Shortening design method for high-speed inner turning inlet duct based on virtual center body

Abstract

The application provides a high-speed internal turning inlet shortening design method based on a virtual center body, which comprises the following steps: step 1, designing a virtual center body reference flow field; step 2, designing a capture profile; step 3, determining an internal turning inlet profile by using a stream line tracking method; step 4, setting a blunted leading edge; step 5, optimizing the internal turning inlet flow field; and step 6, scaling the virtual center body internal turning inlet in proportion according to actual capture flow requirements. The method proposes the concept of a virtual center body, and introduces the idea of a variable center body in order to weaken the intensity of reflected shock waves, thereby solving the problem of strong coupling between shock wave angle and inlet length in the previous internal turning inlet design method. Compared with the traditional internal turning inlet shortening method, the method can shorten the inlet length and improve the total pressure recovery coefficient of the throat under the condition of the same capture flow.

Description

Technical Field

[0001] This invention relates to the design of an internal rotating air intake, specifically a method for shortening a high-speed internal rotating air intake based on a virtual center body. Background Technology

[0002] In recent years, the development of high Mach number (Ma>5) aircraft has become a key research direction in the aerospace field. Among these, the air intake needs to provide the engine with a high-quality, stable, and uniform compression flow field, and its performance directly determines the success or failure of the entire aircraft development. Internal rotating air intakes, due to their advantages such as high compression efficiency, small size, low external drag, and good resistance to back pressure, are increasingly widely used in high Mach number aircraft. However, with the increase of design Mach number, the internal turn-around intake designed using traditional methods faces four major bottlenecks under high Mach number conditions: length, size, viscosity, and drag. First, the incident shock wave angle is relatively small, limiting the compression efficiency and forcing designers to lengthen the channel to compensate for insufficient compression. Second, when the intake length is large, matching it with the fuselage will increase the overall size of the fuselage, which in turn will lead to a significant increase in the overall mass, structural complexity, and thermal protection requirements of the aircraft. Third, the long channel brings an excessively large wetted area, resulting in significant viscous friction and boundary layer thickening effects, and a decrease in the total pressure recovery coefficient. Fourth, when the intake is lengthened in sync with the fuselage, the wetted area, boundary layer, and interference length all increase together, which will lead to a sharp increase in drag.

[0003] Regarding the shortening of internal rotary inlets, Sun Bo et al. designed a high-speed inlet aerodynamic configuration for Mach 7 based on a truncated Busemann baseline flow field. They also conducted numerical simulations and experimental verification of this configuration. The results showed that the shortened inlet still maintained high performance, but shock wave boundary layer interference within the inlet still caused significant energy loss. In 2012, Nan Xiangjun et al. from Nanjing University of Aeronautics and Astronautics introduced the concept of an unconventional variable center body and designed a novel internal contraction basic flow field. This weakened the reflected shock wave into a series of weak compression waves, aiming to reduce flow separation at the inlet shoulder while maintaining compression efficiency. However, this scheme inevitably increases in length under high Mach number conditions.

[0004] Furthermore, under high Mach number conditions, aircraft face extreme aerodynamic and thermal environments during flight, particularly at the leading edge of the air intake. Airflow stagnation can cause ablation points, damaging the intake structure and posing a significant challenge to the heat resistance of materials and structures. Due to this thermal protection requirement, the inner-turn intake also needs a passivated leading edge with a large radius. The passivated, off-board shock wave can generate a gaseous thermal insulation layer on the wall surface, effectively isolating the high-temperature gas from direct contact with the wall, thereby suppressing ablation. The passivated leading edge alters the flow field structure, increasing overflow and generating a thick low-energy flow, significantly impacting the aerodynamic performance of the air intake.

[0005] To address these issues, this invention proposes a method for shortening inward-rotating inlet ducts at hypersonic speeds. It introduces the concept of a "virtual central body," where a capturing section surrounds the central body within an axisymmetric reference flow field. This decouples the lip length from the incident shock wave angle, thereby shortening the inlet duct length. The radius of the "virtual central body" is adjusted to ensure the incident shock wave is close to the inlet. Simultaneously, the radius of the central body is gradually increased to facilitate the construction of a convex inlet duct profile, thereby weakening the intensity of the reflected shock wave and suppressing boundary layer interference and separation at the duct shoulder.

[0006] Compared to traditional inward-rotating air intake designs, this invention offers a larger capture cross-sectional area, thereby increasing its airflow capture capability. To achieve the same capture flow rate as traditional air intake configurations, the shortened lip of the air intake configuration can be scaled proportionally, resulting in a correspondingly shorter air intake configuration size. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of strong coupling between shock wave angle and inlet length, and significant viscous loss due to excessively long channels, in traditional internal rotating inlet designs under high Mach number conditions. It provides a shortening design method for high-speed internal rotating inlets based on a virtual center body. By introducing the concept of a "virtual center body," the shock wave angle and inlet lip length are decoupled. Furthermore, by adding a blunt leading edge, shock wave contact with the inlet is achieved, significantly shortening the inlet length while improving the throat total pressure recovery coefficient and compression efficiency.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for shortening a high-speed internal intake duct based on a virtual center body includes the following steps:

[0010] Step 1: Design the reference flow field of the virtual central inlet intake duct;

[0011] Step 2: Design the intake duct capture profile;

[0012] Step 3: Use the streamline tracing method to determine the profile of the internal rotating air intake;

[0013] Step 4: Design the passivation leading edge;

[0014] Step 5: Flow field optimization;

[0015] Step 6: Scale the virtual central body intake duct proportionally according to the actual capture flow requirements.

[0016] As a preferred embodiment, step 1 specifically comprises:

[0017] Step 1.1: Set the design conditions: Altitude H in Mach number Ma inAngle of attack α in The subscript "in" indicates the air intake.

[0018] Step 1.2: Given a cubic spline function model of the compression law along the inner intake wall: This cubic spline function is derived from the interval [x s ,x m ] and [x m ,x t The expression is constructed by two cubic polynomials on the given endpoints (M). s M t and the first derivative (tanθ) s ,tanθ t ), combined with intermediate control points (x) m M m By taking the function value of the spline function and the continuity conditions of the first and second derivatives, a system of linear equations containing eight equations is established. Solving this system uniquely determines the coefficients of each term of the spline function, and thus obtains the complete distribution law of the Mach number M(x).

[0019] x s and x t These are the x-coordinates of the beginning and end of the reference flow field, respectively; M s The Mach number at the starting point is calculated based on the airflow deflection angle δ at the starting point; θ s M is the inclination angle of the Mach number distribution curve at the starting point, used to control the degree of curvature of the incident shock wave; t Let x be the point t The Mach number at θ is used to control the Mach number at the outlet of the reference flow field and is given according to the design requirements of the reference flow field; t Let x be the point t The inclination angle of the Mach number distribution curve is used to adjust the contraction ratio within the reference flow field; x m and M m Here, x represents the coordinates and Mach number of the control point at the midpoint of the reference flow field, respectively. m and M m The following formula is used to determine the distribution of the contraction ratio inside and outside the reference flow field;

[0020] In the formula, φ and These are the adjustment parameters for the location of the control point in the middle of the condition and the Mach number, respectively, with a value range of [0,1].

[0021] Step 1.3: Virtual Central Body Design: Establish a coordinate system at the origin, with the horizontal axis x representing the lateral distance coordinate of the reference flow field and the vertical axis y representing the longitudinal distance coordinate; the virtual central body's x-axis coordinate at overflow outlet B1 is x c The Y-axis coordinate is R c The starting angle is θ c The X-axis coordinate at the throat C1 is xt The Y-axis coordinate is R t The slope y' is 0; before the overflow outlet B1, the radius of the central body is R. c Starting from overflow outlet B1, the radius of the central body gradually increases, which can be described by a cubic equation in two variables:

[0022] ,

[0023] ,

[0024] In the formula, a, b, c, and d are the coefficients of the equation:

[0025] ,

[0026] ,

[0027] ,

[0028] ,

[0029] Step 1.4: Based on the function model of the compression law along the wall of the internal inlet given in Step 1.2 and the virtual center body shape designed in Step 1.3, the axisymmetric internal contraction flow field is obtained by using the method of characteristics, which serves as the reference flow field for the internal inlet. The method of characteristics refers to solving the system of equations consisting of the characteristic line equation and the compatibility equation of two-dimensional supersonic inviscid flow using the second-order Euler prediction and correction method.

[0030] As a preferred embodiment, step 2 specifically comprises:

[0031] Step 2.1: Based on the axisymmetric reference flow field designed in Step 1, design a capture profile at the inlet of the reference flow field. This capture profile is internally tangent to the inlet of the reference flow field and also internally tangent to or contains a virtual central body.

[0032] As a preferred embodiment, step 3 specifically comprises:

[0033] Step 3.1: Discretize the captured profile into several nodes A1A2A distributed at equal angles. 3…… A n A streamline is emitted from any point and enters the interior of the reference flow field until the reference flow field reflects the shock wave. The envelope formed by the streamlines emitted from the discrete point set on the capturing profile constitutes the capturing flow tube. Finally, the initial aerodynamic profile of the inner intake duct is obtained by intercepting the capturing flow tube with the incident shock wave from the reference flow field. A 11 A 21 A 31…… A n1 This refers to the leading edge profile of the air intake.

[0034] As a preferred embodiment, step 4 specifically comprises:

[0035] Step 4.1: Determine the tangent vector of the leading edge profile of the inward-turning air intake. Local external normal vector and vectors , A defined plane.

[0036] Step 4.2: Given the fillet radius R and the lip cover outward expansion angle θ, generate the passivation plane curve.

[0037] Step 4.3: Rotate the generated passivation plane curve so that the normal vector of the plane containing the curve is aligned with the plane. The diameter direction of the overlapping, passivated section curve is the same as... The cross-sections of the passivated leading edge are obtained by overlapping.

[0038] Step 4.4: Repeat steps 4.1 to 4.3 at each point on the leading edge profile of the inner intake duct to obtain the blunted leading edge surface of the intake duct.

[0039] As a preferred embodiment, step 5 specifically comprises:

[0040] Step 5.1: Determine if the incident shock wave in the reference flow field is close to the target. Virtual central body radius R c Increasing the angle of the incident shock wave will cause it to penetrate into the inlet duct under three-dimensional operating conditions; the use of inlet duct passivation will inevitably increase the angle of the incident shock wave, causing it to hit the outside of the inlet duct. These two factors work together to bring the incident shock wave closer to the inlet lip. If the incident shock wave hits the inlet lip, convergence is considered complete, and the correction ends. If the incident shock wave does not hit the lip, the following two situations exist:

[0041] Case 1: If the incident shock wave from the reference flow field hits the inside of the air intake, then:

[0042] Method 1 is to reduce the initial radius R of the virtual centroid in step 1.3. c Method two involves changing the shape of the capture line in step 2 to bring it closer to the virtual center body. Method one and method two can also be performed simultaneously.

[0043] Case 2: If the incident shock wave from the reference flow field hits the outside of the air intake, then:

[0044] Method 1 is to increase the initial radius R of the virtual centroid in step 1.3. c Method two involves changing the shape of the capture line in step 2, moving it away from the central body. Method one and method two can also be performed simultaneously.

[0045] Step 5.2: Repeat step 5.1 until the incident shock wave of the reference flow field is in contact with the target.

[0046] Step 5.3: Based on step 5.2, the initial angle θ of point B1 in step 1.3 can be adjusted. c This allows for control of the virtual center body's profile B2C2, optimizing the backflow field of the reflected shock wave after the addition of a blunted leading edge. Ultimately, a high-speed inward-rotating intake based on a virtual center body is obtained.

[0047] As a preferred embodiment, step 6 specifically comprises:

[0048] Step 6.1: Scale the virtual central intake duct proportionally to the actual capture flow requirements. Scaling factor S c The expression is as follows:

[0049]

[0050] in ρ is the mass flow rate required by the actual engine. ∞ For the free flow density, V ∞ A0 represents the free flow velocity, and A0 represents the capture cross-sectional area of ​​the intake obtained in step 5.

[0051] Step 6.2: Scale the intake duct proportionally along three dimensions to obtain a high-speed inward-turning intake duct that meets the requirements. The scaling equations are as follows:

[0052]

[0053] Where X1, Y1, and Z1 are the three-dimensional coordinates of the high-speed internal intake duct that meets the requirements. X0, Y0, and Z0 are the three-dimensional coordinates of the internal intake duct obtained in step 5.

[0054] The beneficial effects of this invention are as follows: By introducing the concept of a "virtual central body," that is, setting a capture profile surrounding the central body in an axisymmetric reference flow field, the length of the inlet lip is decoupled from the incident shock wave angle, thereby significantly shortening the inlet length under the same capture flow rate. Simultaneously, combined with a blunted leading edge design, the shock wave contact is further synergistically adjusted. Through the design of a variable central body radius, the intensity of the reflected shock wave can be effectively weakened, shoulder flow separation can be suppressed, and the total pressure recovery coefficient and compression efficiency of the throat can be improved. Finally, through proportional scaling, a high-performance, shortened, inward-turning inlet configuration that meets actual flow requirements can be achieved. Attached Figure Description

[0055] Figure 1 This invention relates to the reference flow field structure of a high-speed internal intake duct based on a virtual central body;

[0056] Figure 2 This is a schematic diagram of the capture profile of the high-speed internal rotating intake based on the virtual center body of the present invention;

[0057] Figures 3(a) and 3(b) are schematic diagrams of the streamline tracing method of the high-speed internal turning intake based on the virtual center body of the present invention. Figure 3(a) shows the intake surface generated by the streamlines emitted from the tracking and capturing profile; Figure 3(b) shows the flow trajectory of the streamlines emitted from A3 in the reference flow field.

[0058] Figure 4 This is a schematic diagram of the design principle of the passivated leading edge of the high-speed internal rotating intake based on the virtual center body of the present invention;

[0059] Figure 5 This is a design result diagram of the high-speed internal rotation intake based on the virtual center body of the present invention;

[0060] Where 1 represents the incoming streamline, 2 is the virtual center body, 3 is the incident shock wave of the reference flow field, 4 is the reference flow field profile, 5 is the reflected shock wave of the reference flow field, 6 is the reference flow field outlet, 7 is the capture profile, 8 is the reference flow field inlet, 9 is the leading edge profile of the internal inlet, 10 is the internal inlet outlet, 11 is the internal inlet surface profile, and 12 is the vector. , The defined plane, 13 is the passivation plane curve, 14 is the tangential vector of the lip cover outward expansion direction, 15 is the incident shock wave after adding the passivation leading edge, 16 is the reflected shock wave after adding the passivation leading edge, and 17 is the central axis of the virtual central body.

[0061] ① represents the incident shock wave dependent region, ② represents the isentropic compression region, ③ represents the reflected shock wave dependent region, and ④ represents the rectification region. Detailed Implementation

[0062] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0063] Example 1

[0064] A method for shortening a high-speed internal intake duct based on a virtual center body includes the following steps:

[0065] Step 1: Design the reference flow field of the virtual central inlet intake duct;

[0066] Step 2: Design the intake duct capture profile;

[0067] Step 3: Use the streamline tracing method to determine the profile of the internal rotating air intake;

[0068] Step 4: Design the passivation leading edge;

[0069] Step 5: Flow field optimization;

[0070] Step 6: Scale the virtual central body intake duct proportionally according to the actual capture flow requirements.

[0071] Example 2

[0072] A high-speed internal intake duct shortening design method based on a virtual center body differs from Example 1 in that:

[0073] Step 1 specifically involves:

[0074] Step 1.1: Set the design conditions: Altitude H in Mach number Ma in Angle of attack α in The subscript "in" indicates the air intake.

[0075] Step 1.2: Given a cubic spline function model of the compression law along the inner intake wall: This cubic spline function is derived from the interval [x s ,x m ] and [x m ,x t The expression is constructed by two cubic polynomials on the given endpoints (M). s M t and the first derivative (tanθ) s ,tanθ t ), combined with intermediate control point (x) m M m By taking the function value of the spline function and the continuity conditions of the first and second derivatives, a system of linear equations containing eight equations is established. Solving this system uniquely determines the coefficients of each term of the spline function, and thus obtains the complete distribution law of the Mach number M(x).

[0076] x s and x t These are the x-coordinates of the beginning and end of the reference flow field, respectively; M s The Mach number at the starting point is calculated based on the airflow deflection angle δ at the starting point; θ s M is the inclination angle of the Mach number distribution curve at the starting point, used to control the degree of curvature of the incident shock wave; t Let x be the point t The Mach number at θ is used to control the Mach number at the outlet of the reference flow field and is given according to the design requirements of the reference flow field; t Let x be the point t The inclination angle of the Mach number distribution curve is used to adjust the contraction ratio within the reference flow field; x m and M m Here, x represents the coordinates and Mach number of the control point at the midpoint of the reference flow field, respectively. m and M mThe following formula is used to determine the distribution of the contraction ratio inside and outside the reference flow field;

[0077]

[0078] In the formula, φ and These are the adjustment parameters for the location of the control point in the middle of the condition and the Mach number, respectively, with a value range of [0,1].

[0079] Step 1.3: Virtual Central Body Design: such as Figure 1 As shown, a coordinate system is established at the origin, with the horizontal axis x representing the lateral distance coordinate of the reference flow field and the vertical axis y representing the longitudinal distance coordinate; the virtual center body 2 has an x-axis coordinate of x at the overflow outlet B1. c The Y-axis coordinate is R c The starting angle is θ c The X-axis coordinate at the throat C1 is x t The Y-axis coordinate is R t The slope y' is 0; before the overflow outlet B1, the radius of the central body is R. c Starting from overflow outlet B1, the radius of the central body gradually increases, which can be described by a cubic equation in two variables:

[0080] ,

[0081] ,

[0082] In the formula, a, b, c, and d are the coefficients of the equation:

[0083] ,

[0084] ,

[0085] ,

[0086] ,

[0087] Step 1.4: Based on the function model of the friction compression law of the inner inlet wall given in Step 1.2 and the virtual center body shape designed in Step 1.3, the axisymmetric inner contraction flow field is obtained using the method of characteristics, which serves as the reference flow field for the inner inlet. Figure 1 As shown, regions ① and ② are designed based on the compression law along the inner intake wall given in step 1.2, while regions ③ and ④ are designed based on the virtual center body shape line designed in step 1.3. The characteristic line method refers to solving a system of equations consisting of the characteristic line equation and the compatibility equation for two-dimensional supersonic inviscid flow using the second-order Euler prediction and correction method.

[0088] Step 2 specifically involves:

[0089] Step 2.1: As Figure 2 As shown, based on the axisymmetric reference flow field designed in step 1, a capture profile 7 is designed at the reference flow field inlet 8. The capture profile is internally tangent to the reference flow field inlet 8 and also internally tangent to or contains the virtual central body 2.

[0090] Step 3 specifically involves:

[0091] Step 3.1: As shown in Figures 3(a) and 3(b), the capture line 7 is discretized into several nodes A1A2A distributed at equal angles. 3…… A n A streamline is emitted from any point and enters the interior of the reference flow field until the reference flow field reflects the shock wave 5. The envelope surface formed by the streamlines emitted from the discrete point set on the capture profile 7 constitutes the capture flow tube. Finally, the capture flow tube is intercepted by the incident shock wave 3 of the reference flow field to obtain the inner inlet duct profile 11, A. 11 A 21 A 31…… A n1 This refers to the leading edge profile 9 of the internal intake duct.

[0092] Step 4 specifically involves:

[0093] Step 4.1: Determine the tangent vector of the leading edge profile 9 of the internal intake duct. Local external normal vector and vectors , Defined plane 12;

[0094] Step 4.2: Given the fillet radius R and the lip cover outward expansion angle θ, generate the passivation plane curve 13;

[0095] Step 4.3: As Figure 4 As shown, the generated passivation plane curve 13 is rotated so that the normal vector of the plane containing the curve is aligned with the plane of passivation. The diameter direction of the overlapping, passivated section curve is the same as... The cross-sections of the passivated leading edge are obtained by overlapping.

[0096] Step 4.4: Repeat steps 4.1 to 4.3 at each point on the leading edge profile 9 of the inner intake duct to obtain the blunted leading edge surface of the intake duct.

[0097] Step 5 specifically involves:

[0098] Step 5.1: Determine if the incident shock wave 3 in the reference flow field is close to the target: radius R of the virtual central body 2 cIncreasing the angle of the reference flow field incident shock wave 3 will cause it to penetrate into the intake duct under three-dimensional operating conditions. Using a blunted leading edge for the intake duct will inevitably increase the angle of the reference flow field incident shock wave 3, causing it to hit the outside of the intake duct. The combined effect of these two factors can bring the reference flow field incident shock wave 3 closer to the lip position. If the reference flow field incident shock wave 3 hits the intake duct lip, it is considered convergence, and the correction ends. If the reference flow field incident shock wave 3 does not hit the lip, the following two situations exist:

[0099] Case 1: If the incident shock wave 3 from the reference flow field hits the inside of the air intake, then:

[0100] Method 1 is to reduce the initial radius R of the virtual central body 2 in step 1.3. c Method 2 is to change the shape of the capture line 7 in step 2 so that the capture line 7 is closer to the virtual center body 2. Method 1 and Method 2 can also be performed simultaneously.

[0101] Case 2: If the incident shock wave 3 from the reference flow field hits the outside of the air intake, then:

[0102] Method 1 is to increase the initial radius R of the virtual central body 2 in step 1.3. c Method 2 is to change the shape of the capture line 7 in step 2, so that the capture line 7 is far away from the virtual center body 2. Method 1 and Method 2 can also be performed simultaneously.

[0103] Step 5.2: Repeat step 5.1 until the incident shock wave 3 of the reference flow field is in contact with the target flow field.

[0104] Step 5.3: Based on step 5.2, the initial angle θ of point B1 in step 1.3 can be adjusted. c This allows for control of the virtual central body's profile B2C2, optimizing the backflow field of the reflected shock wave 16 after the addition of the blunted leading edge. Ultimately, a high-speed internal turning intake based on a virtual central body is obtained. Figure 5 As shown.

[0105] Step 6 specifically involves:

[0106] Step 6.1: Based on the actual capture flow requirements, scale the virtual central body's intake duct proportionally, with a scaling factor S. c The expression is as follows:

[0107]

[0108] in ρ is the mass flow rate required by the actual engine. ∞ For the free flow density, V ∞ Where A0 is the free flow velocity, and A0 is the capture cross-sectional area of ​​the intake obtained in step 5;

[0109] Step 6.2: Scale the intake duct proportionally along three dimensions to obtain a high-speed inward-turning intake duct that meets the requirements. The scaling equations are as follows:

[0110]

[0111] Where X1, Y1, and Z1 are the three-dimensional coordinates of the high-speed internal intake that meets the requirements, and X0, Y0, and Z0 are the three-dimensional coordinates of the internal intake obtained in step 5.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for shortening a high-speed internal intake duct based on a virtual center body, characterized in that, Includes the following steps: Step 1: Design the reference flow field of the virtual central inlet intake duct; Step 2: Design the intake duct capture profile; Step 3: Use the streamline tracing method to determine the profile of the internal rotating air intake; Step 4: Design the passivation leading edge; Step 5: Flow field optimization; Step 6: Scale the virtual central body intake duct proportionally according to the actual capture flow requirements; Step 1 specifically involves: Step 1.1: Set the design conditions: Altitude H in Mach number Ma in Angle of attack α in The subscript "in" indicates the air intake. Step 1.2: Given a cubic spline function model of the compression law along the inner intake wall: This cubic spline function is derived from the interval [x s ,x m ] and [x m ,x t The expression is constructed by two cubic polynomials on the given endpoints (M). s M t and the first derivative (tanθ) s ,tanθ t ), combined with intermediate control points (x) m M m By taking the function value of the spline function and the continuity conditions of the first and second derivatives, a system of linear equations containing eight equations is established. Solving this system uniquely determines the coefficients of each term of the spline function, and thus obtains the complete distribution law of the Mach number M(x). x s and x t These are the x-coordinates of the beginning and end of the reference flow field, respectively; M s The Mach number at the starting point is calculated based on the airflow deflection angle δ at the starting point. θ s M is the inclination angle of the Mach number distribution curve at the starting point, used to control the degree of curvature of the incident shock wave; t Let x be the point t The Mach number at the outlet of the reference flow field is used to control the Mach number at the outlet of the reference flow field and is given according to the design requirements of the reference flow field. θ t Let x be the point t The inclination angle of the Mach number distribution curve is used to adjust the contraction ratio within the reference flow field; x m and M m Here, x represents the coordinates and Mach number of the control point at the midpoint of the reference flow field, respectively. m and M m The following formula is used to determine the distribution of the contraction ratio inside and outside the reference flow field; In the formula, φ and These are the adjustment parameters for the location of the control point in the middle of the condition and the Mach number, respectively, with a value range of [0,1]. Step 1.3: Virtual Central Body Design: Establish a coordinate system at the origin, with the horizontal axis x representing the lateral distance coordinate of the reference flow field and the vertical axis y representing the longitudinal distance coordinate; the virtual central body's x-axis coordinate at overflow outlet B1 is x c The Y-axis coordinate is R c The starting angle is θ c The X-axis coordinate at the throat C1 is x t The Y-axis coordinate is R t， The slope y' is 0; before the overflow outlet B1, the radius of the central body is R. c Starting from overflow outlet B1, the radius of the central body gradually increases, which can be described by a cubic equation in two variables: , , In the formula, a, b, c, and d are the coefficients of the equation: , , , , Step 1.4: Based on the function model of the compression law along the wall of the internal inlet given in Step 1.2 and the virtual center body shape designed in Step 1.3, the axisymmetric internal contraction flow field is obtained by using the method of characteristics, which serves as the reference flow field for the internal inlet. The method of characteristics refers to solving the system of equations consisting of the characteristic line equation and the compatibility equation of two-dimensional supersonic inviscid flow using the second-order Euler prediction and correction method.

2. The high-speed internal intake duct shortening design method based on a virtual center body according to claim 1, characterized in that, Step 2 specifically involves: Step 2.1: Based on the axisymmetric reference flow field designed in Step 1, design a capture profile at the inlet of the reference flow field. The capture profile is internally tangent to the inlet of the reference flow field and may also contain a virtual central body.

3. The high-speed internal intake duct shortening design method based on a virtual center body according to claim 1, characterized in that, Step 3 specifically involves: Step 3.1: Discretize the captured profile into several nodes A1A2A distributed at equal angles. 3…… A n A streamline is emitted from any point and enters the interior of the reference flow field until the reference flow field reflects the shock wave. The envelope formed by the streamlines emitted from the discrete point set on the capture profile constitutes the capture flow tube. Finally, the incident shock wave from the reference flow field is used to intercept the capture flow tube to obtain the profile of the inner inlet. A 11 A 21 A 31…… A n1 This refers to the leading edge profile of the internal intake duct.

4. The high-speed internal intake duct shortening design method based on a virtual center body according to claim 1, characterized in that, Step 4 specifically involves: Step 4.1: Determine the tangent vector of the leading edge profile of the inward-turning air intake. Local external normal vector and vectors , A defined plane; Step 4.2: Given the fillet radius R and the lip cover expansion angle θ, generate the passivation plane curve; Step 4.3: Rotate the generated passivation plane curve so that the normal vector of the plane containing the curve is aligned with the plane. The diameter direction of the overlapping, passivated section curve is the same as... The cross-sections of the passivated leading edge are obtained by overlapping. Step 4.4: Repeat steps 4.1 to 4.3 at each point on the leading edge profile of the inner intake duct to obtain the blunted leading edge surface of the intake duct.

5. The high-speed internal intake duct shortening design method based on a virtual center body according to claim 1, characterized in that, Step 5 specifically involves: Step 5.1: Determine if the incident shock wave in the reference flow field is close to the target: virtual centroid radius R c Increasing the angle of the incident shock wave will cause the reference flow field incident shock wave to penetrate into the intake duct under three-dimensional operating conditions. Using a blunted leading edge for the intake duct will inevitably increase the angle of the incident shock wave, causing it to hit the outside of the intake duct. The combined effect of these two factors can bring the incident shock wave closer to the lip of the intake duct. If the incident shock wave hits the lip, it is considered convergent, and the correction ends. If the incident shock wave does not hit the lip, the following two situations exist: Case 1: If the incident shock wave from the reference flow field hits the inside of the air intake, then: Method 1 is to reduce the initial radius R of the virtual centroid in step 1.

3. c Method 2 is to change the shape of the capture line in step 2 so that the capture line is closer to the virtual center body. Method 1 and Method 2 can also be performed simultaneously. Case 2: If the incident shock wave from the reference flow field hits the outside of the air intake, then: Method 1 is to increase the initial radius R of the virtual centroid in step 1.

3. c Method 2 is to change the shape of the capture line in step 2 so that the capture line is far away from the virtual center body. Method 1 and Method 2 can also be performed simultaneously. Step 5.2: Repeat step 5.1 until the incident shock wave of the reference flow field fits the nozzle; Step 5.3: Based on step 5.2, the initial angle θ of point B1 in step 1.3 can be adjusted. c This allows for the control of the virtual center body profile B2C2, optimization of the backflow field of the reflected shock wave after the addition of the blunted leading edge, and ultimately, the acquisition of a high-speed internal rotation intake based on the virtual center body.

6. The high-speed internal intake duct shortening design method based on a virtual center body according to claim 1, characterized in that, Step 6 specifically involves: Step 6.1: Based on the actual capture flow requirements, scale the virtual central body's intake duct proportionally, with a scaling factor S. c The expression is as follows: , in ρ is the mass flow rate required by the actual engine. ∞ For the free flow density, V ∞ Where A0 is the free flow velocity, and A0 is the capture cross-sectional area of ​​the intake obtained in step 5; Step 6.2: Scale the intake duct proportionally along three dimensions to obtain a high-speed inward-turning intake duct that meets the requirements. The scaling equations are as follows: , Where X1, Y1, and Z1 are the three-dimensional coordinates of the high-speed internal intake that meets the requirements, and X0, Y0, and Z0 are the three-dimensional coordinates of the internal intake obtained in step 5.

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