US3129876A - High speed axial flow compressors - Google Patents

Description

April 1964 v. T. FORSTER HIGH SPEED AXIAL FLOW COMPRESSORS- Filed Oct. 19, 1961 United States Patent "ice 3,129,257 6 HIGH SPEED AXIAL FLOW COMPRESSORS Vincent Trevor Forster, Rugby, England, assignor to The English Electric Company Limited, London, England, a British company Filed Oct. 19, 1961, Ser. No. 146,182 1 Claim. (Cl. 230-120) The present invention relates to axial flow compressors and has the primary object of increasing the swallowing capacity thereof which is often limited by the Mach number of the flow which can be accepted by the first row of rotor blades, or even by the following further two rows of blades. If this Mach number is increased above a critical value, say 0.65 to 0.75 depending on the type, setting and pitch of the blades, shock stalling results because sonic velocities are reached locally on the convex side of the blades with consequent breakdown of the flow.

If the Mach number is further increased, a limiting value is reached when the blade is said to be choked.

By increasing this limiting Mach number the mass flow through a given size of engine and its output could be increased correspondingly, or the size of gas turbine engine incorporating an axial flow compressor could be reduced for the same output.

Attempts at solving this problem by reducing the thickness-chord ratio and by sharpening the nose of the blades have obviously reached their limits. The present invention makes a difierent approach to this problem by applying the so-called area rule established for the design of transonic aircraft, according to which only the integrated cross-section area at any transverse plane is decisive for shock stalling eifects and not the distribution of this area.

According to the present invention the leading edges of one of the first rows of rotor blades are lengthened in the radial direction of the rotor both as compared with the trailing edges of the said rotor blades and with the trailing edges of the immediately preceding stator blades, and recesses flaring out adjacent the tip and root of the said lengthened leading edge are provided in the stator and rotor respectively, so that the cross sectional area of the throat at the entries between consecutive rotor blades of this row is increased.

In order that the invention may be clearly understood and readily carried into eiiect an embodiment thereof will now be described by way of example with reference to 3,129,876 Patented Apr. 21, 1964 the accompanying drawing, which is a diagrammatic part cross section of the first stage of an axial flow compressor, showing one rotor blade and the immediately preceding and subsequent stator blades only.

In the stator -1 of an axial flow compressor a first row 2 and a second row 5 of stator blades are mounted in the usual manner. On the rotor 4, which is rotatable about the axis OO, a first row of rotor blades 3 is mounted, for example by means of the usual serrated roots 6.

The leading edge 7 of the rotor blade 3 is extended in the radial direction of the rotor *4 as compared both with the trailing edge 8 thereof and with the length of the preceding row of stator blades 2. =Recesses flaring out at 9 and 10 adjacent the tip and root of the said lengthened leading edge 7 are provided in the stator l1 and rotor 4, respectively, so that the cross sectional area of the throat at the entries between consecutive rotor blades of this row is increased. In this way the limiting Mach number for the blade can be increased.

What I claim as my invention and desire to secure by Letters Patent is:

A subsonic multi-stage axialdlow compressor compris ing a stator and a rotor defining respectively outer and inner boundaries of an annular-1y converging working fluid pasasge, a row of stator blades mounted in said stator, rotor blades mounted in said rotor and downstream of said stator blades, each rotor blade having a root and a tip, said passage having a diverging portion forming recesses adjacent the root and tip respectively of the leading edges of the rotor blades and being longer than the radial dimension of the adjacent stator blade, whereby the cross-sectional area of the passage at the leading edge is greater in magnitude than the cross-sectional area at the trailing edge of the adjacent stator blade.

References Cited in the file of this patent UNITED STATES PATENTS 2,628,768 Kantrowitz Feb. 17, 1953 2,846,136 Zaba Aug. 5, 1958 FOREIGN PATENTS 996,967 France Sept. 5, 1951 226,168 Great Britain of 1926 564,336 Great Britain Sept. 22, !1944 661,861 Great Britain Nov. 28, 1951

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