Anti-stall tip treatment means

Details Anti-stall tip treatment means Anti-stall tip treatment means

1996-05-02

1998-06-09

Verdier, Christopher

Rotary kinetic fluid motors or pumps

With means for re-entry of working fluid to blade set

Plural, independent, serially acting re-entry means

415119, 4151731, 4151735, 415914, F01D 1108

Patent

active

057624704

DESCRIPTION:

BRIEF SUMMARY
This application claims priority under 35 U.S.C. 371 based on PCT application PCT/GB94/00481, filed Mar. 11, 1994, published as WO94/20759 Sep. 15, 1994, which claims priority based upon Soviet Union Application 93-012990, filed Mar. 11, 1993.
The present invention relates to compressors and more especially to axial-flow, mixed-flow and axial-centrifugal compressors of gas turbine plant. It is particularly concerned with the provision of anti-stall tip treatment means in such compressors.
A centrifugal compressor is known (Soviet Union Author's Certificate No. 273364, published in 1970) which comprises a rotor and a casing closely surrounding the rotor. In the inlet section the compressor casing is provided with an annular cavity is extending over the radially outer edges of the rotor blades. The cavity connected through two adjacent annular passages to the compressor flow path immediately upstream of the rotor and to the leading edge region of the rotor blades. Each passage contains guide ribs circumferentially inclined in opposite senses to the radial direction.
Differences in the processes of gas compression and the designs of axial-flow, centrifugal, mixed-flow and compound compressors put specific requirements upon the construction of anti-stall tip treatment means. Therefore use of the tip treatment means described in the Author's Certificate No. 273364 does not ensure the efficient operation of a multistage axial-flow compressor or an axial-centrifugal compressor with axial first stages over a typical range of operating conditions.
An axial-flow compressor is known (Soviet Union Author's Certificate No. 757774, published in 1980) which comprises a casing with rotor and stator blades therewithin and an annular cavity disposed over the blades. The cavity communicates with the compressor flow path through slots between ribs defining a grid, the ribs being circumferentially inclined to the radial direction.
A disadvantage of this arrangement is that in order to prevent a reduction in compressor efficiency, it is necessary to provide an additional device in the form of a rotatable ring that considerably complicates the construction and reduces its reliability.
It is an object of the present invention to provide an anti-stall tip treatment in axial-flow, mixed-flow and axial-centrifugal compressors to increase the range of aerodynamic and/or aeroelastic stability of the blades while moderating any resulting loss in compressor efficiency. Another object of the invention is to provide a tip treatment against stall conditions that will vary its action without the use of additional control devices. A further object is to provide an anti-stall tip treatment that is relatively simple in construction.
According to the invention, there is provided a compressor comprising a casing in which are annular arrays of rotor blades and stator blades, the casing having an annular cavity extending over at least one said array of blades, the cavity communicating with the flow path through the compressor both upstream of and axially coincident with said array of blades through slots formed by an annular grid of ribs, said ribs being obliquely inclined relative to the radial direction at an angle (.phi..sub.r) of 30.degree. to 50.degree., the pitch (t) of said ribs and the slot width (.delta..sub.s) between ribs being in the ratio of 1.5 to 2.0, the rib radial projection height (h) and the slot width being in the ratio of 1.1 to 1.8, the axial length (L) of the grating of ribs and the blade tip chord axial projection (b') being in the ratio of 0.5 to 1.5, and the cavity height (H) outwardly of said ribs and said axial length (L) of the grating being in the ratio of 0.2 to 0.5.
Preferably the ribs are obliquely inclined with respect to the flow direction through the compressor and this angle may vary along their length.
It is also preferred to arrange that the angle of rib inclination to the radial direction is constant along the length of the series of ribs.
For a better understanding of the present invention, reference will n

REFERENCES:
patent: 4212585 (1980-07-01), Swarden et al.
patent: 4466772 (1984-08-01), Okapuu et al.
patent: 4540335 (1985-09-01), Yamaguchi et al.

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