A numerical simulation method for low flow conditions of buried inlet

Abstract

The present invention discloses a numerical simulation method for low-flow conditions of a buried air inlet. A computer simulation model is established for the applied buried air inlet, and the computer simulation model includes a throttle cone that can be axially advanced. A pressure far-field boundary, an adiabatic solid wall boundary, and a pressure outlet boundary are simulated and set in the computer simulation model. The axial advancement of the throttle cone can generate sufficient inlet outlet back pressure, thereby ultimately maintaining a low flow rate and outlet Mach number for the buried air inlet. At the same time, relatively smooth airflow channels on both sides of the throttle cone reduce the occurrence of backflow, thereby avoiding the situation in which the buried air inlet cannot take in air under low-flow conditions during numerical simulation. The method provides numerically simulated aerodynamic performance and flow field structure for the buried air inlet under low-flow conditions, and provides a relatively complete flight envelope comparison for wind tunnel experiments.

Description

Technical Field

[0001] The invention relates to the technical field of air intake flow control, and in particular to a numerical simulation method for low-flow conditions of a buried air intake. Background Art

[0002] As one of the key aerodynamic components of the aircraft propulsion system, the aerodynamic performance of the embedded air inlet directly affects the efficiency of the propulsion system and the flight envelope of the aircraft. Unlike the traditional pitot-type air inlet and S-bend air inlet, the embedded air inlet opens directly on the fuselage surface and cannot fully utilize the high-energy ram air intake, which makes it difficult or even impossible for this type of air inlet to intake air; and because there is no boundary layer isolation device in front of the embedded air inlet entrance, a considerable proportion of the boundary layer low-energy flow enters the inner channel. The above two reasons make the embedded air inlet prone to low-flow conditions and the air inlet's ability to resist adverse pressure gradients is poor at this time. In real air combat, low-flow conditions and engine air starting are always testing the aerodynamic performance and ability to resist adverse pressure gradients of the embedded air inlet.

[0003] In order to explore the minimum flow rate that can be achieved by the embedded inlet, the current mainstream method is to directly change the outlet pressure boundary conditions under the premise of using numerical simulation to achieve the purpose of throttling and reducing the outlet Mach number. However, under the same inlet model and free flow conditions, through comparison with the experiment, it was found that the method of using a stepper motor to advance the throttle cone in the experiment can push the inlet flow rate and the outlet Mach number to a sufficiently small value, while when using computer numerical simulation, it is impossible to push the inlet flow rate and the outlet Mach number to a value roughly equivalent to the experiment, and even the embedded inlet cannot take in air under a certain inlet outlet back pressure. Therefore, the method of directly changing the outlet pressure boundary conditions when using numerical simulation to explore the minimum flow rate that can be achieved by the embedded inlet is less accurate and cannot be used as an auxiliary means of experiment for reference. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a numerical simulation method for low-flow conditions of a buried air inlet, which accurately fits the experimental conditions through numerical simulation and maximizes the exploration of the minimum flow rate and outlet Mach number that can be achieved by the buried air inlet.

[0005] Technical solution: The present invention provides a numerical simulation method for low-flow conditions of a buried air inlet, and establishes a computer simulation model for the buried air inlet used, the computer simulation model comprising a buried air inlet inner channel extending obliquely inward, an air inlet outlet located behind the buried air inlet inner channel, an air inlet outlet equal straight section located at the tail of the air inlet outlet, and a throttle cone located behind the air inlet outlet equal straight section;

[0006] The pressure far-field boundary, the adiabatic solid wall boundary and the pressure outlet boundary are simulated and set in the computer simulation model; wherein the pressure far-field boundary includes a first annular boundary surrounding the straight section such as the inlet outlet and the throttle cone, and a front boundary located at the front end of the first annular boundary and extending vertically inward, and the front boundary is perpendicular to the throttle cone axis; the adiabatic solid wall boundary includes a second annular boundary surrounding the straight section such as the inlet outlet and a rear boundary located at the rear end of the second annular boundary and extending vertically inward, the front end of the second annular boundary intersects with the front boundary, and the rear boundary is perpendicular to the throttle cone axis and intersects with the rear end of the straight section such as the inlet outlet; the pressure outlet boundary is located at the inlet outlet, the pressure outlet boundary is perpendicular to the throttle cone axis, and the pressure outlet boundary is connected between the rear end of the first annular boundary and the rear end of the throttle cone.

[0007] Beneficial effect: Compared with the prior art, the present invention has a significant feature of establishing a computer simulation model for the embedded air inlet used, the computer simulation model includes an axially propulsive throttle cone, and the pressure far field boundary, the adiabatic solid wall boundary, and the pressure outlet boundary are simulated in the computer simulation model. The axial propulsion of the throttle cone can generate sufficient inlet outlet back pressure, ultimately allowing the embedded air inlet to maintain a low flow rate and outlet Mach number. At the same time, the smoother airflow channels on both sides of the throttle cone reduce the occurrence of backflow, avoiding the situation where the embedded air inlet cannot take in air under low flow conditions during numerical simulation, providing numerically simulated aerodynamic performance and flow field structure for the embedded air inlet under low flow conditions, and providing a relatively complete flight envelope comparison for wind tunnel experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram of the embedded air intake duct provided by the present invention;

[0009] Figure 2 It is a schematic diagram of the partially enlarged dimensions of the throttling cone provided by the present invention;

[0010] Figure 3 is a trend diagram of the intake flow rate and the total pressure recovery coefficient under different schemes of the present invention;

[0011] Figure 4 1. The Mach number cloud diagram of the embedded inlet at different inlet outlet back pressures of the present invention;

[0012] Figure 5 It is a cloud diagram of Mach number of the embedded inlet when the throttle cone is in different positions according to the present invention. DETAILED DESCRIPTION

[0013] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0014] See also Figure 1 and Figure 2As shown, the present invention provides a numerical simulation method for low-flow conditions of a buried air inlet, and a computer simulation model is established for the buried air inlet used, the computer simulation model comprises a buried air inlet inner channel 2 extending obliquely inward, an air inlet outlet 3 located behind the buried air inlet inner channel, an air inlet outlet equal straight section 4 located at the tail of the air inlet outlet, and a throttle cone 5 located behind the air inlet outlet equal straight section, and the buried air inlet also comprises an aircraft fuselage 1;

[0015] The pressure far-field boundary, the adiabatic solid wall boundary, and the pressure outlet boundary 10 are simulated and set in the computer simulation model; wherein the pressure far-field boundary includes a first annular boundary 6 surrounding the inlet outlet equal straight section 4 and the throttle cone 5, and a front boundary 7 located at the front end of the first annular boundary and extending vertically inward, and the front boundary 7 is perpendicular to the axis of the throttle cone 5; the adiabatic solid wall boundary includes a second annular boundary 8 surrounding the inlet outlet equal straight section 4 and a rear boundary 9 located at the rear end of the second annular boundary 8 and extending vertically inward, the front end of the second annular boundary 8 intersects with the front boundary 7, and the rear boundary 9 is perpendicular to the axis of the throttle cone 5 and intersects with the rear end of the inlet outlet equal straight section 4; the pressure outlet boundary 10 is located at the inlet outlet 3, the pressure outlet boundary 10 is perpendicular to the axis of the throttle cone 5, and the pressure outlet boundary 10 is connected between the rear end of the first annular boundary 6 and the rear end of the throttle cone 5;

[0016] Axial cone entry is performed by controlling the length between the apex of the throttling cone 5 and the pressure outlet boundary 10;

[0017] The pressure far field boundary, the adiabatic solid wall boundary, and the pressure outlet boundary 10 together form a small far field region;

[0018] The height of the air inlet duct outlet 3 is D, and the air inlet duct outlet 3 is uniformly extended in the x direction by a length of L1 to form an air inlet duct outlet uniformly straight section 4, 1D≤L1≤2D;

[0019] The length of the rear boundary 9 is L2, 0.1D≤L2≤0.4D, the length of the second annular boundary 8 is L3, 1D≤L3≤2D; the length of the front boundary 7 is L4, L4 is the same as the length of the rear boundary 9, taking L4=L2, the length of the first annular boundary 6 is L5, 3D≤L5≤4D;

[0020] The vertex of the throttle cone 5 forms a certain angle δ, which is 30°≤δ≤90°; the length between the vertex of the throttle cone 5 and the pressure outlet boundary 10 is L6, and the throttle cone 5 can be axially advanced by controlling L6, thereby giving different inlet duct outlet back pressures; the vertical length of the throttle cone 5 is L7, which is consistent with the height D of the inlet duct outlet 3, that is, L7=D;

[0021] Since the apex of the throttle cone 5 forms a certain angle, the tail of the straight section 4 such as the inlet outlet forms an air flow channel biased to both sides. At the same time, since the pressure far field boundary is provided with free inflow from the vertical and horizontal directions respectively, the airflow in the channel 2 of the embedded inlet duct merges with the free inflow of the pressure far field boundary from both sides and enters the small far field area together.

[0022] The pressure far-field boundary, adiabatic solid wall boundary, and pressure outlet boundary are all common knowledge in the technical field. The reference is ANSYS Fluent Users Guide (ANSYS Inc., 2018). The definitions of the pressure far-field boundary, adiabatic solid wall boundary, and pressure outlet boundary are located in Part 3, Chapter 7 of the document, among which the definition of the pressure outlet boundary is recorded in Section 7.4.9 of Chapter 7 of Part 3, the definition of the pressure far-field boundary is recorded in Section 7.4.10 of Chapter 7 of Part 3, and the definition of the adiabatic solid wall boundary is recorded in Section 7.4.15 of Chapter 7 of Part 3.

[0023] Example 1

[0024] In conjunction with a specific embodiment, the numerical simulation method for low-flow conditions of a buried air intake is further explained.

[0025] For the same inlet configuration, two schemes are used for comparison. Scheme 1 sets a pressure outlet boundary at the rear end of the straight section 4 at the inlet outlet, and adopts the method of directly changing the back pressure at the inlet outlet. Scheme 2 adopts a method of combining the throttle cone 5 with the small far field area. The pressure far field free flow Mach number Ma0=0.7, the static pressure P0=26500Pa, the static temperature T0=223K, the inlet outlet 3 height D, the inlet outlet straight section 4 length L1=1.6D, the rear boundary length L2=0.18D, the second annular boundary 8 length L3=1.1D, the front boundary 7 length L4=0.18D, the first annular boundary 6 length L5=3.5D, the vertical length of the throttle cone 5 L7=1D, the throttle cone 5 angle δ=60°, and the degree of the inlet cone can be controlled by changing the length L6 between the vertex of the throttle cone 5 and the pressure outlet boundary 10.

[0026] Scheme 1: Directly change the inlet outlet back pressure P b To throttle, Scheme 2 changes the size of L6 to axially move the throttling cone 5 to throttle. Tables 1 and 2 respectively give the comparison of the aerodynamic performance of the inlet duct when Scheme 1 directly changes the inlet duct outlet back pressure and Scheme 2 axially enters the cone.

[0027] Table 1 Comparison of aerodynamic performance of the inlet duct when the inlet duct outlet back pressure is directly changed in scheme 1

[0028]

[0029] Table 2 Comparison of aerodynamic performance of the inlet duct during axial cone entry in Scheme 2

[0030]

[0031] See also Figure 3 and Figure 4 As shown in the table, the comparison between the table parameters and the curve chart shows that in the scheme 1, the scheme of directly changing the back pressure at the inlet duct outlet shows a trend of slow decline at first, and when P b / P0=1.116 When the flow rate is 13.006kg / s, the intake duct is inlet normally, such as Figure 3 As shown in a, the back pressure at the inlet duct outlet is further increased to make P b / P0=1.117, the intake flow rate drops sharply, the airflow backflows -2.085kg / s, the intake duct cannot intake air normally, the total pressure recovery coefficient rises slightly at first, and then at P b / P0=1.116, it reaches the highest point and then drops sharply. At this time, different inlet outlet back pressures make the Mach number cloud diagram of the buried inlet different. b / P0=1.116, such as Figure 4 As shown in c, when P b / P0=1.117, such as Figure 4 As shown in middle d;

[0032] In scheme 2, the throttle cone is moved 5, and the intake flow and total pressure recovery coefficient continue to maintain a downward trend. Within the research range, the intake flow drops from 12.907kg / s to 0.283kg / s, and the total pressure recovery coefficient drops from 0.935 to 0.773. There is no sharp drop in intake flow, such as Figure 3 As shown in b;

[0033] See also Figure 5 As shown, when the throttle cone 5 is in different positions, such as when L6 / D=1.866, the position of the throttle cone 5 is as follows: Figure 5 As shown in Figure e, when L6 / D = 2.766, the position of the throttle cone 5 is as follows: Figure 5 As shown in middle f, therefore, the Mach number cloud diagram of the embedded inlet varies with the position of the throttle cone 5. As the throttle cone 5 advances axially, the inlet can still take in a small amount of air.

[0034] By combining the throttle cone with the pressure far-field boundary, the adiabatic solid wall boundary, and the pressure outlet boundary for numerical simulation, the aerodynamic performance and flow field structure of the embedded inlet under low-flow conditions can be explored, which is closer to the actual experimental situation and provides a reliable auxiliary reference for wind tunnel experiments.

Claims

1. A numerical simulation method for low flow conditions of a submerged air inlet, characterized in that: A computer simulation model is established for the applied embedded air inlet, the computer simulation model comprising an embedded air inlet inner channel extending obliquely inward, an air inlet outlet located behind the embedded air inlet inner channel, an air inlet outlet equal straight section located at the tail of the air inlet outlet, and a throttle cone located behind the air inlet outlet equal straight section; The pressure far-field boundary, the adiabatic solid wall boundary and the pressure outlet boundary are simulated and set in the computer simulation model; wherein the pressure far-field boundary includes a first annular boundary surrounding the straight section such as the inlet outlet and the throttle cone, and a front boundary located at the front end of the first annular boundary and extending vertically inward, and the front boundary is perpendicular to the throttle cone axis; the adiabatic solid wall boundary includes a second annular boundary surrounding the straight section such as the inlet outlet and a rear boundary located at the rear end of the second annular boundary and extending vertically inward, the front end of the second annular boundary intersects with the front boundary, and the rear boundary is perpendicular to the throttle cone axis and intersects with the rear end of the straight section such as the inlet outlet; the pressure outlet boundary is located at the inlet outlet, the pressure outlet boundary is perpendicular to the throttle cone axis, and the pressure outlet boundary is connected between the rear end of the first annular boundary and the rear end of the throttle cone.

2. The numerical simulation method for low flow conditions of a submerged air intake according to claim 1, characterized in that: The height of the inlet duct outlet is D, the length of the straight section of the inlet duct outlet is L1, and 1D≤L1≤2D.

3. The numerical simulation method for low flow conditions of a submerged air intake according to claim 1, characterized in that: The length of the rear boundary is L2, 0.1D≤L2≤0.4D, and the length of the second annular boundary is L3, 1D≤L3≤2D.

4. The numerical simulation method for low flow conditions of a submerged air intake according to claim 1 or 3, characterized in that: The length of the front boundary is L4, which is the same as the length of the rear boundary, 0.1D≤L4≤0.4D, and the length of the first annular boundary is L5, 3D≤L5≤4D.

5. The numerical simulation method for low flow conditions of a submerged air intake according to claim 1 or 3, characterized in that: The vertex of the throttle cone forms a certain angle δ, which is 30°≤δ≤90°. The length between the vertex of the throttle cone and the pressure outlet boundary is L6. L6 is controlled to axially propel the throttle cone, thereby giving different inlet outlet back pressures; the vertical length of the throttle cone is L7, which is consistent with the inlet outlet height D, that is, L7=D.

6. The numerical simulation method for low flow conditions of a submerged air intake according to claim 5, characterized in that: The tail of the straight section such as the inlet outlet forms an air flow channel biased to both sides. At the same time, since the pressure far field boundary is set with free flow from the vertical and horizontal directions respectively, the airflow in the channel of the buried inlet duct merges with the free flow of the pressure far field boundary from both sides here.

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