Multivariable fuel injection and mixing section with replaceable injection structure for wind tunnel

Abstract

The present invention belongs to the technical field of experimental research on high Mach number air-breathing engines, and particularly relates to a multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel, which solves the problem that the existing mixing section structure is relatively fixed and cannot meet the requirement of the mixing section being reusable for different fuels in experiments. The special features of this mixing section are as follows: It includes a mixing section frame, M strut injection assemblies, and N wall injection assemblies; the mixing section frame is a hollow cuboid with openings on both the left and right walls; at least two windows are symmetrically arranged on the front and rear walls of the mixing section frame in the front-to-back direction; two windows at symmetric positions on the front and rear walls of the mixing section frame are defined as a set of windows; on the upper and lower outer walls of the mixing section frame, at positions above and below each set of windows, there are wall injection grooves penetrating in the front-to-back direction; a set of strut injection assemblies is installed in a set of windows; and a set of wall injection assemblies is installed at a wall injection groove.

Description

Technical Field

[0001] The present invention belongs to the technical field of experimental research on high Mach number air-breathing engines, and particularly relates to a multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel. Background Art

[0002] Fuel injection and mixing is a prerequisite for combustion experiments. In high Mach number air-breathing engine experiments, there are relatively high requirements for the fuel mixing state. Insufficient mixing will lead to incomplete combustion and unstable flames. Research on the multi-variable and repeatable aspects of the mixing section structure is of great significance for the combustion experiments of high Mach number air-breathing engines.

[0003] In a Chinese patent with the application publication number "CN113091096A" and the application publication date "July 9, 2021", and the invention title "A jet injection configuration for a large-scale scramjet engine", a strut jet injection configuration for a scramjet engine is disclosed. Through specific strut structures and arrangements, it can form a strut-wall surface hybrid injection scheme in the combustion chamber. In a Chinese patent with the application publication number "CN112668201A" and the application publication date "April 16, 2021", and the invention title "A fuel injection design method for a supersonic combustion chamber based on non-uniform inlet airflow", a fuel injection design method for a supersonic combustion chamber based on non-uniform inlet airflow is disclosed. It obtains the number of injection holes, injection hole grouping, and the range of injection hole diameters according to the inlet duct and engine parameters. In a Chinese patent application with the application publication number "CN115200044A" and the application publication date "October 18, 2022", and the invention title "A fuel wall injection hole structure for a scramjet engine", a fuel wall injection hole structure for a scramjet engine is disclosed. The shape of the injection hole is oval, and the oval shapes of the injection holes perpendicular to the oncoming flow direction are different to improve the problem of inconsistent jet penetration depths of the combined injection holes caused by the wall boundary layer effect and improve the mixing and combustion efficiency. In a Chinese patent application with the application publication number "CN115013185A" and the application publication date "September 6, 2022", and the invention title "A jet injection configuration for a fuel injection module of a scramjet engine", a jet injection configuration for a fuel injection module of a scramjet engine is disclosed. In this jet injection configuration, the diameters of the arranged fuel injection holes gradually decrease from the center of the fuel injection assembly to both sides, so that the jet penetration depths of the jets ejected from each fuel injection hole are kept consistent, and the mixing and combustion efficiency can also be improved.

[0004] Although the existing injection methods, such as the types of injection holes, their arrangements, and the relative positions of the struts, are all designed to improve the mixing efficiency and further enhance the combustion efficiency, the number of variables is small and the repeatability is low. For example, only the fuel type and injection pressure drop can be changed. However, in experiments, for different fuels, their penetration depths are different and the injection atomization effects are different. Therefore, for different fuels, in order to ensure the combustion efficiency, different fuel injection mixing section structures need to be matched; while the existing fuel injection mixing section structures are relatively fixed and cannot meet the requirement of the repeatable use of the fuel injection mixing section for different fuels under the premise of ensuring the combustion efficiency in experiments. Summary of the Invention

[0005] The object of the present invention is to provide a multi-variable fuel injection mixing section with a replaceable injection structure for a wind tunnel to solve the technical problem that the existing fuel injection mixing section structure is relatively fixed and cannot meet the requirement of the repeatable use of the fuel injection mixing section for different fuels under the premise of ensuring the combustion efficiency in experiments.

[0006] The technical solution adopted by the present invention is that a multi-variable fuel injection mixing section with a replaceable injection structure for a wind tunnel is characterized in that:

[0007] It includes a mixing section frame, M strut injection assemblies, and N wall injection assemblies, where M≥1, N≥0, and both M and N are integers;

[0008] The mixing section frame is a hollow cuboid with openings on both the left and right walls; the opening on the left wall of the mixing section frame is used to communicate with the air inlet of the air inlet structure; the right end of the mixing section frame is used to connect to the combustion chamber or the nozzle structure;

[0009] On the front and rear walls of the mixing section frame, at least two windows are symmetrically arranged in the front and rear, and the sizes of all the windows are the same; two windows at symmetric positions on the front and rear walls of the mixing section frame are defined as a group of windows; on the upper and lower outer walls of the mixing section frame, at symmetric positions above and below each group of windows, wall injection grooves running through in the front-rear direction are correspondingly arranged, and the depth of the middle section of the wall injection groove in the up-down direction in the front-rear direction satisfies that the wall injection groove is connected to the internal flow field of the mixing section frame;

[0010] One group of the strut injection assemblies is detachably installed in one group of windows correspondingly; the number of the strut injection assemblies is less than or equal to the number of groups of windows; an observation window assembly or a sealing cover plate is detachably installed at the window where the strut injection assembly is not installed to seal the window;

[0011] One set of the wall injection components is detachably installed at a corresponding wall injection groove; the number of the wall injection components is less than or equal to the sum of the numbers of all the wall injection grooves; at the wall injection grooves where no wall injection components are installed, wall filling strips are detachably installed to seal the wall injection grooves.

[0012] Both the strut injection components and the wall injection components are used to inject fuel into the internal flow field of the mixing section frame.

[0013] Furthermore, in order to guide the airflow after the boundary layer bleed, the inner sides of the front, rear, and lower frames at the opening of the left wall surface of the mixing section frame are smooth flow channels, and chamfers with acute angles to the due right direction are provided at the outer edge positions, serving as the bleed slopes of the intake duct; for the convenience of connection, a mixing section flange is provided at the right end of the mixing section frame for connection with the combustion chamber or the nozzle structure.

[0014] Furthermore, in order to facilitate replacement and improve the combustion efficiency, each set of the strut injection components includes a strut cover plate, a fixed strut cover plate, and a strut; the strut cover plate is installed on the window located on the front wall surface in a set of windows; the fixed strut cover plate is installed on the window located on the rear wall surface in this set of windows; the fuel inlet end of the strut is connected to the strut cover plate, the other end of the strut opposite to the fuel inlet end of the strut, that is, the rear end of the strut, is connected to the fixed strut cover plate, and the middle section of the strut is located in the internal flow field of the mixing section frame.

[0015] A strut cover plate pressure measurement hole is provided on the upper surface of the strut cover plate, a strut cover plate fuel inlet interface is provided on the lower surface of the strut cover plate, and a strut cover plate fuel outlet is provided on the rear surface of the strut cover plate. The strut cover plate pressure measurement hole, the strut cover plate fuel inlet interface, and the strut cover plate fuel outlet form a tee structure.

[0016] A strut fuel inlet interface is provided on the end surface of the strut at the end where the fuel inlet end of the strut is located.

[0017] The outer contour shape of the middle section of the strut is symmetric about the left and right and up and down respectively; the outer contour shape of the middle section of the strut is a shape formed by stretching the cross-section of the middle section of the strut perpendicular to the front and rear directions along the axis in the front and rear directions, and the shape of the cross-section of the middle section of the strut is a shape combined by symmetric wedges at both left and right ends and a rectangle formed by the four vertices of the large ends corresponding to the symmetric wedges in the middle.

[0018] A strut fuel channel along the front and rear directions is provided on the strut, and the axis of the strut fuel channel coincides with the intersection line of the left-right symmetry plane and the up-down symmetry plane of the outer contour shape of the middle section of the strut; the front end of the strut fuel channel is communicated with the strut cover plate fuel outlet through the strut fuel inlet interface, and the rear end of the strut fuel channel is a sealed end.

[0019] On the middle section of the strut plate, two rows of strut plate fuel injection holes are arranged in an array in the front-rear direction. The axes of the two rows of strut plate fuel injection holes are all parallel to the plane perpendicular to the front-rear direction. The axes of the two rows of strut plate fuel injection holes intersect with the axis of the strut plate fuel passage, and the injection directions corresponding to the axes of the two rows of strut plate fuel injection holes are at angles of +45°±2° and -45°±2° respectively with respect to the due right direction; or the strut plate fuel injection holes are replaced with the form of a Laval nozzle. In this way, for different fuels, different structures can be selected, and thus the combustion efficiency can be ensured.

[0020] Further, for better sealing effect, both the strut plate fuel inlet end and the rear end of the strut plate are of cuboid structures, and the strut plate as a whole is symmetrically structured up and down;

[0021] On the rear surface of the strut plate cover, a strut plate cover rectangular groove extending in the left-right horizontal direction and adapted to the cuboid structure at the strut plate fuel inlet end is provided; on the front surface of the fixed strut plate cover, a fixed strut plate cover rectangular groove extending in the left-right horizontal direction and adapted to the cuboid structure at the rear end of the strut plate is provided; the strut plate and the strut plate cover, and the strut plate and the fixed strut plate cover are all connected by screws;

[0022] The four-sided frame of the window adopts a stepped structure;

[0023] The observation window assembly includes a glass pressing plate and glass. The glass pressing plate is used to fix the glass at the window; the four-sided frames of the strut plate cover, the fixed strut plate cover, the glass pressing plate, and the sealing cover all adopt structures adapted to the stepped structure.

[0024] Further, for convenient replacement and improved combustion efficiency, the cross-sectional shape of the wall injection groove is rectangular;

[0025] Each group of the wall injection assemblies includes a wall injection strip;

[0026] The wall injection strip is a strip-shaped structure with a T-shaped cross-section; the vertical side dimension of the T shape is adapted to the cross-sectional dimension of the wall injection groove and is embedded in the wall injection groove; the two arms of the T shape are located above the outer side of the upper wall surface of the mixing section frame, and the two arms of the T shape are correspondingly distributed on the left and right sides of the wall injection groove and are connected to the mixing section frame;

[0027] A wall fuel passage in the front-rear direction is provided on the wall injection strip, and the axis of the wall fuel passage is located on the left-right symmetry plane of the wall injection strip; the front and rear ends of the wall fuel passage are sealed ends;

[0028] On the upper surface of the wall injection strip, near the midpoint of the wall injection strip in the front-rear direction, a wall injection strip fuel inlet and a wall injection strip pressure measuring hole are provided; the wall injection strip fuel inlet and the wall injection strip pressure measuring hole are arranged in the front-rear direction, and both the wall injection strip fuel inlet and the wall injection strip pressure measuring hole are communicated with the wall fuel channel;

[0029] On the vertical side of the T-shape in the middle section of the wall injection strip in the front-rear direction, wall injection holes arranged in an array in the front-rear direction are provided. The axis of the wall injection hole is parallel to the plane perpendicular to the front-rear direction. The axis of the wall injection hole intersects with the axis of the wall fuel channel. The included angle between the injection direction corresponding to the axis of the wall injection hole and the due right direction is -45°±2° or +45°±2°, and the direction points to the internal flow field direction of the mixing section frame; or the wall injection hole is replaced with a Laval nozzle form. In this way, for different fuels, different structures can be selected, and thus the combustion efficiency can be guaranteed.

[0030] Furthermore, in order to facilitate fuel cleaning after the experiment and facilitate reuse, each group of the support plate injection assemblies further includes a first hexagon socket head cap screw;

[0031] On the end face of one end where the rear end of the support plate is located, a support plate sealing threaded hole coaxial and communicated with the support plate fuel channel is provided; the support plate sealing threaded hole is adapted to the first hexagon socket head cap screw, and the rear end of the support plate fuel channel is sealed by the first hexagon socket head cap screw;

[0032] Each group of the wall injection assemblies further includes two second hexagon socket head cap screws;

[0033] On the front and rear end faces of the wall injection strip, wall fuel channel threaded holes coaxial and communicated with the wall fuel channel are provided; the wall fuel channel threaded holes are adapted to the second hexagon socket head cap screws, and the front and rear ends of the wall fuel channel are respectively sealed by the two second hexagon socket head cap screws one by one.

[0034] Furthermore, in order to conveniently detect the pressures at different positions in the internal flow field of the mixing section frame and provide pressure data support for the experiment, mixing section pressure measuring holes are evenly distributed at positions on the upper and lower wall surfaces of the mixing section frame other than where the wall injection strip and the wall filling strip are installed.

[0035] Furthermore, in order to facilitate connection with the experimental support main structure and to reinforce the mixing section frame, mixing section legs are provided below the outer side of the lower wall surface of the mixing section frame.

[0036] The leg of the mixing section is a plate-shaped structure with 90° bent flanges at both the upper and lower parts; the 90° bent flanges are used as one-way flanges, where the upper one-way flange is used to connect with the lower wall surface of the mixing section frame, and the lower one-way flange is used to connect with the experimental support main structure; the plate surface is perpendicular to the front-rear direction.

[0037] At the upper end of the leg of the mixing section, there are multiple cut grooves in the mixing section leg that run through in the front-rear direction, which are used to avoid the wall injection strips or wall filling strips. With this setting, the replacement of the wall injection strips and wall filling strips can be completed without disassembling the leg of the mixing section.

[0038] Furthermore, in order to reduce the assembly gaps and assembly surfaces and avoid unnecessary shock waves generated by the high Mach number oncoming flow in the flow field during the wind tunnel experiment, which may affect the internal flow field, the surfaces of the splitter plate cover, the fixed splitter plate cover, and the sealing cover on the side of the internal flow field of the mixing section frame are flush and smooth with the corresponding inner wall surfaces of the mixing section frame; in order to avoid the generation of clutter on the external wall surface, which may affect the observation effect of the observation window assembly, the front surface of the splitter plate cover and the rear surface of the fixed splitter plate cover are both flat and smooth structures; the left end of the leg of the mixing section is a wedge-shaped structure.

[0039] Furthermore, in order to adapt to the wind tunnel experiment environment, a fairing is provided above the outer side of the upper wall surface of the mixing section frame or / and below the outer side of the lower wall surface of the mixing section frame, which is used to protect the pipeline and rectify the high Mach number oncoming flow.

[0040] The beneficial effects of the present invention are:

[0041] (1) For the multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel of the present invention, the strut injection assembly can be installed in at least two groups of windows, so there are at least two injection positions to choose from; the wall injection assembly has two upper and lower injection positions to choose from in one group of windows, and there are at least two groups of windows, so there are at least four injection positions to choose from; if it is gaseous fuel, the injection position can be set at the injection position at the rightmost end of the mixing section frame to prevent premature combustion caused by the short ignition delay time of gaseous fuel; if it is liquid fuel, since the ignition delay time of some liquid fuels is long, the injection position can be set at the injection position at the leftmost end of the mixing section frame to allow it to be fully mixed within the mixing section frame; various types and states of fuels can also be added simultaneously for combined injection, and the combination of different injection positions of the strut injection assembly and the wall injection assembly can be set according to the fuel characteristics; and this structure allows the use of more than one pair of wall injection assemblies (one pair is two symmetric upper and lower wall injection assemblies) or more than one strut injection assembly at the same time; thus, for different fuels, the multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel of the present invention can be reused; therefore, the present invention solves the technical problem that the existing fuel injection and mixing section structure is relatively fixed and cannot meet the requirement of the fuel injection and mixing section being reusable under the premise of ensuring combustion efficiency for different fuels in experiments. By using the multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel of the present invention, the combustion state of the engine under different mixing variables can be conveniently studied, or the injection scheme can be adjusted to meet efficient mixing combustion.

[0042] (2) In the present invention, the wall injection strip and the strut structure are small and are replaceable structures. In order to adapt to the injection characteristics of different fuels, such as different penetration depths of different fuels and different injection atomization effects, etc., the wall injection strip and the strut can be redesigned. For example, the wall injection holes on the wall injection strip and the strut and the fuel injection holes on the strut are replaced with the form of a Laval nozzle for injecting gaseous fuel, etc., so as to make full use of the multi-variable fuel injection and mixing section with a replaceable strut injection assembly and wall injection assembly structure and its quantity and position.

[0043] (3) In the present invention, the surfaces of the strut cover plate, the fixed strut cover plate, and the sealing cover plate on the side of the inner flow field of the mixing section frame are respectively flush and smooth with the corresponding inner wall surfaces of the mixing section frame; the front surface of the strut cover plate and the rear surface of the fixed strut cover plate are both flat and smooth structures; the left end of the leg of the mixing section is a wedge-shaped structure; this smooth design of the front and rear outer wall surfaces and the inner flow field structure of the multi-variable fuel injection and mixing section has no protruding structure, avoiding the generation of clutter by the high Mach number oncoming flow during wind tunnel experiments, which affects the flow of the inner flow field and the observation effect of the observation window.

[0044] (4) In the present invention, a fairing is provided above the outer side of the upper wall surface of the mixing section frame and / or below the outer side of the lower wall surface of the mixing section frame, which is used to protect the pipeline and rectify the high Mach number oncoming flow, so as to adapt to the wind tunnel test environment. Description of the Drawings

[0045] Figure 1 is a three-dimensional explosion schematic diagram of the assembly of the embodiment of the present invention;

[0046] Figure 2 is a cross-sectional view corresponding to the rear when the assembly is cut by a plane passing through the midpoint of the mixing section frame in the front-rear direction and perpendicular to the front-rear direction;

[0047] Figure 3 is a cross-sectional view corresponding to the lower when the assembly is cut by a plane passing through the midpoint of the strut in the up-down direction and perpendicular to the up-down direction (the fairing is hidden in the figure);

[0048] Figure 4 is Figure 3 the corresponding enlarged partial view at Ι in

[0049] Figure 5 is the assembly of the embodiment of the present invention and Figure 1 a three-dimensional structure schematic diagram of another perspective with a different perspective;

[0050] Figure 6 is the exploded view corresponding to the left view of the assembly of the embodiment of the present invention;

[0051] Figure 7 is the rear view of the strut cover plate in the embodiment of the present invention;

[0052] Figure 8 is along Figure 7 the cross-sectional view taken along line A-A in

[0053] Figure 9 is the structural schematic diagram of the strut in the embodiment of the present invention;

[0054] Figure 10 is the corresponding partial perspective view of the end where the strut fuel inlet end of the strut is located in the embodiment of the present invention;

[0055] Figure 11 is the corresponding partial view of the end where the rear end of the strut is located in the embodiment of the present invention;

[0056] Figure 12 is the structural schematic diagram of the wall injection strip in the embodiment of the present invention;

[0057] Figure 13 is the partial perspective view of the wall injection strip in the embodiment of the present invention;

[0058] Figure 14 This is a schematic structural view of the fairing in an embodiment of the present invention.

[0059] The descriptions of the reference numerals in the figure are as follows:

[0060] 1. Mixing section frame, 1-1. Inlet duct bleed-off slope, 1-2. Mixing section flange, 1-3. Wall injection groove, 1-4. Mixing section pressure measurement hole, 2. Window, 3. Strut cover plate, 3-1. Strut cover plate through hole, 3-2. Strut cover plate pressure measurement hole, 3-3. Strut cover plate fuel inlet interface, 3-4. Strut cover plate fuel outlet, 3-5. Strut cover plate rectangular groove, 4. Strut, 4-1. Strut fuel inlet end, 4-2. Strut fuel inlet end threaded hole, 4-3. Strut fuel inlet interface, 4-4. Strut rear end, 4-5. Strut rear end threaded hole, 4-6. Strut sealing threaded hole, 4-7. Strut fuel channel, 4-8. Strut fuel injection hole, 5. Fixed strut cover plate, 5-1. Fixed strut cover plate rectangular groove, 6. Sealing cover plate, 7. Glass pressing plate, 8. Mixing section leg, 8-1. Mixing section leg cut groove, 9. Wall injection strip, 9-1. Wall fuel channel, 9-2. Wall fuel channel threaded hole, 9-3. Wall injection strip fuel inlet, 9-4. Wall injection strip pressure measurement hole, 9-5. Wall injection hole, 10. Wall filling strip, 11. Fairing. Detailed implementation manners

[0061] The present invention will be described in detail below with reference to the accompanying drawings and specific implementation manners.

[0062] Refer to Figure 1 , a multi-variable fuel injection mixing section of a replaceable injection structure for a wind tunnel according to the present invention includes a mixing section frame 1, M strut injection assemblies, and N wall injection assemblies, where M≥1, N≥0, and both M and N are integers. The definitions of the x-axis, y-axis, and z-axis in the accompanying drawings of the present invention are as follows: The flow field flow direction from the left to the right of the mixing section frame is the positive direction of the x-axis; the direction perpendicular to the x-axis and pointing directly above the flow channel of the mixing section frame is the positive direction of the y-axis; the positive direction of the z-axis conforms to the right-hand rule, that is, the positive direction of the z-axis points forward.

[0063] Refer to Figure 1, the above-mentioned mixing section frame 1 is a hollow cuboid with openings on both the left and right walls; the opening on the left wall of the mixing section frame 1 is used to communicate with the air inlet of the air inlet structure; the right end of the mixing section frame 1 is used to connect with the combustion chamber or the nozzle structure; on the front and rear walls of the mixing section frame 1, at least two windows 2 are symmetrically arranged in the front and rear, and the sizes of all the windows 2 are the same; two windows 2 at symmetric positions on the front and rear walls of the mixing section frame 1 are defined as a group of windows; on the upper and lower outer walls of the mixing section frame 1, at symmetric positions above and below each group of windows, wall injection grooves 1-3 running through in the front and rear directions are correspondingly arranged, and the depth of the middle section of the wall injection groove 1-3 in the up and down directions along the front and rear directions satisfies that the wall injection groove 1-3 is connected to the internal flow field of the mixing section frame 1; a group of the above-mentioned strut injection assemblies are detachably installed in a group of windows correspondingly; the number of the strut injection assemblies is less than or equal to the number of groups of windows; at the window 2 where the strut injection assembly is not installed, an observation window assembly or a sealing cover plate 6 can be detachably installed to seal the window 2; a group of the above-mentioned wall injection assemblies are detachably installed at a wall injection groove 1-3 correspondingly; the number of the wall injection assemblies is less than or equal to the sum of the numbers of all the wall injection grooves 1-3; at the wall injection groove 1-3 where the wall injection assembly is not installed, a wall filling strip 10 can be detachably installed to seal the wall injection groove 1-3; the above-mentioned strut injection assemblies and wall injection assemblies are both used to inject fuel into the internal flow field of the mixing section frame 1.

[0064] See Figure 1 , Figure 2 , Figure 3 and Figure 5 , in this embodiment, three windows 2 are symmetrically arranged in the front and rear on the front and rear walls of the mixing section frame 1. The above M takes the integer 1, that is, the strut injection assembly is one group. There are two of the above-mentioned observation window assemblies and sealing cover plates 6 respectively. Six wall injection grooves 1-3 are arranged on the upper and lower outer walls of the mixing section frame 1 in total. The above N takes the integer 2, that is, the wall injection assemblies are two groups. There are four of the above-mentioned wall filling strips 10.

[0065] In order to guide the airflow after the boundary layer bleed, see Figure 2 and Figure 5 , in this embodiment, the inner sides of the front, rear, and lower frames at the opening of the left wall of the above-mentioned mixing section frame 1 are flat flow channels, and chamfers with an acute angle to the due right direction are arranged at the outer edge positions, serving as the air inlet bleed slope 1-1. This air inlet bleed slope 1-1 belongs to a non-sealing structure. Except for the structure of this embodiment, a flange can also be arranged at the left end of the mixing section frame 1, and specific adjustments can be made according to the actual experimental situation. For the convenience of connection, see Figure 1 , in this embodiment, the right end of the above-mentioned mixing section frame 1 is provided with a mixing section flange 1-2 for connecting with the combustion chamber or the nozzle structure.

[0066] For the convenience of replacement and to improve the combustion efficiency, refer to Figure 1 , each of the above-mentioned strut injection assemblies includes a strut cover plate 3, a fixed strut cover plate 5, and a strut 4; the above-mentioned strut cover plate 3 is installed on the window located on the front wall surface in a group of windows; the above-mentioned fixed strut cover plate 5 is installed on the window located on the rear wall surface in this group of windows; refer to Figure 1 and Figure 9 , the strut fuel inlet end 4-1 of the above-mentioned strut 4 is connected to the strut cover plate 3, the other end of the above-mentioned strut 4 opposite to the strut fuel inlet end 4-1, that is, the strut rear end 4-4, is connected to the fixed strut cover plate 5, and the middle section of the above-mentioned strut 4 is located in the internal flow field of the mixing section frame 1.

[0067] Refer to Figure 1 , in this embodiment, a strut cover plate through hole 3-1 is provided in a circle around the strut cover plate 3, and threaded holes corresponding to the strut cover plate through hole 3-1 are evenly distributed around the window 2. Screws pass through the strut cover plate through hole 3-1 and are connected to the threaded holes evenly distributed around the window 2 to connect the strut cover plate 3 to the window 2. Refer to Figure 8 , a strut cover plate pressure measurement hole 3-2 is provided on the upper surface of the strut cover plate 3, and its interface size is adjusted according to the actual pressure gauge to detect the pressure before injection; a strut cover plate fuel inlet interface 3-3 is provided on the lower surface of the strut cover plate 3. In this embodiment, the strut cover plate fuel inlet interface 3-3 is coaxial with the strut cover plate pressure measurement hole 3-2 and has the same inner diameter; a strut cover plate fuel outlet 3-4 is provided on the rear surface of the strut cover plate 3. In this embodiment, the strut cover plate fuel outlet 3-4 is located at the center of the rear surface of the strut cover plate 3; the above-mentioned strut cover plate pressure measurement hole 3-2, the strut cover plate fuel inlet interface 3-3, and the strut cover plate fuel outlet 3-4 form a tee structure.

[0068] Refer to Figure 9 , a strut fuel inlet interface 4-3 is provided on the end surface of the strut 4 at the end where the strut fuel inlet end 4-1 is located; refer to Figure 2 and Figure 9 , the outer contour shape of the middle section of the above-mentioned strut 4 is symmetric left and right and up and down; the outer contour shape of the middle section of the above-mentioned strut 4 is a shape formed by stretching the cross-section of the strut middle section perpendicular to the front-rear direction along the axis in the front-rear direction, and the shape of the cross-section of the strut middle section is a symmetric wedge at both left and right ends, and a rectangle surrounded by the four vertices of the large ends corresponding to the symmetric wedge in the middle, and the combined shape of the three; refer to Figure 2 , Figure 3 and Figure 10The support plate 4 is provided with a support plate fuel channel 4-7 along the front-rear direction, and the axis of the support plate fuel channel 4-7 coincides with the intersection of the left-right symmetry plane and the upper-lower symmetry plane of the outer contour shape of the middle section of the support plate 4; see Figure 3 , Figure 4 as well as Figure 8 The front end of the support plate fuel channel 4-7 is connected to the support plate cover plate fuel outlet 3-4 through the support plate fuel inlet interface 4-3, and the rear end of the support plate fuel channel 4-7 is a sealed end; in this embodiment, the support plate fuel inlet interface 4-3 is embedded in the support plate cover plate fuel outlet 3-4, and cooperates with the sealing gasket to play a sealing role. Figure 9 , Figure 10 as well as Figure 11 , two rows of support plate fuel injection holes 4-8 arranged in an array along the front-to-back direction are provided on the middle section of the support plate 4, the axes of the two rows of support plate fuel injection holes 4-8 are parallel to the plane perpendicular to the front-to-back direction, the axes of the two rows of support plate fuel injection holes 4-8 intersect with the axis of the support plate fuel channel 4-7, and the injection directions corresponding to the axes of the two rows of support plate fuel injection holes 4-8 point to the right direction at angles of +45°±2° and -45°±2° respectively; or the support plate fuel injection holes 4-8 are replaced with Laval nozzles. In this way, different structures can be selected for different fuels, thereby ensuring combustion efficiency. During injection, the fuel enters from the support plate fuel inlet interface 4-3, passes through the support plate fuel channel 4-7, and is ejected from the two rows of support plate fuel injection holes 4-8 arranged in an array along the front-to-back direction. In this embodiment, the number of each row of support plate fuel injection holes 4-8 is 49, and the aperture is set according to the required flow rate of the experimental fuel.

[0069] See also Figure 1 and Figure 9 The fixed support plate cover plate 5 is used to embed the support plate rear end 4-4 of the support plate 4 therein, and plays a role of fixing and sealing. Since the size of the window 2 installed on the fixed support plate cover plate 5 is exactly the same as that of the window 2 installed on the support plate cover plate 3, the fixed support plate cover plate 5 and the support plate cover plate 3 have the same appearance, and the connection method between the fixed support plate cover plate 5 and the window 2 is also the same as that between the support plate cover plate 3 and the window 2. The difference is that there is no passage in the fixed support plate cover plate 5, that is, there is no pressure measuring hole, fuel inlet, and fuel outlet connected to the support plate fuel channel 4-7.

[0070] For better sealing, see Figure 9 The support plate fuel inlet end 4-1 and the support plate rear end 4-4 of the support plate 4 are both rectangular parallelepiped structures, and the support plate 4 as a whole is a vertically symmetrical structure; see Figure 7 and Figure 8, on the rear surface of the support plate cover 3, there is provided a rectangular groove 3-5 of the support plate cover extending in the left-right horizontal direction and adapted to the above-mentioned rectangular parallelepiped structure at the fuel inlet end 4-1 of the support plate; see Figure 1 , on the front surface of the fixed support plate cover 5, there is provided a rectangular groove 5-1 of the fixed support plate cover extending in the left-right horizontal direction and adapted to the above-mentioned rectangular parallelepiped structure at the rear end 4-4 of the support plate; in this embodiment, through holes are evenly distributed in the left-right direction in the rectangular groove 3-5 of the support plate cover and the rectangular groove 5-1 of the fixed support plate cover. On the end surface of the support plate 4 at the end where the fuel inlet end 4-1 of the support plate is located, there are evenly distributed support plate fuel inlet end threaded holes 4-2 corresponding to the through holes in the rectangular groove 3-5 of the support plate cover in the left-right direction. On the end surface of the support plate 4 at the end where the rear end 4-4 of the support plate is located, there are evenly distributed support plate rear end threaded holes 4-5 corresponding to the through holes in the rectangular groove 5-1 of the fixed support plate cover in the left-right direction. The above-mentioned support plate 4 and the support plate cover 3, and the support plate 4 and the fixed support plate cover 5 are all connected by screws.

[0071] Meanwhile, for better sealing effect, see Figure 1 , the four peripheral frames of the above-mentioned window 2 adopt a stepped structure. The above-mentioned observation window assembly includes a glass pressing plate 7 and glass. The above-mentioned glass pressing plate 7 is used to fix the glass at the window 2. Through holes corresponding to the threaded holes evenly distributed around the window 2 are evenly distributed around the glass pressing plate 7. The glass pressing plate 7 and the window 2 are connected by screws; the inner sides of the glass pressing plates 7 are flush, and cooperate with a sealing gasket to contact the glass. The observation window assembly is used to monitor and detect the atomization particle size, etc., so as to further obtain the mixing effect. The four peripheral frames of the above-mentioned support plate cover 3, fixed support plate cover 5, glass pressing plate 7 and sealing cover 6 all adopt structures adapted to the above-mentioned stepped structure.

[0072] See Figure 1 and Figure 3 , the above-mentioned sealing cover 6 is used to seal the window 2 where the support plate injection assembly and the observation window assembly are not used. Its structure, compared with the fixed support plate cover 5, does not have the rectangular groove 5-1 of the fixed support plate cover connected to the support plate 4, and the rest of the structure is the same as that of the fixed support plate cover 5.

[0073] For the convenience of replacement and to improve the combustion efficiency, see Figure 1 and Figure 2 , the cross-sectional shape of the above-mentioned wall injection groove 1-3 is rectangular. See Figure 1 , each group of the above-mentioned wall injection assemblies includes a wall injection strip 9; see Figure 1 and Figure 2, the above-mentioned wall injection strip 9 is a strip-shaped structure with a T-shaped cross-section; the vertical side dimension of the above-mentioned T-shape is adapted to the cross-sectional dimension of the wall injection groove 1-3, and is embedded in the wall injection groove 1-3; the two arms of the above-mentioned T-shape are located above the outer side of the upper wall surface of the mixing section frame 1, and the two arms of the above-mentioned T-shape are correspondingly distributed on the left and right sides of the wall injection groove 1-3 and are connected to the mixing section frame 1; in this embodiment, a row of through holes are drilled in each of the two arms of the T-shape along the front-rear direction, and threaded holes corresponding to the through holes are provided on both sides of the wall injection groove 1-3 on the mixing section frame 1 for fixing the wall injection strip 9 on the mixing section frame 1. See Figure 2 and Figure 13 , a wall fuel channel 9-1 along the front-rear direction is provided on the wall injection strip 9, and the axis of the wall fuel channel 9-1 is located on the left-right symmetry plane of the wall injection strip 9; the front and rear ends of the above-mentioned wall fuel channel 9-1 are sealed ends; in this embodiment, the wall fuel channel 9-1 is a circular hole. See Figure 12 , on the upper surface of the wall injection strip 9, near the midpoint of the wall injection strip 9 along the front-rear direction, a wall injection strip fuel inlet 9-3 and a wall injection strip pressure measurement hole 9-4 are provided; the above-mentioned wall injection strip fuel inlet 9-3 and wall injection strip pressure measurement hole 9-4 are arranged along the front-rear direction, and both the wall injection strip fuel inlet 9-3 and the wall injection strip pressure measurement hole 9-4 are communicated with the wall fuel channel 9-1; the wall injection strip pressure measurement hole 9-4 is used to detect the pressure before the wall fuel is injected; See Figure 2 and Figure 13 , on the vertical side of the above-mentioned T-shape in the middle section of the wall injection strip 9 along the front-rear direction, wall injection holes 9-5 arranged in an array along the front-rear direction are provided. The axis of the above-mentioned wall injection holes 9-5 is parallel to the plane perpendicular to the front-rear direction. The axis of the above-mentioned wall injection holes 9-5 intersects the axis of the wall fuel channel 9-1. The included angle between the injection direction corresponding to the axis of the above-mentioned wall injection holes 9-5 and the due right direction is -45°±2° or +45°±2°, and the injection direction points to the internal flow field direction of the mixing section frame 1; that is, when the wall injection strip 9 is located above the mixing section frame 1, the included angle between the injection direction corresponding to the axis of its wall injection holes 9-5 and the due right direction is -45°±2°; when the wall injection strip 9 is located below the mixing section frame 1, the included angle between the injection direction corresponding to the axis of its wall injection holes 9-5 and the due right direction is +45°±2°; or the wall injection holes 9-5 are replaced with the form of a Laval nozzle. In this way, for different fuels, different structures can be selected, and thus the combustion efficiency can be ensured.

[0074] See Figure 1, the above-mentioned wall filling strip 10 is a structure for sealing the wall injection groove 1-3 when the wall injection component is not used. Its external configuration is exactly the same as that of the wall injection strip 9, and its interior is solid. A row of through holes are drilled in each of the two arms of the T-shaped wall filling strip 10 and are connected to the mixing section frame 1 by screws.

[0075] To facilitate fuel cleaning after the experiment and facilitate reuse, each of the above-mentioned strut injection components further includes a first hexagon socket head screw; see Figure 11 , on the end face of one end where the rear end 4-4 of the strut 4 is located, there is provided a strut sealing threaded hole 4-6 coaxial and communicating with the strut fuel passage 4-7; the above-mentioned strut sealing threaded hole 4-6 is adapted to the first hexagon socket head screw, and the rear end of the strut fuel passage 4-7 is sealed by the first hexagon socket head screw. Each of the above-mentioned wall injection components further includes two second hexagon socket head screws; see Figure 12 , on the front and rear end faces of the wall injection strip 9, there are provided wall fuel passage threaded holes 9-2 coaxial and communicating with the above-mentioned wall fuel passage 9-1; the above-mentioned wall fuel passage threaded holes 9-2 are adapted to the second hexagon socket head screws, and the front and rear ends of the wall fuel passage 9-1 are respectively sealed by the two second hexagon socket head screws one by one.

[0076] To conveniently detect the pressures at different positions in the flow field of the mixing section frame and provide pressure data support for the experiment, see Figure 1 and Figure 5 , on the upper and lower wall surfaces of the mixing section frame 1 at positions other than where the wall injection strip 9 and the wall filling strip 10 are installed, mixing section pressure measuring holes 1-4 are evenly distributed.

[0077] To facilitate connection with the experimental support main structure and to reinforce the mixing section frame, see Figure 1 , Figure 2 and Figure 5 , below the lower wall surface outside of the above-mentioned mixing section frame 1, a mixing section leg 8 is provided; the above-mentioned mixing section leg 8 is in the shape of a plate with 90° bending flanges at both the upper and lower parts; the above-mentioned 90° bending flanges are used as one-way flanges, where the upper one-way flange is used to connect to the lower wall surface of the mixing section frame 1, and the lower one-way flange is used to connect to the experimental support main structure; the plate surface of the above-mentioned plate is perpendicular to the front-rear direction; see Figure 5 , at the upper end of the above-mentioned mixing section leg 8, a plurality of mixing section leg slots 8-1 penetrating in the front-rear direction are provided for avoiding the wall injection strip 9 or the wall filling strip 10. With this setting, the replacement of the wall injection strip and the wall filling strip can be completed without disassembling the mixing section leg.

[0078] To reduce the assembly gaps and assembly surfaces and avoid unnecessary shock waves generated by the high Mach number oncoming flow in the flow field during the wind tunnel experiment, which may affect the internal flow field, refer to Figure 3 ; the surfaces of the above-mentioned strut cover plate 3, fixed strut cover plate 5, and sealing cover plate 6 located on the inner flow field side of the mixing section frame 1 are flush and smooth with the corresponding inner wall surfaces of the mixing section frame 1 respectively; to avoid clutter on the external wall surface and affect the observation effect of the observation window assembly, the front surface of the strut cover plate 3 and the rear surface of the fixed strut cover plate 5 are both flat and smooth structures without protruding structures; refer to Figure 5 and Figure 6 ; the left end of the above-mentioned mixing section leg 8 is a wedge-shaped structure.

[0079] To adapt to the wind tunnel experiment environment, refer to Figure 2 , Figure 5 and Figure 14 ; a fairing 11 is provided above the outer side of the upper wall surface or / and below the outer side of the lower wall surface of the above-mentioned mixing section frame 1 for protecting the pipeline and rectifying the high Mach number oncoming flow. In this embodiment, the fairing 11 is provided below the outer side of the lower wall surface of the mixing section frame 1. Threaded holes are provided on the mixing section frame 1, and the fairing 11 is connected to the mixing section frame 1 by screws. The fairing above the outer side of the upper wall surface of the mixing section frame 1 can be designed according to the height of the pressure gauge above, the pipeline layout, etc.

[0080] Before the experiment, assemble the multi-variable fuel injection mixing section with a replaceable injection structure for the wind tunnel of the present invention according to Figure 1 ( Figure 1 For a complete display of its structure, fixing fittings such as screws are not installed), that is: first connect the mixing section leg 8 with the mixing section frame 1, and fix the mixing section frame 1 on the experimental support main structure through the mixing section leg 8; then, according to the requirements of the experimental conditions, determine the quantity and positions of the strut injection components and the wall injection components; and sequentially fix the strut fuel inlet end 4-1 of the strut 4 on the strut cover plate 3, dock and fix the strut cover plate 3 with the window 2, connect the first hexagon socket head screw with the strut sealing threaded hole 4-6 on the strut 4, seal the rear end of the strut fuel channel 4-7 through the first hexagon socket head screw, connect the strut rear end 4-4 of the strut 4 with the fixed strut cover plate 5, and connect the fixed strut cover plate 5 with the window 2; then, for the window 2 that requires observation, install the observation window assembly, and seal the other remaining windows 2 with the sealing cover plate 6; then use two second hexagon socket head screws to seal the wall fuel channel threaded holes 9-2 at the front and rear ends of the wall injection strip 9 respectively, install the wall injection strip 9 in the wall injection groove 1-3, and fill and seal the remaining wall injection grooves 1-3 with the wall filling strip 10; finally, connect the mixing section flange 1-2 provided at the right end of the mixing section frame 1 with the combustion chamber or nozzle structure.

[0081] After the experiment, adjust the number and position of the strut injection component and the wall injection component according to the next experiment and conduct the experiment again.

[0082] The multi-variable fuel injection and mixing section of the replaceable injection structure for wind tunnel of the present invention can be used for the mixing section of a high Mach number air-breathing experimental engine.

Claims

1. A multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel, characterized in that: it includes a mixing section frame (1), M strut injection assemblies, and N wall injection assemblies, where M ≥ 1, N ≥ 0, and both M and N are integers; the mixing section frame (1) is a hollow cuboid with openings on both the left and right walls; the opening on the left wall of the mixing section frame (1) is used to communicate with the air inlet of the air inlet structure; the right end of the mixing section frame (1) is used to connect to a combustion chamber or a nozzle structure; on the front and rear walls of the mixing section frame (1), at least two windows (2) are symmetrically arranged in the front and rear, and the sizes of all windows (2) are the same; two windows (2) in the symmetric positions on the front and rear walls of the mixing section frame (1) are defined as a group of windows; on the upper and lower outer walls of the mixing section frame (1), at the upper and lower symmetric positions above and below each group of windows, wall injection grooves (1-3) running through in the front and rear directions are correspondingly arranged, and the depth of the middle section of the wall injection groove (1-3) in the up and down direction in the front and rear direction satisfies: the wall injection groove (1-3) is connected to the internal flow field of the mixing section frame (1); one group of the strut injection assemblies is detachably installed in one group of windows correspondingly; the number of strut injection assemblies is less than or equal to the number of groups of windows; an observation window assembly or a sealing cover plate (6) is detachably installed at the window (2) where no strut injection assembly is installed to seal the window (2); one group of the wall injection assemblies is detachably installed at one wall injection groove (1-3) correspondingly; the number of wall injection assemblies is less than or equal to the sum of the numbers of all wall injection grooves (1-3); a wall filling strip (10) is detachably installed at the wall injection groove (1-3) where no wall injection assembly is installed to seal the wall injection groove (1-3); both the strut injection assemblies and the wall injection assemblies are used to inject fuel into the internal flow field of the mixing section frame (1).

2. The multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel according to claim 1, characterized in that: the inner sides of the front, rear, and lower borders at the opening on the left wall of the mixing section frame (1) are flat flow channels, and chamfers with an acute angle to the due right direction are arranged at the outer edge positions, serving as the air inlet drainage slope (1-1); the right end of the mixing section frame (1) is provided with a mixing section flange (1-2) for connecting to a combustion chamber or a nozzle structure.

3. The multi-variable fuel injection and mixing section with a replaceable injection structure for a wind tunnel according to claim 1, characterized in that: Each set of the strut injection components includes a strut cover plate (3), a fixed strut cover plate (5), and a strut (4); the strut cover plate (3) is installed on the window on the front wall surface in a set of windows; the fixed strut cover plate (5) is installed on the window on the rear wall surface in this set of windows; the fuel inlet end (4-1) of the strut (4) is connected to the strut cover plate (3), and the other end of the strut (4) opposite to the fuel inlet end (4-1) of the strut, i.e., the rear end (4-4) of the strut, is connected to the fixed strut cover plate (5), and the middle section of the strut (4) is located in the internal flow field of the mixing section frame (1); A strut cover plate pressure measurement hole (3-2) is provided on the upper surface of the strut cover plate (3), a strut cover plate fuel inlet interface (3-3) is provided on the lower surface of the strut cover plate (3), and a strut cover plate fuel outlet (3-4) is provided on the rear surface of the strut cover plate (3). The strut cover plate pressure measurement hole (3-2), the strut cover plate fuel inlet interface (3-3), and the strut cover plate fuel outlet (3-4) form a tee structure; A strut fuel inlet interface (4-3) is provided on the end surface of the end where the fuel inlet end (4-1) of the strut (4) is located; The outer contour shape of the middle section of the strut (4) is symmetric left and right and up and down; the outer contour shape of the middle section of the strut (4) is a shape formed by stretching the cross-section of the middle section of the strut perpendicular to the front-rear direction along the axis in the front-rear direction, and the shape of the cross-section of the middle section of the strut is a shape combined by symmetric wedges at both left and right ends and a rectangle surrounded by the four vertices of the large ends corresponding to the symmetric wedges in the middle; A strut fuel channel (4-7) along the front-rear direction is provided on the strut (4), and the axis of the strut fuel channel (4-7) coincides with the intersection line of the left-right symmetric plane and the up-down symmetric plane of the outer contour shape of the middle section of the strut (4); the front end of the strut fuel channel (4-7) is communicated with the strut cover plate fuel outlet (3-4) through the strut fuel inlet interface (4-3), and the rear end of the strut fuel channel (4-7) is a sealed end; Two rows of strut fuel injection holes (4-8) arranged in an array along the front-rear direction are provided on the middle section of the strut (4). The axes of the two rows of strut fuel injection holes (4-8) are all parallel to the plane perpendicular to the front-rear direction. The axes of the two rows of strut fuel injection holes (4-8) intersect with the axis of the strut fuel channel (4-7), and the included angles between the injection directions corresponding to the axes of the two rows of strut fuel injection holes (4-8) and the positive right direction are +45°±2° and -45°±2° respectively; or the strut fuel injection holes (4-8) are replaced with the form of a Laval nozzle.

4. The multi-variable fuel injection mixing section of the replaceable injection structure for a wind tunnel according to claim 3, characterized in that: Both the fuel inlet end (4-1) and the rear end (4-4) of the strut (4) are rectangular parallelepiped structures, and the strut (4) is a vertically symmetric structure as a whole; On the rear surface of the strut cover plate (3), there is a rectangular groove (3-5) of the strut cover plate extending in the left-right horizontal direction and adapted to the rectangular parallelepiped structure at the fuel inlet end (4-1) of the strut; on the front surface of the fixed strut cover plate (5), there is a rectangular groove (5-1) of the fixed strut cover plate extending in the left-right horizontal direction and adapted to the rectangular parallelepiped structure at the rear end (4-4) of the strut; the strut (4) is connected to the strut cover plate (3) and the fixed strut cover plate (5) by screws respectively; The four-side frame of the window (2) adopts a stepped structure; The observation window assembly includes a glass pressing plate (7) and glass, and the glass pressing plate (7) is used to fix the glass at the window (2); the four-side frames of the strut cover plate (3), the fixed strut cover plate (5), the glass pressing plate (7) and the sealing cover plate (6) all adopt structures adapted to the stepped structure.

5. The multivariable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 3, characterized in that: The cross-sectional shape of the wall injection groove (1-3) is rectangular; Each group of the wall injection assemblies includes a wall injection strip (9); The wall injection strip (9) is a strip-shaped structure with a T-shaped cross-section; the vertical side dimension of the T shape is adapted to the cross-sectional dimension of the wall injection groove (1-3) and is embedded in the wall injection groove (1-3); the two arms of the T shape are located above the outer side of the upper wall surface of the mixing section frame (1), and the two arms of the T shape are correspondingly distributed on the left and right sides of the wall injection groove (1-3) and are connected to the mixing section frame (1); A wall fuel channel (9-1) extending in the front-rear direction is provided on the wall injection strip (9), and the axis of the wall fuel channel (9-1) is located in the left-right symmetry plane of the wall injection strip (9); the front and rear ends of the wall fuel channel (9-1) are sealed ends; On the upper surface of the wall injection strip (9), near the midpoint in the front-rear direction of the wall injection strip (9), a wall injection strip fuel inlet (9-3) and a wall injection strip pressure measuring hole (9-4) are provided; the wall injection strip fuel inlet (9-3) and the wall injection strip pressure measuring hole (9-4) are arranged in the front-rear direction, and both the wall injection strip fuel inlet (9-3) and the wall injection strip pressure measuring hole (9-4) are communicated with the wall fuel channel (9-1); On the vertical side of the T shape in the middle section of the wall injection strip (9) extending in the front-rear direction, wall injection holes (9-5) arranged in an array in the front-rear direction are provided. The axis of the wall injection hole (9-5) is parallel to the plane perpendicular to the front-rear direction. The axis of the wall injection hole (9-5) intersects with the axis of the wall fuel channel (9-1). The included angle between the injection direction corresponding to the axis of the wall injection hole (9-5) and the due right direction is -45°±2° or +45°±2°, and the direction points to the internal flow field direction of the mixing section frame (1); or the wall injection hole (9-5) is replaced by a Laval nozzle form.

6. The multi-variable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 5, characterized in that: Each group of the strut injection assemblies further includes a first hexagon socket head cap screw; On the end face of one end where the rear end (4-4) of the strut is located, a strut sealing threaded hole (4-6) coaxial with and communicating with the strut fuel passage (4-7) is provided; the strut sealing threaded hole (4-6) is adapted to the first hexagon socket head cap screw, and the rear end of the strut fuel passage (4-7) is sealed by the first hexagon socket head cap screw; Each group of the wall injection assemblies further includes two second hexagon socket head cap screws; On the front and rear end faces of the wall injection strip (9), wall fuel passage threaded holes (9-2) coaxial with and communicating with the wall fuel passage (9-1) are provided; the wall fuel passage threaded holes (9-2) are adapted to the second hexagon socket head cap screws, and the front and rear ends of the wall fuel passage (9-1) are respectively sealed by the two second hexagon socket head cap screws in a one-to-one correspondence.

7. The multi-variable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 5, characterized in that: On the upper and lower wall surfaces of the mixing section frame (1) at positions other than where the wall injection strips (9) and wall filling strips (10) are installed, mixing section pressure measurement holes (1-4) are evenly distributed.

8. The multi-variable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 5, characterized in that: Below the lower wall surface outside of the mixing section frame (1), a mixing section leg (8) is provided; The mixing section leg (8) is a plate-shaped structure with 90° bending flanges at both the upper and lower parts; the 90° bending flanges are used as one-way flanges, where the upper one-way flange is used to connect with the lower wall surface of the mixing section frame (1), and the lower one-way flange is used to connect with the experimental support main structure; the plate surface is perpendicular to the front and rear directions; At the upper end of the mixing section leg (8), a plurality of mixing section leg cut grooves (8-1) penetrating in the front and rear directions are provided for avoiding the wall injection strip (9) or the wall filling strip (10).

9. The multi-variable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 8, characterized in that: The surfaces of the strut cover plate (3), fixed strut cover plate (5) and sealing cover plate (6) on the inner flow field side of the mixing section frame (1) are respectively flush and smooth with the corresponding inner wall surfaces of the mixing section frame (1); The front surface of the strut cover plate (3) and the rear surface of the fixed strut cover plate (5) are both flat and smooth structures; the left end of the mixing section leg (8) is a wedge-shaped structure.

10. The multi-variable fuel injection and mixing section of the replaceable injection structure for a wind tunnel according to claim 1, characterized in that: Above the upper wall surface outside of the mixing section frame (1) or / and below the lower wall surface outside of the mixing section frame (1), a fairing (11) is provided for protecting the pipeline and rectifying the high Mach number oncoming flow.

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