Method and device for observing internal flow field of vortex spinning transparent nozzle

Abstract

The invention discloses a method and a device for observing an internal flow field of a vortex spinning transparent nozzle based on a particle image velocity measurement system. The geometric similarity error is less than or equal to 0.5% and the light transmittance is greater than or equal to 92%. According to the device, a transparent nozzle is integrated in a vortex spinning system, and the device is composed of a laser light source module, a high-speed image acquisition module and a tracer particle injection module. According to the method, a PIV (particle image velocimetry) technology is utilized, hollow glass bead tracer particles are uniformly put into air flow, light illumination of a double-pulse laser sheet and synchronous image acquisition of a high-speed camera are combined, and non-contact dynamic observation of flow fields of a vortex cavity, an air inlet channel and a fiber outlet area in the nozzle is realized. PIV algorithm processing is carried out on the image sequence, and high-temporal-spatial-resolution flow field parameters such as a velocity vector field, turbulent flow kinetic energy and pressure distribution can be obtained. The problems of disturbance defects and observation blind areas of traditional intrusive measurement are solved, and accurate experimental data support is provided for vortex spinning nozzle structure optimization and flow field regulation and control.

Description

Technical Field

[0001] The present invention relates to the field of textile engineering, and in particular to a method and device for observing the internal flow field of a vortex spinning transparent nozzle. Background Art

[0002] As an advanced spinning method, vortex spinning technology relies on the use of high-speed airflow to cohere and twist fibers, ultimately forming yarn. The vortex spinning nozzle is a key component in this process. The characteristics of its internal flow field, including velocity distribution, pressure gradient, and turbulence, directly determine the fiber trajectory, cohesion state, and final yarn quality.

[0003] However, the current observation and research on the internal flow field of vortex spinning nozzles still faces significant challenges. On the one hand, the internal flow channel structure of the nozzle is complex, with a spiral fiber guide channel and a conical tip, and the space is small (millimeter level), and the air flow speed is as high as hundreds of meters per second. Traditional invasive measurement techniques, such as the use of microprobes for pressure or velocity measurement, have inherent limitations. The physical intervention of the sensor probe inevitably disturbs the high-speed airflow, causing the measurement data to deviate from the actual flow field, and is particularly prone to distortion of the turbulent structure. In addition, the small internal space limits the layout density of the sensors, resulting in the inability to capture key transient flow phenomena such as local strong shear flow and vortex shedding, forming a "blind spot" for flow field observation. This has made the structural optimization of vortex spinning nozzles rely on empirical trial and error for a long time, making it difficult to achieve precise design based on flow mechanisms.

[0004] On the other hand, although numerical simulations have been widely used in the study of vortex spinning nozzle flow fields, the accuracy of the simulation results is highly dependent on the assumptions of boundary conditions and lacks sufficient experimental verification data. In particular, in scenarios involving multiple airflow coupling and complex fiber-airflow interactions, the accuracy of existing numerical simulations is difficult to meet the actual engineering needs.

[0005] In summary, current methods for observing and studying the flow field inside vortex spinning nozzles suffer from issues such as insufficient precision, strong interference, and a lack of experimental verification. These issues severely restrict the further development of vortex spinning technology and the optimized design of core components. Therefore, the industry urgently needs a non-invasive, high-precision observation method that can truly reflect the characteristics of the flow field inside the nozzle. This method can break through the bottleneck of traditional measurement technology and provide key technical support for the structural optimization of core components of vortex spinning and improve the quality of yarn.

[0006] The present invention aims to provide a solution that can overcome the shortcomings of the prior art. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention aims to provide a method and device for observing the internal flow field of a vortex spinning transparent nozzle, so as to achieve non-invasive, high-precision observation of the internal flow field of the nozzle and truly reflect its flow field characteristics.

[0008] In order to solve the above technical problems, the technical solution of the present invention is: a method for observing the internal flow field of a vortex spinning transparent nozzle, comprising the following steps: S1. preparing a transparent vortex spinning nozzle, wherein the internal flow channel of the transparent vortex spinning nozzle is made of an optically transparent material; S2. A non-contact optical measurement system is provided outside the transparent vortex spinning nozzle, the system comprising a high-speed image acquisition unit and a laser illumination unit, the laser illumination unit emitting a sheet-shaped laser beam after beam shaping, the sheet-shaped laser beam passing through the wall of the transparent vortex spinning nozzle and illuminating the area to be observed in the internal flow channel thereof; S3, uniformly injecting tracer particles having fluid dynamic properties sufficient to follow the airflow and good light scattering properties into the spinning airflow to be observed; S4, injecting the spinning airflow carrying the tracer particles into the internal flow channel of the transparent vortex spinning nozzle; S5, synchronously triggering the laser pulse of the laser illumination unit and the image acquisition of the high-speed image acquisition unit to continuously capture a motion image sequence of the tracer particles in the flow field in the area to be observed; S6. Process the motion image sequence using a particle image velocimetry algorithm to obtain flow field velocity vector distribution and turbulence characteristic parameters in the area to be observed.

[0009] To implement the above technical solution, first, a transparent vortex spinning nozzle made of optically transparent material is prepared to allow external light to penetrate. Next, a non-contact optical measurement system, particularly the laser illumination unit therein, is used to emit a shaped sheet laser beam to precisely illuminate the preset area to be observed in the internal flow channel of the transparent vortex spinning nozzle. Simultaneously, tracer particles with good tracking and light scattering properties are uniformly injected into the airflow to be observed. When the spinning airflow carrying the tracer particles enters the internal flow channel of the transparent vortex spinning nozzle, the high-speed image acquisition unit is triggered synchronously with the laser pulse to continuously capture the movement trajectory of the tracer particles in the flow field. This successfully achieves non-invasive, high-precision observation of the high-speed, complex, and narrow internal flow field of the transparent vortex spinning nozzle. Traditional invasive measurement methods have "blind spots" due to their disturbance of the high-speed airflow and distortion of the turbulent structure, and are unable to accurately capture transient flow phenomena. This method effectively avoids these problems by utilizing a transparent vortex spinning nozzle and non-contact particle image velocimetry (PIV) technology. It can truly reflect the flow field characteristics and obtain detailed velocity vector distribution and turbulence characteristic parameters. This provides a precise design basis based on flow mechanisms for the structural optimization of core vortex spinning components and provides sufficient experimental verification data to support numerical simulation results, thus breaking through existing technical bottlenecks and effectively promoting the further development of vortex spinning technology and improving yarn quality.

[0010] As a preferred embodiment of the present invention, the optically transparent material is optical grade polyphenylene sulfide or polyetherimide; and the preparation step includes: performing nano-level polishing on the inner surface of the transparent vortex spinning nozzle to make the surface roughness Ra ≤ 0.05 μm, and eliminating the internal stress of the material through an annealing process to make the birefringence optical path difference less than 5 nm / mm.

[0011] To implement the above technical solution, first, specific optical-grade materials are selected and nano-level polishing is performed, which greatly reduces the scattering and distortion of light when penetrating the wall of the transparent vortex spinning nozzle. This enables the sheet laser beam to illuminate the internal flow field more clearly and accurately, ensuring the quality of high-speed image acquisition, thereby improving the clarity of the tracer particle image and the accuracy of the flow field measurement. Secondly, the internal stress of the material is eliminated and the birefringence optical path difference is controlled through the annealing process, which effectively avoids the interference of the material's own stress on the polarized light, further ensuring the accuracy of the optical measurement. This highly transparent, low-scattering, low-stress transparent vortex spinning nozzle provides an extremely ideal interface for non-invasive optical measurement, greatly improving the signal-to-noise ratio and reliability of the internal flow field observation of the transparent vortex spinning nozzle, thereby providing high-quality raw data for the subsequent particle image velocimetry algorithm processing, and ultimately achieving more accurate flow field characteristic analysis and transparent vortex spinning nozzle optimization design.

[0012] As a preferred embodiment of the present invention, the tracer particles are hollow glass microspheres, the density of the tracer particles is 0.5-1.0 g / cm³, the particle size is 1-10 μm, and the surface of the tracer particles is modified with a silane coupling agent to perform hydrophobic treatment.

[0013] This technical solution achieves excellent flow-following performance in high-speed airflows by carefully selecting hollow glass microspheres as tracer particles, precisely controlling their density to 0.5-1.0 g / cm³ and setting their particle size to 1-10 μm. This significantly improves the accuracy of particle image velocimetry (PIV) results, ensuring that the particles accurately reflect the motion trajectory of the complex, high-speed airflow within the transparent vortex spinning nozzle. Furthermore, hydrophobic treatment of the tracer particles with a silane coupling agent effectively eliminates potential moisture absorption, agglomeration, or wall adhesion issues in humid environments, thereby ensuring uniform particle dispersion and fluidity in the airflow and further enhancing the continuity, reliability, and representativeness of PIV measurement data.

[0014] As a preferred solution of the present invention, the high-speed image acquisition unit is a high-speed camera with a resolution of not less than 2048×2048 pixels and a frame rate of not less than 1000 fps; the laser illumination unit is a double-pulse laser with a wavelength of 532 nm.

[0015] To achieve this technical solution, a high-speed camera with a resolution of at least 2048×2048 pixels and a frame rate of at least 1000 fps is used as the image acquisition unit. This ensures high spatial and temporal resolution of the microscopic flow field within the transparent vortex spinning nozzle, enabling clear resolution of tracer particles and accurate recording of instantaneous velocity field changes and transient complex flow phenomena in the high-speed airflow. Furthermore, a dual-pulse laser with a wavelength of 532 nm is used as the illumination unit. This wavelength is well matched to the scattering characteristics of the tracer particles. More importantly, this dual-pulse characteristic, combined with the high-speed camera, implements the double-exposure imaging principle of particle image velocimetry (PIV), enabling precise acquisition of particle displacement in an extremely short time, thereby calculating the highly accurate instantaneous velocity vector distribution. This combination of high spatial and temporal resolution enables the present invention to obtain transient full-field velocity information and turbulence characteristic parameters of the flow field, which are unattainable by traditional methods, greatly improving the precision and reliability of flow field observations.

[0016] As a preferred solution of the present invention, the synchronous triggering is achieved through a synchronous controller, which sets the trigger delay between the dual-pulse laser and the high-speed camera so that the high-speed camera continuously captures at least two frames of images at a time interval of microseconds.

[0017] Precise synchronization control is essential for the successful implementation and high-precision data acquisition of particle image velocimetry (PIV) technology. In high-speed flow fields, tracer particles undergo minute displacements in a very short period of time. Accurately capturing these displacements and calculating the instantaneous velocity vector requires an extremely precise and controllable time interval between the two image frames. The synchronization controller, with millisecond or even microsecond timing accuracy, ensures that the camera captures the first image frame upon the first laser pulse, and then, after a set microsecond delay, the second image frame upon the second laser pulse. This precise synchronization and time interval control minimizes the blurring effect of particle motion and ensures that the particles in the two image frames represent the positions of the same batch of particles at different times, thereby providing high-quality raw data for the subsequent accurate calculations of the particle image velocimetry algorithm. Ultimately, this high-precision synchronization technology enables the present invention to reliably capture and quantify key information such as the instantaneous velocity field, vortex structure, and turbulence characteristics of the complex high-speed flow field within a transparent vortex spinning nozzle, significantly improving the accuracy and practicality of the observations.

[0018] As a preferred solution of the present invention, before injecting the spinning airflow, it also includes the steps of: setting a constant temperature shell around the transparent vortex spinning nozzle, and maintaining the wall temperature of the transparent vortex spinning nozzle at 80±1°C through a PID controller.

[0019] The implementation of the above technical solution effectively eliminates the impact of external ambient temperature fluctuations on the stability of the flow field inside the transparent vortex spinning nozzle, ensuring high consistency of physical parameters such as airflow density and viscosity during the measurement process. The application of the PID controller ensures high precision and high stability of temperature control, avoiding measurement errors introduced by temperature changes, especially the impact on the optical measurement system. Ultimately, this precise wall temperature control ensures the stability of flow field parameters and the repeatability of experimental data, and brings experimental conditions closer to actual production conditions, greatly improving the accuracy, reliability and engineering application value of the observation results of the internal flow field of the transparent vortex spinning nozzle.

[0020] As a preferred solution of the present invention, the particle image velocimetry algorithm processing includes background subtraction and noise filtering on the motion image sequence, and then cross-correlation calculation and vector verification.

[0021] To implement the above technical solution, background subtraction and noise filtering are first performed to effectively remove non-particle interference and random noise in the image, greatly improving the signal-to-noise ratio and clarity of the tracer particle image. Subsequently, the core algorithm of cross-correlation calculation is used to efficiently and accurately determine the average displacement of the tracer particle group in the two frames of image, thereby obtaining the instantaneous velocity vector of each area. Finally, the calculation results are screened and corrected through the vector verification step to eliminate outliers and ensure the physical rationality of the flow field vector. Ultimately, the present invention can efficiently, accurately and reliably extract the velocity vector distribution and turbulence characteristic parameters of the internal flow field of the transparent vortex spinning nozzle from the original image, providing high-confidence flow field data support for the optimized design of core components.

[0022] As a preferred solution of the present invention, the cross-correlation calculation adopts a multi-grid algorithm, wherein the query window is set to 32×32 pixels and the overlap rate is 50%.

[0023] To implement the above technical solution, the multi-grid algorithm's coarse-to-fine iterative calculation strategy significantly improves computational speed, robustness, and the ability to handle high-displacement gradient flow fields. At the same time, the optimized query window size ensures the reliability of statistical calculations and the ability to resolve flow field details, while the 50% overlap rate greatly increases the density of velocity vector points, improving the spatial resolution and accuracy of flow field measurements. This series of optimization strategies works synergistically, enabling the present invention to efficiently, accurately, and high-resolution acquire velocity vector data for the complex flow field inside a transparent vortex spinning nozzle, providing a solid data foundation for a deeper understanding of its microscopic flow mechanisms.

[0024] As a preferred solution of the present invention, the step of obtaining turbulence characteristic parameters includes: extracting the Strouhal number by performing Fourier transform analysis on the wake flow at the fiber outlet end; and importing the obtained flow field velocity vector distribution as a boundary condition into the computational fluid dynamics model for comparative verification.

[0025] To implement the above technical solution, first, the Strouhal number can be extracted by performing Fourier transform analysis on the wake at the fiber outlet. The Strouhal number is an important dimensionless parameter that characterizes the frequency characteristics of periodic flow phenomena. By analyzing the spectrum obtained by Fourier transform, the dominant vortex shedding frequency can be identified, thereby quantifying the periodic pulsation characteristics of the wake region within the transparent vortex spinning nozzle. This is crucial for understanding the force state of the fiber at the outlet and the stability during the yarn formation process. Secondly, the present invention imports the acquired flow field velocity vector distribution as a boundary condition into a computational fluid dynamics (CFD) model for comparative verification. This means that the real, high-precision velocity field data obtained through PIV experiments can be directly used as input conditions for numerical simulations, greatly improving the accuracy and credibility of the CFD model. Traditional CFD simulation results often deviate from reality due to inaccurate boundary condition assumptions. The present invention uses experimental data to "feed" and "calibrate" the model, which can effectively verify and correct the numerical simulation results, realize the complementary advantages of experiments and simulations, and thus reveal the complex physical mechanism of the internal flow of transparent vortex spinning nozzles more comprehensively and accurately, providing strong data support and theoretical guidance for the optimal design of transparent vortex spinning nozzles and the improvement of spinning processes.

[0026] The present invention also discloses a device for observing the internal flow field of a vortex spinning transparent nozzle, comprising: The transparent vortex spinning nozzle module has an inner surface roughness Ra ≤ 0.05 μm and a geometric similarity error with the prototype nozzle ≤ 0.5%; a laser light source module configured to emit a sheet-shaped laser beam after beam shaping to illuminate the internal area to be measured of the transparent vortex spinning nozzle module; A high-speed image acquisition module is arranged on one side of the transparent vortex spinning nozzle module and is used to acquire images of tracer particles illuminated by the laser in the area to be measured; a tracer particle injection module, the outlet of which is in communication with the air inlet passage of the transparent vortex spinning nozzle module, for supplying tracer particles into the air flow; A synchronous controller is electrically connected to the laser light source module and the high-speed image acquisition module respectively, and is used to synchronously trigger the pulse emission of the laser light source module and the image acquisition of the high-speed image acquisition module.

[0027] To implement the above technical solution, first, the tracer particle injection module uniformly injects pre-prepared tracer particles with good tracking and light scattering properties into the spinning airflow to be observed. Subsequently, the airflow carrying the tracer particles enters the core component: the internal flow channel of the transparent vortex spinning nozzle module. At the same time, the laser light source module is triggered by the synchronous controller to emit a precisely shaped sheet laser beam. This laser beam penetrates the wall of the transparent vortex spinning nozzle and accurately illuminates the area to be measured inside the transparent vortex spinning nozzle, illuminating the tracer particles moving in the area. Almost at the same moment, the high-speed image acquisition module is also triggered by the synchronous controller to capture a sequence of moving images of the tracer particles illuminated by the laser in the flow field at high speed and continuously. This "laser irradiation-image acquisition" synchronous process is repeated at extremely short time intervals to record the precise position of the particles at different instants. Among them, the high-fidelity transparent vortex spinning nozzle module (inner surface roughness Ra ≤ 0.05μm, geometric similarity error ≤ 0.5%) ensures excellent light transmittance and authenticity of flow field geometry for optical measurement; the laser light source module and the high-speed image acquisition module work together to construct a non-contact measurement system, completely avoiding the disturbance of high-speed airflow caused by traditional probe measurement and capable of capturing transient details of the flow field with high precision; and the precise synergy of the synchronous controller ensures high synchronization of laser emission and image acquisition at the microsecond level, providing a key guarantee for obtaining accurate instantaneous velocity vectors. Combined with the tracer particle injection module, the entire device can stably and efficiently obtain the instantaneous velocity vector distribution and turbulence characteristic parameters of the complex flow field inside the transparent vortex spinning nozzle, providing key and reliable experimental data support for the structural optimization of core components and the improvement of yarn quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an exploded view of the components of the transparent vortex spinning nozzle of the present invention; Figure 2 Schematic diagram of the assembly position of the transparent vortex spinning nozzle component of the present invention; Figure 3 This is an assembly diagram of the transparent vortex spinning nozzle and the constant temperature housing of the present invention; Figure 4 This is an isometric view of Example 2; Figure 5 Schematic diagram of the top view of the structure of Example 2; Figure 6 Schematic diagram of the laser light sheet irradiation area.

[0029] Figure numerals: 1. transparent vortex spinning nozzle; 2. high-speed camera; 3. double-pulse laser; 4. beam shaping optical component; 5. guide body; 6. vortex tube; 7. conical body; 8. hollow tube; 9. constant temperature shell; 10. cross-grooved flat head screw; 11. air compressor; 12. aerosol generator; 13. Venturi mixer; 14. splitter; 15. mass flow controller; 16. reflector; 17. synchronization controller. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings to make the technical solutions of the present invention easier to understand and grasp.

[0031] Example 1: A method for observing the flow field inside a transparent vortex spinning nozzle. This method, based on particle image velocimetry (PIV), uses high-speed imaging and analysis of the trajectory of tracer particles in the airflow inside the transparent vortex spinning nozzle to quantitatively observe the velocity distribution, vortex structure, and turbulence characteristics of the flow field. The method steps are as follows: S1. Fabrication and Pretreatment of Transparent Vortex Spinning Nozzles: Optical-grade polyphenylene sulfide (PPS) particles with a transmittance of ≥92% were used as the substrate. High-precision molds (±5 μm accuracy) were used for injection molding to replicate the prototype vortex spinning nozzle's vortex chamber, air inlet channel, and fiber outlet structure. Complex curved surfaces were corrected using five-axis CNC micromachining to ensure geometric similarity error of ≤0.5% and dimensional deviation of key flow channels of <±3 μm.

[0032] The inner surface of the transparent vortex spinning nozzle undergoes a two-step polishing process: first, it is rough-polished with a 1000-mesh diamond grinding wheel to a Ra ≤ 0.2 μm. Then, it is chemically mechanically polished (CMP) using a nano-cerium oxide suspension (particle size 50 nm) to a Ra ≤ 0.05 μm, eliminating the effects of microscopic wall defects on light scattering.

[0033] After polishing, annealing treatment is carried out (keeping at 180℃ for 2 hours and cooling with the furnace), and the birefringence optical path difference is tested to be less than 5nm / mm to ensure the optical uniformity of the material.

[0034] S2. Prepare tracer particles: Hollow glass microspheres with a density of 0.8 g / cm³ and a particle size of 5 ± 2 μm (surface modified with silane coupling agent, contact angle 95° ± 5°) are selected as tracer particles. The particles are injected into the Venturi mixer through an aerosol generator to control the concentration of The Venturi mixer is installed upstream of the air inlet duct to ensure that the particles are evenly dispersed in the air flow, with the proportion of agglomerates less than 0.5%.

[0035] S3. Set up the PIV system hardware and calibrate the optical path: A dual-pulse laser (wavelength 532 nm) and beam-shaping optics were used to generate a 0.8 mm thick laser sheet. This light was then reflected by a reflector and incident along the axis of the transparent vortex spinning nozzle, illuminating the central cross-section of the vortex cavity. A high-speed camera (resolution ≥ 2048 × 2048 pixels, frame rate ≥ 1000 fps) was used with a polarizing filter placed in front of the lens to eliminate wall reflections and ensure image quality.

[0036] S4. Synchronous Control and Data Acquisition: The trigger delay between the dual-pulse laser and the high-speed camera is set via a synchronization controller. After the first pulse is triggered, the camera continuously captures two frames of images at 1 μs intervals. The pulse interval is adjusted based on the flow rate, and a single measurement covers 100 pulse periods to obtain statistically averaged flow field data.

[0037] S5. Air Supply and Environmental Control: Establish a high-pressure air system. The main and auxiliary jet flows are regulated by mass flow controllers (MFCs, accuracy ±1% FS), with a maximum flow rate of 200 L / min and a pressure range of 0-0.8 MPa. A Venturi mixer is installed upstream of the air intake to ensure uniform dispersion of the tracer particles. A flow splitter is then used to divide the airflow into the main and auxiliary jet channels.

[0038] The transparent vortex spinning nozzle is wrapped with a constant temperature shell, and the wall temperature is maintained at 80±1℃ through a PID controller to control the temperature coefficient of the material's refractive index. , to reduce the impact of temperature fluctuations on optical measurements.

[0039] S6. Data Processing and Analysis: Data processing was performed on a high-performance workstation (CPU: Intel i9-13900K, GPU: NVIDIA RTX A6000, 128GB memory, storage: 8TB SSD array, bandwidth 1.5GB / s). Data were analyzed using PIV post-processing software (e.g., LaVision DaVis 8.4) using the following steps: 1. Background subtraction: Calculate the average value of 10 blank images as the background, subtract the background noise from the original image, and increase the signal-to-noise ratio to above 10:1.

[0040] 2. Noise filtering: 3×3 median filtering is used to remove isolated noise points, and Gaussian smoothing (σ=1) is combined to weaken high-frequency interference.

[0041] 3. Cross-correlation calculation: Set the query window to 32×32 pixels, the overlap rate to 50%, and enable the multi-grid algorithm to improve calculation efficiency. The sub-pixel positioning accuracy reaches 0.1 pixel.

[0042] 4. Vector verification: Abnormal vectors are marked by local velocity gradient threshold and missing or erroneous data are filled using median interpolation.

[0043] 5. Parameter calculation: Generate two-dimensional velocity vector field, vorticity field and streamline diagram.

[0044] VI. Key structure identification: Vortex core area: Detect velocity vector circulation center (absolute value of vortex Boundary layer separation point: locate the vorticity extreme point and the velocity gradient mutation position (error ±5μm). Wake vortex street: analyze the velocity pulsation frequency at the fiber outlet through Fourier transform and extract the Strouhal number (St).

[0045] 7. CFD comparison: Import the measured velocity field into CFD software (such as Fluent 2024R1) as boundary conditions and compare the simulation results (such as pressure distribution and turbulent kinetic energy dissipation rate).

[0046] 8. Report generation: Output flow field parameter report (including velocity peak, vortex core position, boundary layer thickness, etc.), visualization image (vector diagram, cloud diagram, streamline diagram) and error analysis file as the basis for transparent vortex spinning nozzle structure optimization.

[0047] Example 2: A device for observing the internal flow field of a vortex spinning transparent nozzle, comprising the following components: 1. Transparent Vortex Spinning Nozzle: Made from optical-grade polyphenylene sulfide (PPS), the transparent vortex spinning nozzle boasts a light transmittance of ≥92% and excellent high-temperature resistance. Its internal structure, including the guide body, vortex tube, cone, and hollow tube, is manufactured using precision injection molding and CNC micromachining techniques to ensure a geometric similarity error of ≤0.5% with the original vortex spinning nozzle. The inner surface is polished to Ra ≤0.05μm and annealed to eliminate internal stress, maintaining a birefringence path difference of <5nm / mm to ensure optical measurement accuracy.

[0048] The transparent vortex spinning nozzle 1 comprises a guide body 5, a vortex tube 6, a conical body 7, and a hollow tube 8. These are all made of optical-grade polyphenylene sulfide. The guide body 5, vortex tube 6, conical body 7, and hollow tube 8 are connected in sequence. The transparent vortex spinning nozzle is then placed in the groove of a thermostatic housing 9 and secured with four cross-slotted oval-head screws 10. The thermostatic housing 9 is designed as a split left-right design.

[0049] 2. Tracer Particle Injection System: This system uses hollow glass microspheres (surface modified with a silane coupling agent) with a density of 0.8 g / cm³ and a particle size of 5 ± 2 μm as tracer particles. The particles are injected into a Venturi mixer 13 installed upstream of the air intake duct via an aerosol generator 12 to ensure uniform particle dispersion in the airflow.

[0050] III. PIV Measurement System: Includes: 1. Dual-pulse laser 3: 532nm wavelength, generates laser pulses. 2. Beam-shaping optical assembly 4: generates a 0.8mm thick laser sheet. 3. Reflector 16: reflects the laser sheet light into the transparent vortex spinning nozzle. 4. High-speed camera 2: resolution ≥ 2048 × 2048 pixels, frame rate ≥ 1000 fps, with a polarizer placed in front of the lens to reduce wall reflections. 5. Synchronization controller 17: coordinates the triggering timing of dual-pulse laser 3 and high-speed camera 2. High-speed camera 2 is a high-speed CCD camera.

[0051] IV. Airflow Control System: Includes: 1. Air Compressor 11: Provides a high-pressure air source. 2. Mass Flow Controller 15: Precisely controls the flow rate and pressure of the primary and secondary jets. 3. Venturi Mixer: Ensures uniform dispersion of tracer particles. 4. Flow Divider 14: Divides the airflow into the primary and secondary jet channels.

[0052] 5. Constant temperature control system: The constant temperature shell wraps the transparent vortex spinning nozzle, and the wall temperature is maintained at 80±1℃ through the PID controller to control the temperature coefficient of the material refractive index. , reducing the impact of temperature changes on optical measurements.

[0053] 6. Data processing system: including high-performance workstation and PIV post-processing software, used for real-time acquisition, storage and analysis of PIV image data, and generation of flow field parameters and visualization images.

[0054] Figure 6 Schematic diagram of the laser light sheet irradiation area, where the irradiation area is marked in green.

[0055] Of course, the above are only typical examples of the present invention. In addition, the present invention may also have many other specific implementation methods. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims

1. A method for observing the internal flow field of a vortex spinning transparent nozzle, characterized in that: The steps include: S1. preparing a transparent vortex spinning nozzle, wherein the internal flow channel of the transparent vortex spinning nozzle is made of an optically transparent material; S2. A non-contact optical measurement system is provided outside the transparent vortex spinning nozzle, the system comprising a high-speed image acquisition unit and a laser illumination unit, the laser illumination unit emitting a sheet-shaped laser beam after beam shaping, the sheet-shaped laser beam passing through the wall of the transparent vortex spinning nozzle and illuminating the area to be observed in the internal flow channel thereof; S3, uniformly injecting tracer particles having fluid dynamic properties sufficient to follow the airflow and good light scattering properties into the spinning airflow to be observed; S4, injecting the spinning airflow carrying the tracer particles into the internal flow channel of the transparent vortex spinning nozzle; S5, synchronously triggering the laser pulse of the laser illumination unit and the image acquisition of the high-speed image acquisition unit to continuously capture a motion image sequence of the tracer particles in the flow field in the area to be observed; S6. Process the motion image sequence using a particle image velocimetry algorithm to obtain flow field velocity vector distribution and turbulence characteristic parameters in the area to be observed.

2. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: The optically transparent material is optical-grade polyphenylene sulfide or polyetherimide; and the preparation steps include: performing nano-level polishing on the inner surface of the transparent vortex spinning nozzle to make the surface roughness Ra ≤ 0.05 μm, and eliminating the internal stress of the material through an annealing process to make the birefringence optical path difference less than 5 nm / mm.

3. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: The tracer particles are hollow glass microspheres with a density of 0.5-1.0 g / cm³ and a particle size of 1-10 μm. The surfaces of the tracer particles are modified with a silane coupling agent to perform a hydrophobic treatment.

4. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: The high-speed image acquisition unit is a high-speed camera with a resolution of not less than 2048×2048 pixels and a frame rate of not less than 1000 fps; the laser illumination unit is a double-pulse laser with a wavelength of 532 nm.

5. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 4, characterized in that: The synchronous triggering is achieved by a synchronous controller, which sets the trigger delay between the dual-pulse laser and the high-speed camera so that the high-speed camera continuously captures at least two frames of images at a time interval of microseconds.

6. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: Before injecting the spinning airflow, the method further includes the steps of arranging a constant temperature shell around the transparent vortex spinning nozzle and maintaining the wall temperature of the transparent vortex spinning nozzle at 80±1° C. through a PID controller.

7. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: The particle image velocimetry algorithm processing includes background subtraction and noise filtering on the motion image sequence, and then cross-correlation calculation and vector verification.

8. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 7, characterized in that: The cross-correlation calculation uses a multi-grid algorithm, where the query window is set to 32×32 pixels with an overlap rate of 50%.

9. The method for observing the internal flow field of a vortex spinning transparent nozzle according to claim 1, characterized in that: The step of obtaining turbulence characteristic parameters includes: extracting the Strouhal number by performing Fourier transform analysis on the wake flow at the fiber outlet end; and importing the obtained flow field velocity vector distribution as a boundary condition into a computational fluid dynamics model for comparative verification.

10. A device for observing the internal flow field of a vortex spinning transparent nozzle, characterized in that: include: The transparent vortex spinning nozzle module has an inner surface roughness Ra ≤ 0.05 μm and a geometric similarity error with the prototype nozzle ≤ 0.5%; a laser light source module configured to emit a sheet-shaped laser beam after beam shaping to illuminate the internal area to be measured of the transparent vortex spinning nozzle module; A high-speed image acquisition module is arranged on one side of the transparent vortex spinning nozzle module and is used to acquire images of tracer particles illuminated by the laser in the area to be measured; a tracer particle injection module, the outlet of which is in communication with the air inlet passage of the transparent vortex spinning nozzle module, for supplying tracer particles into the air flow; A synchronous controller is electrically connected to the laser light source module and the high-speed image acquisition module respectively, and is used to synchronously trigger the pulse emission of the laser light source module and the image acquisition of the high-speed image acquisition module.

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