A method for designing a front bypass flow path of a variable cycle engine

Abstract

This application provides a flow path design method for the front duct of a variable cycle engine. By controlling the variation law of the typical cross-sectional area along the front duct, the flow path of the front duct is designed. Under the premise of meeting the target front duct outlet area requirements and ensuring that no blockage occurs in the front duct, the method starts from reducing the internal flow loss of the front duct and achieving reasonable front duct ejector valve characteristics. Based on the aerodynamic area of ​​the typical cross-section and the flow path of the inner wall, the meridian length of the typical cross-section is calculated, and then the flow path of the outer wall is determined. This can form a more reasonable variation law of the cross-sectional area along the front duct, reduce the flow loss in the front duct and the idle stroke length of the front duct valve, and obtain reasonable outlet valve characteristics.

Description

Technical Field

[0001] This application belongs to the field of flow path design technology for the front bypass duct of a variable cycle engine, and specifically relates to a flow path design method for the front bypass duct of a variable cycle engine. Background Technology

[0002] Compared to conventional cycle engines, variable cycle engines add a front bypass duct between the core engine drive fan, high-pressure compressor, and outer bypass duct. Multiple support plates are arranged circumferentially inside the front bypass duct, and a valve is installed at the outlet of the front bypass duct. Figure 1 As shown, by controlling the valve opening, the amount of bleed air from the drive fan and high-pressure compressor to the outer bypass duct is adjusted, thereby changing the bypass ratio and enabling the engine to efficiently adapt to different flight conditions.

[0003] Currently, when designing the front bypass duct of a variable cycle engine, the focus is mostly on the structural design of the valves at the outlet and the strength and function of the valve adjustment mechanism. Less attention is paid to the aerodynamic performance of the front bypass duct. As a result, there are often situations where the flow path design of the front bypass duct is inappropriate, leading to large losses, excessively long valve idle stroke, and unreasonable valve characteristics.

[0004] This application is made in view of the aforementioned technical deficiencies.

[0005] It should be noted that the above background information is only used to assist in understanding the inventive concept and technical solution of this invention, and it does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0006] The purpose of this application is to provide a method for designing the flow path of the front bypass duct of a variable cycle engine, so as to overcome or mitigate at least one of the known technical defects.

[0007] The technical solution of this application is:

[0008] A method for designing the flow path of the front bypass duct of a variable cycle engine, comprising:

[0009] The angle α between the inner wall of the front duct and the engine axis is taken to be between 30° and 60°.

[0010] The minimum flow area A in the culvert is calculated based on the maximum flow rate index of the culvert and the maximum allowable Mach number in the culvert.

[0011] The aerodynamic area of ​​the section at the location of the maximum thickness of the support plate is C = max(A, B), where B is the index requirement for the aerodynamic area adjustment range of the front duct outlet.

[0012] Determine the aerodynamic area D at the outlet of the duct, satisfying B≤D≤C;

[0013] Based on the strength requirements, determine the blade shape and number of front duct support plates, as well as the position of the support plates within the front duct. This yields the distances from the intersection of the front and rear edges of the support plates with the inner wall of the front duct along the vertical line to the engine axis: R_support plate inlet 1 and R_support plate outlet 1, and the distances from the aerodynamic section meridian to the engine axis: M_support plate inlet 1 and M_support plate outlet 1.

[0014] Based on the blade profile, R-blade inlet 1, R-blade outlet 1, M-blade inlet 1, and M-blade outlet 1, the distance R-blade max1 from the intersection of the maximum thickness position of the blade and the inner wall of the front duct along the vertical line to the engine axis, and the distance M-blade max1 from the aerodynamic section meridian to the engine axis are calculated.

[0015] Based on C, R support plate max1, and M support plate max1, the distance R support plate max2 from the intersection of the maximum thickness position of the support plate and the outer wall of the front duct along the vertical line to the engine axis, and the distance M support plate max2 from the aerodynamic section meridian to the engine axis are calculated.

[0016] The aerodynamic section meridian length H at the location of the maximum thickness of the support plate is calculated as H = support plate max2 - M support plate max1, and then the intersection of the location of the maximum thickness of the support plate and the outer wall of the front duct is determined.

[0017] Based on D, the distance R2 from the intersection of the valve and the outer wall of the front duct along the vertical line to the engine axis and the distance M2 from the intersection of the valve and the outer wall of the front duct along the aerodynamic section meridian to the engine axis are calculated.

[0018] The meridian length of the aerodynamic section at the outlet of the duct is calculated as K = M2 - M1, and then the intersection of the aerodynamic section at the outlet of the duct and the outer wall of the duct is obtained.

[0019] The outer wall of the front duct is determined based on the intersection of the maximum thickness of the support plate and the outer wall of the front duct, and the intersection of the aerodynamic section at the outlet of the front duct and the outer wall of the front duct.

[0020] According to at least one embodiment of this application, in the above-described variable cycle engine front bypass duct flow path design method, α = 30° to 60°.

[0021] According to at least one embodiment of this application, in the above-described variable cycle engine front bypass duct flow path design method, when C=B, D=B is taken;

[0022] When C = A, take B ≤ D ≤ A.

[0023] This application has at least the following beneficial technical effects:

[0024] This paper presents a method for designing the flow path of the front duct of a variable cycle engine. By controlling the variation law of the typical cross-sectional area along the front duct, the method designs the flow path of the front duct. Under the premise of meeting the target front duct outlet area requirements and ensuring that no blockage occurs in the front duct, the method starts from reducing the internal flow loss of the front duct and achieving reasonable front duct ejector valve characteristics. Based on the aerodynamic area of ​​the typical cross-section and the flow path of the inner wall, the meridian length of the typical cross-section is calculated, and then the flow path of the outer wall is determined. This can form a more reasonable variation law of the cross-sectional area along the front duct, reduce the flow loss in the front duct and the idle stroke length of the front duct valve, and obtain reasonable outlet valve characteristics. Attached Figure Description

[0025] Figure 1 This is a partial schematic diagram of a variable cycle engine provided in an embodiment of this application;

[0026] Figures 2-5 This is a schematic diagram of the design dimensions and positions of the flow path in the front duct of a circulating engine provided in an embodiment of this application.

[0027] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual size of the product. Furthermore, the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. Detailed Implementation

[0028] To make the technical solution and advantages of this application clearer, the technical solution of this application will be described in a clearer and more complete manner below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some embodiments of this application, and are only used to explain this application, not to limit this application. It should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings. Other related parts can be referred to the general design. In the absence of conflict, the embodiments and technical features in the embodiments of this application can be combined with each other to obtain new embodiments.

[0029] Furthermore, unless otherwise defined, the technical or scientific terms used in this application description shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "upper," "lower," "left," "right," "center," "vertical," "horizontal," "inner," and "outer," etc., used in this application description to indicate relative direction or positional relationship are used only to indicate relative orientation or positional relationship, and do not imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. When the absolute position of the described object changes, its relative positional relationship may also change accordingly, and therefore should not be construed as a limitation on this application. The terms "first," "second," "third," and similar terms used in this application description are used only for descriptive purposes to distinguish different components, and should not be construed as indicating or implying relative importance. The terms "a," "one," or "the," etc., used in this application description should not be construed as an absolute limitation on quantity, but should be construed as indicating the existence of at least one. The terms "including," "comprising," etc., used in this application description mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, without excluding other elements or objects.

[0030] Furthermore, it should be noted that, unless otherwise explicitly specified and limited, terms such as “installation,” “connection,” and “linkage” used in the description of this application should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can be a connection within two components. Those skilled in the art can understand its specific meaning in this application according to the specific circumstances.

[0031] The following is in conjunction with the appendix Figures 1 to 4 This application will be described in further detail.

[0032] With the front duct ejector valve fully open, its maximum outlet length L is as follows: Figure 2 As shown, the annular area formed by rotating the outlet length 360° along the engine axis is the maximum geometric area S of the front bypass duct outlet, calculated as follows:

[0033] S=2*π*R2*L……(1)

[0034] in,

[0035] R2 is the radial height of the front duct ejector valve.

[0036] Aerodynamic area is different from geometric area. Aerodynamic area is generally considered to be the area perpendicular to the direction of airflow.

[0037] Assuming the airflow direction within the duct is parallel to the inner wall of the duct, the cross-sectional area perpendicular to the airflow direction at the duct outlet is defined as the aerodynamic area T of the duct outlet. This area is obtained by calculating the difference between the lateral areas of the two cones:

[0038] T=π*R2*M2-π*R1*M1……(2)

[0039] in,

[0040] R1 is the radius of the base of the small cone, and the radial height of the intersection of the aerodynamic area section meridian and the inner wall of the front duct.

[0041] R2 is the radius of the base of the large cone, and is the radial height of the front duct ejector valve;

[0042] M1 and M2 are the generatrices of the two cones, obtained by extending the aerodynamic section meridian and intersecting it with the engine axis.

[0043] Figure 2 Formula (2) describes the aerodynamic area corresponding to the fully open state of the front duct, that is, the maximum available aerodynamic area at the outlet of the front duct. When the opening of the front duct decreases, M2 is taken from the position after the valve is closed, and the actual aerodynamic area under the corresponding opening can be obtained. Formula (2) can be extended to calculate the aerodynamic cross-sectional area of ​​any aerodynamic section in the front duct.

[0044] Based on the above assumptions, the radius R of the vertebral body base, the generatrix M of the vertebral body, and the angle α between the inner wall of the anterior duct and the horizontal line satisfy the following relationship:

[0045] R = M * COS(α)……(3)

[0046] The support plates are arranged circumferentially within the ductwork, which reduces the available aerodynamic area of ​​the cross-section where the support plates are located. The aerodynamic area of ​​the ductwork is most blocked at the location of the support plate's maximum thickness. Therefore, the cross-section at the location of the maximum support plate thickness can be considered a typical characteristic cross-section. The aerodynamic area of ​​this cross-section is calculated as follows:

[0047] Tmax'=Tmax-n*X……(4)

[0048] Tmax=π*Rsupport_plate_max2*Msupport_plate_max2

[0049] -π*R_support_plate_max1*M_support_plate_max1……(5)

[0050] X=I*H=I*(Msupport plate max2-Msupport plate max1)……(6)

[0051] in,

[0052] Tmax' is the aerodynamic area of ​​the support plate minus the maximum thickness section location;

[0053] Tmax is the area of ​​the section with the maximum thickness of the support plate, including the area of ​​the support plate.

[0054] n is the number of support plates;

[0055] X is the cross-sectional area of ​​the support plate at its maximum thickness, I is the maximum thickness of the support plate, and H is the meridian length of the cross-section at the location of the maximum thickness of the support plate.

[0056] R_support_plate_max1, M_support_plate_max1, R_support_plate_max2, and M_support_plate_max2 are the distances corresponding to the intersections of the cross-section at the maximum thickness of the support plate and the inner and outer walls of the front culvert, respectively.

[0057] Based on the above settings, the flow path design method for the front bypass duct of the recirculating engine disclosed in this application can be implemented with reference to the following:

[0058] The flow path design of the inner wall of the front duct is usually limited by the structural design factors of the high-pressure compressor casing. Taking into account factors such as aerodynamic performance, structural design requirements, and engine size limitations, the angle α between the inner wall of the front duct and the horizontal line is taken to be between 30° and 60°, and 45° is usually chosen.

[0059] With the flow path on the inner wall surface already determined, the design of the flow path on the outer wall surface directly determines the area variation pattern of each cross-section within the front duct. The meridian length of each typical cross-section can be calculated back from the aerodynamic area of ​​each typical cross-section and the flow path on the inner wall surface, thereby determining the flow path on the outer wall surface, as detailed below:

[0060] Based on the maximum flow rate index of the duct and the maximum allowable Mach number in the duct, the minimum flow area A in the duct is calculated using the flow rate formula.

[0061] Based on the aerodynamic area adjustment requirements of the front duct outlet, the index requirement B of the aerodynamic area adjustment range of the front duct outlet is compared with A, and the larger value of the two is taken as the aerodynamic area C of the section at the maximum thickness of the support plate, that is, C = max(A, B).

[0062] Determine the aerodynamic area D of the front duct outlet, satisfying B≤D≤C. If C=B and D=B, then the area of ​​the front duct outlet is the same as the area at the position of the maximum thickness of the support plate; if C=A, then B≤D≤A, that is, the area of ​​the front duct outlet is less than the area at the position of the maximum thickness of the support plate.

[0063] Based on the strength requirements, determine the blade shape and number of the front duct support plates, as well as the positions of the support plates within the front duct (R support plate inlet 1, R support plate outlet 1, M support plate inlet 1, M support plate outlet 1), and then obtain the intersection points of the maximum thickness of the support plates with the inner wall of the front duct (R support plate max1 and M support plate max1).

[0064] Based on the aerodynamic area C of the section at the maximum thickness of the support plate and formulas (3), (4), (5), and (6), the maximum values ​​of support plate R and support plate M are calculated.

[0065] Based on H = M_support_plate_max2 - M_support_plate_max1, the meridian length H of the section at the maximum thickness of the support plate is calculated, and then the intersection of the maximum thickness of the support plate and the outer wall of the front culvert is determined.

[0066] Based on the aerodynamic area D at the outlet of the duct and formulas (2) and (3), R2 and M2 are calculated, and the meridian length K of the aerodynamic section at the outlet of the duct is calculated according to K = M2 - M1, thereby determining the intersection point of the aerodynamic section at the outlet of the duct and the outer wall of the duct.

[0067] The lengths H and K of the two meridians are used to determine the flow path from the section with the maximum thickness of the outer duct support plate to the outer wall surface of the outlet section. The flow path of the outer wall surface of the inlet section is determined by extending the line, and the outlet length L of the front duct is obtained.

[0068] The various embodiments in the specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0069] The technical solution of this application has been described in conjunction with the preferred embodiments shown in the accompanying drawings. Those skilled in the art should understand that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A method for designing the flow path of the front bypass duct of a variable cycle engine, characterized in that, include: The angle α between the inner wall of the front duct and the engine axis is taken to be between 30º and 60º. The minimum flow area A in the culvert is calculated based on the maximum flow rate index of the culvert and the maximum allowable Mach number in the culvert. The aerodynamic area of ​​the section at the location of the maximum thickness of the support plate is C = max(A, B), where B is the index requirement for the aerodynamic area adjustment range of the front duct outlet. Determine the aerodynamic area D at the outlet of the duct, satisfying B≤D≤C; Based on the strength requirements, determine the blade shape and number of front duct support plates, as well as the position of the support plates within the front duct. Then, calculate the distance R_support_plate_max1 from the intersection of the maximum thickness position of the support plate and the inner wall of the front duct along the vertical line to the engine axis, and the distance M_support_plate_max1 from the aerodynamic section meridian to the engine axis. Based on C, R support plate max1, and M support plate max1, the distance R support plate max2 from the intersection of the maximum thickness position of the support plate and the outer wall of the front duct along the vertical line to the engine axis, and the distance M support plate max2 from the aerodynamic section meridian to the engine axis are calculated. The aerodynamic section meridian length at the location of maximum support plate thickness was calculated. This allows us to determine the intersection of the maximum thickness of the support plate with the outer wall of the front culvert. Based on D, the distance R2 from the intersection of the valve and the outer wall of the front duct along the vertical line to the engine axis and the distance M2 from the intersection of the valve and the outer wall of the front duct along the aerodynamic section meridian to the engine axis are calculated. The meridian length of the aerodynamic section at the outlet of the duct is calculated as K = M2 - M1, and then the intersection of the aerodynamic section at the outlet of the duct and the outer wall of the duct is obtained. M1 is the distance from the intersection of the aerodynamic section and the inner wall of the duct along the aerodynamic section meridian to the engine axis. The outer wall of the front duct is determined based on the intersection of the maximum thickness of the support plate and the outer wall of the front duct, and the intersection of the aerodynamic section at the outlet of the front duct and the outer wall of the front duct.

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