A design method for alleviating radial thermal stress of high-speed aircraft inlet

Abstract

The present application belongs to the field of high-speed aircraft air inlet structure design, and particularly relates to a high-speed aircraft air inlet radial thermal stress mitigation design method. The method comprises: step one, releasing the air inlet mechanical connection freedom by adjusting the first air inlet parameter; step two, reducing the local stiffness of the air inlet by adjusting the second air inlet parameter; step three, performing thermal coupling calculation, checking the thermal stress level and thermal deformation level of the air inlet, and judging whether the air inlet meets the strength and stiffness requirements; if so, outputting the air inlet parameters that meet the strength and stiffness requirements; if not, increasing the local stiffness of the air inlet by adjusting the third air inlet parameter, and returning to step two. The air inlet structure obtained by the present application can achieve thermal stress mitigation while meeting the requirements of thermal deformation.

Description

Technical Field

[0001] The present application belongs to the field of high-speed aircraft air inlet structure design, and in particular to a high-speed aircraft air inlet radial thermal stress relief design method. Background Art

[0002] High-speed aircraft are subjected to severe aerodynamic heating during flight. The inner wall of the air inlet and the outer skin of the aircraft are directly affected by the hot air flow. For the outer surface of the aircraft, the aircraft skin can be protected by external protection to control the temperature at a normal level. However, since the air inlet is in the shape of a pipe and is located inside the aircraft, it is difficult to install and maintain the external protection structure, resulting in a high temperature on the inner wall of the air inlet, especially in the inlet lip, throat and other areas with more complex structures. Therefore, there is a large temperature difference between the inner wall of the air inlet and the installation structure between the air inlet and the fuselage. Due to the mechanical constraints and temperature gradients between the inner wall of the air inlet and the installation structure of the fuselage, severe thermal stress is generated in the air inlet and the surrounding structures, and the material properties decrease with the increase of temperature, threatening the structural safety; the plastic deformation caused by severe thermal stress leads to reduced aircraft repeatability. Therefore, the thermal stress mitigation design of the air inlet and its connecting structure of high-speed aircraft is particularly important.

[0003] The air inlet is cylindrical, and the radial flange of the air inlet of a high-speed aircraft is connected to the fuselage frame. The heat flow in the inlet section is severe, and it has the characteristics of strong constraints and large loads, resulting in severe thermal stress. In theory, thermal deformation can be released by weakening the constraints, and thermal stress can be alleviated by reducing the temperature difference. On the one hand, since the thermal protection structure cannot be installed on the inner wall of the air inlet, the temperature of the inner wall of the air inlet cannot be reduced. The fuselage is constrained by the temperature resistance requirements of the equipment, and the temperature of the fuselage frame and the fuselage installation side panel cannot be increased, so the purpose of thermal stress alleviation cannot be achieved by reducing the temperature difference. On the other hand, thermal stress can be released by weakening the mechanical constraints, but the weakening of mechanical constraints usually leads to weakening of structural stiffness, which in turn produces large thermal deformation. Large deformation of the inner wall of the air inlet will cause changes in the air flow of the air inlet, and in severe cases, it will cause the engine performance to decline, which is not allowed to happen. At present, the existing methods at home and abroad cannot achieve thermal stress release while taking into account thermal deformation control. A more ingenious design method is needed to release thermal stress, so as to improve the safety and reliability of the air inlet structure of high-speed aircraft.

[0004] Therefore, it is desired to have a technical solution to overcome or at least alleviate at least one of the above-mentioned defects of the prior art. Summary of the invention

[0005] The purpose of the present application is to provide a design method for alleviating radial thermal stress of a high-speed aircraft inlet, so as to solve at least one problem existing in the prior art.

[0006] The technical solution of this application is:

[0007] A high-speed aircraft inlet radial thermal stress mitigation design method, comprising:

[0008] Step 1: releasing the mechanical connection freedom of the air intake duct by adjusting the first air intake duct parameter;

[0009] Step 2: reducing the local stiffness of the intake duct by adjusting the parameters of the second intake duct;

[0010] Step 3: Perform thermal-mechanical coupling calculation to check the thermal stress level and thermal deformation level of the air intake duct to determine whether the air intake duct meets the strength and stiffness requirements;

[0011] If so, output the intake duct parameters that meet the strength and stiffness requirements;

[0012] If not, increase the local stiffness of the intake duct by adjusting the third intake duct parameter and return to step 2.

[0013] In at least one embodiment of the present application, the air inlet comprises:

[0014] An air inlet main body, the air inlet main body is cylindrical, and an air inlet inner skin is arranged on the inner wall of the air inlet main body;

[0015] An air inlet flange, the air inlet flange is arranged on the outer wall of the air inlet body, the air inlet flange is provided with a plurality of flange ears along the circumferential direction, and the flange ears are connected with the air inlet ears on the fuselage frame by bolts;

[0016] The air intake duct ribs are arranged on the outer wall of the air intake duct body.

[0017] In at least one embodiment of the present application, the inlet duct ribs include circumferential ribs and axial ribs, the circumferential ribs are arranged in plurality along the circumferential direction on the outer wall of the inlet duct body, and the axial ribs are arranged in plurality along the axial direction on the outer wall of the inlet duct body.

[0018] In at least one embodiment of the present application, in step 1, releasing the mechanical connection freedom of the intake duct by adjusting the first intake duct parameter includes:

[0019] The mounting holes on the flange ear piece and the air inlet ear piece are set as radial elliptical holes.

[0020] In at least one embodiment of the present application, the radial length L of the radial elliptical hole is:

[0021] L=δL+d

[0022] Wherein, δL is the free expansion space of the inlet duct, and d is the bolt diameter;

[0023] The free expansion space δL of the inlet duct is:

[0024] δL =α*ΔT*D

[0025] Wherein, α is the thermal expansion coefficient, ΔT is the temperature change, and D is the distance from the axis of the inlet duct to the radial outer side of the flange ear.

[0026] In at least one embodiment of the present application, in step 2, reducing the local stiffness of the intake duct by adjusting the second intake duct parameter includes:

[0027] reducing the height of the air inlet flange;

[0028] and / or, reducing the thickness of the air inlet flange;

[0029] And / or, reducing the thickness of the inner skin of the air inlet.

[0030] In at least one embodiment of the present application, the method of reducing the height of the intake duct flange is:

[0031] The height of the air inlet flange at a position where no flange ear is provided is reduced.

[0032] In at least one embodiment of the present application, in step three, increasing the local stiffness of the intake duct by adjusting the third intake duct parameter includes:

[0033] Increasing the number of flange ears of the air inlet flange;

[0034] and / or, increasing the number of the air inlet ribs;

[0035] And / or, increasing the size of the air intake ribs.

[0036] The invention has at least the following beneficial technical effects:

[0037] The radial thermal stress mitigation design method for high-speed aircraft inlet ducts of the present application reduces the radial thermal stress level of the inlet duct by releasing the mechanical connection freedom and reducing the local stiffness of the inlet duct. When the reduction in stiffness brings about the problem of excessive thermal deformation, the local stiffness of the inlet duct is correspondingly increased. The inlet duct parameters are adjusted by optimization and iteration, so that the inlet duct structure can achieve thermal stress mitigation while meeting the requirements of thermal deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of a design method for mitigating radial thermal stress of a high-speed aircraft inlet according to one embodiment of the present application;

[0039] Figure 2 is a schematic diagram of an air intake duct according to an embodiment of the present application;

[0040] Figure 3 It is a schematic diagram of the flange ear connection of an embodiment of the present application.

[0041] in:

[0042] 1- Air inlet body; 2- Air inlet flange; 3- Air inlet ribs. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the implementation of this application clearer, the technical scheme in the embodiment of this application will be described in more detail below in conjunction with the drawings in the embodiment of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of them. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be construed as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0044] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present application.

[0045] The following is combined with Figures 1 to 3 This application is described in further detail.

[0046] The present application provides a design method for mitigating radial thermal stress of a high-speed aircraft inlet, such as Figure 1 As shown, the following steps are included:

[0047] Step 1: releasing the mechanical connection freedom of the air intake duct by adjusting the first air intake duct parameter;

[0048] Step 2: reducing the local stiffness of the intake duct by adjusting the parameters of the second intake duct;

[0049] Step 3: Perform thermal-mechanical coupling calculations to check the thermal stress level and thermal deformation level of the air intake duct to determine whether the air intake duct meets the strength and stiffness requirements;

[0050] If so, output the intake duct parameters that meet the strength and stiffness requirements;

[0051] If not, increase the local stiffness of the intake duct by adjusting the third intake duct parameter and return to step 2.

[0052] In a preferred embodiment of the present application, Figure 2 As shown, the air inlet includes an air inlet body 1, an air inlet flange 2 and an air inlet rib 3. The air inlet body 1 is cylindrical, and an air inlet inner skin is arranged on its inner wall; the air inlet flange 2 is used to connect the air inlet with the fuselage frame, and the air inlet flange 2 is arranged on the outer wall of the air inlet body 1. The air inlet flange 2 is designed as a non-uniform height flange, and a plurality of flange ears for connecting with the fuselage frame are arranged along the circumference thereof, and a height difference is formed between the position where the flange ears are arranged and the position where the flange ears are not arranged, and the flange ears are connected with the air inlet ears on the fuselage frame with bolts; the air inlet rib 3 is arranged on the outer wall of the air inlet body 1. In this embodiment, the air inlet rib 3 includes a circumferential rib and an axial rib, and a plurality of circumferential ribs are arranged along the circumference on the outer wall of the air inlet body 1, and a plurality of axial ribs are arranged along the axial direction on the outer wall of the air inlet body 1.

[0053] The high-speed aircraft inlet radial thermal stress mitigation design method of the present application aims to solve the problem of high radial thermal stress in the inlet by firstly reducing the radial thermal stress level of the inlet by releasing the freedom of the mechanical connection of the inlet.

[0054] In a preferred embodiment of the present application, in step 1, releasing the mechanical connection degree of freedom of the air intake duct by adjusting the first air intake duct parameter includes:

[0055] The mounting holes on the flange ear and the air inlet ear are set as radial elliptical holes.

[0056] In this embodiment, the radial length L of the radial elliptical hole is:

[0057] L=δL+d

[0058] Wherein, δL is the free expansion space of the inlet duct, and d is the bolt diameter;

[0059] The free expansion space δL of the inlet duct is:

[0060] δL =α*ΔT*D

[0061] Wherein, α is the thermal expansion coefficient, ΔT is the temperature change, and D is the distance from the axis of the inlet duct to the radial outer side of the flange ear.

[0062] By designing the connection between the air inlet and the fuselage frame as a radial elliptical hole connection, after the air inlet expands due to heat, there is a free expansion space of δL in the radial direction, thereby achieving the effect of releasing thermal stress.

[0063] The radial thermal stress mitigation design method for the high-speed aircraft inlet of the present application can reduce thermal stress by reducing the local stiffness of the complex structure in addition to the radial elliptical hole connection design.

[0064] In a preferred embodiment of the present application, in step 2, reducing the local stiffness of the inlet duct by adjusting the second inlet duct parameter includes:

[0065] Reduce the height of the air inlet flange 2;

[0066] and / or, reducing the thickness of the air inlet flange 2;

[0067] And / or, reducing the thickness of the inner skin of the air inlet.

[0068] Thermal stress relief is achieved by adjusting the above-mentioned second air inlet parameters. When reducing the height of the air inlet flange 2, the space height limit required by the connection structure is taken into consideration, so a non-uniform height flange is used to reduce the height of the position where the flange ear is not provided on the air inlet flange 2, and then the thickness of the air inlet flange 2 and the air inlet inner skin is optimized to obtain a structural form with minimal thermal stress.

[0069] The radial thermal stress mitigation design method of the high-speed aircraft inlet of the present application combines the above two thermal stress mitigation measures, performs thermal-mechanical coupling calculation on the structurally optimized inlet, verifies the thermal stress level and thermal deformation level of the structure, and can reflect whether the structural strength meets the requirements through the thermal stress level, and whether the structural stiffness meets the requirements through the thermal deformation level. Since the reduction of the local stiffness of the inlet will lead to increased thermal deformation, if the thermal deformation does not meet the design requirements, it is necessary to take certain measures to address the problem of insufficient stiffness and large bulge deformation to achieve thermal deformation control.

[0070] In a preferred embodiment of the present application, in step three, increasing the local stiffness of the intake duct by adjusting the third intake duct parameter includes:

[0071] Increase the number of flange ears of the air inlet flange 2;

[0072] and / or, increasing the number of the air inlet ribs 3;

[0073] And / or, increase the size of the air intake rib 3.

[0074] After adjusting the above-mentioned third air inlet parameters, further optimization and iteration were performed, and comprehensive thermal stress release and thermal deformation control measures were taken to finally obtain an air inlet structure that meets the aircraft's strength and stiffness requirements.

[0075] In one embodiment of the present application, a certain high Mach number aircraft is taken as an example, and a certain high Mach number inlet heat flow is used as the input load to calculate the inlet temperature field; then the thermal stress is calculated based on this temperature field. For the inlet structure without thermal stress mitigation design, the large thermal stress causes the plastic deformation of the inlet flange 2 to exceed 0.0085με in a large area, and the thermal deformation is large, resulting in bulging, which does not meet the strength and stiffness design requirements, and measures need to be taken to reduce the thermal stress.

[0076] First, the mounting holes on the flange ear and the inlet ear are set as radial elliptical holes. The radial length of the radial elliptical holes is 8 mm, and the bolt diameter is 6 mm, that is, 2 mm of free expansion space is reserved to release thermal deformation.

[0077] Then, the height and thickness of the air inlet flange 2, the thickness of the air inlet inner skin, the number of flange ears of the air inlet flange 2, and the number and size of the air inlet ribs 3 are optimized and designed. Through multiple rounds of optimization and iterative design, the smaller the height of the inlet flange 2, the lower the thermal stress, but the bulging is serious, and the structural height required for connection and installation needs to be guaranteed. Therefore, the non-equal height flange is optimized. The height of the position where the flange ear is set on the inlet flange 2 is 13mm, and the height of the position where the flange ear is not set is reduced to 5mm; the thickness of the inlet flange 2 and the inlet inner skin is optimized. The larger the thickness, the smaller the thermal deformation, but the thermal stress increases. The optimal thickness of the inlet flange 2 is 3mm and the thickness of the inlet inner skin is 2.5mm through optimization; through research, it is found that the number and size of the inlet ribs 3 have little effect on reducing the thermal stress, but the inlet ribs 3 can control the bulging deformation, so the axial ribs are added to control the bulging deformation. At the same time, in order to compensate for the problem of severe bulging caused by the reduction of the height of the inlet flange 2, flange ears are added to the corresponding inlet flange 2, which can effectively reduce the degree of bulging. After optimization, the bulging is about 2mm and 3mm, which is reduced by 60% and 63% respectively compared with before optimization. Finally, an air intake configuration that meets the design requirements is obtained.

[0078] The radial thermal stress mitigation design method of the high-speed aircraft inlet of the present application adopts a customized radial elliptical hole at the connection between the inlet flange and the fuselage frame, so that the inlet expands due to heat and releases part of the thermal deformation radially; at the same time, since the thermal expansion constraint is the cause of thermal stress, reducing the local stiffness constraint of the inlet can reduce thermal stress, but the reduction in stiffness will bring about the problem of excessive thermal deformation, so the inlet parameters are adjusted through optimization and iteration, so that the inlet structure can achieve thermal stress mitigation while meeting the requirements of thermal deformation. The present application can be used in other structural parts of the aircraft that need to reduce thermal stress and control thermal deformation, which has positive significance for the structural design of the aircraft. In addition, this thermal stress mitigation method can also be used in other professional engineering fields that need to reduce thermal stress.

[0079] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A design method for alleviating radial thermal stress of a high-speed aircraft inlet, characterized in that: include: Step 1: releasing the mechanical connection freedom of the air intake duct by adjusting the first air intake duct parameter; Step 2: reducing the local stiffness of the intake duct by adjusting the parameters of the second intake duct; Step 3: Perform thermal-mechanical coupling calculation to check the thermal stress level and thermal deformation level of the air intake duct to determine whether the air intake duct meets the strength and stiffness requirements; If so, output the intake duct parameters that meet the strength and stiffness requirements; If not, increase the local stiffness of the intake duct by adjusting the third intake duct parameter, and return to step 2; The air inlet comprises: An air inlet main body (1), the air inlet main body (1) being cylindrical, and an air inlet inner skin being arranged on the inner wall of the air inlet main body (1); An air inlet flange (2), the air inlet flange (2) being arranged on the outer wall of the air inlet body (1), the air inlet flange (2) being provided with a plurality of flange ears along the circumferential direction, the flange ears being connected to the air inlet ears on the fuselage frame by means of bolts; In step 1, the mechanical connection degree of freedom of the air intake duct is released by adjusting the first air intake duct parameter, including: The mounting holes on the flange ear piece and the air inlet ear piece are set as radial elliptical holes; The radial length L of the radial elliptical hole is: L=δL+d Wherein, δL is the free expansion space of the inlet duct, and d is the bolt diameter; The free expansion space δL of the inlet duct is: δL =α*ΔT*D Wherein, α is the thermal expansion coefficient, ΔT is the temperature change, and D is the distance from the axis of the inlet to the radial outer side of the flange ear; In step 2, the local stiffness of the intake duct is reduced by adjusting the parameters of the second intake duct, including: Reducing the height of the air inlet flange (2); and / or, reducing the thickness of the air inlet flange (2); And / or, reducing the thickness of the inner skin of the air inlet.

2. The high-speed aircraft inlet radial thermal stress mitigation design method according to claim 1, characterized in that: The air inlet comprises: Inlet duct ribs (3), the air intake duct ribs (3) being arranged on the outer wall of the air intake duct body (1).

3. The high-speed aircraft inlet radial thermal stress mitigation design method according to claim 2, characterized in that: The air intake duct ribs (3) comprise circumferential ribs and axial ribs, wherein a plurality of circumferential ribs are arranged along the circumferential direction on the outer wall of the air intake duct body (1), and a plurality of axial ribs are arranged along the axial direction on the outer wall of the air intake duct body (1).

4. The high-speed aircraft inlet radial thermal stress mitigation design method according to claim 3, characterized in that: The method of reducing the height of the air inlet flange (2) is as follows: The height of the air inlet flange (2) at a position where no flange ear piece is provided is reduced.

5. The high-speed aircraft inlet radial thermal stress mitigation design method according to claim 4, characterized in that: In step three, the local stiffness of the intake duct is increased by adjusting the third intake duct parameter, including: Increasing the number of flange ears of the air inlet flange (2); and / or, increasing the number of the air inlet ribs (3); And / or, increasing the size of the air intake duct rib (3).

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