Tail cone design method for improving matching of S-bend nozzle of aero-engine

Abstract

A tail cone design method for improving the matching of an S-shaped nozzle of an aero-engine, the tail cone is of an S-shaped structure, and the design method comprises the following steps: determining constraint parameters; determining a variation law of a center line of a cross section of the tail cone; determining a variation control law of a cross section area of the tail cone; solving the cross section area and diameter of a circular cross section; establishing a relationship between the circular cross section and the center line; smoothly connecting profile lines of a plurality of cross sections along a path; carrying out simulation analysis on a flow field of the S-shaped nozzle, and determining an improvement direction according to a simulated result of a bypass ratio; and redesigning the S-shaped tail cone according to the improvement direction and carrying out simulation evaluation until a design requirement is met. The S-shaped tail cone designed in the method has the same parameters as those of the tail cone before improvement except for an eccentricity of a cross section, and a variation law of a center line of the S-shaped tail cone is determined according to a center line law of a flow channel surface of the S-shaped nozzle, so that the obtained S-shaped tail cone surface is adapted to the surface of the S-shaped nozzle, the circumferential non-uniformity of airflow is reduced, and the matching of the S-shaped nozzle is improved.

Description

Technical Field

[0001] This invention relates to the field of aero-engine nozzle design technology, and in particular to a tail cone design method for improving the matching performance of an aero-engine S-curve nozzle. Background Technology

[0002] The S-curve nozzle of an aero-engine possesses excellent stealth performance and has been widely used. Numerous publications have also disclosed related technologies. For example, patent CN208310917U discloses a transition section structure that solves the matching problem between the S-curve nozzle and a turbofan engine. By adding a transition section structure between the exhaust mixer at the tail of the turbofan engine and the S-curve nozzle, the problem of increased bypass ratio caused by modifying the original axisymmetric nozzle at the tail of the turbofan engine to an S-curve nozzle can be effectively solved. This ensures that the engine's operating conditions after the S-curve nozzle modification are essentially the same as when the axisymmetric nozzle is installed, thus enabling the aircraft to possess both high aerodynamic performance and high stealth performance, improving the aircraft's overall air combat capability.

[0003] While S-shaped nozzles offer excellent stealth performance, their integration with the entire aircraft can lead to increased circumferential airflow non-uniformity, altering the bypass ratio and resulting in poor compatibility between the S-shaped nozzle and the aircraft. Conventional methods to improve S-shaped nozzle compatibility include: adjusting the nozzle profile to reduce flow separation caused by high curvature, lowering aerodynamic losses, and improving compatibility; and designing transition sections before the nozzle and after the mixer casing to adjust the outer bypass outlet area and control the flow distribution between the inner and outer bypasses, thereby improving compatibility. However, both methods require redesigning the nozzle profile or even altering its physical form, leading to high costs and long development cycles. Therefore, a new approach is proposed: a tail cone design method to improve the compatibility of S-shaped nozzles in aero-engines without any adjustments to the nozzle profile. Although the S-bend nozzle disclosed in the aforementioned patent CN208310917U has a tail cone structure, the tail cone is conical. The airflow channel area formed by the conical tail cone and the S-bend nozzle is unevenly distributed in the circumferential direction, which in turn causes uneven pressure distribution at the rear end section of the tail cone, increases the internal back pressure, increases the external bypass flow, and increases the bypass ratio, resulting in a mismatch between the conical tail cone and the S-shaped tail cone. Summary of the Invention

[0004] The main objective of this invention is to propose a tail cone design method to improve the matching performance of S-curve nozzles in aero-engines, thereby addressing the aforementioned technical problems.

[0005] To achieve the above objectives, this invention proposes a tail cone design method to improve the matching performance of an aero-engine's S-shaped nozzle. The tail cone has an S-shaped structure, and the S-shaped tail cone design method includes the following steps:

[0006] Step S1: Determine the constraint parameters: Except for the eccentricity ΔS along the cross section, the other parameters are consistent with the parameters of the improved tail cone structure;

[0007] Step S2: Determine the variation law of the centerline of the S-shaped tail cone along the cross section: The variation law of the centerline of the S-shaped tail cone is controlled by Lee curves, Wittsinski curves or polynomial equations with different degrees of change.

[0008] Step S3: Determine the control law of cross-sectional area variation along the path of the S-shaped coccyx;

[0009] Step S4: Solve for the area and diameter of the circular cross-section along the path: Based on the area change pattern in Step S3, and given the areas of the front and rear ends of the tail cone, solve for the area and diameter of the circular cross-section along the path.

[0010] Step S5: Establish the relationship between the circular cross-section along the friction path and the centerline;

[0011] Step S6: Smoothly connect the contour lines of several sections along the process to obtain the S-shaped tail cone surface.

[0012] In step S1, the constraint parameters include the maximum constraints on the front circular cross-sectional area Ai and diameter Di of the tail cone, the eccentricity ΔS of the cross-section along the path, the total axial length, and the rear circular cross-sectional area Ao and diameter Do of the tail cone.

[0013] Preferably, in step S2, the variation law of the S-shaped tail cone centerline is controlled by a Lee curve with a relatively uniform gradient, and the control formula is:

[0014]

[0015] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY j The L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0016] Optionally, in step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a gradual initial change followed by a rapid change, and the control formula is:

[0017]

[0018] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY jThe L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0019] Optionally, in step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a rapid initial change followed by a gradual decrease, and the control formula is:

[0020]

[0021] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY j The L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0022] Preferably, in step S3, the cross-section of the S-shaped tail cone along the travel is designed to be circular; the change in the travel area is controlled by the Vitósinski curve or the Lee curve.

[0023] Preferably, in step S5, the centerline along the path determined in step S2 is passed through and perpendicular to the centers of several cross-sections along the path determined in step S4, according to the following formula:

[0024] z′ k =z k ;

[0025] x′ k =(x k -x i )·cosα+(y k -y i )·sinα+x i ;

[0026] y′ k =-(x k -x i )·sinα+(y k -y i )·cosα+y i ;

[0027] In the formula, the centerline lies in the xy plane, (x i ,y i ) represents the coordinates of the centerline at point i, and α represents the coordinates of point (x, y) on the centerline. i ,y i The tail cone at point (x) rotates about the z-axis by an angle along its circular cross-section. k ,y k ,z k (x') represents the coordinates before rotation. k ,y'k ,z' k ) represents the rotated coordinates.

[0028] Preferably, the method further includes step S7: conducting flow field simulation analysis of the S-bend nozzle to evaluate the influence of the S-shaped tail cone on the bypass ratio.

[0029] In step S7, if the pressure non-uniformity of the S-shaped tail cone's rear end section perpendicular to the flow channel direction is large, resulting in the bypass ratio still being greater than the target bypass ratio, then the offset of the S-shaped tail cone needs to be adjusted further.

[0030] In step S7, when adjusting the offset of the S-shaped tail cone, the offset of the S-shaped tail cone is one-quarter to one-half of the diameter of the front end of the tail cone.

[0031] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0032] (1) In this invention, the S-shaped tail cone designed has the same parameters as the tail cone structure parameters before the improvement, except for the eccentricity of the cross section. At the same time, the variation law of the center line of the S-shaped tail cone is determined according to the center line law of the flow channel of the S-bend nozzle. The resulting S-shaped tail cone profile adapts to the S-bend nozzle profile, reduces the circumferential non-uniformity of the airflow, and thus improves the S-bend matching.

[0033] (2) In this invention, the improved S-shaped tail cone, compared with the existing conical tail cone, has the same parameters as the original tail cone structure parameters except for the change in the eccentricity of the cross section along the path. Therefore, the improved S-shaped tail cone can be installed without changing the existing connection structure. The structure is simple and the design cycle is short. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of the S-shaped tail cone and the S-curved nozzle in this invention;

[0036] Figure 2 This is a flowchart illustrating the design process of the S-shaped tail cone in this invention.

[0037] Figure 3 This is a comparison diagram of the Mach number distribution on the symmetry plane when the conical tail cone of the prior art and the S-shaped tail cone of the present invention are installed in the S-curve nozzle. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0040] Combination Figure 1 , Figure 2 As shown, a tail cone design method for improving the compatibility of an aero-engine's S-shaped nozzle is disclosed. The tail cone has an S-shaped structure, and the S-shaped tail cone design method includes the following steps:

[0041] Step S1: Determine the constraint parameters: The constraint parameters include the maximum constraints on the front circular cross-sectional area Ai and diameter Di of the tail cone, the eccentricity ΔS along the friction section, the total axial length, and the rear circular cross-sectional area Ao and diameter Do of the tail cone. Except for the eccentricity ΔS along the friction section, the other parameters are consistent with the original tail cone structural parameters. The reason for determining the above parameters is that the main indicator affecting the overall matching performance of the S-bend nozzle is the bypass ratio, which is mainly determined by the inner and outer bypass areas at the mixer outlet and the pressure non-uniformity at the rear end of the tail cone. This method does not involve the inner and outer bypass areas at the mixer outlet, so the pressure non-uniformity at the rear end of the tail cone is the most important factor to consider in this method. Through research, it was found that among the above parameters, the eccentricity ΔS along the friction section has a significant impact.

[0042] Step S2: Determine the variation law of the centerline of the S-shaped tail cone along the cross section: In order to match the flow channel profile of the S-bend nozzle, the variation law of the centerline of the S-shaped tail cone is determined according to the centerline law of the flow channel profile of the S-bend nozzle, and Lee curves, Wittsinski curves or polynomial equations with different degrees of change are used for control.

[0043] Step S3: Determine the control law of the cross-sectional area change along the S-shaped tail cone: In order to better play the rectification role and reduce the circumferential non-uniformity of the pressure along the flow path, the cross-section of the S-shaped tail cone is designed to be circular; the change of the flow path area is controlled by the Vitósinski curve or Lee curve law, which can obtain the flow path area change without adverse pressure gradient.

[0044] Step S4: Solve for the area and diameter of the circular cross-section along the path: Based on the area change pattern in Step S3, and given the areas of the front and rear ends of the tail cone, solve for the area and diameter of the circular cross-section along the path.

[0045] Step S5: Establish the relationship between the circular cross-section along the friction path and the centerline;

[0046] Step S6: Smoothly connect the contour lines of several sections along the process to obtain the S-shaped tail cone surface.

[0047] Step S7: Conduct flow field simulation analysis of the S-bend nozzle to evaluate the influence of the S-shaped tail cone on the bypass ratio. Using the bypass ratio as the design improvement target, study the flow field of the S-bend nozzle. If the pressure non-uniformity of the S-shaped tail cone's rear section perpendicular to the flow channel direction is large, resulting in the bypass ratio still being greater than the target bypass ratio, then the offset of the S-shaped tail cone needs to be adjusted further. When adjusting the offset of the S-shaped tail cone, the offset of the S-shaped tail cone should be one-quarter to one-half of the diameter of the front end of the tail cone.

[0048] Step S8: Redesign the S-shaped tail cone according to the improvement direction in Step S7 and conduct simulation evaluation until the bypass ratio of the S-curve nozzle meets the design requirements. If the error of the bypass ratio after improvement is within 0.5% compared with that before the S-curve nozzle was installed, it can be regarded as meeting the design requirements.

[0049] Specifically, in this embodiment, in step S2, the variation law of the S-shaped tail cone centerline is controlled by a Lee curve with a relatively equal degree of change, and the control formula is:

[0050]

[0051] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY j The L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0052] Optionally, in step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a gradual initial change followed by a rapid change, and the control formula is:

[0053]

[0054] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY j The L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0055] Optionally, in step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a rapid initial change followed by a gradual decrease, and the control formula is:

[0056]

[0057] In the formula: x i y i These represent the x and y coordinates of the i-th point on the centerline; y0 represents the initial y coordinate of the centerline; ΔY j The L represents the inlet and outlet offset of the centerline, i.e., the eccentricity ΔS along the cross section. j It is the total axial length of the center line of the coccyx.

[0058] In this embodiment, in step S5, the centerline along the path determined in step S2 is passed through and perpendicular to the centers of several cross sections along the path determined in step S4, according to the following formula:

[0059] z′ k =z k ;

[0060] x′ k =(x k -x i )·cosα+(y k -y i )·sinα+x i ;

[0061] y′ k =-(x k -x i )·sinα+(y k -y i )·cosα+y i ;

[0062] In the formula, the centerline lies in the xy plane, (x i ,y i ) represents the coordinates of the centerline at point i, and α represents the coordinates of point (x, y) on the centerline. i ,y i The tail cone at point (x) rotates about the z-axis by an angle along its circular cross-section. k ,y k ,z k (x') represents the coordinates before rotation. k ,y' k ,z' k ) represents the rotated coordinates.

[0063] Combination Figure 3The figure shows a comparison of the Mach number distribution on the symmetrical plane when a conical tail cone (as described in the prior art) and an S-shaped tail cone (as described in this invention) are installed in an S-curve nozzle. The figure consists of the following parts: an S-curve nozzle 10, a mixer 20, a conical tail cone 30 (before improvement), and an S-shaped tail cone 40 (after improvement). It is clearly visible in the figure that flow separation occurs downstream of the conical tail cone 30 (before improvement), and the pressure non-uniformity at the rear end of the conical tail cone 30 is relatively large. In contrast, there is no flow separation at the rear end of the improved S-shaped tail cone 40, and the non-uniformity is significantly reduced. The bypass ratio of the S-curve nozzle with the improved tail cone is 10% higher than that of the nozzle before installation, while the bypass ratio of the S-curve nozzle with the improved S-shaped tail cone 40 is only 0.2% higher than that before installation. This is because the application of the S-shaped inner cone results in a more uniform airflow cross-section, reduces the pressure non-uniformity at the rear end of the S-shaped inner cone, and has a smaller impact on the distribution of airflow between the inner and outer bypass sections, ultimately ensuring that the bypass ratio meets the design requirements.

[0064] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A tail cone design method for improving the matching performance of an aero-engine's S-curve nozzle, characterized in that, The coccyx has an S-shaped structure, and the design method for this S-shaped coccyx includes the following steps: Step S1: Determine the constraint parameters: Except for the eccentricity ΔS along the cross section, the other parameters are consistent with the parameters of the improved tail cone structure; Step S2: Determine the variation law of the center line of the S-shaped tail cone along the cross section: Determine the variation law of the center line of the S-shaped tail cone according to the center line law of the S-curve nozzle flow channel profile, and use Lee curves, Wittsinski curves or polynomial equations with different degrees of change for control. Step S3: Determine the control law of cross-sectional area variation along the path of the S-shaped coccyx; Step S4: Solve for the area and diameter of the circular cross-section along the path: Based on the area change pattern in Step S3, and given the areas of the front and rear ends of the tail cone, solve for the area and diameter of the circular cross-section along the path. Step S5: Establish the relationship between the circular cross-section along the friction path and the centerline; Step S6: Smoothly connect the contour lines of several sections along the process to obtain the S-shaped tail cone surface; In step S1, the constraint parameters include the maximum constraints on the cross-sectional area Ai and diameter Di of the front end of the tail cone, the eccentricity ΔS of the cross-section along the path, the total length in the axial direction, and the maximum constraints on the cross-sectional area Ao and diameter Do of the rear end of the tail cone. In step S3, the cross-section of the S-shaped tail cone is designed to be circular; the variation of the cross-sectional area is controlled by the Wittsinski curve or the Lee curve. In step S5, the centerline along the path determined in step S2 is passed through and perpendicular to the centers of several cross sections along the path determined in step S4, according to the following formula: ； ； ； In the formula, the centerline lies in the xy plane, (x i , y i ) represents the coordinates of the centerline at point i, and α represents the coordinates of a point (x, y) on the centerline. i , y i The tail cone at point ) rotates about the z-axis by an angle along its circular cross-section. The coordinates before rotation. These are the rotated coordinates.

2. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 1, characterized in that: In step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a relatively uniform gradient, and the control formula is: ； In the formula: In the formula, , Let x and y be the x and y coordinates of the i-th point on the centerline, respectively. Indicates the initial y-coordinate of the centerline; The inlet and outlet offsets of the centerline are represented by the eccentricity ΔS along the cross section. It is the total axial length of the center line of the coccyx.

3. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 1, characterized in that: In step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a gradual initial change followed by a rapid change. The control formula is as follows: ； In the formula: In the formula, , Let x and y be the x and y coordinates of the i-th point on the centerline, respectively. Indicates the initial y-coordinate of the centerline; The inlet and outlet offsets of the centerline are represented by the eccentricity ΔS along the cross section. It is the total axial length of the center line of the coccyx.

4. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 1, characterized in that: In step S2, the variation pattern of the S-shaped tail cone centerline is controlled by a Lee curve with a rapid initial change followed by a gradual decrease. The control formula is as follows: ； In the formula: In the formula, , Let x and y be the x and y coordinates of the i-th point on the centerline, respectively. Indicates the initial y-coordinate of the centerline; The inlet and outlet offsets of the centerline are represented by the eccentricity ΔS along the cross section. It is the total axial length of the center line of the coccyx.

5. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 1, characterized in that: It also includes step S7: conducting flow field simulation analysis of the S-curve nozzle to evaluate the impact of the S-shaped tail cone on the bypass ratio.

6. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 5, characterized in that: In step S7, if the pressure non-uniformity of the S-shaped tail cone's rear end section perpendicular to the flow channel direction is large, resulting in the bypass ratio still being greater than the target bypass ratio, then the offset of the S-shaped tail cone needs to be adjusted further.

7. The tail cone design method for improving the matching performance of the S-curve nozzle of an aero-engine as described in claim 6, characterized in that: The offset of the S-shaped tail cone is one-quarter to one-half of the diameter of the front end of the tail cone.

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