A hypersonic inlet with a high pressure ratio and long forebody and its design method

Abstract

The application provides a high-pressure ratio long precursor hypersonic inlet and a design method thereof, and adopts an inlet wave system configuration method of first-stage shock wave spillage and second-stage shock wave-isentropic compression wave heterotopic convergence; the first-stage planar shock wave has a lag angle, so as to avoid that the precursor shock wave is incident to the lip port of the lip cover in a large attack angle state; a virtual conical surface is constructed, and a characteristic line method is used to determine second and third virtual conical surface profiles; the second-stage conical shock wave is close to the lip port, and the third-stage isentropic compression wave is distributedly incident to the inner side of the lip port; the wave arrangement scheme increases the total pressure recovery coefficient of the inlet, and significantly improves the performance of the inlet; the compression surface adopts a bulge type design, can remove the low-energy flow of the boundary layer, effectively prevents the low-energy flow from entering the inlet, and improves the self-starting performance of the inlet, and simultaneously can reduce the aerodynamic resistance of the inlet; the lip cover adopts a backward sweep design, and the side plate is inwardly deflected to induce a side pressure shock wave, so as to realize the compression of the airflow, and compared with the traditional design, the compression capacity of the inlet is improved.

Description

Technical Field

[0001] This invention relates to the field of aircraft air intakes, specifically to a high-pressure-ratio long-forebody hypersonic air intake and its design method. Background Technology

[0002] Hypersonic vehicles have many advantages, such as high speed, high altitude, long range, and good penetration capabilities, and have broad application potential in the military field.

[0003] Regarding the integrated series arrangement of the forebody / inlet, the forebody's compression effect on the airflow accounts for a relatively small proportion; airflow compression mainly occurs within the inlet. This integrated design fully leverages the design advantages of both the forebody and inlet, improving the overall performance of the inlet, such as total pressure recovery, compression capacity, and flow capture capability. However, it's necessary to consider the mutual interference between the forebody and inlet flow fields, which can lead to the development of a thicker boundary layer. The intake of low-energy flow at the inlet can degrade inlet performance and even prevent the inlet from starting. Therefore, a key technical challenge is how to suppress the boundary layer accumulated by the forebody while maintaining inlet drag, thereby enabling the inlet to have strong self-starting performance.

[0004] For the wave system configuration method of the traditional shock wave / isentropic compression wave convergence lip, how to achieve both a high total pressure recovery coefficient and low inlet drag in the inlet is a design challenge. In addition, the traditional wave system configuration method cannot solve the problem of the inlet exceeding its rated state under high angle of attack conditions. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a hypersonic inlet with a high pressure ratio and long forebody that combines a high total pressure recovery coefficient and a low inlet drag, as well as its design method.

[0006] Technical solution: A design method for a hypersonic inlet with a high pressure ratio and long forebody, comprising the following steps:

[0007] S1 determines the three-stage compression surface type of the inlet based on the requirements of the inlet's capture flow rate and compression amount. The first stage compression surface is planar shock wave compression, the second stage compression surface is conical shock wave compression, and the third stage compression surface is isentropic compression. The corresponding virtual flow field second-stage half-cone angle and third-stage compression angle are given.

[0008] S2 Given the design Mach number and flight angle of attack, solve the plane oblique shock wave formula to obtain the Mach number, shock wave angle and density of the airflow behind the first-stage plane shock wave;

[0009] S3 calculates the inlet capture area using the flow formula based on the Mach number, shock angle, and density of the airflow behind the first-stage planar shock wave, and then calculates the inlet capture height using the inlet capture area. The first-stage planar shock wave does not enter the lip of the lip mask under design conditions. Given a lag angle, which is the angle between the first-stage planar shock wave and the straight line connecting the starting point of the first-stage compression surface and the lip mask, the lip coordinates are calculated based on the shock angle of the first-stage planar shock wave, the inlet capture height, the lag angle, and the coordinates of the starting point of the first-stage compression surface.

[0010] S4 solves the conical shock formula based on the Mach number of the airflow behind the first-stage planar shock wave and the semi-cone angle of the second-stage virtual flow field, obtaining the Mach number of the airflow behind the second-stage conical shock wave and the shock wave angle. The second-stage conical shock wave of the virtual conical surface and the third-stage shock wave of the virtual compression surface are both close to the lip of the lip mask under the design state. The axial position of the virtual conical surface is determined. The virtual conical surface is located below the first-stage compression surface. Given the height of the axis of the second-stage conical surface of the virtual flow field from the first-stage compression surface, the starting point of the second-stage conical surface of the virtual flow field is calculated.

[0011] S5 divides the compression angle of the third-level compression surface of the virtual flow field into several equal parts, and the isentropic compression wave is correspondingly divided into several equal parts.

[0012] S6 calculates the second and third level compression surface profiles of the virtual flow field based on the method of characteristics, determines the starting point of the third level compression surface of the virtual flow field, and the coordinates of the intersection points of several equal-divided isentropic compression waves with the third level compression surface of the virtual flow field.

[0013] S7 Keeps the starting point of the third-level compression surface of the virtual flow field unchanged, gives the compression wave amplification factor, and enlarges the coordinates of the intersection point in step S6 proportionally according to the compression wave amplification factor coefficient. Connects the proportionally enlarged coordinate points in sequence to obtain the profile of the third-level compression surface of the virtual flow field.

[0014] S8 uses the virtual conical shock wave flow field determined in the above steps as the virtual conical shock wave surface for designing the inlet compression surface. It solves for the intersection line between the first-stage planar compression surface and the virtual conical shock wave surface. It selects several discrete points on the first-stage planar compression surface and the virtual conical shock wave surface, and uses the streamline tracing method to continuously trace the streamlines of the discrete points in the virtual conical shock wave flow field. It combines the streamlines into a flow surface to obtain the bulge-shaped second and third-stage compression surfaces of the inlet.

[0015] The S9's lip cover is designed based on lip-mouth coordinates, and the lip cover adopts a swept-back design to complete the air intake design.

[0016] Specifically, the lip mask has several venting slits; furthermore, the several venting slits are of the same size and are located at the shock wave reflection point on the inner surface of the lip mask near the throat.

[0017] Specifically, the lag angle ranges from 1 to 2°.

[0018] Specifically, the compression wave amplification factor ranges from 1.3 to 1.4.

[0019] Specifically, step S9 includes: projecting the starting point of the second-stage cone surface of the virtual flow field onto the inlet surface of the air intake, and drawing a circle with the projection point as the center, which is tangent to the leading edge profile of the lip cover at the center point of the leading edge of the lip cover. The distance from any point of the leading edge profile other than the center point to the projection point is less than the radius of the circle.

[0020] Specifically, the inner surface of the lip cover is compressed inward, with a compression angle ranging from 2 to 4°.

[0021] Specifically, the lip cover side panel is compressed inward at a certain angle.

[0022] The present invention also provides an air intake obtained according to the above-described air intake design method, comprising: a first-stage planar compression surface, a bulge-shaped compression surface extending rearward from the first-stage planar compression surface, and a lip cover located above the bulge-shaped compression surface. The bulge-shaped compression surface is designed based on a conical shock wave virtual flow field, which includes a second-stage conical surface and a third-stage compression surface. The lip cover adopts a swept-back design, with the inner surface of the lip cover compressed inward at a certain angle and the side plate of the lip cover compressed inward at a certain angle.

[0023] Beneficial Effects: Compared with the prior art, the significant advantages of this invention are: This invention adopts an inlet wave configuration method of first-stage shock wave overflow and second-stage shock wave-isentropic compression wave heterogeneous convergence. The first-stage planar shock wave has a lag angle, avoiding the forebody shock wave from incident on the lip of the lip mask at high angles of attack; a virtual cone surface is constructed and the characteristic line method is used to determine the profiles of the second and third-stage virtual cone surfaces. The second-stage conical shock wave is close to the lip, and the third-stage isentropic compression wave is distributed and incident on the inner side of the lip. This wave configuration scheme increases the total pressure recovery coefficient of the inlet and significantly improves the performance of the inlet. Improvements include: a bulge-shaped compression surface that, compared to traditional compression surface designs, can exclude low-energy flow from the boundary layer, effectively preventing low-energy flow from entering the intake and improving the intake's self-starting performance, while also reducing aerodynamic drag; a swept-back lip design that induces lateral pressure shock waves through inward deflection of side plates to compress the airflow, improving the intake's compression capacity compared to traditional designs; and multiple venting slots on the lip that allow low-energy flow from the boundary layer to escape, effectively preventing throat blockage or even intake failure. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the high-pressure ratio long precursor hypersonic inlet bulge-shaped compression surface design of the present invention.

[0025] Figure 2 This is a schematic diagram of the design of the virtual compression surface and the actual compression surface of the hypersonic inlet of the high-pressure ratio long precursor of the present invention.

[0026] Figure 3 This is a schematic diagram of the design of the hypersonic inlet lip cover and lip cover side plate of the high pressure ratio long precursor of the present invention.

[0027] Figure 4 This is a schematic diagram of the high-pressure ratio long precursor hypersonic inlet lip cover venting seam structure of the present invention. Detailed Implementation

[0028] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0029] Please refer to Figure 1 and Figure 2 As shown, this invention discloses a design method for a high-pressure-ratio long forebody hypersonic inlet, comprising the following steps:

[0030] 1. Based on the requirements for intake flow rate and compression, and aerodynamic optimization methods, the compression surface is divided into three stages. The three stages of compression surface types are: the first stage is planar shock wave compression, the second stage is conical shock wave compression, and the third stage isentropic compression. The corresponding virtual flow field is given with the second stage half-cone angle... Third-level compression angle

[0031] 2. Given the design Mach number and flight angle of attack, solve the plane oblique shock wave formula to obtain the Mach number M1, shock wave angle α1, and density ρ1 of the airflow after the first stage plane shock wave.

[0032] 3. The first-stage plane shock wave 1 does not penetrate the lip of the lip mask 4 at the design point to prevent the intake from exceeding its rated capacity under high angle of attack. Based on the Mach number M1 of the airflow behind the first-stage plane shock wave 1, the shock wave angle α1, and the density ρ1, the flow rate formula is used. Calculate the intake duct capture area A c (A c =h c ×l c , where h c To capture height; l c To capture the spanwise length (default is 1), the intake duct capture area A is utilized. c The intake capture height h was calculated. c Given a lag angle δ, 1°≤δ≤2°, where lag angle δ is the angle between the first-stage planar shock wave 1 and the straight line connecting the starting point of the first-stage planar compression surface 5 and the lip of the lip mask 4, based on the shock wave angle α1 of the first-stage planar shock wave 1 and the intake capture height h... c Given the lag angle δ and the coordinates of the starting point O(x0, y0) of the first-stage compression surface, the lip coordinates C(x0, y0) are calculated. c ,y c )=(x0+h c / tan(α1-δ),hc );

[0033] 4. To improve the intake duct's flow capture capability and increase the total pressure recovery coefficient, the virtual cone surface second-stage conical shock wave 2 and the virtual compression surface third-stage shock wave are both close to the lip in the design state. First, determine the axial position of the virtual cone surface 12. The virtual cone surface 12 is below the first-stage planar compression surface 5. Based on the Mach number M1 of the airflow after the first-stage planar shock wave 1, solve the conical shock wave formula to obtain the Mach number M2 of the airflow after the second-stage conical shock wave 2 and the shock wave angle α2. Given the height h1 of the virtual flow field second-stage cone surface 6 axis from the first-stage planar compression surface 5, calculate the starting point A'(x2',y2')=(x c -(h c +h1) / tanα2,-h1);

[0034] 5. To ensure that all isentropic compression waves 3 converge at the inlet point of the lip cover 4, the compression angle of the third-order compression surface 7 of the virtual flow field is adjusted. Divide it into n equal parts, and the isentropic compression wave 3 is divided into n equal parts. The isentropic compression surface profile is a smooth curve, which is discretized into n segments.

[0035] 6. Based on the method of characteristics, calculate the compression surface profiles of the second and third stages of the virtual flow field, determine the starting point of the third-stage compression surface 7 of the virtual flow field, and the intersection point I of the n equal-divided isentropic compression waves with the third-stage compression surface 7 of the virtual flow field. n '(x In ',y In ');

[0036] 7. To ensure that the isentropic compression wave 3 is incident in a distributed manner to the lip, while keeping the coordinates of the starting point I1' of the third-order compression surface 7 of the virtual flow field unchanged, a compression wave amplification factor r is given, 1.3≤r≤1.4. The coordinates of the intersection point I in step 6 are then... n 'Amplify the signal proportionally to the compression amplification factor r, and record the coordinates I of the amplified point.' n (x) In ,y In ")=(rx In ',ry In The convergence of virtual point coordinates C'(x) c ',y c ')=(rx c ,ry c The Mach waves and the lip shock wave 9 interfere with each other, which has a significant impact on suppressing separation at the inlet of the air intake. By connecting the proportionally magnified coordinate points in sequence, the third-stage compression surface 7-type line of the virtual flow field is obtained.

[0037] The innovative wave configuration method proposed in the above steps sacrifices some overflow, but it greatly improves the inlet's internal flow loss performance and capture flow performance under wide speed range and high Mach conditions.

[0038] 8. Please refer to Figure 1 As shown, the virtual conical shock wave flow field determined in the above steps is used as the virtual conical shock wave surface 10 for designing the inlet compression surface. The intersection line of the first-stage planar compression surface 5 and the virtual conical shock wave surface 10 is solved. m discrete points are selected on the first-stage planar compression surface 5 and the virtual conical shock wave surface 10, and the vertical distances of the discrete points from the virtual axis are denoted as d1, d2...d m Discrete point coordinates D1(x) d1 ,y d1 ,z d1 D2(x) d2 ,y d2 ,z d1 ...D m (x dm ,y dm ,z dm ) and the discrete point deflection angle θ1(arctan(z) d1 / y d1 )), θ2…θ m (arctan(z dm / y dm The streamline 11 of the discrete points is continuously tracked in the virtual flow field of the conical shock wave using the streamline tracing method. The streamline 11 are combined into a flow surface to obtain the second and third stage compression surfaces 8 of the bulge-shaped air intake. The concave and convex surfaces effectively remove the low-energy flow of the boundary layer by generating a lateral pressure gradient.

[0039] 9. Please refer to Figure 3 and Figure 4 As shown, the lip cover 4 is designed based on the lip coordinate system. The lip cover 4 adopts a swept-back design, causing the low-energy flow to be displaced to both sides. The starting point A' of the second-stage cone surface 6 of the virtual flow field is projected onto the inlet surface of the air intake, and the projection point is denoted as A”. With A” as the center, a circle is drawn that is tangent to the leading edge profile of the lip cover at the center point M of the leading edge of the lip cover. The radius A”M of the circle is denoted as R. The distance from any point on the leading edge profile other than the center point M to A” is less than R. The inner profile of the lip cover 4 is compressed inward and in the opposite direction by 2-4°, and the compression angle of the lip cover is 13°. Figure 3 As shown, the lip mask's 4 side plates deflect inward at a certain angle to induce lateral pressure shock waves, with a side plate compression angle of 14°. Figure 3 As shown, this achieves the compression of the airflow.

[0040] Please refer to Figure 4As shown, several venting slits 16 of the same size are opened near the reflection point of the shock wave 15 on the inner surface of the lip cover 4. The low energy flow of the boundary layer is discharged from the venting slits 16 under the action of pressure difference, which greatly enhances the venting capacity of the intake duct, prevents the throat from being blocked, and enables the intake duct to start automatically at a lower Mach number.

[0041] Example 1

[0042] This embodiment provides an application example of the design method for the high-pressure-ratio long forebody hypersonic inlet under specific parameter conditions, including the following steps:

[0043] 1. Please refer to Figure 2 As shown, given a design Mach number of 8 and a design angle of attack of 4°, a three-stage compression is adopted. The first stage is planar shock wave compression, the second stage is conical shock wave compression, and the third stage is isentropic compression. The virtual flow field has a second-stage half-cone angle of 4° and a third-stage compression angle of 13°.

[0044] 2. Due to the angle between the incoming airflow and the first-stage plane, an oblique shock wave is induced at the front end of the first-stage plane compression surface 5. After passing through this shock wave, the airflow direction is horizontal. Based on the plane oblique shock wave theory, the Mach number M1 = 7.087, the shock wave angle α1 = 10.02°, and the density ratio ρ1 / ρ0 = 1.676 are calculated after the first-stage plane shock wave 1. Furthermore, based on M1 = 7.087 and the second-stage semi-cone angle of the conical shock wave virtual flow field... The Mach number M2 = 6.352 and the shock angle α2 = 10.919° were obtained after the second-stage conical shock wave.

[0045] 3. Please refer to Figure 2 As shown, based on the back density ρ1 of the first-order plane shock wave 1, the flow rate formula is used... Calculate the intake duct capture area A c (A c =h c ×l c , where h c To capture height; l c To capture the spanwise length (default is 1), the intake duct capture area A is utilized. c The intake capture height h was calculated. c Given a lag angle δ, 1°≤δ≤2°, where lag angle δ is the angle between the first-stage planar shock wave 1 and the straight line connecting the starting point of the first-stage planar compression surface 5 and the lip of the lip mask 4, based on the shock wave angle α1 of the first-stage planar shock wave 1 and the intake capture height h... c The lag angle δ and the starting coordinates O(x0,y0) of the first-stage plane compression surface 5 are used to calculate the lip coordinates C(x). c ,y c )=(x0+h c / tan(α1-δ),h c ).

[0046] 4. Based on the Mach number M1 = 7.087 of the airflow after the first-stage plane shock wave, the second-stage semi-cone angle of the virtual flow field of the conical shock wave is... Solving the formula for the conical shock wave, we obtain the Mach number M2 = 6.352 and the shock angle α2 = 10.919° for the airflow after the second-stage conical shock wave. Given the height h1 of the axis of the second-stage conical surface 6 of the virtual flow field from the first-stage planar compression surface 5, we calculate the starting point A'(x2',y2') of the second-stage conical surface 6 of the virtual flow field. c -(h c +h1) / tanα2,-h1).

[0047] 5. The virtual flow field third-stage compression surface is compressed at angle 7. Divided into 26 equal parts, the isentropic compression wave 3 is divided into 26 equal parts, and the isentropic compression surface profile is a smooth curve, which is discretized into 26 segments.

[0048] 6. Based on the method of characteristics, the compression surface profiles of the second and third stages of the virtual flow field are calculated, the starting point of the third-stage compression surface 7 of the virtual flow field is determined, and the 26 intersection points I1'(x) of the 26 equally divided isentropic compression waves with the third-stage compression surface 7 of the virtual flow field are determined. I1 ',y I1 ')…I 26 '(x I26 ',y I26 ').

[0049] 7. To ensure that the isentropic compression wave 3 is incident in a distributed manner to the lip, and to keep the coordinates of the starting point I1' of the third-order compression surface 7 of the virtual flow field unchanged, given a compression wave amplification factor r = 1.35, the coordinates I1'(x) of the 26 intersection points in step 6 are... I1 ',y I1 ')…I 26 '(x I26 ',y I26 ') Amplify the wave proportionally according to the compression amplification factor r = 1.35, and record the coordinates of the amplified point as I1"(x). I1 ,y I1 ")=(rx I1 ',ry I1 ')…I 26 (x) I26 ,y I26 ")=(rx I26 ',ry I26 The convergence of virtual point coordinates C'(x) c ',y c ')=(rx c ,ry cConnect the proportionally enlarged coordinate points in sequence to obtain the third-level compression surface 7-type line of the virtual flow field.

[0050] 8. Using the virtual conical shock wave flow field determined in the above steps as the virtual conical shock wave surface 10 for designing the inlet compression surface, solve for the intersection line between the first-stage planar compression surface 5 and the virtual conical shock wave surface 10. Select m discrete points on the first-stage planar compression surface 5 and the virtual conical shock wave surface 10, and denote the vertical distances of the discrete points from the virtual axis as d1, d2…d… m Discrete point coordinates D1(x) d1 ,y d1 ,z d1 D2(x) d2 ,y d2 ,z d1 ...D m (x dm ,y dm ,z dm ) and the discrete point deflection angle θ1(arctan(z) d1 / y d1 )), θ2…θ m (arctan(z dm / y dm The streamline 11 of the discrete points is continuously tracked in the virtual flow field of the conical shock wave using the streamline tracing method. The streamline 11 are combined into a flow surface to obtain the second and third stage compression surfaces 8 of the bulge-shaped inlet.

[0051] 9. Please refer to Figure 3 and Figure 4 As shown, the lip cover 4 is designed based on the lip coordinate. The lip cover 4 adopts a swept-back design, which causes the low-energy flow to be displaced to both sides. The starting point A' of the second-stage cone surface 6 of the virtual flow field is projected onto the inlet surface of the air intake, and the projection point is denoted as A”. With A” as the center, a circle is drawn that is tangent to the leading edge profile of the lip cover at the center point M of the leading edge of the lip cover. The radius of the circle A”M is denoted as R = h. c +h1, the distance from any point on the leading edge profile other than the center point M to A” is less than R; the inner profile of the lip cover 4 is compressed inward by 2°, and the side plate of the lip cover 4 is deflected inward by 4°; three identical venting slits 16 are opened near the shock wave 15 reflection point on the inner surface of the lip cover 4, with a spanwise length c = 100 mm, a width d = 2 mm, and a spacing e = 10 mm between each venting slit.

[0052] Please refer to Figure 1 and Figure 3As shown, a high-pressure ratio long-body hypersonic air intake is obtained through the above-mentioned air intake design method, including: a first-stage planar compression surface 5, a bulging-shaped second and third-stage compression surfaces 8 extending rearward from the first-stage planar compression surface 5, and a lip cover 4 located above the bulging-shaped second and third-stage compression surfaces 8. The lip cover 4 adopts a swept-back design, with the inner surface of the lip cover 4 compressed inward at a certain angle, and the side plate of the lip cover 4 compressed inward at a certain angle. Three venting slits 16 are provided on the lip cover 4 near the throat of the air intake. The second and third stage compression surfaces 8 of the intake duct adopt a bulge-shaped design, which, compared with the traditional compression surface design, can exclude low-energy flow in the boundary layer, effectively prevent low-energy flow from entering the intake duct, improve the self-starting performance of the intake duct, and reduce the aerodynamic drag of the intake duct. The lip cover 4 adopts a swept-back design, with the side plates deflected inward to induce lateral pressure shock waves, thereby compressing the airflow. Compared with the traditional design, it improves the compression capacity of the intake duct. Multiple venting slots 16 are opened on the lip cover 4, and the low-energy flow in the boundary layer is discharged from the venting slots, effectively preventing throat blockage or even intake duct failure.

Claims

1. A design method for a high-pressure-ratio long-forehead hypersonic inlet, characterized in that, Includes the following steps: S1 determines the three-stage compression surface type of the inlet based on the requirements of the inlet's capture flow rate and compression amount. The first stage compression surface is planar shock wave compression, the second stage compression surface is conical shock wave compression, and the third stage compression surface is isentropic compression. The corresponding virtual flow field second-stage half-cone angle and third-stage compression angle are given. S2 Given the design Mach number and flight angle of attack, solve the plane oblique shock wave formula to obtain the Mach number, shock wave angle and density of the airflow behind the first-stage plane shock wave; S3 calculates the inlet capture area using the flow formula based on the Mach number, shock angle, and density of the airflow behind the first-stage planar shock wave, and then calculates the inlet capture height using the inlet capture area. The first-stage planar shock wave does not enter the lip of the lip mask under design conditions. Given a lag angle, which is the angle between the first-stage planar shock wave and the straight line connecting the starting point of the first-stage compression surface and the lip mask, the lip coordinates are calculated based on the shock angle of the first-stage planar shock wave, the inlet capture height, the lag angle, and the coordinates of the starting point of the first-stage compression surface. S4 solves the formula for the conical shock wave based on the Mach number of the airflow behind the first-stage planar shock wave and the half-cone angle of the second-stage virtual flow field, thus obtaining the Mach number and shock wave angle of the airflow behind the second-stage conical shock wave. The conical shock wave of the second-stage conical surface of the virtual flow field and the shock wave of the third-stage compression surface of the virtual flow field are both close to the lip of the lip mask under the design state. The axial position of the virtual conical surface is determined. The virtual conical surface is located below the first-stage compression surface. Given the height of the axis of the second-stage conical surface of the virtual flow field from the first-stage compression surface, the starting point of the second-stage conical surface of the virtual flow field is calculated. S5 divides the compression angle of the third-level compression surface of the virtual flow field into several equal parts, and the isentropic compression wave is correspondingly divided into several equal parts. Based on the method of characteristics, S6 calculates the profiles of the second-level cone surface and the third-level compression surface of the virtual flow field, and determines the coordinates of the intersection points of several isentropic compression waves after the starting point of the third-level compression surface of the virtual flow field is equally divided with the third-level compression surface of the virtual flow field. S7 Keeps the starting point of the third-level compression surface of the virtual flow field unchanged, gives the compression wave amplification factor, and enlarges the coordinates of the intersection point in step S6 proportionally according to the compression wave amplification factor coefficient. Connects the proportionally enlarged coordinate points in sequence to obtain the profile of the third-level compression surface of the virtual flow field. S8 uses the virtual conical shock wave flow field determined in the above steps as the virtual conical shock wave surface for designing the inlet compression surface, solves the intersection line of the first-stage compression surface and the virtual conical shock wave surface, selects several discrete points on the first-stage compression surface and the virtual conical shock wave surface, and uses the streamline tracing method to continuously trace the streamlines of the above discrete points in the virtual conical shock wave flow field, and forms the streamlines into a flow surface to obtain the bulge-shaped second and third-stage compression surfaces of the inlet; The S9's lip cover is designed based on lip-mouth coordinates, and the lip cover adopts a swept-back design to complete the air intake design.

2. The intake duct design method according to claim 1, characterized in that: The lip cover has several venting slits.

3. The intake duct design method according to claim 2, characterized in that: The venting slits are all the same size and are located at the shock wave reflection point on the inner surface of the lip mask near the throat.

4. The intake duct design method according to claim 1, characterized in that: The lag angle ranges from 1 to 2°.

5. The intake duct design method according to claim 1, characterized in that: The compression wave amplification factor ranges from 1.3 to 1.

4.

6. The intake duct design method according to claim 1, characterized in that: Step S9 includes: projecting the starting point of the second-stage cone surface of the virtual flow field onto the inlet surface of the air intake, and drawing a circle with the projection point as the center, which is tangent to the leading edge profile of the lip cover at the center point of the leading edge of the lip cover. The distance from any point on the leading edge profile of the lip cover, except for the center point, to the projection point is less than the radius of the circle.

7. The intake duct design method according to claim 1, characterized in that: The inner surface of the lip cover is compressed inward.

8. The intake duct design method according to claim 7, characterized in that: The compression angle range of the inner surface of the lip cover when compressed inward is 2 to 4 degrees.

9. The intake duct design method according to claim 1, characterized in that: The lip cover side panels are compressed inward.

10. A high-pressure ratio long forebody hypersonic inlet obtained by the inlet design method according to any one of claims 1-9, characterized in that, include: The first-stage compression surface, the bulging compression surface extending backward from the first-stage compression surface, and the lip cover located above the bulging compression surface, wherein the bulging compression surface is designed based on a conical shock wave virtual flow field, the conical shock wave virtual flow field includes a virtual flow field second-stage conical surface and a virtual flow field third-stage compression surface; the lip cover adopts a swept-back design, with the inner surface of the lip cover compressed inward at a certain angle, and the side plate of the lip cover compressed inward at a certain angle.

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