Abstract: An arrangement provided for turbine wheels (4) with cover disks (6, 7) which have a contactless sealing region (8, 9) to the housing. An apron-shaped free jet is created within a mixer zone (15) by increasing the transmission cross-section to the housing side in connection to the sealing region (8, 9) in a stepwise manner in the mixer zone (15) adjoining in the same direction and by connection channels (16, 17, 18) from the outer air to the beginning of the mixer zone (15), the air (13) is sucked in and mixed in in order, after steering, to supply the water-air mixture at the rotor wheel outlet end (21) to the main flow (5). Air (13) is thus fed in behind the sealing region (8, 9) which, on the one hand, calms the flow in the main flow (5) behind the rotor wheel under partial load without auxiliary aggregates and, on the other hand, reduces the friction losses between the rotor wheel (4) and housing (1).