Design method of low-outlet-distortion high-Mach-number inward rotation air inlet channel

Abstract

The invention relates to a design method of a low-outlet-distortion high-Mach-number inward rotation air inlet channel. Comprising the following steps: designing an inward turning air inlet reference flow field: giving a pressure rise distribution rule of a reference body compression wall surface, appointing a reference body inlet radius, a center body radius and a leading edge compression angle, giving an incoming flow Mach number and a flight height, and solving a flow field structure of a non-viscous reference flow field through a characteristic line method; generating an air inlet channel molded surface: extracting streamline data of the non-sticky reference flow field, giving a capture molded line, dispersing the molded line, applying a streamline tracking method to obtain data points required by the air inlet channel molded surface, and fitting the data points to obtain an initially generated air inlet channel molded surface; and modifying the generated molded surface of the air inlet channel. The inward turning air inlet channel structure obtained through the method can be controlled through a wall face pressure rise rule function and incoming flow parameters, outlet distortion is small, and the inward turning air inlet channel structure is superior to an inward turning air inlet channel designed through a conventional method in the aspect of outlet flow field uniformity.

Description

Technical Field

[0001] The invention belongs to the field of aircraft air inlet design, and in particular relates to a design method for a high Mach number internal turning air inlet with low outlet distortion. Background Art

[0002] Air-breathing hypersonic vehicles have become a research hotspot for major aerospace powers due to their outstanding advantages in speed, range and penetration capability. As the core power unit, the scramjet engine has high requirements for the quality of the airflow entering the combustion chamber, and the air inlet, as one of the key components of the air-breathing propulsion system, plays a major role in affecting the airflow quality of the engine.

[0003] Compared with conventional dual inlets, axisymmetric inlets and other hypersonic inlets, inward-turning inlets have been widely used in hypersonic vehicles in recent years because of their higher airflow capture capability, higher airflow compression efficiency, less total pressure loss, smaller wetted area and wider adaptability. However, under conditions of high Mach number inflow (Mach number 8 and above) and large angle of attack and large sideslip angle, the inlet outlet flow field is not uniform, and parameters such as total pressure, temperature, and Mach number are greatly distorted, which will greatly affect the combustion chamber and engine working stability. Therefore, it is necessary to start with the design method to improve the uniformity of the inlet outlet flow field and reduce the degree of distortion.

[0004] Li Yongzhou et al. "Design of a Mach number controllable inward-contracting inlet with non-uniform incoming flow [J]. Acta Aeronautica Sinica, 2023, 44(12): 162-174." Under the premise that the distribution laws of the incoming flow Mach number and the wall Mach number are given at the same time, a design method for a controllable inward-contracting inlet with non-uniform incoming flow Mach number distribution is developed. Although the Mach number distribution of the entire flow field is controlled and the compression efficiency is high, the uniformity of the Mach number at the throat and outlet is still poor. Wang Weixing et al. "Study on the flow field organization of an inward-turning inlet based on vortex generators [J / OL]. Propulsion Technology, 1-18 [2024-07-16]." Vortex generators were introduced into the design of inward-turning inlets, and it was found that the vortex generators induced the formation of reverse vortices, weakened the flow vortex strength on the compression surface side, and effectively improved the uniformity of the inlet flow field. However, the design point of this study is low Mach number, and its performance will drop sharply when the incoming flow Mach number increases. In addition, there are structural problems in actual engineering applications when introducing vortex generators.

[0005] At present, most inward-turning inlets are designed below the design point Mach number Ma7, and their reference flow field adopts the traditional wall pressure rise law. The flow field at the outlet of these inlets is greatly distorted and has poor uniformity. Summary of the invention

[0006] The purpose of the present invention is to provide a design method for a high Mach number inward-turning inlet based on a reference flow field with low outlet distortion, thereby improving the outlet uniformity of the inward-turning inlet under high Mach number incoming flow.

[0007] The technical solution to achieve the purpose of the present invention is: a method for designing a high Mach number internal inlet with low outlet distortion, comprising the following steps:

[0008] Step (1): Design the reference flow field of the inward-turning inlet duct: Given the pressure rise distribution law of the compression wall of the reference body, specify the reference body inlet radius R i , the center body radius r and the leading edge compression angle δ i , given the incoming flow Mach number Ma and the flight altitude H, the flow field structure of the inviscid reference flow field is solved by the characteristic line method MOC;

[0009] Step (2): Generate the inlet profile: extract the streamline data of the inviscid reference flow field obtained in step (1), give the capture profile, discretize the profile, use the streamline tracking method to obtain the data points required for the inlet profile, fit the data points, and obtain the initially generated inlet profile;

[0010] Step (3): Modifying the generated inlet duct profile: Perform geometric modification on the inner channel section to the outlet section of the initial inlet duct profile obtained in step (2) to make it meet the regular rectangular outlet and complete the inward-turned inlet duct design.

[0011] Furthermore, the inward-turning inlet reference flow field in step (1) includes the compression wall profile of the reference body, the leading edge incident shock wave, the center body wall profile, the reference flow field outlet and the flow field area.

[0012] Furthermore, the pressure rise distribution law of the reference body compression wall given in step (1) is specifically:

[0013] P w =(ce a(x-b) +c)P s

[0014] Where P s is the static pressure after the incident shock wave at the leading edge, P w is the reference body compression wall pressure, a, b, c are the wall pressure rise law coefficients.

[0015] Furthermore, the Mach number of the design point of the reference flow field is a high Mach number, that is, greater than Ma8, and the design point airspace is a high airspace, that is, higher than 30km.

[0016] Furthermore, the capture profile in step (2) is determined by the capture height H c and aspect ratio B control.

[0017] Furthermore, the initially generated air inlet profile obtained in step (2) includes a clamp-shaped top plate, side plates on both sides, and a clamp-shaped lip plate. The flow channel formed by the top plate, the side plates and the rear half of the lip plate is the inner channel section of the air inlet, the end of the inner channel section is the outlet, and the front edge of the lip plate is the lip.

[0018] Furthermore, step (3) specifically includes the following steps:

[0019] Step (31): Given the inlet duct outlet height h and the scaling ratio μ, the theoretical outlet flow rate is controlled in combination with the capture profile given in step (2), thereby controlling the flow coefficient;

[0020] Step (32): Given a deflection angle σ, cut off the portion from the top plate, side plate and lip plate of the inner channel to the outlet along the rear side of the lip:

[0021] Step (33): According to the outlet height h and the scaling ratio μ given in step (31), geometric reconstruction is performed on the inner channel of the inlet along the symmetric surface of the inlet, and a smooth transition is made to a regular rectangular outlet.

[0022] Compared with the prior art, the present invention has the following significant advantages:

[0023] The present invention is based on a novel low outlet distortion inward-turning reference flow field, and realizes the high Mach number inward-turning inlet profile design through streamline tracing and geometric modification at a high Mach number design point; a novel wall pressure rise law control function is proposed, and the pressure gradient at the reference flow field outlet is controlled by controlling the wall pressure rise law, thereby improving the uniformity of the inlet outlet flow field.

[0024] By giving an intake duct outlet height h and a scaling ratio μ, the present invention can transition the irregular intake duct outlet into a regular rectangular outlet after simple geometric modification, which is beneficial to the design standardization of the downstream engine combustion chamber and improves the degree of internal flow integration of the engine.

[0025] The present invention achieves small intake distortion at high Mach numbers, good flow field uniformity, broadens the working range of the intake duct, has a high degree of integration, does not require additional structural parts, and has great advantages such as simple structure, good economy, excellent performance, and good adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a high Mach number inward-turning air inlet model with low outlet distortion designed by the present invention; wherein (a) is a three-dimensional diagram, (b) is a main view, and (c) is a side view.

[0027] Figure 2 It is the reference flow field structure diagram in the present invention.

[0028] Figure 3 It is a schematic diagram of the capture line in the present invention.

[0029] Figure 4 1 is a comparison diagram of the total pressure cloud diagram at the throat of the air inlet in the embodiments; wherein (a) is the inward-turning air inlet in embodiment 1 of the present invention, and (b) is the conventional inward-turning air inlet.

[0030] Figure 5 It is a comparison chart of the distortion index of the outlet parameters in the embodiment. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0032] A method for designing a high Mach number inner-turn inlet with low outlet distortion comprises the following steps:

[0033] 1) Design the reference flow field of the inward-turning inlet duct: The pressure rise distribution function of the given reference body compression wall 1 is:

[0034] P w =(ce a(x-b) +c)P s

[0035] Where P s is the static pressure after the incident shock wave at the leading edge, P w is the reference body compression wall pressure, a, b, c are the wall pressure rise law coefficients.

[0036] Specify the reference body entrance radius R i , the radius r of the center body 2 and the leading edge compression angle δ i , and then given the incoming flow Mach number Ma and flight altitude H, the flow field structure of the inviscid reference flow field is solved by the characteristic line method (MOC); the inward-turned inlet reference flow field includes the compression wall profile 1 of the reference body, the leading edge incident shock wave 3, the center body wall profile 4, the reference flow field outlet 5, and the flow field area 6 surrounded by the above. In the data processing software, the streamline data of the above flow field area can be extracted.

[0037] 2) Generate the air inlet profile: The streamline data of the reference flow field obtained in step 1) is given a capture profile 7, the profile is discretized, and the streamline tracking method is used to obtain the data points required for the air inlet profile. The data points are fitted in the three-dimensional modeling software to obtain the initial air inlet profile, including a clamp-shaped top plate 11, side plates 12 on both sides, and a clamp-shaped lip plate 13. The flow channel composed of the rear half of the above three components is the inner channel section 8 of the air inlet. The end of the inner channel section 8 is the outlet 9, and the front edge of the lip plate 13 is the lip 10.

[0038] 3) Modifying the generated profile: Perform geometric modification on the inner channel 8 to the outlet 9 section of the initial air inlet profile obtained in step 2) to make it meet the regular rectangular outlet and complete the inner turn air inlet design, specifically:

[0039] 3-1) Given the inlet duct outlet height h and the scaling ratio μ, combined with the capture profile 7 given in step 2), the theoretical outlet flow rate is controlled, thereby controlling the flow coefficient.

[0040] 3-2) Given a deflection angle σ, cut off the portion of the inner channel top plate 11, side plate 12 and lip plate 13 to the outlet along the rear side of the lip 10

[0041] 3-3) According to the outlet height and scaling ratio given in step 3-1), the inner channel of the air inlet is geometrically reconstructed along the air inlet symmetry plane 14 so that it smoothly transitions to a regular rectangular outlet.

[0042] The capture profile in step (2) is determined by the capture height H c and aspect ratio B. By adjusting the above two parameters H c and B can control the inlet geometric parameters such as the inlet length and top plate swept length, and can also control the inlet outlet performance parameters.

[0043] The final inlet profile after modification is as shown in the attached figure. Figure 1 As shown, from the axonometric view (a), it can be seen that the swept length of the top plate and the swept length of the lip plate are both large, which is related to the high design Mach number of the incoming flow; from the front view (b), it can be seen that the transition between the rear geometric modification of the inner channel and the front air inlet is relatively smooth and gentle; from the side view (c), it can be seen that the shape of the air inlet outlet is controlled to be a regular rectangle.

[0044] Example 1

[0045] The design working condition is that the incoming flow Ma=10, the angle of attack is 0, and the flight altitude is H=32.26km. The inward turning air intake duct design under this working condition is carried out by the method described in the present invention:

[0046] 1) According to the working conditions, specify the reference body inlet radius R i =0.25m, center body radius r = 0.0375m, leading edge compression angle δ i =4°, the pressure rise distribution function of the given reference body compression wall is:

[0047] P w =(ce a(x-b) +c)P s

[0048] Given a = 2.3, b = 0.5, c = 1.1. The program is written by the method of characteristic lines (MOC) to solve the flow field structure of the inviscid reference flow field, including the compression wall profile of the reference body, the leading edge incident shock wave, the center body wall profile, the reference flow field outlet, and the flow field area enclosed by the above.

[0049] 2) Extract the streamline data of the reference flow field obtained in step 1) and give the capture height H of the capture profile c =0.1m, the rectangular line width is 0.34m, the height is 0.09m, the line is discretized according to 300 nodes, and the streamline tracing method is used to write a program to obtain the data points required for the inlet surface. The data points are fitted in the 3D modeling software to obtain the initially generated inlet surface.

[0050] 3) In the modeling software, the initial inlet profile obtained in step 2) is cut off along the lip with a given deflection angle σ = 45°, the inlet outlet height h = 0.07m and the scaling ratio μ = 2 are specified, and the cut-off part is geometrically reconstructed with a smooth transition to satisfy the regular rectangular outlet, thus completing the design of the inward-turned inlet.

[0051] The unevenness of the inlet duct outlet cross-sectional parameter φ is expressed by the average root mean square deviation of the flow rate:

[0052]

[0053] Where φ can represent parameters such as total pressure, temperature, and Mach number. It is the flow-weighted average value. It has been verified that under non-viscous conditions, the simulation analysis of the inward-turning inlet and the conventional inward-turning inlet is carried out, and the total pressure distribution cloud diagram at the throat is obtained as follows Figure 4 As shown in the figure, it can be seen that the pressure gradient of the new inward-turning air inlet obtained by the present invention is significantly smaller and more evenly distributed than that of the conventional inward-turning air inlet. Figure 5 The distortion indexes of total pressure, temperature and Mach number of the two inlet ducts at the outlet section were statistically analyzed. Compared with the conventional inward-turning inlet duct, the total pressure distortion index of the new inward-turning inlet duct of the present invention decreased by 25.56%, the temperature distortion index decreased by 47.3%, and the Mach number distortion index decreased by 47.01%. This shows that the flow field distortion of the inward-turning inlet duct designed by the present invention is significantly reduced, and the flow field uniformity is greatly improved.

Claims

1. A method for designing a high Mach number internal inlet with low outlet distortion, characterized in that: The steps include: Step (1): Design the reference flow field of the inward-turning inlet duct: Given the pressure rise distribution law of the compression wall of the reference body, specify the reference body inlet radius R i , the center body radius r and the leading edge compression angle δ i , given the incoming flow Mach number Ma and the flight altitude H, the flow field structure of the inviscid reference flow field is solved by the characteristic line method MOC; Step (2): Generate the inlet profile: extract the streamline data of the inviscid reference flow field obtained in step (1), give the capture profile, discretize the profile, use the streamline tracking method to obtain the data points required for the inlet profile, fit the data points, and obtain the initially generated inlet profile; Step (3): Modifying the generated inlet duct profile: Perform geometric modification on the inner channel section to the outlet section of the initial inlet duct profile obtained in step (2) to make it meet the regular rectangular outlet and complete the inward-turned inlet duct design.

2. The method according to claim 1, characterized in that The inward-turning inlet duct reference flow field in step (1) includes the compression wall profile of the reference body, the leading edge incident shock wave, the center body wall profile, the reference flow field outlet and the flow field area.

3. The method according to claim 2, characterized in that The pressure rise distribution law of the reference body compression wall given in step (1) is specifically: P w =(what a(x-b) +c)P s Where P s is the static pressure after the incident shock wave at the leading edge, P w is the reference body compression wall pressure, a, b, c are the wall pressure rise law coefficients.

4. The method according to claim 3, characterized in that The Mach number of the design point of the benchmark flow field is a high Mach number, that is, greater than Ma8, and the airspace of the design point is a high airspace, that is, higher than 30km.

5. The method according to claim 4, characterized in that The capture profile in step (2) is determined by the capture height H c and aspect ratio B control.

6. The method according to claim 5, characterized in that The initially generated air inlet profile obtained in step (2) includes a clamp-shaped top plate, side plates on both sides, and a clamp-shaped lip plate. The flow channel formed by the top plate, the side plates and the rear half of the lip plate is the inner channel section of the air inlet, the end of the inner channel section is the outlet, and the front edge of the lip plate is the lip.

7. The method according to claim 6, characterized in that Step (3) specifically includes the following steps: Step (31): Given the inlet duct outlet height h and the scaling ratio μ, the theoretical outlet flow rate is controlled in combination with the capture profile given in step (2), thereby controlling the flow coefficient; Step (32): Given a deflection angle σ, cut off the portion from the top plate, side plate and lip plate of the inner channel to the outlet along the rear side of the lip: Step (33): According to the outlet height h and the scaling ratio μ given in step (31), geometric reconstruction is performed on the inner channel of the inlet along the symmetric surface of the inlet, and a smooth transition is made to a regular rectangular outlet.

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