Method for optimizing flow in labyrinth seal cavity of axial flow compressor

Abstract

A method for optimizing the flow characteristics of a grate-sealed cavity in an axial compressor is disclosed. Based on the flow characteristics within the cavity, the interior is divided into a flow control zone and a velocity field matching zone. Then, considering practical engineering constraints, an optimized geometry for the stationary upper endwall of the cavity is designed. Finally, CFD numerical simulation is used to analyze the flow of the optimized geometry and evaluate its impact on the stator blade performance. This invention analyzes the flow characteristics within the grate-sealed cavity, divides the cavity into zones, and designs the flow characteristics of each zone accordingly to obtain an optimized geometric structure. This achieves the goal of reducing the total pressure loss of the stator blades while simultaneously improving their pressurization capacity.

Description

Technical Field

[0001] This invention relates to a technology in the field of turbomachinery, specifically a method for optimizing the flow of the grate sealing cavity in an axial compressor. Background Technology

[0002] Axial compressors are a crucial component of aero engines and ground-based gas turbines. The inner ring of the stator blades, with its inner ring, has a wear-resistant coating at the blade root. This coating, together with the grates machined on the rotor disc, forms the grate-sealed cavity. A radial clearance exists between the two to prevent scraping between the rotor and stator during operation. Existing grate-sealed cavities have relatively simple geometries, and their design methods generally focus on a few specific geometric parameters. However, the geometric freedom of the cavity wall lines is high, and existing design methods have limitations. Currently, there is a lack of effective methods for optimizing the geometry of axial compressor grate-sealed cavities. Summary of the Invention

[0003] This invention addresses the problem that existing grate sealing cavities have relatively simple geometries and limited design methods. It proposes a method for optimizing the flow of grate sealing cavities in axial compressors. By analyzing the flow characteristics within the grate sealing cavity, the cavity is divided into zones, and the flow of each zone is designed accordingly to obtain an optimized geometric structure. This achieves the goal of reducing the total pressure loss of the stator blades while improving their pressurization capacity.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for optimizing the flow of a grate seal cavity in an axial compressor. Based on the flow characteristics within the grate seal cavity, the cavity is divided into a flow control zone and a velocity field matching zone. Then, considering practical engineering constraints, the optimized geometry of the stationary upper end wall of the grate seal cavity is designed. Finally, CFD numerical simulation is used to analyze the flow of the optimized geometry and evaluate its impact on the performance of the stator blades.

[0006] The flow control zone is specifically located near the inlet, in front of the grate teeth, and between the grate teeth. It is used to impede flow and reduce leakage loss. The cross-sectional shape of the flow control zone satisfies the following: it is a straight line near the inlet and between the grate teeth, two arcs in front of the grate teeth, and a straight line between the grate teeth.

[0007] The velocity field matching zone is specifically located after the grates of the sealing cavity and near the outlet. It is used to control the velocity field of the flow leaving the sealing cavity to match the velocity field of the mainstream flow in order to reduce mixing losses. The cross-sectional shape of the velocity field matching zone satisfies the following conditions: two straight lines after the grates and one arc near the outlet.

[0008] The velocity field includes radial velocity, circumferential velocity, and axial velocity.

[0009] The aforementioned practical engineering constraints refer to the constraints considered in actual processing due to the safe operation and manufacturing assembly requirements of the axial compressor.

[0010] The aforementioned CFD numerical simulation calculation refers to solving the Reynolds-averaged Navier-Stokes equations using numerical simulation methods. ,in: For a conserved parameter vector, , and These are inviscid vector flux and viscous vector flux, respectively. , , For heat source items, , For stress, , The symbol for Kronecker. Q is the source term. , Represents external forces. This represents the work done by these external forces. .

[0011] The performance referred to is the total pressure loss coefficient of the stator blades. With pressure coefficient They are respectively and , where: p * Let be the total pressure, p be the static pressure, and the subscripts in and out be the inlet and outlet, respectively. These parameters are obtained by calculating the mass average of the total pressure or static pressure over the entire inlet and outlet plane after completing numerical simulation calculations. To obtain better performance, the total pressure loss coefficient should be as small as possible, and the pressure coefficient should be as high as possible.

[0012] Technical effect

[0013] This invention employs a zoned approach, tailoring the design to the flow characteristics of different zones to ensure optimal stator blade performance. This invention improves the design efficiency of the axial compressor grate sealing cavity, shortens the development time of aero-engines or ground-based gas turbines, and saves research and development time and labor costs. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the constraints of the comb sealing cavity, where the thick lines represent the design objects;

[0015] Figure 2 This is a schematic diagram of the optimized grate sealing cavity geometry and flow partitioning obtained through an optimization design method;

[0016] Figure 3The diagram shows the limit streamlines inside the optimized comb-shaped sealing cavity;

[0017] Figure 4 To optimize the geometry of the prototype tooth sealing cavity and its internal limit streamline diagram before design. Detailed Implementation

[0018] like Figure 2 As shown in the figure, this embodiment relates to a method for optimizing the flow of the grate sealing cavity of an axial compressor, wherein the origin of the x-axis and y-axis is located at the lower left corner of the grate sealing cavity; the method includes:

[0019] 1) Determine the geometry of the sealing cavity near the inlet in the flow control zone: The purpose of flow control near the inlet of the sealing cavity is mainly to hinder the flow in the mainstream channel from entering the sealing cavity as much as possible, so as to reduce leakage flow rate and leakage loss. In this embodiment, the cross-sectional shape at this point is a straight line with an obtuse angle between it and the mainstream, which is used to hinder the airflow from entering the sealing cavity.

[0020] 2) Determine the geometry of the sealing cavity in front of the grate in the flow control zone: The flow in front of the grate enters from the inlet and is about to pass through the grate. The geometry of this zone needs to control the flow of vortices within the sealing cavity to minimize leakage flow. In this embodiment, a curvature flow control method is used to form strong vortices that fill the entire channel, achieving vortex blocking effect. The geometry of this zone consists of two circular arcs.

[0021] The aforementioned curvature flow control method controls the acceleration and deceleration of the flow by controlling the contraction and expansion of the flow channel area and the curvature of the wall curve.

[0022] The two arcs are specifically as follows: in the downstream direction, the radius of the first arc is 7.28 mm, the center is located at x = 76.07 mm, y = 20.85 mm, and the central angle is 69°; the radius of the second arc is 8.71 mm, the center is located at x = 69.92 mm, y = 6.09 mm, and the central angle is 63.97°.

[0023] 3) Determine the geometry of the sealing cavity at the location of the grates in the flow control zone: The purpose of flow control at the location of the grates is also to reduce the leakage flow rate, which mainly requires controlling the grate tip gap to be as small as possible. In this embodiment, the cross-sectional shape at this location is a straight line, and the grate gap value is taken as 1.1 mm.

[0024] 4) Determine the geometry of the sealing cavity after the grate in the velocity field matching zone: The flow after the grate has passed through the grate and is ready to enter the mainstream through the sealing cavity outlet. This velocity field matching zone requires flow control within the sealing cavity to match the velocity field of the mainstream flow. In this embodiment, the cross-sectional shape at this location is expansion-type, consisting of two straight lines. The cross-sectional area of ​​the grate sealing cavity gradually increases to reduce the velocity of the leaking flow and achieve the purpose of matching the mainstream velocity field.

[0025] The included angle between the two straight lines is 173.2°.

[0026] 5) Determine the geometry of the sealing cavity near the outlet of the sealing cavity in the velocity field matching zone: The mixing effect between the sealing cavity outlet and the mainstream needs to be considered more specifically near the outlet. In this embodiment, the cross-sectional shape at this location is an arc, with the tangent at the sealing cavity outlet forming an acute angle with the mainstream direction. This helps the leaked flow smoothly enter the mainstream and reduces mixing losses.

[0027] The radius of the arc is 5.6 mm, the center is located at x = 8.87 mm, y = 20 mm, and the central angle is 118.8°.

[0028] 6) Based on the above design method and actual engineering constraints, design the following using simple circular arc and straight line equations: Figure 1 The optimized grate sealing cavity geometry is shown. In this coordinate system, the geometric shape expression of the grate sealing cavity is as follows: Within the flow control region, the equation of the straight line near the inlet is... The equations of the two arcs in front of the comb teeth, in the downstream direction, are respectively and The equation of the straight line between the teeth is: Within the velocity field matching region, the equations of the straight line behind the grating teeth, in the downstream direction, are as follows: and The equation of the circular arc near the exit is: , where x and y are both in mm.

[0029] The actual engineering constraints mentioned include:

[0030] ① Constraints on the distance between the transverse section of the wall and the blade: The transverse section of the wall at this location must not be lower than the height of the grating teeth, and at the same time, it must not be too close to the blade. Therefore, the distance between the transverse section and the blade must be between 3mm and 10mm.

[0031] ② Constraints on the distance between the stationary wall and the rotating wall in the vertical section near the inlet;

[0032] ③ The distance between the stationary wall and the rotating wall in the vertical section near the exit must be limited and cannot be too small.

[0033] ④ Constraints on the distance between the stationary wall and the blades in the vertical section near the inlet;

[0034] ⑤ The distance between the stationary wall and the blade in the vertical section near the exit must be limited and cannot be too small.

[0035] After comprehensively considering the above constraints ② to ⑤, it is determined that the distance at constraint ② must be greater than 5mm, the distance at constraint ③ must be greater than 3mm, and the distances at constraints ④ and ⑤ must both be greater than 3.2mm.

[0036] 7) After completing the optimized profile shape, flow analysis is performed using CFD numerical simulation. Figure 3 and Figure 4 The diagrams show the limiting streamlines inside the optimized grate-shaped sealing cavity obtained through the above design method, compared to the original grate-shaped sealing cavity before optimization. As can be seen from the diagrams, the vortex structure inside the optimized sealing cavity is significantly altered in regions 1 and 2 compared to the prototype. Due to the increased cross-sectional area of ​​the channel in region 1, the single-vortex structure transforms into a double-vortex structure. In region 2, the vortices near the grate move to the vicinity of the sealing cavity inlet, and the vortex structure is significantly larger, almost covering the entire front of the sealing cavity. Compared to the prototype, the vortex structure near the inlet in the optimized sealing cavity is more effective at impeding leakage flow. For regions 4 and 5 near the outlet, the difference in vortex structure between the prototype and the optimized design is smaller. The streamlines of the optimized design fit more closely to the sealing cavity wall near the outlet, indicating that this geometry better matches the leakage flow with the mainstream velocity field, thus reducing mixing losses.

[0037] 8) The impact of the optimized model on the performance of the stator blade was evaluated. The performance parameters of the optimized model and the prototype below 20% of the blade height are compared in Table 1.

[0038] Table 1. Comparison of performance parameters between the optimized and prototype models below 20% of leaf height.

[0039] As can be seen from the table, compared with the prototype, the total pressure loss below 20% blade height of the optimized model is significantly reduced, with a reduction rate of 12.23%. While the total pressure loss is reduced, the pressure boosting capacity of the blade is also slightly improved, with the pressure coefficient increasing by 1.57%. This indicates that the optimized design can both reduce the total pressure loss and improve the pressure boosting capacity of the blade, thus achieving the purpose of optimization design.

[0040] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for optimizing the flowability of the grate sealing cavity in an axial compressor, characterized in that, Based on the flow characteristics within the grate sealing cavity, the cavity is divided into a flow control zone and a velocity field matching zone. Then, considering actual engineering constraints, the optimized geometry of the stationary upper end wall of the grate sealing cavity is designed. Finally, CFD numerical simulation is used to perform flow analysis on the optimized geometry and evaluate its impact on the performance of the stator blade. The flow control zone is specifically located near the inlet, in front of the grate teeth, and between the grate teeth. It is used to impede flow and reduce leakage loss. The cross-sectional shape of the flow control zone satisfies the following: it is a straight line near the inlet and between the grate teeth, two arcs in front of the grate teeth, and a straight line between the grate teeth. The velocity field matching zone is specifically located after the grates of the sealing cavity and near the outlet. It is used to control the velocity field of the flow leaving the sealing cavity to match the velocity field of the mainstream flow in order to reduce mixing losses. The cross-sectional shape of the velocity field matching zone satisfies the following conditions: two straight lines after the grates and one arc near the outlet. The velocity field includes radial velocity, circumferential velocity, and axial velocity.

2. The method for optimizing the flowability of the axial compressor grate sealing cavity according to claim 1, characterized in that, The aforementioned practical engineering constraints refer to the constraints considered in actual processing due to the safe operation and manufacturing assembly requirements of the axial compressor.

3. The method for optimizing the flowability of the axial compressor grate sealing cavity according to claim 1, characterized in that, The aforementioned CFD numerical simulation calculation refers to solving the Reynolds-averaged Navier-Stokes equations using numerical simulation methods. ,in: For a conserved parameter vector, , and These are inviscid vector flux and viscous vector flux, respectively. , , For heat source items, , For stress, , The symbol for Kronecker. Q is the source term. , Represents external forces. The work done by an external force. .

4. The method for optimizing the flowability of the axial compressor grate sealing cavity according to claim 1, characterized in that, The performance referred to is the total pressure loss coefficient of the stator blades. With pressure coefficient , respectively and , where: p * ρ represents the total pressure, p represents the static pressure, and the subscripts in and out represent the inlet and outlet, respectively.

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