Design method for air inlet channel of high-stealth unmanned aerial vehicle

Abstract

The invention discloses a high-stealth unmanned aerial vehicle air inlet channel design method, and belongs to the technical field of unmanned aerial vehicle design. The method comprises the following steps: designing a corresponding throat Mach number Mth according to design requirements and design constraints of a high-stealth unmanned aerial vehicle air inlet channel, and giving out a throat area according to a throat area calculation formula; the shape of the throat and the shape of the cross section at the outlet of the air inlet channel need to be matched with related connecting structures of an airplane, and the cross section at the throat is set as a control section 1. Generating first, second and third sections of S-bend inner pipelines with the lengths of L1, L2 and L3 through an ending control section; an equal straight section is generated by controlling the cross section 4, and the length is L4; and the center lines and area distribution rules of the first, second and third sections of S-bend inner pipelines all adopt a slow and urgent equivalent form. By the adoption of the technology, the design of the air inlet channel in the complex constraint environment can be effectively completed, the stealth performance of the air inlet channel is improved, and the air inlet channel has the good aerodynamic characteristic.

Description

Technical Field

[0001] The present invention belongs to the technical field of UAV design, and relates to a method for designing a high-stealth UAV air inlet. The method adopts multi-section control and multi-section S-bend inner pipes to construct a high-stealth air inlet, which can effectively complete the design of a high-stealth air inlet in a complex constrained environment. Background Art

[0002] The aircraft air inlet is an important part that connects the aircraft and the engine. The air inlet needs to provide a certain quality of high-quality airflow to the engine. As the requirements for aircraft stealth performance become higher and higher, and the air inlet is one of the three major scattering sources of the aircraft, the stealth design of the air inlet faces major challenges.

[0003] For an air inlet that meets the requirements of high stealth design, its inner pipe must be S-shaped, and the inlet section of the engine must be shielded in all directions through the bending of the inner surface of the inlet. At this time, the total pressure loss of the airflow passing through the inlet is large, and the airflow velocity distribution in the inlet outlet section is very uneven, which will bring about more serious inlet matching problems and pose a safety hazard to the flight of the UAV.

[0004] Existing stealth inlet design technology often improves the stealth performance of the inlet through a single S-bend. Generally, the inlet designed by this method is difficult to block the engine inlet cross section in all directions. In the actual UAV design process, the inlet design is often constrained by the overall layout. Faced with a complex constraint environment, the single S-bend internal pipe design is difficult to meet the high stealth inlet design requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a high-stealth air inlet design method with multi-section control and multi-section S-bend inner pipes, which can effectively meet the design requirements and the air inlet has good aerodynamic characteristics.

[0006] The technical solution of the present invention:

[0007] A method for designing the air intake of a high stealth UAV, such as Figure 2 The air intake design process is given, and the specific process is as follows:

[0008] Step 1: Design the corresponding throat Mach number M according to the design requirements and design constraints of the high stealth UAV inlet th , according to the throat area calculation formula, the throat area is given; the throat shape and the cross-sectional shape at the inlet outlet need to be adapted to the aircraft's related connection structure, see Figure 3 , assume that the cross section at the throat is the control section 1.

[0009] Furthermore, the calculation formula of throat area is:

[0010]

[0011] In the formula, A th is the theoretical throat area (m 2 );

[0012] W c Design conversion flow rate at the engine inlet (kg / s);

[0013] M th is the throat Mach number;

[0014] σ d is the total pressure recovery coefficient of the pipe section from the throat to the engine inlet;

[0015]

[0016] K is the throat area magnification factor considering the boundary layer and cooling air requirements.

[0017] Step 2: Generate the first section of the S-bend inner pipe through control section 1 and control section 2, with a length of L1; generate the second section of the S-bend inner pipe through control section 2 and control section 3, with a length of L2; generate the third section of the S-bend inner pipe through control section 3 and control section 4, with a length of L3; generate an equal straight section through control section 4, with a length of L4.

[0018] Step 3: The center lines and area distribution rules of the first section of the S-bend inner pipe, the second section of the S-bend inner pipe and the third section of the S-bend inner pipe are all in a form of equal speed. Assume that the total length of the air inlet is L, L = L1 + L2 + L3 + L4.

[0019] Furthermore, assuming that the total length of the air intake duct is L, L = L1 + L2 + L3 + L4. The control section 2 adopts a "quasi-equilateral triangle" and the control section 3 adopts a "quasi-inverted triangle" form, so as to achieve the minimum offset y2 (y2 = 10% L ~ 15% L) and achieve the shielding requirement of the air intake duct entrance section to the engine section at all angles.

[0020] Furthermore, the pipeline in each S-bend is generated in the following way:

[0021] The center line of each section of the S-bend pipe adopts a fairly slow and fast change rule. For each section of the S-bend pipe, a rectangular coordinate system is established based on the axial section of the air inlet duct, with the length direction of the air inlet duct as the x-axis and the starting point of the center line of each section of the S-bend pipe as the coordinate zero point. The mathematical expression of the center line of each section of the S-bend pipe is:

[0022]

[0023] Wherein, x and y represent the horizontal and vertical coordinates of the center line of the pipeline in each S-bend, respectively, Δy represents the longitudinal offset of the pipeline in each S-bend, and L' represents the length of the pipeline in each S-bend.

[0024] Furthermore, the area distribution of the pipe in each S-bend adopts a change rule of equal slowness and urgency, and the mathematical expression of the area of ​​the pipe in each S-bend is:

[0025]

[0026] Among them, A is the cross-sectional area of ​​the pipe inside the S-bend, and A1 and A2 are the inlet and outlet cross-sectional areas of the pipe inside each section of the S-bend, respectively.

[0027] Furthermore, by using the super ellipse equation, the coordinates of each discrete point of the cross section of each S-bend pipe can be constructed, thereby generating an S-bend pipe.

[0028] Furthermore, the above parameters give a reasonable design range, Mth = 0.65 ~ 0.75, L1 = 8% ~ 13% L, L2 = 30% ~ 40% L, L3 = 35% ~ 45% L, L4 = 8% ~ 12% L, K = 1.01 ~ 1.05.

[0029] Beneficial effects of the invention: The invention controls the cross-sectional shape, area and position to carry out a multi-stage air inlet design process. The technology of the invention can effectively complete the air inlet design under complex constrained environments, improve the stealth performance of the air inlet, and the air inlet has good aerodynamic characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of an S-bend pipe.

[0031] Figure 2 It is a design flow chart of the present invention.

[0032] Figure 3 It is a schematic diagram of the control section.

[0033] Figure 4 This is a schematic diagram of the final intake design.

[0034] Figure 5 It is the aerodynamic characteristic of the air inlet. DETAILED DESCRIPTION

[0035] A method for designing the air intake of a high stealth UAV, such as Figure 2 The air intake design process is given, and the specific process is as follows:

[0036] Step 1: Design the corresponding throat Mach number M according to the design requirements and design constraints of the high stealth UAV inlet th , according to the throat area calculation formula, the throat area is given; the throat shape and the cross-sectional shape at the inlet outlet need to be adapted to the aircraft's related connection structure, see Figure 3 , assume that the cross section at the throat is the control section 1.

[0037] The calculation formula of throat area is:

[0038]

[0039] In the formula, A th is the theoretical throat area (m 2 );

[0040] W c Design conversion flow rate at the engine inlet (kg / s);

[0041] M th is the throat Mach number;

[0042] σ d is the total pressure recovery coefficient of the pipe section from the throat to the engine inlet;

[0043]

[0044] K is the throat area magnification factor considering the boundary layer and cooling air requirements.

[0045] Step 2: Generate the first section of the S-bend inner pipe through control section 1 and control section 2, with a length of L1; generate the second section of the S-bend inner pipe through control section 2 and control section 3, with a length of L2; generate the third section of the S-bend inner pipe through control section 3 and control section 4, with a length of L3; generate an equal straight section through control section 4, with a length of L4.

[0046] Step 3: The center lines and area distribution rules of the first section of the S-bend inner pipe, the second section of the S-bend inner pipe and the third section of the S-bend inner pipe are all in a form of equal speed. Assume that the total length of the air inlet is L, L = L1 + L2 + L3 + L4.

[0047] Assume that the total length of the intake duct is L, L = L1 + L2 + L3 + L4. Control section 2 adopts a "quasi-equilateral triangle" and control section 3 adopts a "quasi-inverted triangle" form, so as to achieve the minimum offset y2 (y2 = 10% L ~ 15% L) and achieve the shielding requirement of the intake duct entrance section to the engine section at all angles.

[0048] The method of generating the pipeline in each S-bend section is as follows:

[0049] 1) The center line of each section of the S-bend pipe adopts a fairly slow and fast change rule. For each section of the S-bend pipe, a rectangular coordinate system is established based on the axial section of the inlet duct, with the length direction of the inlet duct as the x-axis and the starting point of the center line of each section of the S-bend pipe as the coordinate zero point. The mathematical expression of the center line of each section of the S-bend pipe is:

[0050]

[0051] Wherein, x and y represent the horizontal and vertical coordinates of the center line of the pipeline in each S-bend, respectively, Δy represents the longitudinal offset of the pipeline in each S-bend, and L' represents the length of the pipeline in each S-bend.

[0052] 2) The area distribution of the pipe in each S-bend adopts a change rule of equal speed. The mathematical expression of the area of ​​the pipe in each S-bend is:

[0053]

[0054] Among them, A is the cross-sectional area of ​​the pipe inside the S-bend, and A1 and A2 are the inlet and outlet cross-sectional areas of the pipe inside each section of the S-bend, respectively.

[0055] 3) Using the superellipse equation, the coordinates of each discrete point of the cross section of each S-bend pipe can be constructed to generate an S-bend pipe.

[0056] The above parameters give a reasonable design range, Mth = 0.67, L1 = 10% L, L2 = 40% L, L3 = 40% L, L4 = 10% L, K = 05.

[0057] Figure 5 An implementation example of the technology is given. The air intake duct can cover the engine inlet cross section in all directions and has good aerodynamic characteristics.

Claims

1. A method for designing an air inlet for a high stealth UAV, characterized in that: The specific steps are as follows: Step 1: Design the corresponding throat Mach number M according to the design requirements and design constraints of the high stealth UAV air intake th , according to the throat area calculation formula, the throat area is given; the throat shape and the cross-sectional shape at the inlet outlet need to be adapted to the aircraft related connection structure, and the cross-sectional shape at the throat is set as the control section 1; Step 2: Generate the first section of the S-bend inner pipe through control sections 1 and 2, with a length of L1; generate the second section of the S-bend inner pipe through control sections 2 and 3, with a length of L2; generate the third section of the S-bend inner pipe through control sections 3 and 4, with a length of L3; generate an equal straight section through control section 4, with a length of L4; Step 3: The center lines and area distribution patterns of the first section of the S-bend pipe, the second section of the S-bend pipe and the third section of the S-bend pipe are all in a form of equal urgency.

2. The method for designing an air inlet of a high stealth UAV according to claim 1, characterized in that: The calculation formula of throat area is: In the formula, A th is the theoretical throat area; W c Design the converted flow at the engine inlet; M th is the throat Mach number; σ d is the total pressure recovery coefficient of the pipe section from the throat to the engine inlet; q(M th )=1.2 3 ·M th ·(1+0.2M th 2 ) -3 K is the throat area magnification factor considering the boundary layer and cooling air requirements.

3. The method for designing an air inlet of a high stealth UAV according to claim 1 is characterized in that: Assume that the total length of the intake duct is L, L = L1 + L2 + L3 + L4; control section 2 adopts a "quasi-equilateral triangle" and control section 3 adopts a "quasi-inverted triangle" form, so as to achieve the minimum offset y2 and realize the shielding requirement of the intake duct entrance section to the engine section in all directions, y2 = 10% L ~ 15% L.

4. The method for designing an air inlet of a high stealth UAV according to claim 1 is characterized in that: The method of generating the pipe inside each S-bend is as follows: 1) The center line of each section of the S-bend pipe adopts a fairly slow and fast change rule. For each section of the S-bend pipe, a rectangular coordinate system is established based on the axial section of the inlet duct, with the length direction of the inlet duct as the x-axis and the starting point of the center line of each section of the S-bend pipe as the coordinate zero point. The mathematical expression of the center line of each section of the S-bend pipe is: Among them, x and y represent the horizontal and vertical coordinates of the center line of the pipeline in each S-bend, respectively, Δy represents the longitudinal offset of the pipeline in each S-bend, and L' represents the length of the pipeline in each S-bend; 2) The area distribution of the pipe in each S-bend adopts a change rule of equal slowness and urgency. The mathematical expression of the area of ​​the pipe in each S-bend is: Among them, A is the cross-sectional area of ​​the pipe inside the S-bend, A1 and A2 are the inlet and outlet cross-sectional areas of the pipe inside each section of the S-bend respectively; 3) Using the superellipse equation, the coordinates of each discrete point of the cross section of each S-bend pipe can be constructed to generate an S-bend pipe.

5. The method for designing an air inlet of a high stealth UAV according to claim 1 is characterized in that: The above parameters give a reasonable design range, Mth = 0.65 ~ 0.75, L1 = 8% ~ 13% L, L2 = 30% ~ 40% L, L3 = 35% ~ 45% L, L4 = 8% ~ 12% L, K = 1.01 ~ 1.05.

Images