Visual large-expansion-ratio ground test spray pipe

Abstract

The invention discloses a visual large-expansion-ratio ground test jet pipe, and belongs to the field of solid rocket engine jet pipe ground testing. The device comprises a standard welding straight joint flange, a round-to-square air pipe, a square air pipe, a honeycomb device, a plane spray pipe main body, two side cover plates of the spray pipe, a visual window and a window cover plate, the standard welding straight joint flange is a connecting device of the spray pipe and a high-pressure cold air source; the round-to-square air pipe is a connecting part of the standard welding straight joint flange and the downstream square air pipe; the square air pipe is a connecting part of the spray pipe inlet and the round-to-square air pipe; the honeycomb device is placed into the mounting groove from one side and is connected, pressed and fixed through a flange; the honeycomb device is a rectifying component in the square spray pipe; regular hexagonal holes with large length-diameter ratios are densely distributed in the honeycomb and are used for dividing airflow and weakening vortex components in the airflow; cover plates on the two sides of the spray pipe are thick metal plates provided with window installation grooves. The pressure distribution condition of the expansion section of the nozzle can be accurately recorded, and the flow separation point position can be captured.

Description

Technical Field

[0001] This invention relates to a ground-based testing device for a solid rocket motor with a large expansion ratio, belonging to the field of ground testing of solid rocket motor nozzles. Background Technology

[0002] High-performance, high-reliability solid rocket motors are the ideal power source for next-generation missile weapons. The nozzle, as a crucial component for energy conversion in solid rocket motors, directly affects the engine's flight performance. Large missiles and other vehicles using solid rocket motors are often designed with performance targets set at a specific operating altitude, as they fly from sea level to that altitude during operation. To meet performance requirements at this altitude, the nozzle expansion ratio is designed to be very high. Therefore, the engine is not always operating in its ideal design state throughout the entire flight. At low altitudes, the higher ambient pressure causes the nozzle to over-expand. When the solid rocket motor nozzle is over-expanded, the high back pressure often leads to unsteady, asymmetric, and complex wave systems within the nozzle. In practice, over-expansion is often unavoidable, causing airflow separation within the nozzle. This separated flow is asymmetric and unsteady, resulting in lateral loads on the nozzle, accompanied by pressure and lateral force oscillations. These dynamic lateral loads not only affect the engine's performance indicators but can also jeopardize the nozzle's structural stability and even damage related engine structures or the nozzle itself. Therefore, it is of great significance to investigate the flow separation phenomenon inside the nozzle and obtain the flow separation law of the nozzle by conducting ground cold flow tests on nozzles with large expansion ratio.

[0003] Currently, ground-based cold flow tests typically use large expansion ratio circumferential nozzles. Therefore, it is difficult to directly observe the shock wave structure generated by flow separation in the nozzle's expansion section, especially to accurately determine the location of the flow separation point. Only nozzle wall pressure measurements and estimations of the separation point location are possible. This invention uses a schlieren spectrometer to observe the flow field of a planar nozzle with a viewing window, while simultaneously employing a pressure scanning valve to perform intensive pressure sampling on the nozzle wall. A high-speed camera can then accurately record the flow separation in the nozzle's expansion section. Summary of the Invention

[0004] The purpose of this invention is to provide a visualized ground test nozzle with a large expansion ratio. By using a schlieren and a high-speed camera, the flow separation phenomenon in the expansion section of the nozzle with a large expansion ratio can be accurately recorded, and the flow field shock wave can be recorded. By using pressure measurement points with densely distributed fine holes on the wall and pressure scanning valve to measure the pressure, the pressure distribution in the expansion section of the nozzle can be accurately recorded, and the location of the flow separation point can be captured.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] This invention discloses a visual high expansion ratio ground test nozzle for recording nozzle flow, comprising a standard welded straight-through flange, a round-to-square air pipe, a square air pipe, a honeycomb device, a planar nozzle body, two side caps on the nozzle, a visualization window, and a window cover.

[0007] The standard welded straight-through flange is a device for connecting the nozzle to the high-pressure cold air source. There are 6 through holes evenly distributed on the flange, which are connected to the downstream air pipe by bolts.

[0008] The round-to-square gas pipe is a standard welded straight-through flange connecting to a downstream square gas pipe. Both ends of the round-to-square gas pipe have flanges with six evenly distributed through holes for connecting upstream and downstream components. One of the flanges has a sealing groove for installing an O-ring, which is used to seal the flange connection.

[0009] The square air tube serves as the connection between the nozzle inlet and the round-to-square air tube. Both ends of the square air tube have flanges with six evenly spaced through holes for connecting upstream and downstream components. One flange has a sealing groove for installing an O-ring, which is used to seal the flange connection. On the side where the square air tube connects to the round-to-square air tube, there is a mounting groove for a honeycomb inserter. The square cross-section of the mounting groove is slightly larger than the square cross-section of the air tube. The honeycomb inserter is placed into the mounting groove from one side and secured by the flange connection. The flow channel shape of the square air tube matches the shape of the nozzle inlet.

[0010] The honeycomb nozzle is an internal flow straightening component of a square nozzle. It is densely covered with regular hexagonal holes with a large aspect ratio, used to divide the airflow and weaken vortex components within it.

[0011] The planar nozzle body comprises a flange with six evenly distributed through holes, a short rectangular air pipe, and a planar high expansion ratio nozzle body. The flange on the nozzle body has a sealing groove for installing O-rings, which are used to seal the flange connection. The cross-section of the short rectangular air pipe on the nozzle body is the same as the nozzle inlet cross-section. The planar high expansion ratio nozzle is a square nozzle with a nozzle profile machined at the center. The upper and lower walls of the nozzle and the hollow portions of the side cover plates form airflow channels. One side wall of the planar high expansion ratio nozzle body is densely covered with pressure measurement holes, which connect to a pressure scanning valve via a pressure tapping pipe. Steps are machined on both sides of the planar high expansion ratio nozzle, and flat rubber gaskets are used for sealing.

[0012] The nozzle's side covers are thick metal plates with viewing window mounting slots. Six bolt holes are pre-drilled at the top and bottom of the metal covers. These are bolted together to press the covers firmly onto the main body of the large expansion ratio flat nozzle, and sealed by flat rubber gaskets pressed against the nozzle's steps. The viewing window mounting slots on the metal covers have a stepped structure. Several evenly distributed threaded holes are located around the viewing window mounting slots on the metal covers for fixing the viewing window covers, thereby securing the viewing window.

[0013] The visualization window is a stepped window with O-ring mounting grooves machined around the relatively large window body, sealing the window portion with O-rings. The materials used for the visualization window are not limited to various transparent materials. The length of the smaller step in the visualization window is slightly greater than the height of the relatively smaller step on the metal cover plate. The shape of the visualization window is not limited to circular or square.

[0014] The window cover is a hollow metal frame with a recessed step. Slightly larger through holes corresponding to the threaded holes on the metal cover are distributed in the thicker part of the frame. The window is embedded in the step and fixed by the window cover and the threaded holes on the metal cover.

[0015] The present invention discloses a method for operating a ground test nozzle with a large expansion ratio for visualization: After assembling the nozzle system, a pressure sensor is installed on the sensor base and connected to the data acquisition instrument via a signal line for real-time data acquisition; a pressure tapping pipe led out from the pressure measuring hole on the nozzle wall is connected to the pressure scanning valve, and the pressure scanning valve is connected to the computer via a network cable for real-time signal acquisition; the schlieren system measurement optical path is adjusted to pass through the two windows of the planar nozzle body, and the nozzle flow channel is placed within the measurement range of the schlieren system; the position of the schlieren system knife edge is adjusted so that the knife edge blocks half of the light source image; the focus of the high-speed camera is adjusted to be at the center of the expansion section flow channel of the planar visualized nozzle; the high-speed camera is connected to the computer via a network cable for transmitting the flow field video captured by the high-speed camera. At the start of the experiment, the data acquisition instrument, pressure scanning valve, and high-speed camera were controlled on the computer to begin data recording. At the same time, the output valve of the air supply system, set to the predetermined output pressure, was opened. The airflow flowed in from the welded straight joint, and after passing through the round-to-square air passage, the cylindrical flow was transformed into a square flow. After being rectified by the honeycomb device, the airflow flowed into the nozzle inlet through the square air passage. The inlet pressure was recorded by the high-frequency pressure sensor. The airflow was accelerated to supersonic speed through the Laval nozzle and discharged from the nozzle outlet. The nozzle wall pressure was recorded by the pressure scanning valve, and the flow field schlieren of the nozzle expansion section was recorded by the high-speed schlieren system, thus realizing the visualization of the large expansion ratio nozzle ground test.

[0016] Beneficial effects:

[0017] 1. The present invention discloses a ground test nozzle for visualization of large expansion ratio. The schlieren system used is not limited to single-mirror schlieren system, "Z" type schlieren system, etc. The schlieren instrument and high-speed camera can accurately record the flow separation phenomenon in the expansion section of the nozzle with large expansion ratio and record the flow field shock wave.

[0018] 2. This invention discloses a ground-based test nozzle for visualization of large expansion ratio. The nozzle has a standard welded straight-through connector upstream for connecting to a high-pressure cold air source. The airflow passes through a round-to-square air pipe into a square air pipe, then through a honeycomb structure within the square air pipe, finally flowing into the nozzle inlet and being accelerated and discharged through the nozzle. A pressure sensor is positioned before the nozzle inlet to monitor the pressure of the incoming airflow. Numerous densely distributed pressure measuring points are located on the wall of the nozzle's expansion section to measure the pressure distribution within the expansion section. By using these densely distributed pressure measuring points on the wall and employing a pressure scanning valve, the pressure distribution within the nozzle's expansion section can be accurately recorded, and the location of flow separation points can be captured. Attached Figure Description

[0019] Figure 1 For visualization of the overall assembly drawing of the high expansion ratio nozzle system;

[0020] Figure 2 To visualize the cross-sectional view of a high expansion ratio nozzle system;

[0021] Figure 3 This is a schematic diagram of the nozzle system;

[0022] Among them: 1—Standard welded straight-through flange, 2—Round to square air pipe, 3—Square air pipe, 4—Sensor base, 5—Planar nozzle body, 6—Both side covers of nozzle, 7—Viewing window cover, 8—Visual window, 9—Honeycomb unit, 10—Pressure measuring hole on nozzle wall, 11—High-frequency pressure sensor, 12—Schizolithography mirror, 13—Pressure scanning valve, 14—Coaxial light source, 15—Knife edge, 16—High-speed camera, 17—Computer, 18—Data acquisition device. Detailed Implementation

[0023] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0024] Example 1:

[0025] like Figure 1 As shown in the figure, the visual large expansion ratio ground test nozzle disclosed in this embodiment is mainly composed of a standard welded straight-through joint flange 1, a round-to-square air pipe 2, a square air pipe 3, a sensor base 4, a planar nozzle body 5, two side cover plates of the nozzle 6, a viewing window cover plate 7, a visual viewing window 8, a honeycomb device 9, and a pressure measuring hole 10 on the nozzle wall.

[0026] Connection relationship: such as Figure 1As shown, the standard welded straight-through flange 1 is connected to the round-to-square air pipe 2 via a flange. The flange of the round-to-square air pipe 2 has a standard O-ring sealing groove. The two flanges are connected by six hexagonal bolts, and the O-ring is deformed under pressure to achieve a seal. The round-to-square air pipe 2 is connected to the square air pipe 3 via a flange. The flange of the square air pipe 3 has a standard O-ring sealing groove. The two flanges are connected by six hexagonal bolts, and the O-ring is deformed under pressure to achieve a seal. The square air pipe 3 is connected to the flat nozzle body 5 via a flange. The flange of the flat nozzle body 5 has a standard O-ring sealing groove. The two flanges are connected by six hexagonal bolts, and the O-ring is deformed under pressure to achieve a seal. The nozzle side cover plates 6 are pressed onto the nozzle body by six hexagonal bolts and sealed by pressing rubber gaskets. The viewing window cover plate 7 is connected to the nozzle side cover plates 6 by eight internal hexagonal bolts, simultaneously pressing the viewing window 8 onto the flat nozzle body 5. The visualization window 8 is machined with a standard O-ring sealing groove. The O-ring is deformed by being squeezed through the viewing window holes of the cover plates 6 on both sides of the nozzle to achieve a seal.

[0027] Except for the standard welded straight-through flange 1, all flanges with machined standard O-ring grooves have circumferential bosses machined on them for positioning, and corresponding grooves are also machined on the flanges. The standard welded straight-through flange has a small circular boss machined at the circular air passage for positioning. Circumferential positioning is achieved by six hexagonal bolts.

[0028] The standard welded straight connector flange 1 is connected to the gas supply system using a standard welded straight connector, and is sealed by the standard welded straight connector and the O-ring on the flange.

[0029] The sensor base 4 is used to mount a high-frequency pressure sensor during the test to measure the nozzle inlet pressure value during the test.

[0030] During installation, the honeycomb unit 9 is first assembled into the pre-reserved mounting slot of the square air pipe 3, and then the round-to-square air pipe 2 is used to press the honeycomb unit together via a flange connection. The honeycomb unit is assembled with an interference fit to eliminate abnormal noise during testing.

[0031] The pressure measuring hole 10 on the nozzle wall has an inner diameter of 1 mm. Due to its small diameter and large depth, it is difficult to process using traditional machining methods. Except for the flange and a small section of square air passage at the front of the nozzle, which are machined using traditional methods, the main body of the planar nozzle is printed using metal 3D printing technology, followed by precision machining to achieve tolerance control. A stainless steel sheet with an inner diameter of 1 mm and an outer diameter of 2 mm is bonded to the outside of the pressure measuring hole 10, and the wall pressure is measured by connecting it to a pressure scanning valve via a pressure tapping pipe. This invention allows for the replacement of planar nozzle bodies 5 with different shapes to conduct planar visual nozzle tests.

[0032] The working method of a ground test nozzle with a large expansion ratio disclosed in this embodiment is as follows: After assembling the nozzle system according to the connection relationship of the ground test nozzle with a large expansion ratio, a high-frequency pressure sensor 11 is installed on the sensor base 4 and connected to the data acquisition instrument 18 through a signal line for real-time data acquisition; the pressure tapping pipe led out from the pressure measuring hole 10 on the nozzle wall is connected to the pressure scanning valve 13, and the pressure scanning valve 13 is connected to the computer 17 through a network cable for real-time signal acquisition; the schlieren system measurement optical path is adjusted to pass through the two windows of the planar nozzle body 5, and the nozzle flow channel is placed within the measurement range of the schlieren system; the position of the schlieren system knife edge 15 is adjusted so that the knife edge blocks half of the light source image; the focus of the high-speed camera 16 is adjusted to be at the center of the expansion section flow channel of the planar visualized nozzle; the high-speed camera 16 is connected to the computer 17 through a network cable for transmitting the flow field video captured by the high-speed camera 16. At the start of the experiment, the data acquisition instrument 18, pressure scanning valve 13, and high-speed camera 17 are controlled on computer 17 to begin data recording. Simultaneously, the output valve of the air supply system, set to the predetermined output pressure, is opened. Airflow enters from the welded straight connector, and after passing through the round-to-square air passage, the cylindrical inflow is transformed into a square inflow. After being rectified by the honeycomb device, it finally flows into the nozzle inlet through the square air passage. The inlet pressure is recorded by the high-frequency pressure sensor 11. The airflow is accelerated to supersonic speed through the Laval nozzle and discharged from the nozzle outlet. The nozzle wall pressure is recorded by the pressure scanning valve 13, and the flow field schlieren of the nozzle expansion section is recorded by the high-speed schlieren system. This completes the ground test of the large expansion ratio nozzle for visualization.

[0033] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A ground-based test nozzle with a large expansion ratio for visualization, characterized in that: Includes standard welded straight-through flange, round-to-square air pipe, square air pipe, honeycomb unit, flat nozzle body, nozzle side cover plates, viewing window, and viewing window cover plate; The standard welded straight-through flange is a device for connecting the nozzle to the high-pressure cold air source. The flange has 6 through holes evenly distributed on it, which are connected to the downstream air pipe by bolts. The round-to-square air pipe is a standard welded straight-through joint flange connecting to the downstream square air pipe; both ends of the round-to-square air pipe are flanges with 6 evenly distributed through holes for connecting upstream and downstream components. One of the flanges has a sealing groove for installing an O-ring, and the flange connection is sealed by the O-ring. The square air tube is the connecting component between the nozzle inlet and the round-to-square air tube. Both ends of the square air tube have flanges with six evenly distributed through holes for connecting upstream and downstream components. One of the flanges has a sealing groove for installing an O-ring, which is used to seal the flange connection. On the side where the square air tube connects to the round-to-square air tube, there is a mounting groove for installing a honeycomb device. The square cross-section of the mounting groove is slightly larger than the square cross-section of the air tube. The honeycomb device is placed into the mounting groove from one side and pressed and fixed by the flange connection. The shape of the flow channel of the square air tube is consistent with the shape of the nozzle inlet. The honeycomb nozzle is an internal flow straightening component of a square nozzle; the honeycomb nozzle is densely covered with regular hexagonal holes with a large aspect ratio, which are used to divide the airflow and weaken the vortex component in the airflow; The planar nozzle body comprises a flange with six evenly distributed through holes, a short rectangular air pipe, and a planar high expansion ratio nozzle body. The flange on the nozzle body has a sealing groove for installing O-rings, which are used to seal the flange connection. The cross-section of the short rectangular air pipe on the nozzle body is the same as the nozzle inlet cross-section. The planar high expansion ratio nozzle is a square nozzle with a nozzle profile machined at the center. The upper and lower walls of the nozzle and the hollow portions of the side cover plates form airflow channels. One side wall of the planar high expansion ratio nozzle body is densely covered with pressure measurement holes, which are connected to a pressure scanning valve via a pressure tapping pipe. Steps are machined on both sides of the planar high expansion ratio nozzle, and flat rubber gaskets are used for sealing. The nozzle's side cover plates are thick metal plates with viewing window mounting slots. The metal cover plates have six bolt holes pre-drilled at the top and bottom. The cover plates are pressed tightly onto the main body of the large expansion ratio flat nozzle by bolt connection, and sealed by flat rubber gaskets pressed onto the steps of the large expansion ratio flat nozzle. The viewing window mounting slots on the metal cover plates have a stepped structure. There are several evenly distributed threaded holes around the viewing window mounting slots on the metal cover plates for fixing the viewing window cover plates, thereby fixing the viewing window.

2. The ground test nozzle with a large expansion ratio as described in claim 1, characterized in that: The visualization window is a stepped window, with O-ring mounting grooves machined around the relatively large window body, and the O-rings seal the window part; the length of the smaller step of the visualization window is greater than the height of the relatively smaller step on the metal cover plate.

3. The ground test nozzle with a large expansion ratio as described in claim 2, characterized in that: The shape of the visualization window is either circular or square.

4. The ground test nozzle with a large expansion ratio as described in claim 3, characterized in that: The window cover is a hollow metal frame with a recessed step. Slightly larger through holes corresponding to the threaded holes on the metal cover are distributed in the thicker part of the frame. The window is embedded in the step and fixed by the window cover and the threaded holes on the metal cover.

5. A ground-based test nozzle with a large expansion ratio as described in claim 1, 2, 3, or 4, characterized in that: After assembling the nozzle system, install a pressure sensor on the sensor base and connect it to the data acquisition instrument via a signal line for real-time data acquisition. Connect the pressure tapping pipe from the pressure measuring hole on the nozzle wall to the pressure scanning valve, and connect the pressure scanning valve to the computer via a network cable for real-time signal acquisition. Adjust the schlieren system's measurement optical path to pass through the two viewing windows of the planar nozzle body, and place the nozzle flow channel within the schlieren system's measurement range. Adjust the position of the schlieren system's blade so that it blocks half of the light source image. Adjust the high-speed camera's focus to be at the center of the planar visualized nozzle expansion section flow channel. Connect the high-speed camera to the computer via a network cable for high-speed camera data transmission. The flow field was recorded. At the start of the experiment, the data acquisition instrument, pressure scanning valve, and high-speed camera were controlled on the computer to start data recording. At the same time, the output valve of the air supply system, which was set to the predetermined output pressure, was opened. The airflow flowed in from the welded straight joint, and the cylindrical flow was transformed into a square flow through the round-to-square air passage. After being rectified by the honeycomb device, the airflow flowed into the nozzle inlet through the square air passage. The inlet pressure was recorded by the high-frequency pressure sensor. The airflow was accelerated to supersonic speed through the Laval nozzle and discharged from the nozzle outlet. The nozzle wall pressure was recorded by the pressure scanning valve, and the flow field schlieren of the nozzle expansion section was recorded by the high-speed schlieren system, thus realizing the visualization of the ground test of the large expansion ratio nozzle.

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