A pulsating back pressure experimental device capable of simulating single and dual frequency disturbance

Abstract

The application discloses a pulsating back pressure experimental device capable of simulating single and double frequency disturbance, which comprises an experimental support table, an experimental observation module, a pulsating back pressure generating module and a downstream expansion module; the pulsating back pressure generating module comprises a back pressure section frame and a throttling disturbance unit; the throttling disturbance unit comprises a side plate assembly, a worm gear mechanism, a follower plate assembly, a cam top rod driving mechanism, a swing block swing rod transmission mechanism, a transmission circular shaft and an elliptical shaft; the cross section of the elliptical shaft is elliptical; the worm gear mechanism drives the follower plate assembly to rotate by a preset angle and then to be positioned, so that the two elliptical shafts are horizontally coplanar, vertically coplanar or obliquely coplanar; the power output end of the cam top rod driving mechanism is in transmission connection with the shaft end of the transmission circular shaft through the swing block swing rod transmission mechanism. The application can simulate low frequency pulsation (hundred hertz level) back pressure disturbance generated in a cold flow experiment of a scramjet combustor, and can carry out reliable simulation experiments on the influence law of multiple low frequency pulsating back pressure on upstream flow in a wide range and under multiple working conditions.

Description

Technical Field

[0001] This invention belongs to the field of design and experimental research technology of supersonic and hypersonic aircraft, and specifically relates to a pulsating back pressure experimental device that can simulate single and dual frequency disturbances. Background Technology

[0002] Hypersonic vehicles powered by scramjet engines play a leading role in aerospace technology. Their main structure includes an inlet, isolator, combustion chamber, and exhaust nozzle. The isolator is the intermediate component between the inlet and the combustion chamber. On one hand, it slows down and pressurizes the upstream gas to provide oxidizer for combustion in the downstream combustion chamber; on the other hand, it isolates the high-temperature, high-pressure airflow in the combustion chamber, maintaining stable airflow in the inlet. The high pressure in the combustion chamber downstream of the isolator is commonly referred to as back pressure. In practice, due to the instability of combustion itself, inflow disturbances, and changes in engine operating modes, the back pressure in the isolator typically varies over time, exhibiting pulsating characteristics. This pulsating back pressure has a wide spectral range, with relatively large amplitude low-frequency oscillations in the hundreds of Hertz range. Pulsating back pressure in the isolator can induce oscillations in the upstream flow (e.g., shock train oscillations within the isolator), generating pulsating loads and even causing inlet malfunction and engine shutdown. Due to the high cost and inherent dangers of combustion research, the back pressure environment of the combustion chamber is typically simulated under cold flow conditions using back pressure experimental devices. Existing simulation devices can be divided into two categories:

[0003] 1. Place a blockage block at the intake outlet to reduce the flow area and generate back pressure by blocking and accumulating airflow.

[0004] 2. Back pressure is generated downstream of the intake duct through the combined effect of the mass addition of the external gas jet and the jet disturbance.

[0005] The characteristics and limitations of existing patent-holding institutions include:

[0006] 1. A motor-driven throttle fan is used downstream of the isolation section outlet to periodically block the airflow, creating a pulsating back pressure by switching between "blocked" and "unblocked" states. Although this method can generate high-frequency pulsating back pressure, the back pressure generated by this device outside the intake duct is significantly different from the pulsating back pressure in the confined space inside the intake duct.

[0007] 2. A linear stepper motor is used downstream of the isolation section to control the movement of the throttling cone / wedge along the flow direction, thereby changing the throttling area to generate back pressure. However, this device is limited by external space and it is difficult to achieve combustion back pressure pulsation at the level of hundreds of hertz.

[0008] 3. A periodically moving throttling block is placed in the square groove downstream of the isolation section to simulate downstream back pressure disturbance. However, this type of device is for exploring single-frequency disturbance problems, and the method for simulating back pressure disturbance is limited to single-frequency disturbance. It cannot be used to study problems involving multiple frequencies of disturbance, and it is not applicable to the dual-frequency pulsating back pressure of hypersonic inlets.

[0009] Furthermore, when using external gas jets or pulse jets to generate pulsating back pressure, the frequency and intensity of the pulsating back pressure are difficult to control due to interference from the jets and the mainstream flow field, and a large amount of gas is consumed during the experiment. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention proposes a pulsating back pressure experimental device capable of simulating single and dual-frequency disturbances. This device simulates multiple low-frequency pulsating (hundred-hertz level) back pressure disturbances generated in the combustion chamber of a scramjet engine during cold flow experiments, enabling reliable simulation experiments on the influence of multiple low-frequency pulsating back pressures on upstream flow over a wide range of conditions.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0012] A pulsating back pressure experimental device capable of simulating single and dual frequency disturbances includes an experimental support platform, an experimental observation module, a pulsating back pressure generation module, and a downstream extension module, which are sequentially fixed on the top of the experimental support platform. The central axes of the experimental observation module, the pulsating back pressure generation module, and the downstream extension module coincide, and the internal flow channels of the experimental observation module, the pulsating back pressure generation module, and the downstream extension module are sequentially connected to form a gas flow channel.

[0013] The pulsating back pressure generating module includes a back pressure section frame and throttling disturbance units centrally symmetrically distributed on both sides of the back pressure section frame. The throttling disturbance unit includes a cam push rod drive mechanism and a rocker arm transmission mechanism fixedly installed on the outside of the back pressure section frame, a side plate assembly fixedly embedded in the side wall of the back pressure section frame, a worm gear mechanism fixedly installed on the outer surface of the side plate assembly, a follower plate assembly rotatably installed in the side plate assembly, a transmission shaft rotatably installed in the eccentric position of the follower plate assembly, and an elliptical shaft detachably connected to the inner shaft end of the transmission shaft. The other end of the elliptical shaft is rotatably installed in the end face of the follower plate assembly of another throttling disturbance unit. The cross-section of the elliptical shaft is elliptical. The two elliptical shafts are arranged parallel to each other in the internal flow channel of the back pressure section frame and perpendicular to the flow direction of the internal flow channel.

[0014] In each throttling disturbance unit, the output end of the worm gear mechanism is connected to the shaft end of the follower plate assembly. After driving the follower plate assembly to rotate by a preset angle, it is then positioned so that the axes of the two elliptical axes are horizontally coplanar, vertically coplanar, or inclined coplanar. The power output end of the cam push rod drive mechanism is connected to the shaft end of the transmission shaft through the rocker arm drive mechanism. The transmission shaft is driven to reciprocate at a period corresponding to the output speed of the cam push rod drive mechanism, thereby driving the major axis / minor axis of the elliptical axis to reciprocate between the 0° position and the 90° position.

[0015] Furthermore, the cam push rod drive mechanism includes a fixedly mounted motor bracket and two bearing seats. A drive motor is fixedly mounted on the motor bracket, and a cylindrical cam is fixedly connected to the output shaft end of the drive motor. The two shaft ends of the cylindrical cam are respectively rotatably mounted in the two bearing seats. A cam groove with a preset trajectory is opened on the cylindrical surface of the cylindrical cam, and a pin located on one side of the cylindrical cam and horizontally positioned is movably embedded in the cam groove.

[0016] Furthermore, the rocker arm transmission mechanism includes a fixedly mounted guide rod bracket, a guide rod inclinedly fixedly mounted on the top of the guide rod bracket, a slider slidably mounted on the guide rod, and a rocker arm bracket fixedly mounted on the top of the guide rod bracket and located below the guide rod. A rocker arm shaft is rotatably mounted inside the rocker arm bracket. A rocker arm is fixedly mounted at one end of the rocker arm shaft near the cam push rod drive mechanism, and a central gear is fixedly mounted at the other end of the rocker arm away from the cam push rod drive mechanism. A rocker arm is slidably inserted inside the rocker arm. The inner side of the top end of the rocker arm is rotatably mounted inside the side of the slider, and the pin is movably inserted into the outer side of the top end of the rocker arm.

[0017] Furthermore, a planetary gear that meshes with the central gear is fixedly installed on the outer shaft end of the transmission shaft.

[0018] Furthermore, the worm gear mechanism includes two worm brackets fixedly disposed on the outer side of the side plate assembly, a worm rotatably installed in the worm brackets, and a rotating central shaft fixedly installed at the axis of the follower plate assembly, with a worm wheel meshing with the worm fixedly installed at the shaft end of the rotating central shaft.

[0019] Furthermore, the side plate assembly includes an inner side plate and an outer side plate. A central cylindrical cavity is provided inside the end faces of the inner side plate and the outer side plate that are in contact with each other. The follower plate assembly is coaxially rotatably disposed in the central cylindrical cavity. An inner through hole communicating with the central cylindrical cavity is opened at the center of the end face of the inner side plate, and an outer through hole communicating with the central cylindrical cavity is opened at the center of the end face of the outer side plate. The inner side plate and the outer side plate are fixedly connected to the outer wall of the counter-pressure section frame by bolts.

[0020] Furthermore, the follower plate assembly includes an inner moving plate and an outer moving plate, which are fixedly connected. An inner frustum is integrally provided at the center of the end face of the inner moving plate and is rotatably sleeved in the inner through hole. An outer frustum is integrally provided at the center of the end face of the outer moving plate and is rotatably sleeved in the outer through hole.

[0021] Furthermore, a first sealing ring is provided between the end face of the inner side plate and the outer wall of the counter-pressure section frame, a second sealing ring is provided between the end faces of the inner side plate and the outer side plate that are in contact, a third sealing ring is provided between the end faces of the inner moving plate and the outer moving plate that are in contact, a fourth sealing ring is provided between the end face of the inner moving plate and the end face of the inner side plate, and a fifth sealing ring is provided between the end face of the outer moving plate and the end face of the outer side plate.

[0022] Furthermore, the internal flow channel of the experimental observation module is a rectangular flow channel, the internal flow channel of the pulsating back pressure generation module is a rectangular flow channel, and the internal flow channel of the downstream expansion module is a funnel-shaped square-to-circular flow channel with a small opening and a large outlet.

[0023] Furthermore, the experimental observation module includes a flow channel frame and an annular frame detachably connected to the outer wall of the flow channel frame, wherein the annular frame and the flow channel frame are fixedly clamped together to hold the observation glass.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention can achieve a wide range of controllable adjustment of the throttling frequency by changing the speed of the drive motor and the transmission ratio of the gear set: a pair of gear sets are set in the transmission between the drive motor and the elliptical shaft. By setting the gear transmission ratio, the speed of the drive motor can be amplified, allowing the elliptical shaft to output a larger speed, thereby increasing the throttling frequency.

[0026] 2. This invention can achieve the mutual conversion between single-frequency and dual-frequency operating conditions by changing the throttling frequency of the two elliptical shafts: two drive motors and gear sets are respectively placed on both sides of the counter-pressure section frame, driving the two elliptical shafts to rotate. By placing the drive motors and gear sets on both sides of the counter-pressure section frame, the throttling frequency of the two elliptical shafts can be changed. When the throttling frequencies of the two elliptical shafts are the same, single-frequency operating condition is achieved; when the throttling frequencies of the two elliptical shafts are different, dual-frequency operating condition is achieved.

[0027] 3. This invention can achieve the change of throttling disturbance configuration through a worm gear mechanism: rotating the worm adjusts the relative position of the two elliptical axes, and automatically locks them through the reverse stroke self-locking principle of the worm gear and worm; rotating the worm can make both elliptical axes located at the center of the vertical direction of the flow channel, at which time the generated throttling disturbance is located at the center of the vertical direction of the flow channel, and the vertical distance between the two elliptical axes is also minimum to 0; rotating the worm can make the two elliptical axes vertically symmetrical, the generated throttling disturbance is vertically symmetrically distributed along the center of the flow channel, and the vertical distance between the two elliptical axes is also maximum; rotating the worm can make the two elliptical axes tilted symmetrically, the generated throttling disturbance is unevenly distributed along the flow channel, and the vertical distance between the two elliptical axes is between maximum and minimum.

[0028] 4. This invention can adjust the range of throttling ratio by changing the lengths of the major and minor semi-axes of the elliptical axis and the throttling disturbance configuration: Regardless of whether it is a single-frequency or dual-frequency operation, the magnitude of the throttling ratio is related to the lengths of the major and minor semi-axes of the elliptical axis and the throttling disturbance configuration. When the axis of the major semi-axe of the elliptical axis is rotated to be perpendicular to the flow direction, the throttling ratio is at its maximum, i.e., the back pressure is at its maximum, and the maximum back pressure is related to the length of the major semi-axe of the elliptical axis; when the axis of the major semi-axe of the elliptical axis is rotated to be horizontal to the flow direction, the throttling ratio is at its minimum, i.e., the back pressure is at its minimum, and the minimum back pressure is related to the length of the minor semi-axe of the elliptical axis; when the throttling disturbance configuration is such that both elliptical axes are located at the center of the vertical direction of the flow channel, the throttling ratio generated by the two elliptical axes is at its maximum value; when the throttling disturbance configuration is such that the two elliptical axes are placed vertically or obliquely symmetrically, the throttling ratios generated by the two elliptical axes are directly superimposed.

[0029] 5. This invention can achieve the change of pulsating back pressure waveform through the contour curve design of the cam groove: the cam push rod drive mechanism drives the transmission shaft to rotate, thereby realizing the reciprocating rotation of the major axis / minor axis of the elliptical shaft between the 0° position and the 90° position within the back pressure section frame, causing periodic blockage of the airflow in the back pressure section. The roller on the rocker arm is inserted into the cam groove, and the elliptical shaft can be made to rotate more complexly by adjusting the contour curve of the cam groove, thereby realizing the change of pulsating back pressure waveform.

[0030] This invention incorporates a mechanical device capable of generating periodic pulsating back pressure. A cam-driven mechanism rotates an elliptical transmission shaft, causing it to reciprocate within the back pressure section frame. This results in periodic airflow blockage and the generation of periodic pulsating back pressure. The throttling frequency can be controlled and adjusted over a wide range by changing the drive motor speed and gear ratio. Switching between single-frequency and dual-frequency operation can be achieved by altering the throttling frequencies of the two elliptical shafts. The throttling disturbance configuration can be modified using a worm gear mechanism. The throttling ratio range can be adjusted by changing the lengths of the major and minor semi-axles of the elliptical shaft. Furthermore, the waveform of the pulsating back pressure can be varied through the design of the cam groove's contour curve. This allows for better simulation and study of the strong unsteady phenomena caused by high-frequency pulsating back pressure during actual operation of the isolation section, leading to more reliable experimental results. Therefore, this invention has strong applicability, and key components can be disassembled individually for easy replacement under different operating conditions. Attached Figure Description

[0031] Figure 1 This is one of the three-dimensional structural schematic diagrams of the present invention;

[0032] Figure 2 This is a second three-dimensional structural schematic diagram of the present invention;

[0033] Figure 3This is one of the three-dimensional structural diagrams showing the assembled state of the three main modules in this invention;

[0034] Figure 4 This is the second three-dimensional structural diagram of the three main modules in the present invention in their assembled state;

[0035] Figure 5 This is a cross-sectional structural diagram of the three main modules in the assembled state of the present invention;

[0036] Figure 6 This is a three-dimensional structural diagram of the experimental observation module in this invention;

[0037] Figure 7 This is a three-dimensional structural diagram of the counter-pressure section frame in this invention;

[0038] Figure 8 This is a three-dimensional structural diagram of the downstream extension module in this invention;

[0039] Figure 9 This is a three-dimensional structural diagram of the pulsating back pressure generation module in this invention;

[0040] Figure 10 This is a top view of the pulsating back pressure generation module in this invention.

[0041] Figure 11 This is one of the three-dimensional structural schematic diagrams of the pulsating back pressure generation module in the present invention in the state of removing the back pressure section frame;

[0042] Figure 12 This is the second three-dimensional structural schematic diagram of the pulsating back pressure generating module in the present invention in the state of removing the back pressure section frame;

[0043] Figure 13 This is a top view of the pulsating back pressure generation module in the present invention with the back pressure section frame removed.

[0044] Figure 14 This is one of the three-dimensional structural schematic diagrams of the cam push rod drive mechanism in this invention;

[0045] Figure 15 This is the second three-dimensional structural schematic diagram of the cam push rod drive mechanism in this invention;

[0046] Figure 16 This is a schematic diagram of the mounting structure of the cylindrical cam described in this invention;

[0047] Figure 17 This is one of the three-dimensional structural schematic diagrams of the rocker arm transmission mechanism in this invention;

[0048] Figure 18 This is the second three-dimensional structural schematic diagram of the rocker arm transmission mechanism in this invention;

[0049] Figure 19 This is a three-dimensional cross-sectional view of the rocker arm transmission mechanism in this invention;

[0050] Figure 20 This is a three-dimensional structural diagram of the two side plate components and their assembly state in this invention;

[0051] Figure 21 This is a cross-sectional view of the side panel assembly and its internal components in this invention.

[0052] Figure 22 This is a schematic diagram of three throttling disturbance configurations in this invention;

[0053] Figure 23 This is a schematic diagram of the pulsating back pressure waveform in the embodiment.

[0054] In the diagram: 1. Experimental observation module; 11. Flow channel frame; 12. Annular frame; 13. Observation glass; 2. Pulsating back pressure generation module; 21. Back pressure section frame; 211. Embedded through hole; 212. First annular groove and side plate assembly; 221. Inner side plate; 222. Outer side plate; 223. Second sealing ring; 23. Worm gear mechanism; 231. Worm support; 232. Worm; 233. Rotating central shaft; 234. Worm gear; 235. Handle; 24. Follower plate assembly; 241. Inner moving plate; 242. Outer moving plate; 243. Third sealing ring; 244. Fourth sealing ring; 245. Fifth sealing ring; 25. Cam push rod drive mechanism; 251. Drive motor; 252. Motor support; 253. Coupling; 2 54. Bearing housing; 255. Cylindrical cam; 256. Pin; 257. Cam shaft; 258. Roller; 259. Spring; 26. Rocker arm transmission mechanism; 261. Guide rod bracket; 262. Guide rod; 263. Slider; 264. Rocker bracket; 265. Rocker shaft; 266. Rocker; 267. Central gear; 268. Rocker arm; 269. Bearing cover plate; 27. Transmission shaft; 271. Planetary gear; 272. Sixth sealing ring; 28. Elliptical shaft; 291. First mounting bracket; 292. Second mounting bracket; 293. Third mounting bracket; 3. Downstream expansion module; 4. Positioning mounting bracket; 41. Mounting plate; 5. Experimental support platform; 61. First flange; 62. Second flange; 63. Third flange. Detailed Implementation

[0055] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0056] See Figures 1 to 21An experimental device for simulating single- and dual-frequency disturbances involving pulsating back pressure includes an experimental support platform 5, an experimental observation module 1, a pulsating back pressure generating module 2, and a downstream extension module 3, which are sequentially fixed on the top of the experimental support platform 5. The central axes of the experimental observation module 1, the pulsating back pressure generating module 2, and the downstream extension module 3 coincide, and their internal flow channels are sequentially connected to form a gas flow channel. Specifically, three positioning mounting brackets 4 are provided at the top of the experimental support platform 5, and each positioning mounting bracket 4 has a mounting plate 41 at its top, which is used to support the experimental observation module 1, the pulsating back pressure generating module 2, and the downstream extension module 3, respectively. First flanges 61 (such as...) are sleeved and connected to both ends of the experimental observation module 1. Figure 6 As shown), the two ends of the pulsating back pressure generating module 2 are respectively fitted with second flanges 62 (as shown). Figure 7 As shown), the downstream expansion module 3 has a third flange 63 (as shown) fitted at both ends. Figure 8 (As shown). The experimental observation module 1 and the pulsating back pressure generating module 2 are connected via a first flange 61 and a second flange 62. The pulsating back pressure generating module 2 and the downstream expansion module 3 are connected via a second flange 62 and a third flange 63, as shown. Figures 3 to 5 As shown. Meanwhile, the internal flow channel of the experimental observation module 1 is a rectangular flow channel, the internal flow channel of the pulsating back pressure generation module 2 is a rectangular flow channel, and the internal flow channel of the downstream expansion module 3 is a funnel-shaped square to round flow channel with a small opening and a large outlet.

[0057] like Figure 6 As shown, the experimental observation module 1 includes a flow channel frame 11 and an annular frame 12 detachably connected to the outer wall of the flow channel frame 11. An observation glass 13 is fixedly clamped between the annular frame 12 and the flow channel frame 11. The flow channel frame 11 is a rectangular cross-section metal frame with a hollow channel of rectangular cross-section inside. At least one side is provided with an observation glass 13 to allow for direct observation of the internal conditions of the flow channel during the experiment. The annular frame 12 is detachably connected to the outer wall of the flow channel frame 11 by screws to facilitate the disassembly, cleaning, or replacement of the observation glass 13.

[0058] like Figures 9 to 13As shown, the pulsating back pressure generating module 2 includes a back pressure section frame 21 and throttling disturbance units that are centrally symmetrically distributed on both sides of the back pressure section frame 21. The throttling disturbance unit includes a cam push rod drive mechanism 25 and a rocker arm transmission mechanism 26 fixedly installed on the outside of the back pressure section frame 21, a side plate assembly 22 fixedly embedded in the side wall of the back pressure section frame 21, a worm gear mechanism 23 fixedly installed on the outer surface of the side plate assembly 22, a follower plate assembly 24 rotatably installed in the side plate assembly 22, a transmission shaft 27 rotatably installed in the eccentric position of the follower plate assembly 24, and an elliptical shaft 28 detachably connected to the inner shaft end of the transmission shaft 27. The other end of the elliptical shaft 28 is rotatably installed in the end face of the follower plate assembly 24 of another throttling disturbance unit. The cross-section of the elliptical shaft 28 is elliptical. The two elliptical shafts 28 are arranged parallel to each other in the internal flow channel of the back pressure section frame 21 and are perpendicular to the flow direction of the internal flow channel. Since the two throttling disturbance units have the same structure and are connected to each other, the specific structure and working process of the pulsating back pressure generation module 2 will be explained below by using a set of throttling disturbance units on one side.

[0059] Specifically, the side plate assembly 22 includes an inner side plate 221 and an outer side plate 222, which are sequentially fixedly connected. Both the inner side plate 221 and the outer side plate 222 are disc-shaped. The inner end face of the inner side plate 221 is integrally provided with a first cylindrical boss. The side wall of the counterpressure section frame 21 is provided with an insert through hole 211 that matches the outer diameter of the first cylindrical boss. Through the combination of the first cylindrical boss and the insert through hole 211, the inner side plate 211 is positioned on the outer wall of the counterpressure section frame 21. The flow channel cross-section of the counterpressure section frame 21 is rectangular, and the central axis of the first cylindrical boss is located on the horizontal mid-section of the flow channel.

[0060] like Figure 21As shown, a central circular groove, coaxially arranged with the first cylindrical boss, is formed on the end faces where the inner side plate 221 and the outer side plate 222 meet. This creates a central cylindrical cavity within the inner side plate 221 and the outer side plate 222 after assembly. The follower plate assembly 24 is coaxially rotatable within this central cylindrical cavity. The follower plate assembly 24 includes an inner moving plate 241 and an outer moving plate 242. Both the inner moving plate 241 and the outer moving plate 242 are also disc-shaped, and their outer diameter is not greater than the diameter of the central cylindrical cavity. An inner through hole communicating with the central cylindrical cavity is provided at the center of the end face of the inner side plate 221, and an outer through hole communicating with the central cylindrical cavity is provided at the center of the end face of the outer side plate 222; an inner frustum integrally provided at the center of the end face of the inner moving plate 241 is rotatably fitted in the inner through hole, and an outer frustum integrally provided at the center of the end face of the outer moving plate 242 is rotatably fitted in the outer through hole. Through the rotational engagement of the inner frustum and the inner through hole, and the rotational engagement of the outer frustum and the outer through hole, the follower plate assembly 24 is rotatably set in the side plate assembly 22, and the side plate assembly 22 is fixedly connected to the counter-pressure section frame 21.

[0061] To ensure the sealing of the connection between the side plate assembly 22 and the follower plate assembly 24 and the counter-pressure section frame 21, a first annular groove 212 is provided on the outer side wall of the counter-pressure section frame 21 that mates with the inner side plate 221. A first sealing ring is provided in the first annular groove 212, thereby achieving a static seal between the end face of the inner side plate 221 and the outer side wall of the counter-pressure section frame 21. A second annular groove is provided on the end face of the outer side plate 222 that mates with the inner side plate 221, located outside the central cylindrical cavity. A second sealing ring 223 is provided in the second annular groove, thereby achieving a static seal between the inner side plate 221 and the outer side plate 222. The outer moving plate 242 has a second annular groove located on the end face that mates with the inner moving plate 241. A third annular groove is provided on the surface, and a third sealing ring 243 is provided in the third annular groove to achieve a static seal between the inner moving plate 241 and the outer moving plate 242. A fourth annular groove located outside the inner frustum is provided on the inner end face of the inner side plate 221 that contacts the inner moving plate 241, and a fourth sealing ring 244 is provided in the fourth annular groove to achieve a dynamic seal between the inner side plate 221 and the inner moving plate 241. A fifth annular groove located outside the outer frustum is provided on the inner end face of the outer side plate 222 that contacts the outer moving plate 242, and a fifth sealing ring 245 is provided in the fifth annular groove to achieve a dynamic seal between the outer side plate 222 and the outer moving plate 242. In this embodiment, the sealing ring used for static sealing is a fluororubber O-ring, and the sealing ring used for dynamic sealing is a Glycol ring.

[0062] In each throttling disturbance unit, the output end of the worm gear mechanism 23 is connected to the follower plate assembly 24 for transmission. After driving the follower plate assembly 24 to rotate by a preset angle, it is then positioned so that the axes of the two elliptical axes 28 are horizontally coplanar, vertically coplanar, or inclined coplanar. Specifically, as shown in... Figure 21As shown, a rotating central shaft 233 is fixedly installed at the axis of the follower plate assembly 24. A coaxial through hole is formed at the center of the outer moving plate 242, and a coaxial blind hole is formed at the center of the inner end face of the inner moving plate 241. Positioning grooves are formed at the inner ports of the through hole and the blind hole. A shoulder is formed in the middle of the rotating central shaft 233. The inner end of the rotating central shaft 233 is inserted into the blind hole, and the outer end is inserted into the through hole and located on the outside of the outer moving plate 242. The shoulder is embedded in the positioning groove and fixedly connected to the positioning groove with screws, so that the rotating central shaft 233 will not rotate relative to the follower plate assembly 24. In this way, under the driving force of external force, the rotating central shaft 233 can drive the follower plate assembly 24 to rotate synchronously and be positioned.

[0063] like Figure 20 As shown, the worm gear mechanism 23 includes two worm supports 231 fixedly mounted on the outer surface of the side plate assembly 22, a worm 232 rotatably mounted within the worm supports 231, and a worm wheel 234 fixedly mounted at the end of the rotating shaft 233, meshing with the worm 232. By rotating the worm 232, the rotating shaft 233 can be driven to rotate synchronously with the follower plate assembly 24 under the action of meshing transmission, thereby adjusting the spatial position of the two elliptical shafts 28 connected thereon. By utilizing the self-locking characteristic of the worm gear mechanism itself, the position of the follower plate assembly 24 after adjustment is locked. To facilitate the rotation operation of the worm 232, a handle 235 is also fixedly provided at one end of the worm 232.

[0064] An eccentric circular groove is provided on the inner end face of the inner moving plate 241 and the inner end face of the outer moving plate 242, so that after the inner moving plate 241 and the outer moving plate 242 are assembled, an eccentric cylindrical cavity is formed at the eccentric position inside. The transmission shaft 27 is coaxially rotatably arranged in the eccentric cylindrical cavity. Both ends of the transmission shaft 27 are rotatably connected to rolling bearings, and the rolling bearings at both ends are axially positioned by bushings. An inner eccentric through hole is provided on the outer end face of the inner moving plate 241 and is coaxially arranged with the eccentric cylindrical cavity. An outer eccentric through hole is provided on the outer end face of the outer moving plate 242 and is coaxially arranged with the eccentric cylindrical cavity. The inner end of the transmission shaft 27 is located in the inner eccentric through hole, and the outer end is located in the outer eccentric through hole and extends to the outer side of the outer moving plate 242. Meanwhile, a sixth sealing ring 272 is provided between the inner end of the transmission shaft 27 and the inner eccentric through hole to achieve dynamic sealing between the transmission shaft 27 and the inner moving plate 241, so as to further ensure the sealing of the connection position between the side plate assembly 22 and the follower plate assembly 24 and the counter-pressure section frame 21.

[0065] The inner moving plate 241, located within the counter-pressure section frame 21, has a bearing groove on its end face. The axis of the bearing groove and the axis of the eccentric cylindrical cavity are symmetrically distributed on both sides of the axis of the central cylindrical cavity. One end of the elliptical shaft 28 is threadedly connected to the inner end face of the transmission shaft 27 and is coaxially arranged. The other end is rotatably connected to a rolling bearing embedded in the moving plate 241 of another throttling disturbance unit. In this way, the transmission shaft 27 can transmit the externally input rotational driving force to the elliptical shaft 28 to achieve synchronous rotation.

[0066] The power output end of the cam push rod drive mechanism 25 is connected to the shaft end of the transmission shaft 27 through the rocker arm transmission mechanism 26, driving the transmission shaft 27 to reciprocate in a period corresponding to the output speed of the cam push rod drive mechanism 25, thereby driving the elliptical shaft 28 to reciprocate between the 0° position and the 90° position.

[0067] like Figures 14 to 16As shown, the cam push rod drive mechanism 25 includes a fixedly mounted motor bracket 252 and two bearing seats 254. A drive motor 251 is fixedly mounted on the motor bracket 252. A cylindrical cam 255 is fixedly connected to the output shaft end of the drive motor 251. The two shaft ends of the cylindrical cam 255 are rotatably mounted in the two bearing seats 254 respectively. A cam groove 2551 with a preset trajectory is opened on the cylindrical surface of the cylindrical cam 255. A pin 256 located on one side of the cylindrical cam 255 and horizontally arranged is movably embedded in the cam groove 2551. Specifically, the bottom end of the motor bracket 252 is fixedly connected to the mounting plate 41 via the first mounting bracket 291. The bottom end of the bearing seat 254 on the side closer to the drive motor 251 is fixedly connected to the side of the first mounting bracket 291, and the bottom end of the bearing seat 254 on the side farther from the drive motor 251 is fixedly connected to the mounting plate 41 via the second mounting bracket 292. The first mounting bracket 291 and the second mounting bracket 292 are used to adjust the horizontal and vertical positions of the drive motor 251 and the bearing seat 254 to meet the spatial arrangement requirements of the transmission. A cam shaft 257 is fixedly provided at the center of the cylindrical cam 255. One end of the cam shaft 257 away from the drive motor 251 is rotatably mounted in the bearing seat 254 at the corresponding position via a rolling bearing, and the other end of the shaft is rotatably mounted in the bearing seat 254 at the corresponding position via a pair of tapered rollers. This end is connected to the output shaft of the drive motor 251 via a coupling 253. A roller 258 is fitted onto the end of the pin 256. The roller 258 is embedded in the cam groove 2551, and its outer circular surface rolls in contact with the two side walls of the cam groove 2551. When the drive motor 251 drives the cylindrical cam 255 to rotate continuously, the curved side walls of the cam groove 2551 exert a force on the roller 258, causing the axis of the roller 258 (pin 256) to move horizontally and reciprocally forward and backward along the axis of the cylindrical cam 255. In this embodiment, the drive motor 251 is a Panasonic MINAS A6 series MHMF042L1U2M servo motor with a rated speed of 3000 rpm and a rated power of 400W.

[0068] like Figures 17 to 19As shown, the rocker arm transmission mechanism 26 includes a fixed guide rod bracket 261, a guide rod 262 fixedly mounted on the top of the guide rod bracket 261, a slider 263 slidably sleeved on the guide rod 262, and a rocker arm bracket 264 fixedly mounted on the top of the guide rod bracket 261 and located below the guide rod 262. A rocker arm shaft 265 is rotatably mounted inside the rocker arm bracket 264. A rocker arm 266 is fixedly mounted at one end of the rocker arm shaft 265 near the cam push rod drive mechanism 25, and a central gear 267 is fixedly mounted at the other end away from the cam push rod drive mechanism 25. A rocker arm 268 is slidably inserted inside the rocker arm 266. The inner side of the top end of the rocker arm 268 is rotatably sleeved inside the side of the slider 263, and a pin 256 is movably inserted into the outer side of the top end of the rocker arm 268.

[0069] Specifically, the bottom end of the guide rod bracket 261 is fixedly connected to the top surface of the mounting plate 41 via a third mounting bracket 293. The spatial position of the rocker arm transmission mechanism 26 can be adjusted via the third mounting bracket 293 to meet the needs of transmission assembly. The guide rod bracket 261 is U-shaped, with its top two vertical sidewalls at different heights, and each vertical sidewall has a fixing connection hole at its top. The two ends of the guide rod 262 are fixedly connected to the fixing connection holes on the top two vertical sidewalls of the guide rod bracket 261, forming an inclined guide rail. See also... Figure 19 The slider 263 is slidably sleeved on the outside of the guide rod 262, forming a sliding pair with the guide rod 262. A cylindrical sleeve is integrally provided on the side of the slider 263 near the cam push rod drive mechanism 25. The top of the rocker arm 268 is a cylindrical structure with its axis set horizontally. The inner end of the cylindrical structure is rotatably sleeved in the cylindrical sleeve, so that the top of the rocker arm 268 can rotate relative to the slider 263. A stepped hole is opened at the center of the outer end face of the cylindrical structure. A spring 259 is provided in the small hole at the center of the stepped hole. The end of the pin 256 away from the roller 258 is movably inserted into the large hole of the stepped hole and contacts the end of the spring 259. The spring 259 is always in a compressed state. The axial thrust applied by the spring 259 to the pin 256 can reliably embed the roller 258 in the cam groove 2551 during the transmission process. The rocker block support 264 has bearing mounting holes on its side. The two ends of the rocker block shaft 265 are rotatably mounted in these holes via a pair of rolling bearings. A bearing cover plate 269 is fixedly connected to the outside of the bearing mounting holes to achieve axial positioning of the rolling bearings and the rocker block shaft 265. The outer end of the rocker block shaft 265 extends out of the rocker block support 264 and is fixedly inserted into the rocker block 266. The inner end of the rocker block shaft 265 extends out of the rocker block support 264 and is fixedly connected to the central gear 267. The lower end of the rocker arm 268 is a flat rod structure. The rocker block 266 has an insertion hole inside that matches the cross-sectional shape of the flat rod structure of the rocker arm 268. The lower part of the rocker arm 268 is movably inserted into the insertion hole, forming a sliding pair with the rocker block 266.

[0070] When the drive motor 251 drives the pin 256 (roller 258) to move horizontally and reciprocally forward and backward along the axis of the cylindrical cam 255 via the cylindrical cam 255, the relative position between the pin 256 and the slider 263 is fixed, and the guide rod 262 restricts the sliding direction of the slider 263. Therefore, as the pin 256 moves horizontally forward, it also moves downward along the length of the guide rod 262. Conversely, as the pin 256 moves horizontally backward, it also moves downward along the length of the guide rod 262. The length of 62 moves upward; while the axis of the rocker arm 265 remains fixed. Therefore, the axis of the pin 256 oscillates back and forth around the axis of the rocker arm 265. The sliding pair between the rocker arm 268 and the rocker arm 266 allows the rocker arm 266 and the rocker arm 265 to oscillate back and forth around the axis of the rocker arm 265. The sliding adjustment of the rocker arm 268 within the rocker arm 266 is to adaptively meet the changes in distance between the axis of the pin 256 and the axis of the rocker arm 265. A planetary gear 271, which meshes with the central gear 267, is fixedly installed on the outer end of the transmission shaft 27. The circumferential rotation continuously output by the cam push rod drive mechanism 25 can be converted into the reciprocating rotation of the transmission shaft 27 (elliptical axis 28) through the rocker arm transmission mechanism 26.

[0071] The axis of the rocker shaft 265 coincides with the axis of the rotating central shaft 233. The position of the follower plate assembly 24 can be adjusted by the worm gear mechanism 23, thereby adjusting the spatial relative position of the two elliptical shafts 28 to achieve different throttling disturbance configurations. During the rotation of the transmission shaft 27 around the rotating axis 233, the axis of the planetary gear 271 rotates synchronously around the axis of the central gear 267 (the axis of the rocker shaft 265) and maintains a meshing connection. Therefore, it can ensure a tight transmission from the fixed-position drive motor 251 to the changing-position transmission shaft 27.

[0072] Before the experiment, the throttling frequency of the two elliptical axes 28 was changed to determine whether the experiment was a single-frequency or dual-frequency operation; and the relative position of the two elliptical axes 28 was changed through the worm gear mechanism 23 to determine the configuration of the throttling disturbance. Figure 22As shown, there are three configurations for the throttling disturbance: the two elliptical axes 28 are horizontally coplanar, vertically coplanar, or inclined coplanar. During the experiment, the high-speed airflow sequentially passes through the experimental observation module 1, the pulsating back pressure generation module 2, and the downstream extension section 3 before entering the vacuum tank. When flowing through the pulsating back pressure generation module 2, the drive motor 251 drives the cylindrical cam 255 to rotate, which in turn drives the rocker arm 268 to swing back and forth, thereby causing the elliptical axis 28 to rotate back and forth within the back pressure section. The major axis / minor axis of the elliptical axis 28 rotates back and forth between the 0° and 90° positions. Since the cross-section of the elliptical axis 28 is elliptical and has major and minor semi-axes, the vertical projected area of ​​the elliptical axis 28 along the flow direction is also different when its spatial orientation changes due to different rotation angles, thus achieving a change in the blockage area and generating periodic turbulent back pressure on the airflow.

[0073] The experimental technical conditions of this invention are described as follows:

[0074] The experiment was conducted at the downstream exit of a supersonic or hypersonic wind tunnel. The high-speed airflow generated in the wind tunnel passed sequentially through the experimental observation module 1, the pulsating back pressure generation module 2, and the downstream extension section 3 before entering the vacuum tank. When flowing through the pulsating back pressure generation module 2, the cam push rod drive mechanism 25 drove the transmission shaft 27 to reciprocate, thereby realizing the reciprocating rotation of the elliptical axis 28 within the back pressure section frame 21. This caused periodic blockage of the airflow in the back pressure section frame 21, generating periodic pulsating back pressure. The throttling frequency can be controlled and adjusted over a wide range by changing the speed of the drive motor 251 and the gear ratio; the throttling frequency of the two elliptical shafts 28 can be changed to switch between single-frequency and dual-frequency operating conditions; the throttling disturbance configuration can be changed by the worm gear mechanism 23; the range of throttling ratio can be adjusted by changing the shape of the major half-axis a and the minor half-axis b of the elliptical shaft cross-section; and the change of the pulsating back pressure waveform can be achieved by designing the contour curve of the cam groove 2551. This allows for better simulation and study of the strong unsteady phenomenon caused by the high-frequency pulsating back pressure that occurs during the actual operation of the isolation section, making the experimental results more reliable.

[0075] The working principle of this invention is explained in detail below:

[0076] When the major semi-axis of ellipse 28 rotates to be horizontal with the airflow direction (x-direction), the throttling ratio is at its minimum, i.e., the back pressure is at its minimum. When the major semi-axis of ellipse 28 rotates to be perpendicular with the airflow direction (x-direction), the throttling ratio is at its maximum, i.e., the back pressure is at its maximum. The throttling ratio curve is smooth. Taking the two ellipse axes 28 as the initial state with vertical symmetry, the throttling ratio can be calculated by taking twice the lateral (y-direction) distance from the highest point of the ellipse to the center point during the rotation of the ellipse around the center and dividing it by the overall height of the flow channel. Let the center of the ellipse axis be the origin; then the equation of the ellipse axis is:

[0077]

[0078] The throttling ratio formula under single-frequency operating conditions is:

[0079]

[0080] The throttling ratio formula under dual-frequency operation is:

[0081]

[0082] Where: a1 and b1 are the lengths of the major and minor semi-axes of the first elliptical axis, respectively; a2 and b2 are the lengths of the major and minor semi-axes of the second elliptical axis, respectively; θ1 is the rotation angle of the first elliptical axis, and θ2 is the rotation angle of the second elliptical axis. The rotation angles θ1 and θ2 are functions related to the throttling frequencies f1 and f2 and time t, depending on the curve design of the cam groove. Where f1 is the throttling frequency of the first elliptical axis, and f2 is the throttling frequency of the second elliptical axis; H is the flow channel height; and t is time.

[0083] I. The throttling frequency f of this invention can be adjusted by changing the rotational speed of the drive motor 251 and the transmission ratio between the central gear 267 and the planetary gear 271. Since the ellipse is a symmetrical figure, the throttling cycle generated by one rotation of the elliptical axis 28 is twice. The rotational speed of the elliptical axis 28 determines the magnitude of the throttling frequency. The formula for calculating the throttling frequency is: f = n1 / 30. Furthermore, since the rotational speed of the elliptical axis 28 is comprehensively controlled by the rotational speed of the drive motor 251 and the transmission ratio between the central gear 267 and the planetary gear 271, and the input and output cycles of the rocker arm transmission mechanism 26 are the same, n1 = n2 / m, f = n2 / (30*m), where: f is the throttling frequency in Hz; m is the transmission ratio of the gear set; n1 is the rotational speed of the elliptical axis 28 in r / min; n2 is the rotational speed of the drive motor 251 in r / min.

[0084] Example 1:

[0085] In this embodiment, a gear set with a comprehensive transmission ratio m of 0.5 and a drive motor 251 with a maximum speed of 6000 r / min are selected. Without changing the gear set, the required speed n2 of the drive motor 251 is calculated in reverse using the known throttling frequency f and the formula f = n2 / (30*m).

[0086] For example, if the required output throttling frequency f is 400Hz, according to the formula, n2 = 6000r / min. At this time, the speed n2 of the drive motor 251 is adjusted and set to 6000r / min to obtain the 400Hz throttling frequency f.

[0087] For example, if the required output throttling frequency f is 300Hz, according to the formula, n2 = 4500r / min. At this time, the speed n2 of the drive motor 251 is adjusted and set to 4500r / min to obtain the throttling frequency f of 300Hz.

[0088] Example 2:

[0089] In this embodiment, a drive motor 251 with a maximum speed of 6000 r / min is selected. Without adjusting the motor speed, different throttling frequencies f can be obtained by changing the transmission ratio m of the central gear 267 and planetary gear 271 according to the formula f = n² / (30*m). While keeping the center distance between the central gear 267 and planetary gear 271 constant, the transmission ratio of the gear set can be changed by adjusting the number of teeth on the central gear 267 and planetary gear 271.

[0090] For example, when the speed n2 of the drive motor 251 is 6000 r / min, the transmission ratio m of the gear is 1, and its output throttling frequency f is 200 Hz.

[0091] For example, when the speed n2 of the drive motor 251 is 6000 r / min, the transmission ratio m of the gear is 0.5, and its output throttling frequency f is 400 Hz.

[0092] For example, when the speed n2 of the electric drive motor 251 is 6000 r / min, the transmission ratio m of the gear is 0.25, and its output throttling frequency f is 800 Hz.

[0093] II. The experimental operating conditions of this invention can be adjusted by changing the throttling frequency f. Two drive motors 251 are placed on both sides of the reverse pressure section, respectively driving two elliptical shafts 28. Referring to Examples 1 and 2, the throttling frequencies f1 and f2 are changed by adjusting the rotational speed of the two drive motors 251 placed on both sides of the reverse pressure section and the transmission ratio of the gear set. When f1 = f2, a single-frequency operating condition is achieved; when f1 ≠ f2, a dual-frequency operating condition is achieved.

[0094] Example 3:

[0095] For example, the throttling frequency f1 output by one of the elliptical axes 28 is 400Hz, and the throttling frequency f2 output by the other elliptical axis 28 is also 400Hz, thus achieving single-frequency operation.

[0096] For example, one elliptical axis 28 outputs a throttling frequency f1 of 400Hz, and the other elliptical axis 28 outputs a throttling frequency f2 of 600Hz, thus achieving dual-frequency operation.

[0097] Third, the throttling disturbance configuration of the present invention can be adjusted by the worm gear mechanism 23. The positions of the two elliptical axes 28 and their relative positions can be adjusted by the worm gear mechanism 23, thereby changing the configuration of the throttling disturbance. When the worm 232 is in the initial position, i.e., the worm wheel 234 rotates 0°, the two elliptical axes 28 are located at the center position of the upper and lower directions of the flow channel (i.e., the position of the horizontal center plane). At this time, the axes of the two elliptical axes 28 are located in the same horizontal plane, and the vertical distance between the axes is the minimum of 0, and the throttling disturbance is located at the center position of the upper and lower directions of the flow channel. When the worm 232 is rotated so that the worm wheel 234 rotates 90°, the two elliptical axes 28 are placed vertically symmetrically, and the axes of the two elliptical axes 28 are located in the same vertical plane. The vertical distance between the axes is the maximum, and the throttling disturbance is symmetrically distributed along the horizontal center plane of the flow channel. When the worm 232 is rotated so that the worm wheel 234 rotates by an angle that is not an integer multiple of 90°, the axes of the two elliptical axes 28 are placed obliquely symmetrically. At this time, the vertical distance between the axes is between the maximum and minimum, and the throttling disturbance is unevenly distributed along the flow channel.

[0098] Example 4:

[0099] like Figure 22 As shown in (a), the two elliptical axes 72 are located at the center of the flow channel in the upper and lower directions, respectively, and the vertical distance between the two elliptical axes 28 is minimal, resulting in a throttling disturbance located at the center of the flow channel in the upper and lower directions. Figure 22 As shown in (b), the two elliptical axes 28 are placed vertically symmetrically, with the maximum vertical distance between them, resulting in a throttling disturbance that is symmetrically distributed along the center of the flow channel. Figure 22 As shown in (c), the two elliptical axes 28 are symmetrically placed in a 45° inclined plane, and the vertical distance between the two elliptical axes 28 is between the maximum and minimum, resulting in a non-uniform distribution of throttling disturbances along the flow channel.

[0100] IV. The range of throttling ratio variation of the present invention (i.e., TR) max and TR minThe throttling ratio can be achieved by adjusting the lengths of the major and minor semi-axes of the elliptical axis 28 and the throttling disturbance configuration. Regardless of whether it's a single-frequency or dual-frequency operation, the throttling ratio is related to the lengths of the major and minor semi-axes of the elliptical axis and the throttling disturbance configuration. When the major semi-axis of the elliptical axis 28 is rotated perpendicular to the flow direction, the throttling ratio is at its maximum, i.e., the back pressure is at its maximum. The maximum back pressure is related to the length 'a' of the major semi-axis of the elliptical axis 28. When the major semi-axis of the elliptical axis 28 is rotated horizontally to the flow direction, the throttling ratio is at its minimum, i.e., the back pressure is at its minimum. The minimum back pressure is related to the length 'b' of the minor semi-axis of the elliptical axis 28. When the throttling disturbance configuration is such that the two elliptical axes 28 are located at the center of the flow channel in the upper and lower directions, the throttling ratio generated by the two elliptical axes 28 is at its maximum value. When the throttling disturbance configuration is such that the two elliptical axes 28 are placed vertically or obliquely symmetrically, the throttling ratios generated by the two elliptical axes 28 are directly superimposed. The flow channel height of the back pressure section frame 21 is set according to experimental needs; in this embodiment, it is 100 mm.

[0101] Example 5:

[0102] For example, when the throttling disturbance configuration is that the two elliptical axes 28 are located at the center of the upper and lower directions of the flow channel, the elliptical axes 28 with a major semi-axis of 20mm and a minor semi-axis of 5mm are selected, and the throttling ratio varies from 0.05 to 0.2.

[0103] For example, when the throttling disturbance configuration is that the two elliptical axes are located at the center of the upper and lower directions of the flow channel, an elliptical axis 28 with a major semi-axis of 10 mm and a minor semi-axis of 5 mm is selected, and the throttling ratio varies from 0.05 to 0.1.

[0104] For example, when the throttling disturbance configuration is two elliptical axes 28 placed vertically or obliquely symmetrically, an elliptical axis 28 with a major semi-axis of 20mm and a minor semi-axis of 5mm is selected, and the throttling ratio varies from 0.1 to 0.4.

[0105] For example, when the throttling disturbance configuration is two elliptical axes 28 placed vertically or obliquely symmetrically, an elliptical axis 28 with a major semi-axis of 10mm and a minor semi-axis of 5mm is selected, and the throttling ratio varies from 0.1 to 0.2.

[0106] IV. The pulsating back pressure waveform of the present invention (i.e., the functional relationship between the rotation angle and the throttling frequency f and time t) can be adjusted by the contour curve of the cam groove 2551 of the cylindrical cam 255. The stroke of the rocker follower (pin 256 and slider 263) depends on the axial stroke distance of the contour curve of the cam groove 2551 and the bottom circumference 2r of the cylindrical cam 255, which has a larger stroke than that of a planar cam; in this embodiment, the length of the rocker 268 is 33mm and the bottom radius r of the cam is 33mm.

[0107] Example 6:

[0108] like Figure 23 As shown in (a), the first motion law of the pendulum 268 is: constant acceleration forward stroke (0°-90°) - stationary (90°-180°) - constant acceleration return stroke (180°-270°) - stationary (270°-360°). Figure 23 As shown in (c), this is a graph of the horizontal and vertical coordinates of the curve profile of the cam groove 2551 in the outer circular side surface development diagram of the cylindrical cam 255 under this motion law.

[0109] like Figure 23 As shown in (b), this illustrates the second motion law of the pendulum 268: constant-speed forward stroke (0°-120°) - constant-speed return stroke (120°-240°) - stationary (240°-360°). Figure 23 As shown in (d), this is a graph of the horizontal and vertical coordinates of the curved profile of the cam groove 2551 in the outer circular side surface development diagram of the cylindrical cam 255 under this motion law.

[0110] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A pulsating back pressure experimental device capable of simulating single and dual frequency disturbances, comprising an experimental support platform (5), an experimental observation module (1), a pulsating back pressure generating module (2), and a downstream extension module (3) sequentially fixed on the top of the experimental support platform (5), wherein the central axes of the experimental observation module (1), the pulsating back pressure generating module (2), and the downstream extension module (3) coincide, and the internal flow channels of the experimental observation module (1), the pulsating back pressure generating module (2), and the downstream extension module (3) are sequentially connected to form a gas flow channel, characterized in that: The pulsating back pressure generating module (2) includes a back pressure section frame (21) and two throttling disturbance units that are centrally symmetrically distributed on both sides of the back pressure section frame (21). The throttling disturbance unit includes a cam push rod drive mechanism (25) and a rocker arm transmission mechanism (26) fixedly installed on the outside of the back pressure section frame (21), a side plate assembly (22) fixedly embedded in the side wall of the back pressure section frame (21), a worm gear mechanism (23) fixedly installed on the outer surface of the side plate assembly (22), and a rotating part installed on the side plate assembly (22). The following plate assembly (24) is rotatably set in the eccentric position of the following plate assembly (24), the transmission round shaft (27) and the elliptical shaft (28) are detachably connected to the inner shaft end of the transmission round shaft (27), and the other end of the elliptical shaft (28) is rotatably installed in the end face of the following plate assembly (24) of another throttling disturbance unit. The cross section of the elliptical shaft (28) is elliptical. The two elliptical shafts (28) are arranged in parallel in the internal flow channel of the counter-pressure section frame (21) and are perpendicular to the flow direction of the internal flow channel. In each throttling disturbance unit, the output end of the worm gear mechanism (23) is connected to the follower plate assembly (24) for transmission. After the follower plate assembly (24) is driven to rotate by a preset angle, it is then positioned so that the axes of the two elliptical shafts (28) are set horizontally coplanar, vertically coplanar, or inclined coplanar. The power output end of the cam push rod drive mechanism (25) is connected to the shaft end of the transmission shaft (27) through the rocker arm transmission mechanism (26), driving the transmission shaft (27) to reciprocate at a period corresponding to the output speed of the cam push rod drive mechanism (25), thereby driving the major axis / minor axis of the elliptical shaft (28) to reciprocate between the 0° position and the 90° position.

2. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 1, characterized in that: The cam push rod drive mechanism (25) includes a fixed motor bracket (252) and two bearing seats (254). A drive motor (251) is fixedly installed on the motor bracket (252). A cylindrical cam (255) is fixedly connected to the output shaft end of the drive motor (251). The two shaft ends of the cylindrical cam (255) are respectively rotatably installed in the two bearing seats (254). A cam groove (2551) with a preset trajectory is opened on the cylindrical surface of the cylindrical cam (255). A pin (256) located on one side of the cylindrical cam (255) and horizontally arranged is movably embedded in the cam groove (2551).

3. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 2, characterized in that: The rocker arm transmission mechanism (26) includes a fixed guide rod bracket (261), a guide rod (262) fixedly mounted on the top of the guide rod bracket (261), a slider (263) slidably mounted on the guide rod (262), and a rocker arm bracket (264) fixedly mounted on the top of the guide rod bracket (261) and located below the guide rod (262). A rocker arm shaft (265) is rotatably mounted inside the rocker arm bracket (264). A rocker arm (266) is fixedly mounted at one end of the rocker arm shaft (265) near the cam push rod drive mechanism (25), and a central gear (267) is fixedly mounted at the other end away from the cam push rod drive mechanism (25). A rocker arm (268) is slidably inserted inside the rocker arm (266). The inner side of the top end of the rocker arm (268) is rotatably mounted inside the side of the slider (263). The pin (256) is movably inserted into the outer side of the top end of the rocker arm (268).

4. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 3, characterized in that: A planetary gear (271) that meshes with the central gear (267) is fixedly installed on the outer shaft end of the transmission shaft (27).

5. A pulsating back pressure experimental apparatus for simulating single- and dual-frequency disturbances according to any one of claims 1 to 4, characterized in that: The worm gear mechanism (23) includes two worm brackets (231) fixedly mounted on the outer side of the side plate assembly (22) and a worm (232) rotatably mounted in the worm brackets (231). A rotating central shaft (233) is fixedly mounted at the axis of the follower plate assembly (24), and a worm wheel (234) that meshes with the worm (232) is fixedly mounted at the shaft end of the rotating central shaft (233).

6. A pulsating back pressure experimental apparatus for simulating single- and dual-frequency disturbances according to any one of claims 1 to 4, characterized in that: The side plate assembly (22) includes an inner side plate (221) and an outer side plate (222). The inner side plate (221) and the outer side plate (222) have a central cylindrical cavity inside their mating end faces. The follower plate assembly (24) is coaxially rotatably disposed in the central cylindrical cavity. An inner through hole communicating with the central cylindrical cavity is opened at the center of the end face of the inner side plate (221), and an outer through hole communicating with the central cylindrical cavity is opened at the center of the end face of the outer side plate (222). The inner side plate (221) and the outer side plate (222) are fixedly connected to the outer wall of the counter-pressure section frame (21) by bolts.

7. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 6, characterized in that: The follower plate assembly (24) includes an inner moving plate (241) and an outer moving plate (242). The inner moving plate (241) and the outer moving plate (242) are fixedly connected. An inner frustum is integrally provided at the center of the end face of the inner moving plate (241) and is rotatably sleeved in the inner through hole. An outer frustum is integrally provided at the center of the end face of the outer moving plate (242) and is rotatably sleeved in the outer through hole.

8. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 7, characterized in that: A first sealing ring is provided between the end face of the inner side plate (221) and the outer side wall of the counter-pressure section frame (21), a second sealing ring (223) is provided between the end faces of the inner side plate (221) and the outer side plate (222) that are in contact with each other, a third sealing ring (243) is provided between the end faces of the inner moving plate (241) and the outer moving plate (242) that are in contact with each other, a fourth sealing ring (244) is provided between the end face of the inner moving plate (241) and the end face of the inner side plate (221), and a fifth sealing ring (245) is provided between the end face of the outer moving plate (242) and the end face of the outer side plate (222).

9. The pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 1, characterized in that: The internal flow channel of the experimental observation module (1) is a rectangular flow channel, the internal flow channel of the pulsating back pressure generation module (2) is a rectangular flow channel, and the internal flow channel of the downstream expansion module (3) is a funnel-shaped square to round flow channel with a small opening and a large outlet.

10. A pulsating back pressure experimental device for simulating single and dual-frequency disturbances according to claim 1 or 9, characterized in that: The experimental observation module (1) includes a flow channel frame (11) and an annular frame (12) detachably connected to the outer wall of the flow channel frame (11), wherein the annular frame (12) and the flow channel frame (11) are fixedly clamped together to hold an observation glass (13).

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