Patent GB-1352206-A (GB)
Title: Fluid handling apparatus
IPC: F02C9/18
Filed: 1971-11-18
Abstract: 1352206 Axial-flow compressors; gas turbine engines GENERAL ELECTRIC CO 18 Nov 1971 [27 Nov 1970] 53601/71 Heading F1C and F1G Fluid handling apparatus comprises first and second independently rotatable compressor rotors arranged in series in a common passage, one rotor having a greater ratio of inertia to available torque than the other, at least one bypass passageway intermediate the rotors, means for controlling the bypass flow area as a predetermined scheduled function of operational variables of the second rotor, and means for resetting the predetermined schedule in response to at least one signal indicative of change of speed of the second rotor, whereby fluid in excess of that which the second rotor can handle is bypassed to substantially prevent stall of the first rotor. The two compressor rotors may form part of a turbojet engine or a turbofan engine. In the case of a turbofan engine, the second compressor rotor is driven by an H. P. turbine, while the first compressor rotor is driven by an L. P. turbine which also drives the fan. Bypass passageways between the first and second compressor rotors are controlled by bypass valves 52 operated by an actuator 54. The servo valve 74 of the actuator is controlled in accordance with the corrected rotational speed of the second compressor rotor by means of a three-dimensional cam 64 which is rotatable in accordance with the rotational speed N 2  of the second rotor by a governor 60 and axially movable in accordance with the inlet temperature T 2  of the second rotor by means of a bellows 62, follow-up being provided by linkage 70, 94. A further cam 110 subjected to the speed N 2  and temperature T 2  (or, instead, a cam 112 connected to the throttle lever 68) acts via a follower 114 to control a bleed valve 122 to vary the pressure in a fluid supply duct 116 downstream of an orifice 118. On deceleration of the engine, the follower 114 is moved in the direction 124, pivoting about an instantaneously fixed connection 146 and, through a connection 125, moving a rod 126 to close the bleed valve 122. The resultant rise in pressure in the duct 116 moves a piston 103 downwardly to alter the position of the pivot 98 of the linkage 70, thereby increasing the opening of the bypass valves 52 to compensate for the fact that the second compressor rotor decelerates more rapidly than the first compressor rotor, because of its smaller ratio of inertia to available torque, whereby the output of the first rotor is temporarily greater than can be accepted by the second rotor. The upward movement of the rod 126 increases the opening of a valve port 132, thereby decreasing the pressure downstream of an orifice 140. The resultant reduction in the pressure acting on the underside of a piston 150 causes a downward movement of the connection 146 and consequently a re-opening of the bleed valve 122 and also a reduction of the opening of the port 132 which re-balances the piston 150. If the second compressor rotor is of greater ratio of inertia to available torque than the first compressor rotor, the cam 110 or 112 is shaped to cause closure of the bleed valve 122 during acceleration rather than deceleration. The actuator 54 may be replaced by, e.g. a ball - screw actuator.