Centrifugal compressor diffuser turning section concave cavity flow guide structure and pneumatic optimization method thereof

Abstract

The invention discloses a centrifugal compressor diffuser turning section concave cavity flow guide structure and a pneumatic optimization method thereof.The centrifugal compressor diffuser turning section concave cavity flow guide structure comprises an annular concave cavity structure, an annular concave cavity is formed in a turning section between a radial diffuser and an axial diffuser of a centrifugal compressor, and the annular concave cavity is communicated with an outlet of the radial diffuser and an inlet of the axial diffuser; and the annular concave cavity is sunken downwards from the bent section, so that airflow output by the radial diffuser forms a stable vortex in the sunken space of the annular concave cavity, the vortex forms airflow approximately parallel to the upper end wall of the turning section, airflow separation on the wall surface below the turning section is restrained, and energy loss is reduced. Compared with a traditional method that a smooth transition structure is usually adopted in the turning section between the radial diffuser and the axial diffuser, the turning section of the axial diffuser adopts the concave cavity design, airflow separation can be restrained, energy loss is reduced, and the stable working range of the gas compressor is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engines, and in particular to a concave cavity flow guide structure of a turning section of a centrifugal compressor diffuser and an aerodynamic optimization method thereof. Background Art

[0002] A centrifugal compressor is a device that compresses gas through centrifugal force. During operation, the gas is flung from the center of the impeller to the outer edge under the action of centrifugal force, causing the pressure to increase. The turning section is usually located in the flow path of the centrifugal compressor. After the gas flows out of the impeller, its flow direction needs to change. The turning section plays the role of guiding the gas to change its flow direction, allowing the gas to smoothly enter the subsequent flow path or components, such as the diffuser, according to the design requirements. The design of the turning section affects performance indicators such as gas flow uniformity and pressure loss. A reasonable turning section design can help improve the overall efficiency and performance of the centrifugal compressor.

[0003] Traditional centrifugal compressors typically use a smooth transition structure in the turning section between the radial diffuser and the axial diffuser. However, this design has the following key issues:

[0004] 1. Aerodynamic separation and energy loss. Due to the centrifugal force, the airflow is prone to separation on the wall below the turning section, forming turbulent vortices, which leads to a decrease in the total pressure recovery coefficient and causes secondary flow losses.

[0005] 2. Insufficient stability. The randomness of the separation vortex will induce pressure pulsation and increase the risk of surge, which is especially significant under low flow or variable operating conditions. Summary of the Invention

[0006] In view of this, the present invention provides a concave cavity guide structure of the turning section of a centrifugal compressor diffuser and an aerodynamic optimization method thereof to solve the problems of airflow separation and insufficient stability of the centrifugal compressor diffuser, so as to improve the efficiency and stable operating range of the centrifugal compressor.

[0007] In a first aspect, the present invention provides a concave cavity flow guide structure of a centrifugal compressor diffuser turning section, comprising:

[0008] An annular concave cavity structure, wherein the annular concave cavity is arranged in the turning section between the radial diffuser and the axial diffuser of the centrifugal compressor, and the annular concave cavity connects the outlet of the radial diffuser and the inlet of the axial diffuser; the annular concave cavity is recessed downward from the bending section, so that the airflow output from the radial diffuser forms a stable vortex in the recessed space of the annular concave cavity, and the vortex forms an airflow that is approximately parallel to the upper end wall of the turning section, thereby suppressing the separation of the airflow on the wall below the turning section and reducing energy loss.

[0009] The beneficial effects of the concave cavity guide structure of the turning section of the centrifugal compressor diffuser mentioned above are as follows: the present invention sets an annular concave cavity in the turning section, so that the airflow forms a stable vortex in the concave space of the cavity. The vortex constructs an airflow that is approximately parallel to the upper end wall, effectively constrains the mainstream direction, suppresses the airflow separation on the lower wall, reduces the generation of turbulent vortices, reduces the total pressure loss, and significantly improves the total pressure recovery coefficient.

[0010] The annular cavity of the present invention replaces the random separation vortex with a stable vortex, reduces the amplitude and frequency of pressure pulsation, effectively improves the stability of the compressor under non-design conditions, expands the stable operating range, and reduces the probability of surge.

[0011] The airflow formed by the annular cavity can guide the airflow to complete large-angle turns more smoothly, avoiding the backflow or separation phenomenon caused by excessive turning angles in traditional smooth structures, reducing the lateral flow and vortex dissipation of the airflow in the turning section, reducing secondary flow losses, and thus improving the overall efficiency of the compressor.

[0012] Compared with separate discrete cavities, the annular cavity has a more uniform circumferential distribution of airflow; stress is not easily concentrated; high-precision positioning is not required, and the manufacturing difficulty and processing cost are low.

[0013] Compared with the traditional method that usually adopts a smooth transition structure in the turning section between the radial diffuser and the axial diffuser, the turning section of the present invention adopts a concave cavity design, which can suppress airflow separation, reduce energy loss, and improve the stable operating range of the compressor.

[0014] In an optional embodiment, the annular concave cavity structure includes a bottom wall and a shroud assembly, the bottom wall is connected to the side wall of the radial diffuser, one end of the shroud assembly is connected to the bottom wall, and the other end of the shroud assembly is connected to the lower wall of the axial diffuser, and an annular concave cavity is formed between the shroud assembly, the bottom wall and the side wall of the radial diffuser.

[0015] In an optional embodiment, the air guide cover assembly includes a guide ring and an air guide cover shell, the bottom wall is connected to the guide ring, the guide ring is connected to the inner wall of the air guide cover shell, and the air guide cover shell is connected to the lower wall of the axial diffuser.

[0016] In an optional embodiment, the annular cavity structure forms an expanding shape with an opening gradually increasing from bottom to top.

[0017] In an optional embodiment, the annular cavity is integrally formed with the radial diffuser and the axial diffuser using additive manufacturing technology, or the annular cavity is separately assembled with the radial diffuser and the axial diffuser.

[0018] In a second aspect, the present invention provides an aerodynamic optimization method for a concave cavity flow guide structure of a centrifugal compressor diffuser turning section, comprising the following steps:

[0019] S1. Design input and state parameter determination:

[0020] Based on the preliminary design of the centrifugal compressor, clarify the design indicators, determine the design point and the deviation point, and determine the stable operating flow range;

[0021] S2. Design of pneumatic channel parameters of the concave cavity in the turning section:

[0022] According to the centrifugal compressor outlet flow field characteristics and structural interference constraints, the initial values of the annular cavity parameters are determined;

[0023] The impact of the cavity on performance and flow improvement was verified through CFD simulation, and the cavity parameters were parametrically controlled.

[0024] Conduct parameter sensitivity analysis and use orthogonal test method or genetic algorithm to perform multivariable optimization of cavity parameters, set multiple objectives, and use the objective function as total pressure recovery coefficient, surge margin and circumferential non-uniformity to determine the best parameter combination;

[0025] S3. Design of concave cavity structure in turning section:

[0026] According to the pneumatic channel parameters, the cavity structure is designed using 3D modeling software.

[0027] In an optional embodiment, in step S2, the annular cavity parameters include an upper axial width, a lower axial width, a radial depth, and a curvature radius; the upper axial width is determined according to the flow channel length of the turning section and the flow field acceleration effect; the lower axial width is determined according to the structural interference; the radial depth is determined according to the structural interference; the curvature radius is the transition curvature between the outlet of the annular cavity structure and the axial diffuser, which meets the transition requirement of avoiding sudden changes at the outlet.

[0028] In an optional embodiment, after performing step S3, the method further includes the following steps:

[0029] S4. Static strength assessment:

[0030] For the design of the concave cavity structure in the turning section, a three-dimensional numerical simulation template that has been verified by experiments was used. Strength verification conditions were selected to conduct static strength assessment under given total pressure, temperature and assembly constraints, including yield strength reserve coefficient, ultimate strength reserve coefficient, and stress distribution in each area of the concave cavity.

[0031] If the evaluated corresponding strength reserve coefficient meets the standard, the turning section concave cavity structure design scheme in step S3 is feasible; otherwise, the turning section concave cavity structure design process returns to step S3 for redesign based on the difference.

[0032] In an optional embodiment, after step S4, the method further includes the following steps:

[0033] S5. Drawing and processing of the concave structure of the turning section:

[0034] According to the selected processing method, the structural design scheme is determined, and the corresponding cavity structure drawing and processing are completed.

[0035] In an optional embodiment, during the processing of the cavity structure, the geometric tolerance of the cavity structure is controlled: the cavity structure drawing is completed according to the processing method, and the contour tolerance of the annular cavity is controlled to be ≤0.1mm, and the surface roughness Ra is ≤1.6μm or 6.3μm.

[0036] In summary, the technical solution of the present invention has the following advantages:

[0037] The turning section of the present invention adopts an annular concave cavity structure design, which can suppress airflow separation, reduce energy loss, and improve the stable operating range of the compressor.

[0038] The present invention designs a whole-circle annular cavity, parameterizes the width, depth, and curvature radius of the cavity, and then performs multivariable optimization to quickly obtain the best combination.

[0039] Compared with separate discrete cavities, the annular cavity of the present invention has a more uniform circumferential distribution of airflow; stress is not easily concentrated; high-precision positioning is not required, and the manufacturing difficulty and processing cost are low.

[0040] The structural design of this invention can be adapted to suit different processing requirements and working environments by employing different design methods. A welded air deflector can be used to maintain the concave aerodynamic channel, ensuring machining accuracy. Alternatively, the annular concave cavity and diffuser body can be integrally formed using additive manufacturing techniques to avoid stress concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 This is a schematic diagram of the design dimensions of the pneumatic channel of the air guide cover assembly of the present invention;

[0043] Figure 2A schematic diagram of the assembly relationship of a turning section air guide cover assembly and related components of a centrifugal compressor diffuser turning section concave cavity air guide structure provided by the present invention;

[0044] Figure 3 Schematic diagram of the aerodynamic fluid domain of the turning section and axial diffuser of the present invention;

[0045] Figure 4 Schematic diagram of the three-dimensional streamline distribution in the turning section and axial diffuser of the present invention;

[0046] Figure 5 Schematic diagram of velocity vectors in the turning section and axial diffuser of the present invention;

[0047] Figure 6 This is a schematic diagram of the total pressure in the turning section and axial diffuser of the present invention;

[0048] Figure 7 This is a schematic diagram of the total temperature in the turning section and the axial diffuser of the present invention;

[0049] Figure 8 A flow chart of an aerodynamic optimization method for a concave cavity guide structure in a turning section of a centrifugal compressor diffuser provided by the present invention.

[0050] Description of reference numerals:

[0051] 1. Radial diffuser, 2. Diffuser casing assembly, 3. Axial diffuser, 4. Guide ring, 5. Guide cover, 6. Bottom wall. DETAILED DESCRIPTION

[0052] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0053] Currently, most centrifugal compressor turns utilize smooth transition designs (with both upper and lower walls being continuous curved surfaces). For example, a "constant cross-sectional area change rate" turn design approach (e.g., turn and recirculator flow optimization) has been employed. While CFD simulations have demonstrated improved total pressure recovery coefficients, flow separation still persists. Another improvement, such as the asymmetric endwall diffuser, employs convex / concave surfaces to adjust the flow area to mitigate asymmetric flow in the volute, but these approaches lack structural optimization for the turn.

[0054] Other studies have set grooves between the impeller outlet and the diffuser to suppress the secondary flow and vortex diffusion on the end wall through serrated choke units, but they have not been applied to the turning section.

[0055] In the hypersonic field, concave cavity structures are used to form local low-pressure areas to control separation vortices, but their design goals are to reduce drag and prevent heat, and do not involve the coordinated optimization of the compressor.

[0056] The main shortcomings of existing technologies are: 1. Insufficient flow control: The smooth transition structure cannot effectively suppress the separation of airflow on the wall below the turning section, resulting in instability of the mainstream channel and energy dissipation. 2. Efficiency bottleneck: The traditional diffuser and the turning section are not well designed, the pressure recovery coefficient is not significantly improved, and the secondary flow loss is high. 3. Stability limitations: Although existing flow-blocking structures (such as sawtooth units) can limit vortex clusters, the fixed design cannot adapt to the flow characteristics of different working conditions.

[0057] Based on this, the present invention provides a concave cavity guide structure of the turning section of a centrifugal compressor diffuser and a coordinated aerodynamic optimization method thereof. By optimizing the concave cavity structure of the turning section, airflow separation is suppressed, energy loss is reduced, and the stable operating range of the compressor is improved.

[0058] The following combination Figures 1 to 8 , the aerodynamic optimization method of the concave cavity guide structure of the turning section of the centrifugal compressor diffuser of the first aspect of the present invention and the concave cavity guide structure of the turning section of the centrifugal compressor diffuser of the second aspect of the present invention are elaborated in detail.

[0059] According to an embodiment of the present invention, in the first aspect, a centrifugal compressor diffuser turning section concave cavity guide structure is provided, Figure 1 and Figure 2 As shown, it includes an annular cavity structure. The annular cavity is arranged in the turning section between the radial diffuser 1 and the axial diffuser 3 of the centrifugal compressor, and the annular cavity connects the outlet of the radial diffuser 1 and the inlet of the axial diffuser 3. The radial diffuser 1 and the outer side of the axial diffuser 3 are connected through the diffuser casing assembly 2. The annular cavity is recessed downward from the bending section, so that the airflow output from the radial diffuser 1 forms a stable vortex in the recessed space of the annular cavity, and the vortex forms an airflow that is approximately parallel to the upper end wall of the turning section, thereby suppressing the separation of the airflow on the wall below the turning section and reducing energy loss.

[0060] In traditional smooth transition structures, centrifugal force causes airflow to separate on the wall below the turn, forming turbulent vortices. This reduces the total pressure recovery coefficient and increases secondary flow losses. The present invention incorporates an annular cavity in the turn, allowing the airflow to form a stable vortex within the concave space. This vortex creates an airflow approximately parallel to the upper end wall, effectively constraining the mainstream direction and suppressing airflow separation on the wall below. This design reduces the formation of turbulent vortices, lowers total pressure losses, and significantly improves the total pressure recovery coefficient.

[0061] The random nature of the detached vortex in traditional structures can induce pressure pulsation, which is particularly prone to surge at low flow rates or under variable operating conditions. The annular cavity of the present invention replaces the random detached vortex with a stable vortex, reducing the amplitude and frequency of pressure pulsation. This effectively improves the compressor's stability under off-design conditions (such as low flow rates and variable speeds), expands the stable operating range, and reduces the probability of surge.

[0062] The airflow formed by the annular cavity guides the airflow more smoothly through large-angle turns (such as 140°), avoiding the backflow and separation caused by excessive turns in traditional smooth structures. This design reduces lateral flow and vortex dissipation in the turning section, reducing secondary flow losses and thus improving overall compressor efficiency.

[0063] Compared with separate discrete cavities, the annular cavity has a more uniform circumferential distribution of airflow; stress is not easily concentrated; high-precision positioning is not required, and the manufacturing difficulty and processing cost are low.

[0064] Compared with the traditional method that usually adopts a smooth transition structure in the turning section between the radial diffuser and the axial diffuser, the turning section of the present invention adopts a concave cavity design, which can suppress airflow separation, reduce energy loss, and improve the stable operating range of the compressor.

[0065] In some embodiments, the annular cavity structure includes a bottom wall 6 and a shroud assembly, the bottom wall 6 is connected to the side wall of the radial diffuser 1, one end of the shroud assembly is connected to the bottom wall 6, and the other end of the shroud assembly is connected to the lower wall surface of the axial diffuser 3, and an annular cavity is formed between the shroud assembly, the bottom wall 6 and the side wall of the radial diffuser 1.

[0066] In this embodiment, the connection between the bottom wall 6 and the radial diffuser sidewalls, the connection between the shroud assembly and the bottom wall and the lower wall of the axial diffuser, and other surrounding components collectively define the geometric boundaries of the annular cavity. The connection between the shroud assembly, the bottom wall 6, the lower wall of the axial diffuser, and the attachment of the bottom wall to the radial diffuser sidewalls form a closed annular support structure, enhancing the overall rigidity of the turn section and preventing structural deformation caused by airflow pulsation or mechanical vibration.

[0067] More specifically, the air guide cover assembly includes a guide ring 4 and an air guide cover shell 5 , the bottom wall 6 is connected to the guide ring 4 , the guide ring 4 is connected to the inner wall of the air guide cover shell 5 , and the air guide cover shell 5 is connected to the lower wall of the axial diffuser 3 .

[0068] In some embodiments, the annular cavity structure forms an expanding shape with an opening gradually increasing from bottom to top.

[0069] In some embodiments, the annular cavity is integrally formed with the radial diffuser 1 and axial diffuser 3 using additive manufacturing, or the annular cavity is assembled separately from the radial diffuser 1 and axial diffuser 3. Regarding structural design, a dual-path adaptation of traditional machining and additive manufacturing is employed, with different structural design approaches employed for different machining methods. Traditional machining methods can ensure the aerodynamic path of the cavity by welding a shroud, ensuring machining accuracy. Alternatively, additive manufacturing techniques can be used to integrally form the annular cavity with the diffuser body to avoid stress concentration.

[0070] Additive manufacturing technology can integrate the annular cavity with the radial and axial diffusers, eliminating the connection interfaces (such as welds and bolt holes) in traditional split assembly and avoiding local stress concentration caused by welding or bolting due to differences in material thermal expansion and assembly gaps. The lack of connection interfaces means no risk of airflow leakage, ensuring the stability of the vortex shape within the annular cavity and further suppressing airflow separation. Additive manufacturing can accurately achieve cavity expansion shapes that are difficult to achieve through traditional machining (such as a curved surface with a gradual opening from bottom to top), ensuring contour tolerance and surface roughness.

[0071] The split assembly solution (the annular cavity and radial / axial diffuser are machined separately and then assembled) is suitable for traditional machining processes and offers advantages in cost control, ease of maintenance, and flexible material adaptability. Easy maintenance: If the annular cavity becomes worn or damaged due to long-term operation, only the shroud assembly needs to be disassembled and the cavity replaced, without having to replace the entire diffuser. Flexible material adaptability: The optimal material can be selected based on the operating conditions of different components.

[0072] According to an embodiment of the present invention, in a second aspect, a method for aerodynamic optimization of a concave cavity flow guide structure of a centrifugal compressor diffuser turning section is provided, comprising the following steps:

[0073] S1. Design input and state parameter determination:

[0074] Based on a centrifugal compressor with a completed preliminary design, clarify relevant indicators such as design speed, reduced flow rate, pressure ratio, efficiency, and surge margin. Determine the design point and operating point deviation from the design speed. Combined with the centrifugal compressor's stable operating range characteristics, determine the centrifugal compressor's stable operating flow rate range at the design speed.

[0075] S2. Design of pneumatic channel parameters of the concave cavity in the turning section:

[0076] S21. According to the flow field characteristics of the centrifugal compressor outlet (such as velocity gradient, pressure distribution), and under the premise of avoiding interference with adjacent blade channels and oil pipes, the initial values of the annular cavity parameters are determined. Figure 1 The parameters of the annular cavity include the upper axial width, the lower axial width, the radial depth, and the curvature radius.

[0077] Upper axial width W1: Adjust the starting position of the cavity according to the length of the flow channel in the turning section and the flow field acceleration effect.

[0078] Lower axial width W2: Determine the axial width of the lower end based on structural interference (surrounding parts such as oil pipes).

[0079] Radial depth H: Determine the radial depth of the cavity based on structural interference (surrounding parts such as oil pipes).

[0080] Curvature radius R: A transition curvature is required between the cavity outlet and the axial diffuser to meet the transition requirement of avoiding sudden changes at the outlet.

[0081] S22. CFD simulations were used to preliminarily verify the performance impact of the cavity (the cavity structure improved efficiency by 1% and surge margin by 2%) and the flow improvement effect. Cavity parameters such as cavity width W, depth H, and curvature radius R were parameterized. The CFD simulations compared the flow separation between the smooth and cavity structures using streamline plots and velocity contours to verify the cavity's improved flow.

[0082] S23. Perform parameter sensitivity analysis and use orthogonal test method or genetic algorithm to perform multivariable optimization of cavity parameters such as cavity width, depth and curvature radius. Set multiple objectives, and the objective functions are total pressure recovery coefficient (maximization), surge margin (maximization) and circumferential non-uniformity (minimization) to determine the optimal parameter combination.

[0083] In this embodiment, the geometric design of the entire annular cavity is parameterized with respect to the width, depth, and curvature radius of the cavity, and then multivariable optimization is performed to quickly obtain the optimal combination.

[0084] Example: Combining Figure 5-Figure 8 The flow field diagram shows that the axial diffuser equipped with this centrifugal compressor has a large airflow turning angle of about 140 degrees ( Figure 1 The angle α in the diffuser is significantly greater than a normal 90-degree radial-axial deflection. Conventional double-wall designs with parallel upper and lower endwalls can cause deflection at the lower endwall, leading to backflow or separation. However, the current cavity design allows for a relatively stable vortex to form within the concave space, creating an airflow that is approximately parallel to the upper endwall. This allows the fluid in the diffuser to smoothly deflect nearly 140 degrees without significant backflow or separation, while also reducing friction losses on the solid wall surface.

[0085] S3. Design of concave cavity structure in turning section:

[0086] After completing the aerodynamic channel design of the turning section cavity, the structural design of the cavity guide cover assembly can be further carried out using 3D modeling software, thereby obtaining the cavity guide cover assembly of the aerodynamic channel that meets the performance requirements.

[0087] The structure is designed for process adaptability. The structural design can adopt a traditional processing mode or a structural integration design. Different structural design methods are used for different processing methods to adapt to various complex processing requirements and working environments.

[0088] The structural integration design is achieved by integrating the annular cavity and the diffuser body into one piece using technologies such as additive manufacturing.

[0089] If traditional machining and separate assembly are used, the cavity shroud assembly undergoes structural design. This includes the types of components and the connections between them. This design also includes the connection between the shroud, the surrounding diffuser assembly, and the axial diffuser. This connection can be achieved by welding or other methods, such as using spigots.

[0090] Example: A centrifugal compressor uses traditional processing methods to combine the assembly relationship of the turning section cavity guide cover assembly and related parts. Figure 2 As shown, from Figure 2 As can be seen in the figure, the shroud assembly primarily consists of two parts: the guide ring 4 and the shroud shell 5. These two parts are welded together (weld B). The right bottom of the shroud shell 5 is welded to the axial diffuser 3 via weld (weld A). The left side of the shroud shell 5 is then compressed with the radial diffuser 1 (at point M). The compression at point M is 0.985 to 0.695. Welds A and B must be flush with the adjacent material surfaces and have a smooth transition.

[0091] S4. Static strength assessment:

[0092] For the design of the concave cavity structure in the turning section, a 3D numerical simulation template (including mesh, material properties, and pre-processing settings) was used, validated by experiments. Strength verification conditions (including surge transient loads) were selected, and a static strength assessment was conducted under given total pressure, temperature, and assembly constraints. This assessment included the yield strength reserve factor, the ultimate strength reserve factor, and the stress distribution in each cavity zone. During the static strength assessment, the strength verification conditions were selected to ensure that the yield strength reserve factor was ≥1.0, the ultimate strength reserve factor was ≥1.5, and the local strain concentration factor was <1.5.

[0093] Yield strength standard, take σ 0.1 , required to be no less than 1.0;

[0094] Ultimate strength standard, take σ b, the requirement is not less than 1.5;

[0095] The local strain concentration factor is required to be less than 1.5.

[0096] If the evaluated corresponding strength reserve coefficient and other factors meet the standards, the design scheme of the turning section cavity structure in step S3 is feasible; otherwise, the turning section air guide cover structure design process is returned to step S3 for redesign based on the difference, and finally a three-dimensional numerical simulation is performed using the same method as above until the strength reserve coefficient under the given speed, temperature and assembly constraints meets the corresponding requirements, thus completing the design of the final turning section air guide cover.

[0097] S5. Drawing and processing of the concave structure of the turning section:

[0098] Based on the selected machining method, the structural design is determined, and the corresponding cavity structure drawing and machining are completed. To ensure the airflow adhesion effect and reduce flow friction losses, geometric tolerances must be controlled: the cavity profile tolerance is ≤ 0.1mm, and the surface roughness Ra is ≤ 1.6μm (1.6μm is the traditional machining requirement, and 6.3μm is required for additive manufacturing plus polishing).

[0099] The concave cavity guide structure of the turning section of a centrifugal compressor diffuser and the coordinated aerodynamic optimization method thereof described in the present invention have been processed and tested, and the feasibility of the technical solution has been proved.

[0100] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A concave flow guide structure for a centrifugal compressor diffuser turning section, characterized in that: include: An annular cavity structure is provided, wherein the annular cavity is arranged in a turning section between a radial diffuser (1) and an axial diffuser (3) of a centrifugal compressor, and the annular cavity communicates with the outlet of the radial diffuser (1) and the inlet of the axial diffuser (3); the annular cavity is recessed downward from the bending section, so that the airflow output from the radial diffuser (1) forms a stable vortex in the recessed space of the annular cavity, and the vortex forms an airflow that is approximately parallel to the upper end wall of the turning section, thereby suppressing the separation of the airflow on the wall below the turning section and reducing energy loss.

2. The centrifugal compressor diffuser turning section concave cavity flow guide structure according to claim 1, characterized in that: The annular concave cavity structure comprises a bottom wall (6) and a shroud assembly, wherein the bottom wall (6) is connected to the side wall of the radial diffuser (1), one end of the shroud assembly is connected to the bottom wall (6), and the other end of the shroud assembly is connected to the lower wall surface of the axial diffuser (3), and an annular concave cavity is formed between the shroud assembly, the bottom wall (6) and the side wall of the radial diffuser (1).

3. The centrifugal compressor diffuser turning section concave cavity flow guide structure according to claim 2, characterized in that: The deflector assembly comprises a deflector ring (4) and a deflector shell (5); the bottom wall (6) is connected to the deflector ring (4); the deflector ring (4) is connected to the inner wall of the deflector shell (5); and the deflector shell (5) is connected to the lower wall of the axial diffuser (3).

4. The centrifugal compressor diffuser turning section concave cavity flow guide structure according to claim 1, characterized in that: The annular cavity structure forms an expanding shape with an opening gradually increasing from bottom to top.

5. The centrifugal compressor diffuser turning section concave cavity flow guide structure according to any one of claims 1 to 4, characterized in that: The annular cavity is integrally formed with the radial diffuser (1) and the axial diffuser (3) using additive manufacturing technology, or the annular cavity is separately assembled with the radial diffuser (1) and the axial diffuser (3).

6. An aerodynamic optimization method for a concave cavity flow guide structure in a centrifugal compressor diffuser turning section, characterized in that: The method is a method for optimizing the concave cavity guide structure of the centrifugal compressor diffuser turning section according to any one of claims 1 to 5, comprising the following steps: S1. Design input and state parameter determination: Based on the preliminary design of the centrifugal compressor, clarify the design indicators, determine the design point and the deviation point, and determine the stable operating flow range; S2. Design of pneumatic channel parameters of the concave cavity in the turning section: According to the centrifugal compressor outlet flow field characteristics and structural interference constraints, the initial values of the annular cavity parameters are determined; The impact of the cavity on performance and flow improvement was verified through CFD simulation, and the cavity parameters were parametrically controlled. Conduct parameter sensitivity analysis and use orthogonal test method or genetic algorithm to perform multivariable optimization of cavity parameters, set multiple objectives, and use the objective function as total pressure recovery coefficient, surge margin and circumferential non-uniformity to determine the best parameter combination; S3. Design of concave cavity structure in turning section: According to the pneumatic channel parameters, the cavity structure is designed using 3D modeling software.

7. The aerodynamic optimization method for the concave cavity flow guide structure of the centrifugal compressor diffuser turning section according to claim 6, characterized in that: In step S2, the annular cavity parameters include upper axial width, lower axial width, radial depth, and curvature radius; the upper axial width is determined according to the flow channel length of the turning section and the flow field acceleration effect; the lower axial width is determined according to the structural interference; the radial depth is determined according to the structural interference; the curvature radius is the transition curvature between the outlet of the annular cavity structure and the axial diffuser, which meets the transition requirement of avoiding sudden changes at the outlet.

8. The aerodynamic optimization method for the concave cavity flow guide structure of the centrifugal compressor diffuser turning section according to claim 6, characterized in that: After step S3, the method further includes the following steps: S4. Static strength assessment: For the design of the concave cavity structure in the turning section, a three-dimensional numerical simulation template that has been verified by experiments was used. Strength verification conditions were selected to conduct static strength assessment under given total pressure, temperature and assembly constraints, including yield strength reserve coefficient, ultimate strength reserve coefficient, and stress distribution in each area of the concave cavity. If the evaluated corresponding strength reserve coefficient meets the standard, the turning section concave cavity structure design scheme in step S3 is feasible; otherwise, the turning section concave cavity structure design process returns to step S3 for redesign based on the difference.

9. The aerodynamic optimization method for the concave cavity flow guide structure of the centrifugal compressor diffuser turning section according to claim 8, characterized in that: After step S4, the method further includes the following steps: S5. Drawing and processing of the concave structure of the turning section: According to the selected processing method, the structural design scheme is determined, and the corresponding cavity structure drawing and processing are completed.

10. The aerodynamic optimization method for the concave cavity flow guide structure of the centrifugal compressor diffuser turning section according to claim 9, characterized in that: During the processing of the cavity structure, the geometric tolerance of the cavity structure is controlled: the cavity structure drawing is completed according to the processing method, and the contour tolerance of the annular cavity is controlled to be ≤0.1mm, and the surface roughness Ra is ≤1.6μm or 6.3μm.

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