GB1286652A - Improvements in gas turbine engine air intakes - Google Patents

Abstract

1286652 Air intakes for gas turbine engines ROLLS-ROYCE Ltd 23 Sept 1969 56751/69 Heading F1G A gas turbine engine comprising a bladed compressor has an air intake in the form of a duct the downstream end of which faces a number of blades of the compressor, the number of blades being sufficiently small so that in operation a pressure wave generated across the opening by the passing blades is defined by substantially parallel pressure bands; the duct comprises also an upstream flow portion the height of which perpendicular to the length of the bands is smaller than the corresponding height of the downstream opening to the extent of substantially producing acoustic cut-off in respect of a discrete tone generated by the pressure wave. In the embodiment shown the compressor is of the centrifugal type comprising a rotor 32 having blades 33. The compressor comprises also a casing which extends upstream of the blades to form a plenum chamber 35 having a front wall 36 in which are formed two square openings 37 to which the silencer ducts 38 extend. Each duct 38 comprises a downstream end 40 defined by the opening 37, and an upstream end 41 of narrow rectangular form, the centre line 42 of the rectangle being radial with respect to the rotor. The sides of the tapered portion 39 are flat, the flow area of the duct being uniform throughout its length. The upstream end merges with a parallelsided flow portion 43. The theory underlying the invention is described.