Flow field dynamic visualization system and method in high-energy laser damage process

Abstract

The invention discloses a system and a method for dynamically visualizing a flow field in a high-energy laser damage process, and relates to the technical field of laser damage effect detection.The schlieren method is applied to dynamic visualization of the flow field in a high-energy laser and high-speed airflow coupling scene for the first time, and by means of the schlieren method principle, a coaxial point light source lamp serves as a light source, and the dynamic visualization of the flow field is realized. Light beams emitted by the point light source pass through the schlieren mirror to be focused to the knife edge position of the blade, when the light beams penetrate through a to-be-measured flow field area, the light beams deflect due to the gas density gradient, flow field imaging is achieved through the light beam deflection caused by the gas density gradient, the light beams are cut into light beams with bright and dark stripes through the blade, and the light beams are focused to the knife edge position of the blade. According to the technical scheme, the light beam deflection and light beam cutting process is optically isolated, and the background radiation of the high-energy laser and the target material combustion flame is inhibited through the light filtering module, so that the flow field structure and the flow field flow state are clearly captured and distinguished through optical isolation and spectral filtering under the strong wide-spectrum radiation generated by the high-energy laser and the combustion flame.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser damage effect detection, in particular to a flow field dynamic visualization system and method under high-energy laser damage process. BACKGROUND

[0002] The damage process of high-energy laser on high-speed aircraft involves complex multi-physical field coupling, including strong heat flow, material ablation, mass injection, shock wave formation and turbulent evolution; when the laser continuous irradiation leads to the perforation of the target material, the external high-speed tangential airflow enters the internal cavity, interacts with the high-temperature residual gas, combustion products and injection, and forms a highly non-steady, strong gradient complex flow field; the flow field directly affects the stability of the internal electron-optical system and is a key link for evaluating the laser damage efficiency.

[0003] At present, the mainstream flow field observation technology mainly includes particle image velocimetry (PIV) and Schlieren method; the PIV technology relies on the light scattering characteristics of tracer particles, and has problems such as poor particle followability, low signal-to-noise ratio in high-speed, high-temperature and strong radiation environment, and needs expensive ICCD camera and complex optical filter system; in the high-energy laser ablation scene, the strong laser background light (such as 1080nm wavelength) is easy to cause image saturation, and it is difficult to clearly distinguish the flow field structure; although the traditional Schlieren method has the advantages of non-contact and high sensitivity, it is mainly used in wind tunnel or independent heat source experiment, and has not been effectively integrated in the extreme scene of high-energy laser ablation and high-speed airflow coupling; under the strong wide-spectrum radiation of high-energy laser and combustion flame, it is difficult to capture and distinguish the flow field flow state.

[0004] Therefore, the existing flow field observation technology in the high-energy laser ablation scene is difficult to clearly capture and distinguish the flow field structure and flow field flow state under the strong wide-spectrum radiation of high-energy laser and combustion flame. SUMMARY

[0005] The embodiment of the present application provides a flow field dynamic visualization system and method under high-energy laser damage process, which can solve the problems in the prior art.

[0006] The embodiment of the present application provides a flow field dynamic visualization system under high-energy laser damage process, which comprises a sealed cavity, a laser ablation system, a high-speed airflow system and a Schlieren imaging system. The laser ablation system comprises a high-power optical fiber laser, the high-speed airflow system comprises an air compressor and a duckbill nozzle, and the Schlieren imaging system comprises a Schlieren mirror, a coaxial point light source, a blade, a light filter module and a high-speed CCD camera. The coaxial point light source is located on one side of the schlieren mirror, the blade is located at the focal point on the other side of the schlieren mirror, the high-speed CCD camera is located on the other side of the blade, and the filter module is located between the blade and the high-speed CCD camera; the sealed cavity is located between the coaxial point light source and the schlieren mirror. During dynamic flow field visualization, a high-power fiber laser irradiates a target material within a sealed cavity to perforate it. Simultaneously, an air compressor generates gas, which is then blown out from a duckbill nozzle, creating a high-speed tangential airflow that is directed downwards towards the target material. This airflow is perpendicular to the laser incident direction and parallel to the target material plane, forming a transient flow field with a spatial density gradient. A beam emitted from a coaxial point source is focused onto the blade's cutting edge by a schlieren mirror. As the beam propagates, it passes through the transient flow field. Changes in gas density within the transient flow field deflect the beam, which is then reflected and focused onto the blade's cutting edge by the schlieren mirror. The blade cuts the beam, creating light and dark stripes that are received by a high-speed CCD camera, forming an image sequence corresponding to the density gradient for dynamic flow field visualization. When the light beam with bright and dark stripes is received by a high-speed CCD camera, the filter module is used to suppress the background radiation of high-energy laser and target combustion flame.

[0007] Preferably, the high-power fiber laser is positioned in front of the sealed cavity, and the duckbill nozzle is positioned directly above the sealed cavity in the Z direction; The sealed cavity is also filled with inert gas to create a slightly positive pressure environment inside the sealed cavity.

[0008] Preferably, the laser ablation system further includes a focusing lens group; When a high-power fiber laser irradiates a target, the laser emitted by the high-power fiber laser passes through a focusing lens group to irradiate the target. The focusing lens group is used to focus the laser to perform high-energy perforation of the target.

[0009] Preferably, the schlieren mirror is a concave mirror, and the blade edge is positioned at the focal point of the concave mirror. The proportion of the cutting beam is controlled by adjusting the position and angle of the blade edge.

[0010] Preferably, the filter module includes a narrowband pass filter, a full-band neutral density attenuator, and a short-wave pass filter; The narrow-band pass filter, the full-band neutral density attenuator, and the short-wave pass filter are sequentially arranged at the front end of the high-speed CCD camera to suppress near-infrared radiation generated by high-energy lasers and target combustion flames.

[0011] Preferably, it further includes a synchronization control system, which includes a synchronization oscilloscope and a control computer; When performing dynamic visualization of the flow field, a synchronous oscilloscope is used to receive the starting signal of the air compressor that generates high-speed tangential airflow or the target material perforation signal detected by the photodetector as an external trigger source for the control computer. This controls the acquisition frequency, exposure time of the high-speed CCD camera, and the light output sequence of the high-power fiber laser to achieve time synchronization.

[0012] This invention also provides a method for dynamic visualization of the flow field during a high-energy laser damage process. The method utilizes the aforementioned dynamic visualization system for the flow field during a high-energy laser damage process, and includes the following steps: A high-power fiber laser is used to irradiate the target material to perforate it. At the same time, a gas compressor generates gas and ejects a high-speed tangential airflow through a duckbill nozzle. A beam of light is emitted using a coaxial point light source. After being focused by a schlieren, the beam passes through the transient flow field region inside the sealed cavity. The gas density gradient in the flow field causes the beam to deflect. The deflected beam is then focused by the schlieren onto the blade's edge. By adjusting the blade edge to block part of the light, a beam of light with contrasting bright and dark stripes is formed. By using narrow-band pass filters, full-band neutral density attenuators, and short-wave pass filters, near-infrared radiation doped in light beams with contrasting bright and dark stripes can be suppressed. The suppressed light and dark contrast stripes of the light beam are received by a high-speed CCD camera to form an image sequence corresponding to the gas density gradient in the transient flow field, so as to perform dynamic visualization of the flow field.

[0013] This invention provides a dynamic visualization system and method for the flow field during high-energy laser destruction, which has the following advantages compared with the prior art: This invention is the first to apply schlieren to the dynamic visualization of flow fields in scenarios involving coupling high-energy lasers and high-speed airflow. Utilizing the principle of schlieren, a coaxial point light source is used as the light source. The beam emitted by the point light source is focused onto the blade edge position after being reflected by a schlieren mirror. When the beam passes through the flow field region to be measured, it is deflected due to the gas density gradient. The flow field imaging is achieved by utilizing the beam deflection caused by the gas density gradient. The blade cuts the beam into beams of light and dark stripes, thus optically isolating the beam deflection and beam cutting processes. Furthermore, a filter module suppresses the background radiation from the high-energy laser and the combustion flame of the target material. Therefore, under the strong broadband radiation generated by the high-energy laser and the combustion flame, the flow field structure and flow state can be clearly captured and distinguished through optical isolation and spectral filtering. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the execution framework of a flow field dynamic visualization system under high-energy laser damage process provided in an embodiment of the present invention; Figure 2This is a schematic diagram of the physical test structure of a flow field dynamic visualization system under high-energy laser damage process provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the effect of black smoke being ejected from the rear cavity in a flow field dynamic visualization system during a high-energy laser destruction process, provided by an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the combined effect of flame and black smoke in a flow field dynamic visualization system during a high-energy laser destruction process, provided as an embodiment of the present invention. Figure 5 This is a schematic diagram of a dynamic visualization system for the flow field during a high-energy laser destruction process, provided by an embodiment of the present invention. After the airflow enters the perforated plate and becomes uniform, the entire transparent cavity turns black. Figure 6 This is a schematic diagram illustrating the effect of a flow field dynamic visualization system under the high-energy laser ablation process provided in an embodiment of the present invention, which first fills the cavity with nitrogen to effectively remove the flame and then separates the laser ablation of the plate into two separate laser ablation processes before the jet flow is effectively removed. Figure 7 This is a schematic diagram of a dynamic visualization system for the flow field during a high-energy laser destruction process, provided in an embodiment of the present invention; wherein: (A) represents the dynamic deflection process after the back cavity airflow enters; (B) represents the dynamic deflection process after the back cavity airflow enters after the shape of the pit is changed once; (C) represents the dynamic deflection process after the back cavity airflow enters after the shape of the pit is changed twice; and (D) represents the dynamic deflection process after the back cavity airflow enters after the shape of the pit is changed three times. Detailed Implementation

[0015] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0016] Currently, flow field observation techniques for the damage process of high-energy lasers on high-speed aircraft mainly include particle image velocimetry (PIV) and schlieren imaging. PIV technology relies on the light scattering characteristics of tracer particles, which suffers from poor particle tracking, low signal-to-noise ratio, and the need for expensive ICCD cameras and complex filtering systems in high-speed, high-temperature, and high-radiation environments. Furthermore, strong laser background light can easily lead to image saturation, making it difficult to clearly distinguish the flow field structure. Although traditional schlieren systems have the advantages of being non-contact and highly sensitive, they are mostly used in wind tunnel or independent heat source experiments and have not yet been effectively integrated into extreme scenarios where high-energy laser ablation is coupled with high-speed airflow. They face the following challenges: high-energy lasers (such as 1080nm) and combustion flames produce strong broadband radiation, which seriously interferes with the imaging signal-to-noise ratio of 632.8nm helium-neon lasers; the airflow changes drastically at the moment of perforation, requiring microsecond-level synchronization precision to capture the initial flow state; and combustion products and smoke inside the cavity cause light scattering and absorption, reducing imaging contrast.

[0017] In existing technologies, for example, the literature "Research on Dynamic Behavior of Laser Ablation Based on In-situ Observation" uses carbon fiber lay-up as a natural tracer and records the ablation layer peeling process with a high-speed camera. However, its observation object is the evolution of the material surface morphology, rather than the internal flow field dynamics after perforation, and it cannot reflect key structures such as vortices, shock waves and boundary layer transitions after the airflow enters the cavity.

[0018] Currently, in the process of high-energy laser ablation of composite materials (such as spacecraft skin), the coupling of high-speed tangential airflow and laser thermal effect leads to complex flow fields (shock waves, vortices, boundary layer separation), and the main problems include: PIV technology: During laser ablation, strong light and smoke interfere with the laser beam itself (especially continuous wave 600W), which will produce strong scattered light; the ablation area produces high temperature plasma or incandescent carbon particles with extremely high brightness; resulting in image overexposure, saturation, and loss of detail, making it impossible to see the ablation front and jet structure; the tracer particles (glycerol / CO2) have poor tracking ability in the subsonic flow field, interfering with the authenticity of the flow field.

[0019] Molecular tracing: weak signal requires ICCD camera, which is expensive and has complex calibration.

[0020] Traditional schlieren method: Not optimized for laser ablation environment, and susceptible to interference from high temperature radiation.

[0021] Based on the existing problems, this invention provides a dynamic visualization method and system for laser ablation perforation flow field under high-speed airflow using schlieren method. The method of this invention achieves high-contrast and high spatiotemporal resolution imaging of the transient flow field after perforation through optical isolation, spectral filtering, precise synchronization and inert environment control, etc., solving the problems of strong background light interference and dynamic flow field capture, and providing direct visual evidence and quantitative analysis basis for laser damage effect assessment.

[0022] The present invention provides a flow field dynamic visualization system based on schlieren, which mainly includes: 1. Laser Damage Subsystem: Used to generate high-energy laser light and apply it to the target material to create a perforation; mainly includes: High-power fiber laser (1080nm, continuous or pulsed), focusing lens group.

[0023] Air compressors and duckbill nozzles are used to generate tangential high-speed airflow (Mach number 0–1.0).

[0024] A photodetector is used to detect the laser penetration signal in real time and mark the perforation time t0.

[0025] Flow field visualization subsystem (schlieren system): used for non-contact imaging of the flow field inside the perforated cavity.

[0026] 2. Light source module: coaxial point light source.

[0027] Test area module: sealed cavity (10×10×10 cm³), target material is mounted on the front, and optical quartz glass window is on the side.

[0028] 3. Imaging module: cemented doublet convex lens (focal length f), adjustable blade device, high-definition CCD camera.

[0029] 4. Filter module: The following are set up in sequence on the front end of the CCD: Narrow-band pass filter (center wavelength 632.8±5nm, bandwidth 10nm), full-band neutral density attenuator (OD=2–4), and short-wave pass filter (cutoff 1064nm) further suppress near-infrared radiation.

[0030] 5. Synchronization control subsystem: The synchronous oscilloscope receives the start-up signal of the air compressor or the perforation signal of the photodetector as an external trigger source. The computer controls the high-speed CCD acquisition frequency (≥10,000fps), exposure time (≤10μs), high-energy laser emission timing, and coaxial cable network through the 10 Gigabit Ethernet and GPIB interface to achieve time synchronization.

[0031] Auxiliary environmental control module: nitrogen cylinder and flow controller, used to fill the sealed cavity with high-purity nitrogen before the experiment to suppress material combustion and smoke generation.

[0032] The present invention provides a flow field dynamic visualization method based on schlieren, comprising the following steps: Step 1: Fix the target material to the front of the sealed cavity and fill the cavity with nitrogen to positive pressure; adjust the schlieren system to be coaxial and confocal so that the helium-neon laser beam irradiates the perforated area evenly, with the blade located at the focal point.

[0033] Step 2: Parameter Settings Set the high-speed CCD acquisition frequency and exposure time; set the high-energy laser power and action time.

[0034] Set the air compressor pressure and the nozzle z-direction perpendicular to the laser and the plate.

[0035] Step 3: Synchronous Triggering: When the air compressor is started, its start signal triggers a synchronous oscilloscope.

[0036] The oscilloscope synchronously triggers the high-energy laser to emit light and the high-speed CCD to begin acquisition, ensuring that recording begins the instant the hole is punched.

[0037] Step 4: Flow field imaging: High-energy lasers ablate and perforate the target material, and high-speed airflow enters the cavity, forming a density gradient field. Helium-neon parallel light passes through the flow field and is deflected due to the change in refractive index. The deflected light is focused by a doublet lens, and the blade blocks part of the light intensity, forming a contrasting image. CCD acquires a sequence of images, which are then filtered and attenuated to obtain a high-contrast schlieren image.

[0038] like Figure 2 As shown, this invention provides a dynamic observation device for the flow field of laser ablation perforation under high-speed airflow based on the schlieren method. It is used for non-contact, high-contrast real-time imaging of the internal flow field of a composite material target after perforation, under the coupling effect of high-energy laser irradiation and high-speed tangential airflow. The specific observation system consists of:

[0039] The observation device includes a sealed cavity, a laser ablation system, a high-speed airflow system, a schlieren imaging system, a synchronous control system, and an environmental control module.

[0040] The sealed cavity is a 10 cm × 10 cm × 10 cm cube structure. The front has a target mounting groove for securing a carbon fiber composite target. The left and right sides of the cavity have optical quartz glass windows for optical observation. The top and bottom are made of acrylic, offering high cost-effectiveness and ensuring airtightness. Two 0.1 mm wide slots are cut on the side directly behind the target, large enough to accommodate a washable acrylic plate. During the first laser ablation of the target, a large amount of black smoke, black flocculent material from carbonized carbon fibers, and a pungent yellow odor accumulate in the cavity. Inserting two plates from the two slots at the rear of the cavity prevents black smoke from contaminating the viewing windows during laser ablation of the target.

[0041] The schlieren imaging system employs a unique optical path layout, including a schlieren mirror (114mm in diameter, 500mm in focal length), a coaxial point light source (body height 93mm, width 51mm, thickness 44.5mm; window area 40*40mm, 1 / 4 inch mounting hole at the bottom, Type-C power supply; white light, 5W power, 2A current), a blade, and a high-speed CCD camera (400,000 pixels, frame rate 523pfs, minimum exposure time adjustable to 3.2μs, pixel size 6.9*6.9um). All optical components are mounted on a sliding optical platform via a base, allowing other equipment to remain in a horizontal position.

[0042] The laser ablation system includes a high-power fiber laser (wavelength 1080 nm, maximum power 300 W), a plano-convex lens for forming a high-energy-density spot on the target surface, and a total reflection mirror for changing the direction of the light path so that the laser acts on the center of the plate.

[0043] The high-speed airflow system consists of an air compressor and a flat duckbill nozzle. The nozzle is positioned in front of the target material, with its outlet direction tangential to the target surface and perpendicular to the laser incident direction and the target plane in the z-direction. It is used to simulate the incoming flow on the surface of an aircraft. The airflow speed can be controlled within the range of 0-1.0mA by adjusting the air compressor pressure.

[0044] The synchronous control system includes a synchronous oscilloscope and a control computer, which are connected to the air compressor start signal output, the high-energy laser controller, and the high-speed CCD camera trigger input via coaxial cables.

[0045] The filtering assembly includes a narrow bandpass filter (center wavelength 632.8±5 nm) and a neutral density attenuator (OD=3) mounted on the front of the high-speed CCD camera to suppress background light interference.

[0046] The environmental control module includes a nitrogen cylinder and a gas pipeline, which are connected to the air inlet at the rear of the sealed cavity.

[0047] The specific operating steps include: 1. System preparation.

[0048] The carbon fiber composite target is fixed in the mounting groove on the front of the sealed cavity to ensure a good seal. The nitrogen cylinder is turned on and high-purity nitrogen (99.99% purity) is continuously introduced into the cavity for 5 minutes to create a slightly positive pressure environment in order to suppress the oxidation and combustion reaction of the material during laser ablation and reduce the interference of flame and smoke on the optical path.

[0049] Start the schlieren system and adjust the positions of the helium-neon laser, collimator, cemented doublet convex lens, and high-speed CCD camera to ensure the laser beam passes through the collimator along the optical axis, forming uniform parallel light that illuminates the perforated area. Adjust the concave lens and knife-edge device so that the parallel light, after being focused by the lens, is precisely focused at the edge of the knife edge (i.e., in a "partially blocked" state), achieving the schlieren imaging configuration with maximum sensitivity.

[0050] 2. Parameter settings.

[0051] The following experimental parameters are set using the computer control system: The high-speed CCD camera has a sampling frequency of 8,000 Hz and an exposure time of 10 μs.

[0052] The high-energy fiber laser has an output power of 600W and its operating time is set to continuous output mode.

[0053] The air compressor pressure is set to 1.5 MPa, which corresponds to an airflow velocity of approximately 240 m / s at the nozzle outlet.

[0054] The flat duckbill nozzle is adjusted so that its air outlet direction is strictly perpendicular to the laser incident direction and the target surface in the z-axis direction to ensure the formation of a stable tangential high-speed airflow.

[0055] 3. Synchronous triggering.

[0056] When the air compressor is started, the electrical signal generated at the moment of its start-up is used as an external trigger signal input to the synchronous oscilloscope. After receiving the signal, the synchronous oscilloscope immediately outputs a trigger command to the high-energy laser and the high-speed CCD camera, ensuring that the high-energy laser starts irradiating the target material at the same time that the high-speed CCD camera starts image acquisition.

[0057] During the laser ablation process of carbon fiber plates: Dominant gases: CO, H2, CO2, CH4, H2O vapor.

[0058] Secondary gases: N2 (entrained air), C2H2, benzene compounds, etc. Solid particles: carbon microparticles (soot), carbon fiber fragments, coke particles.

[0059] Possible combustion products: If the pyrolysis gas is ignited by localized high temperature, there will be flames and more CO2 or H2O.

[0060] Solid particles mixed with the dominant gas will form a large amount of black smoke; this invention proposes a two-hit method for carbon fiber plates. For example, it takes 9 seconds to penetrate a 1mm target material. The experiment adopts a two-hit method. The second laser action time is 20% of the first action time. This experiment is divided into a 7.2 + 1.8s penetration method, which can effectively remove black smoke and other yellow gases, resulting in a clear schlieren image of the jet.

[0061] like Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, where Figure 3 This is a diagram illustrating the effect of black smoke being ejected from the rear cavity. Figure 4 An illustration showing the combined effect of flames and black smoke; Figure 5 This image shows the effect of the entire transparent cavity turning completely black after airflow is uniformly introduced into the perforated board. Figure 6 The effect of first filling the cavity with nitrogen to effectively remove the flame and then splitting the laser ablation of the plate into two stages before spraying the jet.

[0062] 4. Flow field imaging.

[0063] A high-energy laser continuously irradiates the surface of the target material. After about 80ms, the laser penetrates the target material to form a perforation with a diameter of about 1.5 mm. A photodetector detects the transmitted light signal and marks the time of perforation.

[0064] At the moment of perforation, a high-speed external airflow enters the sealed cavity through the hole, creating a strong density gradient field within the cavity. When the parallel beam from the helium-neon laser passes through this non-uniform flow field region, it is locally deflected due to the change in the gas refractive index. The deflected beam is focused by a cemented doublet convex lens, creating a change in light intensity distribution at the focal plane; an adjustable knife-edge device blocks part of the light, converting the beam deflection into image brightness contrast; a high-speed CCD camera, through a narrow-bandpass filter and an attenuator, acquires a series of high-contrast schlieren images, clearly recording the entire process of airflow entering through the perforation, forming vortices within the cavity, and mixing shock waves with turbulence.

[0065] like Figure 7 As shown, the vertical axis of (A), (B), (C), and (D) represents the tilt angle of the airflow entering the back cavity after the plate is perforated, and the horizontal axis represents the time axis. The breakpoint indicates that the laser is applied in two separate sessions. In Figure (A), the plate is perforated 0.15s after the laser is turned on for the second time. The airflow enters the back cavity in 6.15s. The airflow will immediately change from 90° to 79° within 0.5s and continue until the airflow is turned off, showing the dynamic deflection process of the airflow after entering the back cavity. This achieves the goal of visualizing the flow field and records the change of airflow. After three repeated experiments, the final dwell angle was found to be 79°. Based on this, the shape of the pit (diameter-to-depth ratio) was changed and the experiment was carried out. The experimental results are shown in Figures (B), (C), and (D).

[0066] After the acquired image sequences are stored in a computer, they can be further processed through grayscale analysis, background subtraction, and cross-correlation algorithms to achieve qualitative and quantitative visualization of the flow field structure.

[0067] This invention is the first to apply schlieren to the visualization of the flow field after perforation in a coupled scenario of "high-energy laser ablation + high-speed tangential airflow," solving the technical bottleneck of PIV failure under strong light conditions. It proposes a three-in-one anti-interference scheme of "narrow-band filtering + full-band attenuation + nitrogen inerting," which significantly improves the imaging signal-to-noise ratio and contrast. It achieves millisecond-level synchronization based on the perforation signal of the photodetector, ensuring the capture of the flow field evolution process. The closed nitrogen cavity design effectively suppresses the combustion flame, improving the exposure problem from the source. Black smoke removal: a two-stage laser penetration method is used to reduce the generated substances during pyrolysis.

[0068] This invention overcomes the bottleneck of strong light interference: through spectral selection and physical attenuation, it successfully achieves schlieren imaging against a 1080nm high-energy laser background; it overcomes the bottleneck of black smoke interference generated by ablation of carbon fiber plates, employing an 82-mode, two-step approach; it achieves millisecond-level dynamic capture: with a synchronization accuracy of ±1ms, it can clearly record the entire process of flow field evolution within 1-2 seconds after perforation; it supports quantitative analysis: the image data can be used to invert density distribution, providing verification basis for numerical simulation; the system is low-cost and highly reliable: it does not require expensive equipment such as ICCDs, and ordinary high-speed CCDs can meet the requirements.

[0069] This invention successfully achieved millisecond-level dynamic capture of the internal flow field after laser perforation under the coupling conditions of strong laser background (1080nm) and high-speed airflow (240m / s). The obtained schlieren image has a high signal-to-noise ratio and clear flow field boundaries, effectively suppressing the interference of combustion flame and reflected light, verifying the feasibility and superiority of this invention for non-contact flow field observation in complex environments.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A dynamic visualization system for the flow field during high-energy laser destruction, characterized in that, include: Sealed cavity, laser ablation system, high-speed airflow system, and schlieren imaging system; The laser ablation system includes a high-power fiber laser, the high-speed airflow system includes an air compressor and a duckbill nozzle, and the schlieren imaging system includes a schlieren mirror, a coaxial point light source, a blade, a filter module, and a high-speed CCD camera. The coaxial point light source is located on one side of the schlieren mirror, the blade is located at the focal point on the other side of the schlieren mirror, the high-speed CCD camera is located on the other side of the blade, and the filter module is located between the blade and the high-speed CCD camera; the sealed cavity is located between the coaxial point light source and the schlieren mirror. During dynamic flow field visualization, a high-power fiber laser irradiates a target material within a sealed cavity to perforate it. Simultaneously, an air compressor generates gas, which is then blown out from a duckbill nozzle, creating a high-speed tangential airflow that is directed downwards towards the target material. This airflow is perpendicular to the laser incident direction and parallel to the target material plane, forming a transient flow field with a spatial density gradient. A beam emitted from a coaxial point source is focused onto the blade's cutting edge by a schlieren mirror. As the beam propagates, it passes through the transient flow field. Changes in gas density within the transient flow field deflect the beam, which is then reflected and focused onto the blade's cutting edge by the schlieren mirror. The blade cuts the beam, creating light and dark stripes that are received by a high-speed CCD camera, forming an image sequence corresponding to the density gradient for dynamic flow field visualization. When the light beam with bright and dark stripes is received by a high-speed CCD camera, the filter module is used to suppress the background radiation of high-energy laser and target combustion flame.

2. The flow field dynamic visualization system under high-energy laser destruction process according to claim 1, characterized in that, The high-power fiber laser is positioned in front of the sealed cavity, and the duckbill nozzle is positioned directly above the sealed cavity in the Z direction; The sealed cavity is also filled with inert gas to create a slightly positive pressure environment inside the sealed cavity.

3. The flow field dynamic visualization system under high-energy laser destruction process according to claim 1, characterized in that, The laser ablation system also includes a focusing lens group; When a high-power fiber laser irradiates a target, the laser emitted by the high-power fiber laser passes through a focusing lens group to irradiate the target. The focusing lens group is used to focus the laser to perform high-energy perforation of the target.

4. The flow field dynamic visualization system under high-energy laser destruction process according to claim 1, characterized in that, The schlieren mirror is a concave mirror, and the blade is positioned at the focal point of the concave mirror. The proportion of the cutting beam is controlled by adjusting the position and angle of the blade.

5. The flow field dynamic visualization system under high-energy laser destruction process according to claim 1, characterized in that, The filter module includes a narrowband pass filter, a full-band neutral density attenuator, and a short-wave pass filter; The narrow-band pass filter, the full-band neutral density attenuator, and the short-wave pass filter are sequentially arranged at the front end of the high-speed CCD camera to suppress near-infrared radiation generated by high-energy lasers and target combustion flames.

6. The flow field dynamic visualization system under high-energy laser destruction process according to claim 1, characterized in that, It also includes a synchronization control system, which includes a synchronization oscilloscope and a control computer; When performing dynamic visualization of the flow field, a synchronous oscilloscope is used to receive the starting signal of the air compressor that generates high-speed tangential airflow or the target material perforation signal detected by the photodetector as an external trigger source for the control computer. This controls the acquisition frequency, exposure time of the high-speed CCD camera, and the light output sequence of the high-power fiber laser to achieve time synchronization.

7. A method for dynamic visualization of the flow field during a high-energy laser destruction process, comprising using a dynamic visualization system for the flow field during a high-energy laser destruction process as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A high-power fiber laser is used to irradiate the target material to perforate it. At the same time, a gas compressor generates gas and ejects a high-speed tangential airflow through a duckbill nozzle. A beam of light is emitted using a coaxial point light source. After being focused by a schlieren, the beam passes through the transient flow field region inside the sealed cavity. The gas density gradient in the flow field causes the beam to deflect. The deflected beam is then focused by the schlieren onto the blade's edge. By adjusting the blade edge to block part of the light, a beam of light with contrasting bright and dark stripes is formed. By using narrow-band pass filters, full-band neutral density attenuators, and short-wave pass filters, near-infrared radiation doped in light beams with contrasting bright and dark stripes can be suppressed. The suppressed light and dark contrast stripes of the light beam are received by a high-speed CCD camera to form an image sequence corresponding to the gas density gradient in the transient flow field, so as to perform dynamic visualization of the flow field.

Images