An S-shaped convergent-divergent nozzle with an adjustable cover plate and method

Abstract

An S-shaped convergent-divergent nozzle with an adjustable cover plate and a method thereof according to the present invention belong to the field of aero-engines; it includes an S-shaped convergent section, an open-hole divergent section and a jet control mechanism; a plurality of holes are opened on the upper and lower wall surfaces of the open-hole divergent section as ventilation holes; the jet control mechanism is connected to the ventilation holes of the open-hole divergent section, and the jet flow in the divergent section is adjusted by controlling the opening / closing of the ventilation holes. The jet control mechanism includes an upper cover plate, a lower cover plate, an upper control device and a lower control device; the upper control device and the lower control device are respectively connected to the upper cover plate and the lower cover plate, and the movement positions of the upper cover plate and the lower cover plate are controlled to complete the adjustment of the opening or closing state of the ventilation holes. The present invention solves the problem of flow instability caused by the interference between the shock wave boundary layer and the appearance of the double separation vortex system when the S-shaped convergent-divergent nozzle is in an over-expanded state by adopting the jet control mechanism, and ensures that the aerodynamic performance of the nozzle is not affected when it is in the designed state.

Description

Technical Field

[0001] The present invention belongs to the field of aeroengines, and particularly relates to an S-shaped convergent-divergent nozzle with an adjustable cover plate and a method thereof. Background Art

[0002] With the continuous deepening of the informatization level of modern warfare and the rapid development of detection technologies, the survival environment of fighter jets has become increasingly harsh. As the main infrared radiation and radar scattering source of an aircraft, the aeroengine tail nozzle urgently needs to reduce its infrared radiation intensity and radar scattering signal to enhance its stealth ability. Due to its special S-shaped and non-axisymmetric configuration, the S-shaped nozzle can block the internal high-temperature components, enhance the mixing of the internal and external flows, and greatly improve the stealth ability of the nozzle. However, future military aircraft have strict requirements for the power system. They not only require high stealth performance but also pursue higher aerodynamic efficiency. The conventional convergent configuration S-shaped nozzle can no longer meet the requirements. For future fighter jets covering subsonic, transonic, and supersonic flight envelopes, the exhaust system has a large range of variation in the pressure ratio drop (up to 10.0 at most), and in most operating conditions, the working pressure ratio of the exhaust system is greater than 5.0. Therefore, the engine exhaust system needs to use a convergent-divergent configuration, that is, an S-shaped convergent-divergent nozzle. However, when the S-shaped convergent-divergent nozzle is in an over-expanded state, due to the back pressure being higher than the pressure inside the nozzle, serious flow separation will occur. The flow separation inside the nozzle is mainly the boundary layer separation caused by the shock wave, and a double separation vortex system structure is also generated at the rear of the nozzle, affecting the stability of the flow inside the nozzle. The unstable flow may also cause asymmetric separation inside the nozzle, resulting in unexpected thrust deflection, seriously interfering with the control of the aircraft, and even causing the control to get out of control and fail. In the 27th issue of "Shock Waves" in 2017, pages 441-455, "Flow in a planar convergent-divergent nozzle", boundary layer bleeding is used to solve the problem of lateral loads caused by asymmetric separation in the over-expanded state of the nozzle, but this method will cause thrust loss and reduce the aerodynamic performance of the nozzle.

[0003] The prior art discloses a porous configuration that can control the off-design separation flow in the nozzle by promoting the stable separation of the exhaust gas and can provide obvious separation control. However, the presence of the porous structure will affect the flow of the nozzle in the design state, increase the flow loss, and cause unnecessary thrust loss. Therefore, the present invention designs a jet control mechanism, which can improve the unstable separation phenomenon of the nozzle in the over-expanded state while fully utilizing the energy of the exhaust gas flow and avoiding affecting the aerodynamic performance of the nozzle in the design state. Summary of the Invention

[0004] Technical Problems to be Solved

[0005] To avoid the deficiencies of the prior art, the present invention provides an S-shaped convergent-divergent nozzle with an adjustable cover plate and a method, which adopts a jet flow control mechanism (a movable upper / lower cover plate structure) to solve the problem of flow instability caused by the shock wave boundary layer interference and the appearance of the double separation vortex system structure when the S-shaped convergent-divergent nozzle is in an over-expanded state, and ensures that the aerodynamic performance of the nozzle in the designed state is not affected.

[0006] The technical solution of the present invention is: an S-shaped convergent-divergent nozzle with an adjustable cover plate, characterized in that: it includes an S-shaped convergent section, an opening-expanded section, and a jet flow control mechanism; the inlet of the S-shaped convergent section is installed in cooperation with the outlet of the engine turbine, and the connection between its outlet and the opening-expanded section forms the nozzle throat; a number of holes are opened on the upper and lower wall surfaces of the opening-expanded section as ventilation holes; the jet flow control mechanism is connected to the ventilation holes of the opening-expanded section, and the jet flow of the expanded section is adjusted by controlling the opening / closing of the ventilation holes.

[0007] A further technical solution of the present invention is: the jet flow control mechanism includes an upper cover plate, a lower cover plate, an upper control device, and a lower control device; the upper cover plate and the lower cover plate are respectively arranged on the outer sides of the upper and lower wall surfaces of the opening-expanded section, and a number of protrusions are arranged on their inner surfaces, and the protrusions and the ventilation holes on the opening-expanded section are complementary installation structures in one-to-one correspondence; the upper control device and the lower control device are respectively connected to the upper cover plate and the lower cover plate, and the moving positions of the upper cover plate and the lower cover plate are controlled to complete the adjustment of the opening or closing state of the ventilation holes.

[0008] A further technical solution of the present invention is: the holes on the upper wall surface and the lower wall surface of the opening-expanded section are symmetrically arranged, 4 to 6 rows of small holes are arranged at equal intervals along the axial direction of the opening-expanded section, and the interval is controlled between 0.1L and 0.12L, where L is the axial length of the opening-expanded section; 5 to 7 columns of small holes are arranged at equal intervals along the span direction, and the interval is controlled between 0.1W and 0.15W, where W is the radial cross-sectional width of the opening-expanded section.

[0009] A further technical solution of the present invention is: the ventilation holes on the upper and lower wall surfaces are symmetric with respect to the symmetry plane of the S-shaped convergent-divergent nozzle.

[0010] A further technical solution of the present invention is: the holes on the upper and lower wall surfaces are all cylindrical small holes, and the diameters of the small holes are the same, and the diameter range is 0.01W to 0.02W, and the opening positions are controlled between 0.1L and 0.9L of the upper and lower wall surfaces of the opening-expanded section.

[0011] A further technical solution of the present invention is: the upper cover plate and the lower cover plate are flat plate structures with the same structure, and the protrusions on their inner surfaces are cylindrical structures; the height of the cylinder is equal to the thickness of the nozzle wall surface, and the diameter is the same as the inner diameter of the cylindrical small hole of the opening-expanded section; the outer sides of the upper and lower cover plates are connected to the upper and lower control devices through connection reinforcing plates.

[0012] A further technical solution of the present invention is that: both the upper and lower control devices include a linear motor, a mover seat and a connecting rod. One end of the connecting rod is connected to the connecting reinforcement plate, and the other end is fixedly connected to the mover seat fixed on the linear motor. The linear motor is electrically connected to the controller, and the linear motor drives the connecting rod to move along the normal direction of the upper / lower wall surface of the opening expansion section, and at the same time drives the upper cover plate and the lower cover plate to move along the normal direction of the upper / lower wall surface, so as to control the on / off of the ventilation holes on the upper / lower wall surfaces.

[0013] A further technical solution of the present invention is that: the opening expansion section includes an opening upper wall surface, an opening lower wall surface and an unopened side wall surface. The opening upper wall surface and the opening lower wall surface respectively expand towards the upper side and the lower side of the nozzle, and the expansion angles are equal, and the angle change range is 10° to 25°. There is no expansion angle on the two side wall surfaces of the nozzle.

[0014] A further technical solution of the present invention is that: the S-shaped converging section is a double S-bend circular-to-square channel. The inlet of the S-shaped converging section is the inlet of the S-bend convergent-divergent nozzle, which is matched with the turbine outlet of the engine. The outlet of the S-shaped converging section is the nozzle throat surface. The radial cross-sectional shape of the entire converging section changes from a circle to a quasi-rectangle from the inlet to the throat surface, and the area gradually converges.

[0015] A jet flow control method for an S-bend convergent-divergent nozzle with adjustable cover plates, which is characterized in that the specific steps are as follows:

[0016] Step 1: The monitoring system monitors the pressure drop ratio of the nozzle to determine the flow state of the nozzle.

[0017] Step 2: The controller receives the transmission signal from the engine monitoring system and outputs a control signal to the upper and lower control devices.

[0018] Step 3: The upper and lower control devices adjust the moving positions of the upper / lower cover plates.

[0019] When it is detected that the pressure drop ratio of the nozzle is lower than the designed pressure drop ratio, that is, the nozzle is in an over-expanded state, the upper / lower cover plates move outwards along the normal direction of the upper / lower wall surfaces of the opening expansion section to form a porous structure. When it is detected that the pressure drop ratio of the nozzle is equal to or greater than the designed pressure drop ratio, that is, the nozzle is in a designed state or an under-expanded state, the upper / lower cover plates move inwards along the normal direction of the upper / lower wall surfaces of the opening expansion section until the wall surface fits with the main board of the cover plate, and the porous structure disappears.

[0020] Beneficial effects

[0021] The beneficial effects of the present invention are as follows: For the S-bend convergent-divergent nozzle structure with an adjustable cover plate applying the technical solution of the present invention, when the nozzle is in an over-expanded state, the upper / lower cover plate is moved along the outer normal direction of the upper / lower wall surfaces of the opening expansion section by applying force through the upper / lower control device, forming a porous structure, so that a series of stable and vertically symmetric wave systems are generated inside the nozzle. Through the more gentle compression by the impact of the porous structure, the jet instability phenomenon caused by the unstable and asymmetric complex wave system appearing in the convergent-divergent nozzle is improved. When the nozzle is in the designed state, the upper / lower cover plate is moved along the inner normal direction of the upper / lower wall surfaces of the opening expansion section to fit the wall surface with the main board of the cover plate through the upper / lower control device, and the porous structure disappears, without affecting the aerodynamic performance of the nozzle in the designed state.

[0022] The technical difficulty of the present invention lies in that the design of the porous structure needs to be adjusted and matched according to the actual control effect required by the nozzle. The arrangement of the holes along the spanwise direction ensures that no holes are opened at the position of the side wall surface of the nozzle close to the non-expansion angle. The arrangement of the holes along the axial direction ensures that the control effect can be achieved within a certain range of pressure drop ratios when the nozzle is in the over-expanded state. The size of the hole diameter also needs to be reasonably selected. If the hole diameter is too large, the influence on the flow is too great, which may bring unexpected effects. If the hole diameter is too small, the flow control effect is not obvious. Brief Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention;

[0024] Figure 2 is a front view of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention;

[0025] Figure 3 is a schematic diagram of the upper control device of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention and its fixedly connected cover plate connecting plate;

[0026] Figure 4 is a partially enlarged view of the S-bend convergent-divergent nozzle with holes in the expansion section of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention;

[0027] Figure 5 is a front view of the upper cover plate of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention and its fixedly connected connecting rod;

[0028] Figure 6 is a partial view of the upper cover plate of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention and its fixedly connected connecting rod;

[0029] Figure 7It is a schematic diagram of the working principle before improvement in the over-expanded state of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention. The dotted lines are wave systems, and the solid lines are streamlines;

[0030] Figure 8 It is a sectional view of the position of the cover plate in the over-expanded state of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention;

[0031] Figure 9 It is a schematic diagram of the working principle after improvement in the over-expanded state of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention. The dotted lines are wave systems, and the solid lines are streamlines;

[0032] Figure 10 It is a sectional view of the position of the cover plate in the designed state of an S-bend convergent-divergent nozzle structure with an adjustable cover plate according to an embodiment of the present invention;

[0033] Description of reference numerals: 1. S-shaped convergent section; 2. Open-hole divergent section; 3. Upper cover plate; 4. Lower cover plate; 5. Upper control device; 6. Lower control device; 21. Unopened side wall surface; 22. Upper wall surface of the opening; 23. Lower wall surface of the opening; 24. Wall hole; 31. Upper cover plate connection reinforcement plate; 32. Upper cover plate main board; 33. Upper cover plate protruding cylinder group; 41. Lower cover plate connection reinforcement plate; 42. Lower cover plate main board; 43. Lower cover plate protruding cylinder group; 51. Linear motor of the upper control device; 52. Rotor seat of the upper control device; 53. Connecting rod of the upper control device. Detailed implementation manners

[0034] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0036] An embodiment of the present invention is an S-bend convergent-divergent nozzle with an adjustable cover plate, as Figure 1 、 2, as shown in Figures 3, 4, and 5, it includes: S-shaped converging section 1, perforated expanding section 2, upper cover plate 3, lower cover plate 4, upper control device 5, lower control device 6, unperforated side wall surface 21, perforated upper wall surface 22, perforated lower wall surface 23, wall holes 24, upper cover plate connection reinforcement plate 31, upper cover plate main board 32, upper cover plate protruding cylinder group 33, lower cover plate connection reinforcement plate 41, lower cover plate main board 42, lower cover plate protruding cylinder group 43, upper control device linear motor 51, upper control device mover seat 52, upper control device connecting rod 53.

[0037] For the S-bend converging-diverging nozzle structure with adjustable cover plates applying the technical solution of the present invention, when the nozzle is in an over-expanded state, the upper / lower cover plates are moved along the outer normal directions of the upper / lower wall surfaces of the perforated expanding section by applying forces through the upper / lower control devices, forming a porous structure, so that a series of stable and vertically symmetric wave systems are generated inside the nozzle, improving the jet instability phenomenon caused by the unstable and asymmetric complex wave systems that appear inside the converging-diverging nozzle. When the nozzle is in the design state, the upper / lower cover plates are moved along the inner normal directions of the upper / lower wall surfaces of the perforated expanding section to fit the wall surfaces with the main boards of the cover plates through the upper / lower control devices, and the porous structure disappears, without affecting the aerodynamic performance of the nozzle in the design state.

[0038] Specifically, the S-shaped converging section 1 is a double S-bend circular-to-square channel. The inlet of the S-shaped converging section 1 is the inlet of the S-bend converging-diverging nozzle, which is matched with the turbine outlet of the engine. The outlet of the S-shaped converging section 1 is the nozzle throat surface. The cross-sectional shape of the entire converging section changes from circular to quasi-rectangular from the inlet to the throat surface, and the area gradually converges. Inside this double S-bend circular-to-square channel, the air flow first deflects downward and then upward.

[0039] The S-shaped converging section 1 is fixedly connected to the perforated expanding section 2. The center line of the cross-section of the perforated expanding section 2 is a horizontal line, and the cross-sectional shape is a rectangle. The perforated upper wall surface 22 and the perforated lower wall surface 23 expand toward the upper side and the lower side of the nozzle respectively, and the expansion angles (the angles formed by the upper / lower wall surfaces and the horizontal plane) are equal. When the design state of the engine is determined, too small an expansion angle will increase the length of the nozzle, and too large an expansion angle is likely to generate greater flow losses and reduce the nozzle efficiency. Therefore, the angle change range is selected as 10° to 25°. The unperforated side wall surface 21 is parallel to the vertical plane and has no expansion angle.

[0040] The upper wall surface 22 and the lower wall surface 23 of the opening have a completely symmetric opening layout. 4 to 6 rows of small holes are evenly spaced along the axial direction, and the spacing is controlled between 0.1L and 0.12L, where L is the axial length of the opening expansion section 2. 5 to 7 rows of small holes are evenly spaced along the span direction, and the spacing is controlled between 0.1W and 0.15W, where W is the width of the cross-section of the opening expansion section 2, that is, the width along the radial direction. And it is ensured that the holes are symmetrically distributed about the left and right sides of the nozzle. Each small hole has the same diameter, and the diameter selection range is 0.01W to 0.02W. The opening position is controlled between 0.1L and 0.9L of the opening expansion section 2.

[0041] The upper cover plate 3 and the lower cover plate 4 are respectively connected to the upper wall surface 22 and the lower wall surface 23 of the opening. The upper cover plate 3 and the lower cover plate 4 have the same structure. On one side of the cover plate main board 32 is the upper cover plate protruding cylinder group 33. Each cylinder corresponds to the opening position of the opening expansion section 2 and matches the structural size of the opening hole type to ensure that the cover plate can move along the inner and outer normal directions of the upper wall surface 22 of the opening. The height of the cylinder is the same as the wall thickness to ensure that when the cover plate main board 32 is in full contact with the upper wall surface 22 of the opening, the top of the upper cover plate protruding cylinder group 33 is flush with the inner wall surface of the nozzle, and the inner wall surface of the nozzle is smooth. The diameter of the cylinder is the same as the opening diameter of the nozzle to avoid air leakage and affect the performance of the nozzle. On the other side of the cover plate main board 32 is the connection reinforcement plate 31, which is used to connect the cover plate main board 32 and the upper control device 5 on the one hand, and can slow down the stress concentration on the surface of the cover plate main board 32 and reduce the maximum thickness that the cover plate main board 32 can be designed. The lower cover plate 4 is the same as the upper cover plate 3, so it will not be elaborated here.

[0042] The upper control device 5 and the lower control device 6 have the same structure, including a controller, a linear motor, a mover seat, and a connecting rod. One end of the connecting rod is fixedly connected to the cover plate connecting plate, and one end is fixedly connected to the mover seat fixed on the linear motor. The linear motor is electrically connected to the controller. The controller receives the transmission signal of the engine monitoring system, monitors the pressure drop ratio of the nozzle to judge the flow state inside the nozzle, and then applies force to the upper / lower cover plates simultaneously to control their movement along the normal directions of the upper wall surface 22 and the lower wall surface 24 of the opening to open and close the porous structure.

[0043] In the embodiment of the present invention, the high-temperature gas flow flows out from the engine turbine and flows into the S-shaped convergent section 1 from the inlet surface of the S-bend convergent-divergent nozzle. In the S-shaped convergent section 1, it first deflects downward and then upward. The gas flow gradually accelerates and reduces pressure in the S-shaped convergent section 1. When it reaches the nozzle throat surface, the Mach number of the gas flow reaches the maximum. When the nozzle is in the critical and supercritical state, the Mach number reaches 1. Then the gas flow enters the opening expansion section 2. The flow state in the expansion section depends on the pressure drop ratio of the nozzle. When the nozzle is in the over-expanded state, due to the higher back pressure, shock wave boundary layer interference and double separation vortex system structure appear inside the nozzle, causing flow instability phenomena, such as Figure 6As shown, at this time, the upper control device 5 and the lower control device 6 respectively control the upper plate 3 and the lower cover plate 4 to move along the outer normal directions of the wall surfaces of the upper wall surface 22 and the lower wall surface 23 of the opening, forming a porous structure, such as Figure 7 As shown, at this time, the porous structure will generate a series of stable and vertically symmetric wave systems in the nozzle, promoting the stable separation of the exhaust flow to control the off-design separation in the nozzle, improving the unstable flow phenomenon inside the nozzle, and the improved flow state is as Figure 8 As shown, when the nozzle is in the design state, the existence of the porous structure will make the flow inside the nozzle more complex, generate unnecessary flow losses, and reduce the aerodynamic performance of the nozzle. Therefore, the upper control device 5 and the lower control device 6 respectively control the upper cover plate 3 and the lower cover plate 4 to move along the inner normal directions of the upper wall surface 22 and the lower wall surface 23 of the opening until the cover plate main board fits with the wall surface, closing the porous structure, such as Figure 8 As shown, at this time, the upper and lower wall surfaces of the nozzle are smooth wall surfaces, which do not affect the flow inside the nozzle and avoid affecting the aerodynamic performance of the nozzle in the design state.

[0044] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. A variable cover plate S-bend convergent-divergent nozzle, characterized in that: It includes an S-shaped converging section, an open-hole expanding section, and a jet flow control mechanism; the inlet of the S-shaped converging section is fitted and installed with the outlet of the engine turbine, and the nozzle throat is formed at the connection between its outlet and the open-hole expanding section; a number of holes are opened on both the upper and lower wall surfaces of the open-hole expanding section as ventilation holes; the jet flow control mechanism is connected to the ventilation holes of the open-hole expanding section, and the jet flow in the expanding section is adjusted by controlling the opening / closing of the ventilation holes; The jet flow control mechanism includes an upper cover plate, a lower cover plate, an upper control device, and a lower control device; the upper cover plate and the lower cover plate are respectively arranged on the outer sides of the upper and lower wall surfaces of the open-hole expanding section, and a number of protrusions are arranged on their inner surfaces. The protrusions and the ventilation holes on the open-hole expanding section are complementary installation structures in one-to-one correspondence; the upper control device and the lower control device are respectively connected to the upper cover plate and the lower cover plate, and the opening or closing state of the ventilation holes is adjusted by controlling the moving positions of the upper cover plate and the lower cover plate; The holes on the upper wall surface and the lower wall surface of the open-hole expanding section are symmetrically arranged. 4 to 6 rows of small holes are equally spaced along the axial direction of the open-hole expanding section, and the spacing is controlled between 0.1L and 0.12L, where L is the axial length of the open-hole expanding section; 5 to 7 columns of small holes are equally spaced along the span direction, and the spacing is controlled between 0.1W and 0.15W, where W is the radial cross-sectional width of the open-hole expanding section; The ventilation holes on the upper and lower wall surfaces are symmetrical with respect to the symmetry plane of the S-bend convergent-divergent nozzle.

2. The S-shaped convergent-divergent nozzle with an adjustable cover plate according to claim 1, wherein: The holes on the upper and lower wall surfaces are all cylindrical small holes, and the diameters of the small holes are the same. The diameter range is 0.01W to 0.02W, and the opening positions are controlled between 0.1L and 0.9L of the upper and lower wall surfaces of the open-hole expanding section.

3. The S-shaped convergent-divergent nozzle with an adjustable cover plate according to claim 1, wherein: The upper cover plate and the lower cover plate are flat plate structures with the same structure, and the protrusions on their inner surfaces are cylindrical structures; the height of the cylinder is equal to the thickness of the nozzle wall surface, and the diameter is consistent with the inner diameter of the cylindrical small holes of the open-hole expanding section; The outer sides of the upper and lower cover plates are connected to the upper and lower control devices through connection reinforcing plates.

4. The S-shaped convergent-divergent nozzle with an adjustable cover plate according to claim 1, wherein: The upper and lower control devices both include linear motors, mover seats, and connecting rods. One end of the connecting rod is connected to the connection reinforcing plate, and the other end is fixedly connected to the mover seat fixed on the linear motor; the linear motor is electrically connected to the controller, and the linear motor drives the connecting rod to move along the normal direction of the upper / lower wall surface of the open-hole expanding section, and at the same time drives the upper cover plate and the lower cover plate to move along the normal direction of the upper / lower wall surface to control the opening and closing of the ventilation holes on the upper / lower wall surface.

5. The S-shaped convergent-divergent nozzle with an adjustable cover plate according to claim 1, wherein: The open-hole expanding section includes an open-hole upper wall surface, an open-hole lower wall surface, and an unopened side wall surface; the open-hole upper wall surface and the open-hole lower wall surface expand towards the upper side and the lower side of the nozzle respectively, and the expansion angles are equal, and the angle change range is 10° to 25°; there is no expansion angle on the two side wall surfaces of the nozzle.

6. The S-shaped convergent-divergent nozzle with an adjustable cover plate according to claim 1, wherein: The S-shaped converging section is a double-S-curved circular-to-square channel. The inlet of the S-shaped converging section is the inlet of the S-bend convergent-divergent nozzle, which matches the outlet of the engine turbine. The outlet of the S-shaped converging section is the nozzle throat surface. The radial cross-sectional shape of the entire converging section changes from circular to quasi-rectangular from the inlet to the throat surface, and the area gradually converges.

7. A jet flow control method for the S-shaped convergent-divergent nozzle with an adjustable cover plate according to any one of claims 1-6, characterized in that The specific steps are as follows: Step 1: The monitoring system monitors the pressure drop ratio of the nozzle to determine the flow state of the nozzle; Step 2: The controller receives the transmission signal from the engine monitoring system and outputs a control signal to the upper and lower control devices; Step 3: The upper and lower control devices adjust the moving positions of the upper / lower cover plates; When it is detected that the nozzle pressure ratio is lower than the designed pressure ratio, i.e., the nozzle is in an over-expanded state, the upper / lower cover plates move outward along the normal directions of the upper / lower walls of the opening expansion section to form a porous structure; when it is detected that the nozzle pressure ratio is equal to or greater than the designed pressure ratio, i.e., the nozzle is in the designed state or under-expanded state, the upper / lower cover plates move inward along the normal directions of the upper / lower walls of the opening expansion section until the walls are in contact with the main plates of the cover plates, and the porous structure disappears.

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