Axial flow compressor surge margin improvement

摘要

The casing 28 of an axial flow compressor for a gas turbine engine is provided with a plurality of axially extending circumferentially spaced slots 30 in its internal cylindrical surface 32 adjacent the tips of at least one row of blades 26. A benefit in both stall margin improvement and a reduction in efficiency deficit may be achieved by positioning the leading edge of the slot 30 such that it leads the leading edge 30(a) of the blade 26 by an amount termed the overhang A or by reducing the closed to open ratio m/M of the slots 30. A further reduction in efficiency deficit may be achieved by combining the overhang A which individually gave the best stall margin improvement with a slot closed to open ratio m/M somewhat higher than the value which individually gave the best stall margin improvement. IMAGE