a particular problem is with respect to secondary flows about the hub 32 and shroud 34 sweeping low momentum fluid upwards in the direction of arrowheads e causing problems at the peak suction point on the suction surface of the rotors 31 it will be appreciated that fig2 only illustrates one rotor 31 and one stator 33 but in a practical engine there will be a plurality of such rotors 31 and stators 33 the rotors 31 on the hub 32 will sweep past the stators 33 for fluid flow control in accordance with the present invention the stator shroud 34 includes a collector slot 35 and an outlet slot 36 angled relative to each other for flow coupling with a return slot 37 in the rotor hub 32 in operation secondary flow is collected at an inlet 38 of the collector slot 35 and passes along a collector passage towards the return slot 37 the collected flow is projected and given impulse by rotation of the rotor hub 32 as it sweeps past the shroud 34 thus the return slot 37 pumps the collected secondary flow towards the outlet passage 36 where it is taken sufficiently downstream and angled sufficiently such that there are no or at least fewer problems.