The present disclosure relates to electrical machines and methods for cooling active elements of electrical machines. More in particular, the present disclosure relates to rotors of electrical machines. An electrical machine may for example be a generator for a direct drive wind turbine. An electrical machine comprises a rotor comprising a plurality of active rotor elements, a stator comprising a plurality of active stator elements, and an air gap separating the active rotor elements and the active stator elements. The rotor further comprises one or more rotor openings configured for letting air flow enter the electrical machine and cool the active rotor elements and/or active stator elements in response to a rotation of the rotor.