A simulation method for small flow test of intake duct

Abstract

The present invention provides a simulation method for an inlet duct small flow test. The simulation method simulates the influence of different engine speed working conditions on the upstream inlet duct flow rate by arranging a throttle cone at the downstream outlet of the inlet duct, and changes the throttling area by changing the position of the throttle cone, thereby changing the flow capacity of the inlet duct. Compared with the traditional method of simulating the engine speed by changing the back pressure condition, the method avoids the non-physical phenomenon of "full flow backflow" that is easy to appear in the inlet duct when simulating the large angle of attack and small flow state of the aircraft while ensuring the authenticity and reliability of the simulation, solves the problem that it is difficult to simulate the large angle of attack and small flow working state of the inlet duct through numerical calculation, and provides technical support for the integrated design of the inlet duct / engine.

Description

Technical Field

[0001] The invention relates to the field of aircraft air inlet performance test, and in particular to a simulation method for an air inlet small flow test. Background Art

[0002] In order to obtain better aerodynamic performance, maneuverability, stealth performance and structural efficiency, the integration degree between modern aircraft and engines is getting higher and higher. At the same time, in order to improve the stealth performance of aircraft, the design process of the air inlet needs to rely on the highly twisted pipe structure of the air inlet to block the reflection of the engine blades on the radar waves, making the flow structure inside the air inlet more complicated. In addition, the working state of the engine downstream of the air inlet will significantly affect the flow field structure inside the air inlet. In the face of the flight requirements of future aircraft in a wide speed range, the working state of the engine will inevitably become more variable, and the design of the air inlet of future aircraft will face many challenges. In order to meet the flight requirements of future aircraft in a wide speed range, the air inlet needs to provide high-quality air for the downstream engine under a wide range of flight conditions. Under existing research conditions, the design process of the air inlet usually includes theoretical analysis, simulation prediction and scaled model experiments.

[0003] In the conventional research process, during the simulation and prediction stage of the inlet flow field, the influence of the engine working state downstream of the inlet outlet on the inlet flow field structure is simulated. The method usually adopted is to connect a straight section downstream of the inlet outlet section and give different pressures at the outlet of the straight section to simulate different engine working states. However, the inlet flow field structure obtained by this simulation method is still quite different from the flow field structure under the actual working state of the inlet, making it difficult to study the small flow characteristics of the inlet.

[0004] In addition, the aircraft has a working state of large angle of attack and small flow in its flight envelope. The use of traditional simulation methods is likely to cause the non-physical phenomenon of "full flow backflow", which is contrary to the actual situation. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a simulation method for a small flow test in an intake duct by introducing a throttle cone structure to accurately simulate the working state of a downstream engine.

[0006] Technical solution: A simulation method for an inlet duct small flow test, characterized in that it includes the following steps:

[0007] S1 Given the intake duct data to be simulated, three-dimensional modeling of the intake duct is performed, and at the same time, a throttle cone is modeled at the intake duct outlet to obtain a digital model of the intake duct, including the intake duct, an equal straight section, an expansion section, and a throttle cone; the intake duct is connected to the expansion section through the equal straight section, the expansion section is a truncated cone-shaped pipeline, and the end of the expansion section with a smaller opening is connected to the equal straight section; the throttle cone is arranged in the expansion section; the throttle cone includes a spherical segment, a first truncated cone, and a second truncated cone, the bottom surface of the spherical segment coincides with the bottom surface on the first truncated cone, and the lower bottom surface of the first truncated cone coincides with the bottom surface on the second truncated cone;

[0008] S2 meshes the air intake duct digital model obtained in step S1, and inputs the meshed air intake duct model into a fluid simulation software to perform a small flow simulation;

[0009] S3 gives initial boundary conditions, performs simulation calculations on the meshed intake duct model based on the initial boundary conditions, and sets a monitoring surface at the intake duct inlet section to monitor the intake duct inlet flow rate;

[0010] S4 obtains the intake duct flow corresponding to the throttle cone position when the intake duct inlet flow tends to be horizontal with the number of iterations;

[0011] S5 adjusts the throttle cone position, repeats steps S2-S4, obtains multiple groups of intake duct flow data, and performs data calculation and trend analysis based on each group of parameters.

[0012] Specifically, a throttling throat is formed between the interface between the first truncated cone and the second truncated cone and the expansion section, and the cross section of the throttling throat is perpendicular to the wall surface of the expansion section.

[0013] Specifically, the area of ​​the throttle throat is the throttle area A4:

[0014]

[0015] Wherein: A4 is the throttling area; R3' is the radius of the expansion section at the throttling throat; R3 is the radius of the interface between the first truncated cone and the second truncated cone, and α1 is the vertex angle corresponding to the expansion section.

[0016] Specifically, when the throttling cone moves toward the outlet of the expansion section, the throttling area A4 increases.

[0017] Specifically, the ratio of the throttle area A4 to the intake throat area is defined as the throttle area ratio θ, different throttle cone positions correspond to different throttle area ratios θ, and trend analysis is performed using the throttle area ratio θ and the corresponding intake flow data.

[0018] Specifically, the axial length of the straight section is greater than or equal to 4 times the radius of the inlet duct outlet cross-section.

[0019] Specifically, the vertex angle α1 of the expansion section frustum, the vertex angle α2 of the first frustum, and the vertex angle α3 of the second frustum satisfy: α2>α1>α3.

[0020] Specifically, the spherical segment is smaller than or equal to a hemisphere.

[0021] Specifically, the boundary pressure at the expansion section outlet is set to the free flow static pressure.

[0022] Beneficial effect: Compared with the prior art, the significant effect of the present invention is: compared with the traditional method of simulating the engine state downstream of the inlet by applying back pressure, the present invention simulates the influence of the engine working at different speeds on the upstream inlet by setting a throttle cone at the outlet of the straight section downstream of the inlet, and changes the throttling area by changing the position of the throttle cone, thereby changing the flow capacity of the inlet. Under the premise of ensuring the real reliability of the simulation, the non-physical phenomenon of "full flow backflow" in the inlet is avoided when simulating the large angle of attack and small flow state of the aircraft, which provides technical support for the integrated design of the inlet / engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional schematic diagram of the digital model of the air intake duct of the present invention.

[0024] Figure 2 It is a schematic diagram of the expansion section of the air inlet duct and the throttle cone angle of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods.

[0026] The present invention provides a simulation method for an intake duct small flow test, comprising the following steps:

[0027] (1) Please refer to Figure 1 As shown, given the intake duct data to be simulated, the intake duct is three-dimensionally modeled using UG software, and the throttle cone 4 is modeled at the intake duct outlet to obtain an intake duct digital model, including an intake duct 1, a straight section 2, an expansion section 3, and a throttle cone 4;

[0028] Specifically, the air inlet 1 is connected to the expansion section 3 through the straight section 2, the outlet interface 8 of the air inlet 1 is smoothly connected to the straight section 2, the expansion section 3 is a truncated cone-shaped pipe, and the end of the expansion section 3 with a smaller opening is connected to the straight section 2; the throttling cone 4 includes a spherical segment 5, a first truncated cone 6, and a second truncated cone 7, the spherical segment 5 is smaller than or equal to a hemisphere, the bottom surface of the spherical segment 5 coincides with the upper bottom surface of the first truncated cone 6, and the lower bottom surface of the first truncated cone 6 coincides with the upper bottom surface of the second truncated cone 7; the axial length of the straight section 2 is greater than or equal to 4 times the radius of the outlet cross-section of the air inlet 1 to avoid interference of downstream throttling on the air inlet flow; please refer to Figure 2As shown, the vertex angle α1 of the cone of the expansion section 3, the vertex angle α2 of the first cone 6 and the vertex angle α3 of the second cone 7 satisfy: α2>α1>α3.

[0029] (2) meshing the air intake duct digital model obtained in step S1 using Ansys ICEM software, and inputting the meshed air intake duct digital model into Ansys Fluent software for small flow simulation;

[0030] (3) Given the initial boundary conditions, the boundary pressure at the outlet of the expansion section 3 is set to the free flow static pressure, and the meshed inlet duct digital model is simulated based on the initial boundary conditions. At the same time, a monitoring surface is set at the inlet section of the inlet duct 1 to monitor the inlet flow rate;

[0031] (4) When the inlet flow rate tends to be horizontal with the number of iterations, the corresponding inlet flow rate at the position of the throttle cone 4 is obtained;

[0032] (5) Adjust the position of the throttle cone 4, repeat steps S2-S4, obtain multiple sets of intake duct flow data, and perform data calculation and trend analysis:

[0033] A throttling throat 10 is formed between the interface 9 between the first truncated cone 6 and the second truncated cone 7 and the expansion section 3, and the cross section of the throttling throat 10 is perpendicular to the wall of the expansion section 3. The area of ​​the throttling throat is defined as the throttling area A4:

[0034]

[0035] Wherein: A4 is the throttling area; R3' is the radius of the expansion section 3 at the throttling throat; R3 is the radius of the interface between the first truncated cone and the second truncated cone.

[0036] When the throttle cone moves toward the outlet of the expansion section, the throttle area A4 increases. The ratio of the throttle area A4 to the area of ​​the inlet throat 12 is defined as the throttle area ratio θ. Different throttle area ratios θ correspond to different throttle area ratios θ at different throttle cone 4 positions. Trend analysis is performed using the throttle area ratio θ and the corresponding inlet flow data.

[0037] An embodiment of the above method under specific parameter conditions is given below.

[0038] Example 1

[0039] Given the intake duct data to be simulated, in this embodiment, the cross-sectional area of ​​the intake duct throat 12 is A1 = 1484000 mm 2, the radius of the interface between the spherical segment 5 and the first truncated cone 6 is R2=90mm, the radius of the interface 9 between the first truncated cone 6 and the second truncated cone 7 is R3=138mm, the radius of the lower bottom surface of the second truncated cone 7 is R4=170mm, the cross-sectional radius of the equal straight section 2 is R'2=150mm, the outlet cross-sectional radius of the expansion section 3 is R'4=215mm, and the length of the equal straight section is L5=600mm; in order to form a throttling throat 10 in the expansion section 3 downstream of the inlet duct 1, according to the design requirements of the vertex angles of each truncated cone, in this embodiment, the virtual vertex angle α1=30° corresponding to the truncated cone of the expansion section 3, the virtual vertex angle α2=37.6° corresponding to the first truncated cone 6 and the virtual vertex angle α3=18.4° corresponding to the second truncated cone 7 are given; at the same time, in order to quantify the position of the throttling cone 4, the axial position L of the throttling cone is defined plug , whose value is the distance between the interface 9 of the two truncated cones and the outlet 11 of the equal straight section. Each throttling cone axial position L plug Corresponding to a throttle area ratio θ, the size of the throttle area ratio θ reflects the speed state of the engine downstream of the intake duct.

[0040] According to the downstream engine state of the intake duct to be simulated, adjust the throttle cone axial position L plug , simulate according to steps (1)-(5) under the above parameter conditions and obtain the following Table 1.

[0041] Table 1

[0042] Throttle cone position / (mm) <![CDATA[Throttle area / (mm 2 )]]> Throttle area ratio θ Engine status 600 675767.1 45.54％ / 900 956149.2 64.43％ local 1000 1053341.5 70.98％ / 1200 1253323.7 84.46％ / 1300 1356113.6 91.39％ Maximum flow 1400 1460769.2 98.44％ / 1800 1898050.2 127.91％ /

[0043] It can be seen from the data in Table 1 that under this design parameter condition, the adjustment range of the throttling area ratio θ is 45.54% to 127.91%. When θ = 64.43%, the engine is in an idling state, that is, the minimum speed state at which the engine can maintain stable operation; when θ = 91.39%, the engine flow is the largest.

[0044] Based on the above verification, it can be known that the small flow simulation method for the intake duct provided in this embodiment is simple to operate and has excellent simulation effect. According to different simulation conditions, the axial position of the throttle cone is changed. Under the premise of ensuring the authenticity and reliability of the simulation, the non-physical phenomenon of "full flow backflow" that is easy to occur under large angle of attack and small flow conditions is avoided. This solves the problem that it was difficult to simulate the working state of large angle of attack and small flow in the intake duct through numerical calculation in the past, and provides technical support for the integrated design of the intake duct / engine.

Claims

1. A simulation method for a small flow test of an air intake duct, characterized in that: The following steps are involved: S1 Given the intake duct data to be simulated, the intake duct is three-dimensionally modeled, and the throttle cone (4) is modeled at the outlet of the intake duct to obtain a digital model of the intake duct, including the intake duct (1), the straight section (2), the expansion section (3), and the throttle cone (4); the intake duct (1) and the expansion section (3) are connected through the straight section (2), the expansion section (3) is a truncated cone-shaped pipeline, and the end of the expansion section (3) with a smaller opening is connected to the straight section (2); the throttle cone (4) includes a spherical segment (5), a first truncated cone (6) , a second truncated cone (7), the bottom surface of the spherical segment (5) coincides with the upper bottom surface of the first truncated cone (6), and the lower bottom surface of the first truncated cone (6) coincides with the upper bottom surface of the second truncated cone (7); a throttling throat (10) is formed between the interface between the first truncated cone (6) and the second truncated cone (7) and the expansion section (3), and the cross section of the throttling throat (10) is perpendicular to the wall surface of the expansion section (3); the vertex angle α1 of the truncated cone of the expansion section (3), the vertex angle α2 of the first truncated cone (6) and the vertex angle α3 of the second truncated cone (7) satisfy: α2>α1>α3; S2 meshes the intake duct digital model obtained in step S1, and inputs the meshed intake duct digital model into a fluid simulation software to perform a small flow simulation; S3 gives an initial boundary condition, performs simulation calculation on the meshed intake duct model based on the initial boundary condition, and simultaneously sets a monitoring surface at the inlet section of the intake duct (1) to monitor the inlet flow of the intake duct (1); S4 obtains the intake duct flow rate corresponding to the position of the throttle cone (4) when the inlet flow rate of the intake duct (1) tends to be horizontal as the number of iterations changes.

2. The simulation method according to claim 1, characterized in that: The simulation method further comprises the following steps: S5 adjusts the position of the throttle cone (4), repeats steps S2-S4, obtains multiple sets of intake duct flow data, and performs data calculation and trend analysis.

3. The simulation method according to claim 1, characterized in that: The area of ​​the throttle throat (10) is the throttle area A4: Wherein: A4 is the throttling area; R3' is the radius of the expansion section (3) at the throttling throat; R3 is the radius of the interface between the first frustum (6) and the second frustum (7); α1 is the vertex angle corresponding to the expansion section (3).

4. The simulation method according to claim 3, characterized in that: When the throttling cone (4) moves towards the outlet direction of the expansion section (3), the throttling area A4 increases.

5. The simulation method according to claim 4, characterized in that: Step S5 comprises: the ratio of the throttle area A4 to the intake throat area is defined as the throttle area ratio θ, different throttle cone (4) positions correspond to different throttle area ratios θ, and trend analysis is performed through the throttle area ratios θ and the corresponding intake flow data.

6. The simulation method according to claim 1, characterized in that: The axial length of the straight section (2) is greater than or equal to 4 times the radius of the outlet cross section of the air inlet duct (1).

7. The simulation method according to claim 1, characterized in that: The spherical segment (5) is smaller than or equal to a hemisphere.

8. The simulation method according to claim 1, characterized in that: The boundary pressure at the outlet of the expansion section (3) is set to the static pressure of the free flow.

Images