A low-loss wedge diffuser self-circulating stability augmentation device

Abstract

The present application belongs to the field of centrifugal compressor stability expansion design, and particularly relates to a low-loss wedge diffuser self-circulation stability expansion device, which comprises an impeller, a wedge diffuser and a self-circulation stability expansion device. The self-circulation stability expansion device is composed of an upstream air passage, a downstream air passage and an air bleed bridge, and is circumferentially and interval arranged in the diffuser flow channel. The downstream air passage is located behind the diffuser throat, and the upstream air passage is located in the bladeless area of the diffuser. According to the flow law of the centrifugal compressor itself and the high sensitivity of the diffuser throat pressure to the compressor flow, the self-adaptive adjustment of different working points is realized by the pressure difference balance of the upstream and downstream air passages of the self-circulation device, and the matching of the impeller and the diffuser is changed. When the flow of the centrifugal compressor increases, the backflow flows from the upstream air passage to the downstream air passage, the through-flow capacity of the diffuser throat is improved, the shock loss of the diffuser blade leading edge is reduced, and the choke point flow is increased. When the flow of the centrifugal compressor decreases, the backflow flows from the downstream air passage to the upstream air passage and is mixed with the main flow, so that the impeller outflow angle and the diffuser blade installation angle are more matched, the diffuser throat choking is reduced, the stall occurrence is delayed, and the stall margin is expanded. The self-circulation stability expansion device has small geometric size and simple structure, and can effectively prevent the decrease of the centrifugal compressor efficiency while expanding the stable flow range of the high-performance centrifugal compressor with the wedge diffuser.

Description

Technical Field

[0001] This invention belongs to the field of centrifugal compressor expansion and stabilization design, specifically relating to a low-loss wedge diffuser self-circulating expansion and stabilization device, which can expand the stable flow range of a high-performance centrifugal compressor with a wedge diffuser. Background Technology

[0002] Centrifugal compressors are small in size and have a high single-stage pressure ratio, making them widely used in various power plants, especially small and medium-sized aero-engines, including turboshaft engines and auxiliary power units (APUs). Modern high-performance centrifugal compressor designs are constantly evolving towards higher loads and higher thrust-to-weight ratios, which also brings about flow instability problems (rotating stall and surge). Researchers have made unremitting efforts to reliably and effectively improve the compressor's stall margin and expand its stable operating range through flow control. Extensive practical experience shows that compressor stability enhancement technology should be specifically analyzed in conjunction with its internal flow conditions. The inherent unsteady flow phenomena of the compressor itself are the main cause of its rotating stall and surge problems, which are the main problems limiting the development of turbomachinery. Stability design must be based on a deep understanding of the internal flow mechanism of the compressor, suppressing or even eliminating stall-inducing disturbances to achieve the goal of expanding the compressor's stable flow range.

[0003] Casing treatment, as a passive control method, is characterized by its simple structure and strong adaptability, and generally includes methods such as "slotted," "slotted," and self-circulating casings. However, traditional casing treatments, such as circumferential slotted and axial slotted casings, cannot balance stability margin and design operating efficiency, and can cause a significant decrease in pressure rise and efficiency. Self-circulating treatment technology, by opening holes in the compressor hub or casing, introduces downstream high-pressure gas upstream to form a recirculation, which can improve the flow field structure, effectively suppress separation, thereby increasing the compressor's stable operating range, and has a smaller impact on efficiency.

[0004] The casing treatment of the centrifugal compressor blade tip section is difficult to implement in practical applications due to its structural nature, which involves axial to radial rotation. The inner wall of the casing is not a simple toroidal surface, and some casing treatment methods widely used in axial compressors are unsuitable for centrifugal compressors. Structures specifically designed for centrifugal compressor casing treatment are relatively few, primarily used in self-circulating systems for turbochargers. These are mainly based on Fisher's self-circulating casing treatment structure, which establishes a circulation channel between the compressor impeller inlet guide vane throat and the compressor inlet. The pressure difference between these two locations drives gas flow within this circulation channel, improving the compressor's stable operating range. Subsequent research has largely built upon Fisher's treatment method or optimized parameters for specific compressor geometries. Improvements to this structure include adding guide vanes within the circulation channel or combining self-circulating casing treatment with other casing treatments, boundary layer suction methods, and other stability-enhancing designs. This combined stabilization method often results in complex structures, severe damage to the casing or blade structure, easy stress concentration, and difficult processing, leading to poor feasibility. This is a major reason why centrifugal compressor casing treatment is rarely used. Furthermore, the internal space of aerospace centrifugal compressors is small and highly integrated, making excessively large self-circulation devices unsuitable for practical applications.

[0005] Aero-engine centrifugal compressors often employ a design that integrates blades within the diffuser to meet requirements for high pressure ratios, high efficiency, and small size. The purpose of stability design is to suppress stall-inducing disturbances, improve flow field structure, and increase the stable flow range. As the compressor flow rate gradually decreases, the impeller-diffuser matching deteriorates, the diffuser inlet swirl angle increases, the throat pressure rise coefficient surges, and the adverse pressure gradient increases. These factors combined cause a decrease in the diffuser throat's flow capacity, expansion of the near-casing separation zone until a stall cluster forms, and eventually, as the stall cluster develops towards the hub side, it evolves into a stage stall.

[0006] Therefore, for aero-machine centrifugal compressors with bladed diffusers, it is necessary to start from the flow matching of the impeller diffuser and design a design that can improve the flow characteristics of the diffuser inlet region under low flow conditions, thereby increasing the stable flow range of the centrifugal compressor, and has the characteristics of low loss, simple structure, and small size. Summary of the Invention

[0007] The technical problem to be solved is that the existing self-circulating diffusion and stabilization devices of centrifugal compressors are generally located in the axial part of the centrifugal compressor inlet, which has a certain effect on suppressing tip stall. However, for high-performance centrifugal compressors that use wedge diffusers, due to the flow mismatch between the impeller and the diffuser, the stall initiation position is inside the diffuser. The self-circulating diffusion and stabilization design previously applied to the impeller rotor is difficult to work. The tubular self-circulating casing bleed air bridge designed for blade diffusers is too large and difficult to apply in practice. The jet velocity direction is opposite to the mainstream flow direction, resulting in greater losses. Furthermore, it does not make full use of the high sensitivity of the pre-compression section of the wedge diffuser to flow rate. When the flow rate is high, the diffuser throat acts like a constricting nozzle, accelerating the flow out of the impeller and reducing the pressure at the diffuser throat. The area of ​​the diffuser throat limits the maximum flow rate, i.e., the maximum blocked flow rate. When the flow rate is low, the diffuser throat acts like an expanding nozzle, slowing down and diffusing the flow into the throat. The lower the flow rate, the more tangentially the impeller outflow enters the diffuser, causing a surge in pressure at the diffuser throat. This increases the blockage until the diffuser loses its diffusion capacity, and the diffuser begins to stall. Therefore, it is essential to fully utilize the flow characteristics of the wedge diffuser in a centrifugal compressor and rationally design a self-circulating diffusion and stabilization device for the wedge diffuser to achieve low-loss diffusion and stabilization of the centrifugal compressor.

[0008] The present invention provides a low-loss wedge diffuser self-circulating stabilizing device, characterized in that: the impeller and the wedge diffuser with self-circulating casing treatment include large and small blades, impeller hub and air intake channel, wedge diffuser blades, and the self-circulating mechanism for forming backflow is composed of the internal flow channel of the upper cover plate, which can be specifically divided into three parts: upstream vent, air intake bridge and downstream vent.

[0009] This invention is applicable to high-performance centrifugal compressors with bladed diffusers. It utilizes the inherent flow characteristics of the centrifugal compressor, specifically the high sensitivity of the pressure at the throat of the wedge diffuser to the compressor flow rate. By relying on the pressure difference balance between the upstream and downstream vents of the self-circulating device, it achieves adaptive adjustment at different operating points, optimizing the internal flow field structure of the wedge diffuser and altering the matching between the impeller and diffuser. When the centrifugal compressor flow rate increases, the backflow flows from the upstream vent to the downstream vent, improving the flow capacity at the diffuser throat, reducing shock wave losses at the leading edge of the diffuser blades, and increasing the flow rate at the clogging point. When the centrifugal compressor flow rate decreases, the backflow flows from the downstream vent to the upstream vent and mixes with the mainstream, making the impeller outlet angle and diffuser blade installation angle more closely matched, reducing clogging at the diffuser throat, delaying stall, and increasing the stall margin. Compared to traditional self-circulating devices that only improve the compressor stall margin, this invention can increase the flow rate at the clogging point while improving the stall margin, and it features low losses, small size, and simple structure.

[0010] The technical solution of this invention is:

[0011] 1. A low-loss wedge diffuser self-circulating stabilizing device, comprising an impeller hub (1), main blades (2), flow divider blades (3), wedge diffuser blades (4), upper cover plate (5), lower cover plate (6), drive shaft (7), diffuser throat (8), diffuser channel (9), diffuser bladeless area (10), diffuser semi-bladeless area (11), downstream vent (12), upstream vent (13), and induced draft bridge (14). The device is characterized in that: the impeller hub (1), its main blades (2), and flow divider blades (3) constitute the impeller part; the diffuser blades (4), the diffuser bladeless area (10), the diffuser semi-bladeless area (11), and the diffuser channel (9) constitute the wedge diffuser part; the downstream vent (12), the upstream vent (13), and the induced draft bridge (14) constitute the self-circulating stabilizing device.

[0012] 2. Furthermore, the impeller hub (1) is mounted on the drive shaft (7) to drive rotation, and together with the main blade (2) and the diverter blade (3) on it, drive the fluid to flow to the diffuser.

[0013] 3. Furthermore, the wedge diffuser can be divided into two parts by the diffuser throat (8). Downstream of the diffuser throat (8) is the diffuser channel (9), which is expansion type, so that the airflow can be decelerated and pressurized. In front of the diffuser throat (8) is the pre-compression part, which can be divided into the diffuser bladeless area (10) and the diffuser semi-bladeless area (11).

[0014] 4. Furthermore, the self-circulating stabilizing device is not installed in every channel of the wedge diffuser, but is installed at intervals of one channel. While completing the stabilizing task, it reduces the cost of the device manufacturing process. The downstream vent (12) is located after the diffuser throat (8), and the arc of the vent is tangent to the throat. The upstream vent (13) is located in the middle of the bladeless area (10) of the diffuser. When the centrifugal compressor flow rate increases, the diffuser throat is equivalent to a constricting nozzle. The impeller outflow accelerates and is accompanied by shock wave loss. The pressure of the upstream vent (13) is higher than that of the downstream vent (12). The return flow flows from the upstream vent (13) to the downstream vent (12). This is equivalent to increasing the flow area of ​​the diffuser throat (8), improving the diffuser's flow capacity, and reducing shock wave loss to a certain extent, thus improving the compressor efficiency. On the other hand, when the centrifugal compressor flow rate decreases, the impeller outflow is more... With increased tangential velocity, the diffuser exhibits a tendency for suction surface separation, causing a surge in pressure at the throat of the wedge diffuser. The pressure at the downstream vent (12) is higher than that at the upstream vent (13), and the backflow flows from the downstream vent (12) to the upstream vent (13) and mixes with the mainstream. The line connecting the centers of the downstream vent (12) and the upstream vent (13) forms a 60° angle with the throat (8) of the diffuser. This reduces the tangential velocity of the mainstream while increasing the radial velocity, making the mainstream direction more compatible with the installation direction of the wedge diffuser blades (4).

[0015] 5. Furthermore, the diameters of the downstream vent (12) and the upstream vent (13) are different. The diameter of the downstream vent (12) is 5 mm, and the diameter of the upstream vent (13) is 3 mm. The air intake bridge (14) connects the downstream vent (12) and the upstream vent (13). The cross-section of the air intake bridge (14) is circular. It gradually contracts to the upstream vent (13) according to the arched guide line to form a contraction channel, which accelerates the airflow and reduces the loss of airflow inside the bridge. At the upstream vent (13), the jet direction is controlled to be 30° with the inner wall of the upper cover plate (5) to avoid excessive loss of mainstream velocity.

[0016] The advantages and positive effects of this invention are:

[0017] 1. Compared with existing self-circulation devices applied to centrifugal compressor impellers, the present invention is applicable to high-performance centrifugal compressors with blade diffusers. The self-circulation devices are periodically and discretely distributed in space and installed at intervals of one flow channel. The self-circulation devices are small in size and easy to process and form, meeting the limited space requirements inside the centrifugal compressor. At the same time, the smaller size corresponds to a smaller total pressure loss.

[0018] 2. Compared with existing self-circulating diffuser stabilization devices applied to blade diffusers, this invention fully utilizes the flow characteristics of wedge diffusers. It leverages the sensitivity of the pre-compression section to flow rate, specifically the characteristic that the diffuser throat pressure surges as flow rate decreases. By placing the downstream vent after the diffuser throat, when the centrifugal compressor flow rate increases, the backflow flows from the upstream vent to the downstream vent, improving the flow capacity of the diffuser throat and reducing the shock wave loss at the diffuser blade leading edge. When the centrifugal compressor flow rate decreases, the backflow flows from the downstream vent to the upstream vent and mixes with the mainstream, making the impeller outlet angle and diffuser blade installation angle more closely matched. This reduces blockage in the diffuser throat, delays stall, and expands the stability margin.

[0019] 3. The air intake bridge of the self-circulating device is arched, the flow channel cross-section is circular and the flow channel gradually shrinks, avoiding the corner losses that exist in rectangular flow channels. The selection of the jet direction is determined by numerical calculation. While improving the flow structure of the diffuser and increasing the stability margin, the corresponding flow loss is small. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of the centrifugal compressor impeller and wedge diffuser.

[0021] Figure 2 yes Figure 1 A partial view of the AA section.

[0022] Figure 3 yes Figure 1 An enlarged view of part I in the image.

[0023] Wherein: 1-Impeller hub, 2-Main blade, 3-Branch blade, 4-Wedge diffuser blade, 5-Upper cover plate, 6-Lower cover plate, 7-Drive shaft, 8-Diffuser throat, 9-Diffuser channel, 10-Diffuser bladeless zone, 11-Diffuser semi-bladeless zone, 12-Downstream vent, 13-Upstream vent, 14-Intake bridge. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0025] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] Implementation Case 1

[0027] like Figure 1 As shown, a low-loss wedge diffuser self-circulating stabilizing device is characterized in that: the impeller hub (1) and its main blades (2) and the diverter blades (3) constitute the impeller part; the diffuser blades (4) and the diffuser bladeless area (10), the diffuser semi-bladeless area (11) and the diffuser channel (9) constitute the wedge diffuser part; the downstream vent (12), the upstream vent (13) and the air intake bridge (14) constitute the self-circulating stabilizing device.

[0028] like Figures 2 to 3As shown, the downstream vent (12) of the self-circulating diffuser is located at the throat (8) of the diffuser, and the upstream vent (13) is located in the middle of the bladeless area (10) of the diffuser. It is installed in the flow channel of the wedge diffuser with a flow channel spaced apart. While completing the diffusion and stabilization task, it reduces the loss caused by the mixing of self-circulating backflow and mainstream flow. When the flow rate of the centrifugal compressor increases, the backflow flows from the upstream vent (13) to the downstream vent (12), which improves the flow capacity of the diffuser throat (8) and reduces the shock wave loss at the leading edge of the wedge diffuser blade (4). When the flow rate of the centrifugal compressor decreases, the backflow flows from the downstream vent (12) to the upstream vent (13) and mixes with the mainstream flow, making the impeller outlet angle and the installation angle of the wedge diffuser blade (4) more closely match, reducing the blockage of the diffuser throat (8), delaying the occurrence of stall, and expanding the stability margin.

[0029] The downstream vent (12) has a different diameter than the upstream vent (13). The downstream vent (12) has a diameter of 5 mm, and the upstream vent (13) has a diameter of 3 mm. The air intake bridge (14) connects the upstream vent (13) and the downstream vent (12). The cross-section of the air intake bridge (14) is circular. It gradually contracts to the upstream vent (13) according to the arched guide line to form a contracting flow channel, which accelerates the airflow and reduces the mechanical energy loss of the airflow inside the bridge. At the downstream vent (12), the jet direction is controlled to be 30° with the inner wall of the upper cover plate (5) to avoid excessive loss of mainstream velocity. The line connecting the center of the downstream vent (12) and the upstream vent (13) forms a 60° angle with the throat of the diffuser (8). While reducing the mainstream tangential velocity, it also increases the radial velocity, making the mainstream direction more compatible with the installation direction of the wedge diffuser blade (4).

[0030] The low-loss wedge diffuser self-circulating stabilizing device of the present invention is suitable for high-performance centrifugal compressors with bladed diffusers. It utilizes the inherent flow characteristics of the centrifugal compressor, namely the high sensitivity of the wedge diffuser throat pressure to the compressor flow rate. By relying on the pressure difference balance between the upstream and downstream vents of the self-circulating device, it achieves adaptive adjustment at different operating points, optimizing the internal flow field structure of the wedge diffuser and altering the matching between the impeller and the diffuser. When the centrifugal compressor flow rate increases, the backflow flows from the upstream vent to the downstream vent, improving the diffuser throat... The improved flow capacity of the diffuser reduces shock wave losses at the leading edge of the diffuser blades and increases the flow rate at the clogging point. When the centrifugal compressor flow rate decreases, the backflow flows from the downstream vent to the upstream vent and mixes with the mainstream, making the impeller outlet angle and diffuser blade installation angle more compatible. This reduces clogging at the diffuser throat, delays stall, and expands the stall margin. Compared to traditional self-circulating devices that can only improve the compressor stall margin, this invention can increase the flow rate at the clogging point while improving the stall margin, and it also features low loss, small size, and simple structure.

[0031] While preferred embodiments have been described, various modifications or substitutions may be made to the embodiments without departing from the spirit and scope of the invention. Therefore, it is understood that the invention has been described in an exemplary manner rather than a restrictive one.

Claims

1. A low-loss wedge diffuser aero-centrifugal compressor, comprising an impeller hub (1), main blades (2), splitter blades (3), diffuser blades (4), upper cover plate (5), lower cover plate (6), drive shaft (7), diffuser throat (8), diffuser channel (9), diffuser bladeless region (10), diffuser semi-bladeless region (11), downstream vent (12), upstream vent (13), and bleed air bridge (14), characterized in that: The impeller hub (1), main blades (2) and split blades (3) form the impeller part. The diffuser blades (4), the diffuser bladeless area (10), the diffuser semi-bladeless area (11) and the diffuser channel (9) form the wedge diffuser. The wedge diffuser is divided into two parts by the diffuser throat (8). Downstream of the diffuser throat (8) is the diffuser channel (9), which is expansion type, so that the airflow can be decelerated and pressurized. In front of the diffuser throat (8) is the pre-compression part, which is divided into the diffuser bladeless area (10) and the diffuser semi-bladeless area (11). The downstream vent (12), the upstream vent (13) and the air intake bridge (14) form the self-circulating diffusion and stabilization device. The impeller hub (1) is installed on the drive shaft (7) to drive rotation, and together with the main blades (2) and split blades (3) on it, drive the fluid to flow to the wedge diffuser. The self-circulating diffuser is not installed in every channel of the wedge diffuser, but rather at intervals of one channel. The downstream vent (12) is located after the diffuser throat (8), and the arc of the downstream vent (12) is tangent to the diffuser throat (8). The upstream vent (13) is located in the middle of the bladeless region (10) of the diffuser. When the centrifugal compressor flow rate increases, the diffuser throat (8) acts as a constricting nozzle, causing the impeller outflow to accelerate and be accompanied by shock wave losses. The pressure at the upstream vent (13) is higher than that at the downstream vent (12), and the backflow flows from the upstream vent (13) to the downstream vent (12). On the other hand, when the flow rate of the centrifugal compressor decreases, the impeller outflow becomes more tangential, the diffuser blades (4) tend to separate the suction surfaces, the pressure at the diffuser throat (8) surges, the pressure at the downstream vent (12) is higher than that at the upstream vent (13), and the backflow flows from the downstream vent (12) to the upstream vent (13) and mixes with the mainstream. The downstream vent (12) has a diameter of 5 mm, the upstream vent (13) has a diameter of 3 mm, and the air intake bridge (14) connects the upstream vent (13) and the downstream vent (12). The cross-section of the air intake bridge (14) is circular and gradually shrinks to the upstream vent (13) according to the arched guide line to form a shrinking flow channel. At the downstream vent (12), the jet direction is controlled to be 30° with the inner wall of the upper cover plate (5). The line connecting the center of the downstream vent (12) and the upstream vent (13) forms a 60° angle with the throat of the diffuser (8).

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