basically, adhesion causes the fluid to "drag" the rotor along, spiraling toward the center as it transfers energy to the mechanism. It then flows through the rotor cutouts to an exhaust at the end of the shaft.