JP2008111435A - Asymmetric compressor air extraction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for mistuning rotating stall aerodynamics by preventing the formation of coherent unsteady loads. <P>SOLUTION: Compressor air is extracted in an asymmetric circumferential pattern (16). The asymmetric extract pattern disrupts the rotating stall cell (10) rotational pattern, preventing the formation of a coherent aerodynamic excitation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an asymmetric compressor bleed method.

  The axial flow gas turbine for the power generation industry is designed to operate optimally at a constant rotational speed and power. In addition, conventional industrial axial flow gas turbine compressors have limited variable vane stages and extraction sections. These three factors, constant speed operation, limited variable blade stage, and limited bleed, result in significant off-design aerodynamic conditions during start and stop operations. An axial compressor causes a rotating stall during such non-design operation.

  The turning stall appears as a local stall cell that rotates at about half the wheel speed. These stall cells provide coherent unsteady aerodynamic loads on both the moving and stationary blades. As the rotor speed changes, the number of stalled cells changes and a different nodal diameter is set. The vibration response of the moving and stationary blades due to a rotating stall aerodynamic load increases the sensitivity of the blades to normal damage and can lead to premature failure.

  The present invention enhances the durability of axial flow compressor blades and stationary blades by eliminating or reducing coherent aerodynamic forces due to swirling stall. Specifically, the present invention provides a method for preventing the formation of a coherent unsteady load by mistuning the turning stall aerodynamic force.

  The present invention is a method for controlling the air flow in a compressor, wherein a series of circumferentially asymmetric separations in a predetermined axial portion of the compressor with respect to flow disturbances caused by part speed or non-design operation. The present invention is embodied as a method that includes extracting a flow at the location and generating a bleed pattern that counteracts the flow disturbance.

  The present invention is a method for controlling the air flow in a compressor, the method comprising operating the extraction of the compressor air asymmetrically around the outer casing of the compressor so as to counteract disturbances such as swirling stall. Is also materialized.

  The axial flow gas turbine for the power generation industry is designed to operate optimally at a constant rotational speed and power. In addition, conventional industrial axial flow gas turbine compressors have limited variable vane stages and extraction sections. These three factors create significant non-design aerodynamic conditions during start and stop operations. Axial flow compressors can cause rotational stall during such non-design operations.

The turning stall shown schematically in FIG. 1 appears as a local stall cell 10 (ω _{stall cells} ˜½ω _engine ) that rotates at about half the wheel speed. These stall cells provide coherent unsteady aerodynamic loads on both the moving blades and the stationary blades 12. As the rotor speed changes, the number of stalled cells changes and different excitation characteristics (known as nodal diameters) are set. The vibration response of the moving and stationary blades due to the rotating stall aerodynamic load increases the sensitivity of the blades to normal damage and can lead to premature failure.

  The durability of the axial compressor blade is improved by eliminating or reducing the coherent aerodynamic force caused by the rotating stall. This reduction in aerodynamic vibration load increases the blade's damage resistance to normal operating damage such as blade tip friction, corrosion, and leading edge foreign object damage.

  The present invention improves the durability of the axial compressor rotor blades and stationary blades by eliminating or reducing the aerodynamic excitation of the axial compressor rotor blades and stationary blades due to rotational stall. Specifically, the present invention provides a method for mistuning a rotating stall aerodynamic force by preventing the occurrence of a coherent unsteady load.

  Therefore, specifically, a new method for eliminating or reducing disturbances such as turning stall in the compressor is proposed. For example, at a predetermined axial position (stage) of one or more, the compressor air is selectively moved in the circumferential direction according to the vibration source so as to cancel the flow disturbance of the rotating stall. Extract asymmetrically selectively. In such a case, the bleed process is initiated and the turning stall condition or potential stall condition is canceled by asymmetric extraction of air. Since this is a phenomenon determined by the operating state (part speed and / or part load), no sensor is required.

  In the exemplary embodiment of the present invention as schematically shown in FIGS. 2 and 3, the compressor air is asymmetric circumferentially through a series of generally shaped holes or slots provided in the outer diameter channel wall 18. Extracted by pattern. The bleed pattern is determined as a function of the turning stall node diameter pattern and the aerodynamic strength of the cell. The asymmetric multistage bleed pattern disturbs the rotation pattern of the rotating stall cell and prevents the formation of coherent aerodynamic excitation.

  FIG. 3 schematically illustrates an axial compressor with a generally shaped bleed hole or slot according to an exemplary embodiment of the present invention. A generally shaped bleed hole or slot 16 is defined to selectively bleed the compressor air through the compressor casing. The inlet is corrected by a conduit (not shown) through a high speed shut-off valve (not shown) for removing the extracted air and recirculating the extracted air as needed or desired. When similar bleed holes are provided at several axial positions, the bleed pipes corresponding to the circumferential direction at two or more axial positions may share the same control valve. When the circumferential bleed holes or slot trains are normally operated simultaneously, the circumferential bleed tube rows may be connected to a common control valve. To conserve high pressure air extraction, one or more valves should be closed in the controller once the stall cell is suppressed. In one exemplary embodiment, the extraction ends after a predetermined period of time. In another exemplary embodiment, the amount of bleed is gradually reduced after extraction begins. Other extraction protocols may be employed as needed or desired.

  As described above, in order to prevent the formation of coherent unsteady loads and mistune the rotating stall aerodynamic force, the present invention provides a series of general shapes on the outer diameter flow path wall 18 as shown in the embodiment of FIG. An assembly is provided for extracting compressor air through holes or slots 16 in an asymmetric circumferential pattern. The bleed pattern can be determined by experiment or analysis as a function of the turning stall node diameter pattern and the aerodynamic strength of the cell. These bleed parts can be arranged at a single axial position or at multiple axial positions depending on the nature of the turning stall, the required bleed flow rate and the engine configuration constraints. As seen in FIG. 3, this exemplary embodiment represents an asymmetric extraction arrangement at two axial positions. The number of axial positions, the length of the circumferential arc, and the shape and number of bleed holes are defined based on the properties of the turning stall. The asymmetric multi-stage bleed pattern disturbs the rotational pattern of the rotating stall cell and prevents the formation of coherent aerodynamic excitation as conceptually shown in FIG.

As will be apparent from the above description, the asymmetric bleed mechanism has a total bleed required within a predetermined arc length Θ _arc at a predetermined circumferential position at a predetermined axial position 20 of each compressor casing 18. An asymmetrically spaced bleed portion 16 having a predetermined extraction shape that provides a flow rate is included. In the exemplary embodiment, the arc length Θ _arc is approximately 90 degrees.

  For split casing applications, the bleed portion 16 is disposed in the top half casing and can be easily modified in the field, resulting in improved access to the bleed manifold and piping (not shown). As is apparent from the above description, multi-stage bleed will require a bleed manifold to flow from the unit.

  Therefore, according to the present invention, 1) reduction / elimination of coherent unsteady aerodynamic excitation at the blade, 2) modification of the existing engine with a split casing design is possible, and 3) realization with the latest aerodynamic blade. ) Benefits of improved compressor blade durability due to increased damage resistance to blade tip friction, corrosion holes and leading edge damage.

  Although the present invention has been described with respect to the most practical and preferred embodiments at the present time, the present invention is not limited to the disclosed embodiments, and the technical idea and scope of the claims. Various modifications and equivalent configurations belonging to the above are included.

Schematic of turning stall. 1 is a schematic diagram of an asymmetric compressor bleed according to an exemplary embodiment of the present invention. FIG. 1 is a schematic perspective view of a compressor adapted for asymmetric compressor bleed according to an exemplary embodiment of the present invention. FIG.

Explanation of symbols

10 Stall cell 12 Wings 16 Bleed holes or slots 18 Compressor casing / wall 20 Axial position

Claims (10)

A method for controlling the air flow in a compressor, in which the high-pressure air is passed through a casing (18) from the vicinity or downstream of a predetermined axial portion (20) of the compressor, and the circumferential direction cancels out flow disturbances such as swirling stall. Extracting with an asymmetric pattern (16). The method according to claim 1, wherein the extraction of the high-pressure air takes place through a plurality of holes or slots (16) arranged asymmetrically around the outer circumference of the compressor casing (18). The method of claim 1, wherein the casing is a split casing, and the extraction of the high pressure air is performed through a plurality of holes or slots disposed in a top casing portion of the split casing. 2. The method of claim 1, comprising extracting high pressure air through a plurality of holes or slots disposed in an arc Θ _arc defined by the required flow rate and the nature of the swirl stall formation. The method of claim 4, wherein the holes or slots (16) are disposed asymmetrically within the arc Θ _arc . The method of claim 1, wherein the extraction is terminated after a predetermined period. The method of claim 1, wherein the extraction is gradually reduced after its start. A method for controlling air flow in a compressor, comprising operating a compressor air extraction (16) asymmetrically around the circumference of the compressor casing (18) to counteract disturbances such as swirling stall. Method. Extraction of high pressure air is performed through a plurality of holes or slots (16) disposed in an arc Θ _{arc on} the outer periphery of the compressor casing (18), which arc is determined by the required flow rate and the nature of the rotating stall formation. The method according to claim 8. The method according to claim 8, wherein the casing is a split casing, and the extraction of the high-pressure air is performed through a plurality of holes or slots disposed in a top casing portion of the split casing.