System and method for measuring gas-liquid two-phase slip velocity of unsteady cavitation flow
By using a Venturi-type experimental section and a gas-liquid two-phase synchronous imaging velocimetry system, the problem of measuring gas-liquid slip velocity in unsteady cavitation flow was solved. This enabled synchronous and independent measurement of gas and liquid phase velocities, providing high-precision experimental data support and improving the accuracy of cavitation flow models.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technologies struggle to simultaneously and independently measure the slip velocity of the gas and liquid phases in unsteady cavitation flows, resulting in large measurement errors that fail to accurately reflect the momentum transfer process between phases, thus affecting the accuracy of cavitation flow structure evolution and cavitation risk assessment.
A Venturi-type experimental section and a gas-liquid two-phase synchronous imaging velocimetry system are adopted. Four CCD cameras and optical filtering technology are used to separate gas and liquid signals. The three-dimensional velocity field is reconstructed by combining the principle of stereo vision, so as to realize the synchronous and independent measurement of gas phase and liquid phase velocity.
It enables independent and accurate calculation of the three-dimensional transient velocity fields of the gas and liquid phases at the same spatiotemporal point, providing high-precision slip velocity data and reliable experimental data support for the correction of cavitation numerical models.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of multiphase flow measurement technology, and in particular to a measurement system and method for the slip velocity of unsteady cavitation flow gas-liquid two-phase flow. Background Technology
[0002] Cavitation refers to the vaporization of a liquid when the local pressure is lower than its saturated vapor pressure, resulting in a two-phase flow phenomenon where vapor (gas phase) and liquid (liquid phase) coexist. During the development of cavitation, the dynamic behaviors of bubble generation, expansion, deformation, and collapse cause significant relative motion between the gas and liquid phases, i.e., gas-liquid two-phase velocity slip.
[0003] However, current numerical simulations of cavitation flows widely employ homogeneous flow models. These models treat the gas and liquid phases as a single mixed medium with equivalent density and viscosity, whose properties continuously vary with the local gas phase volume fraction, and are solved using the same set of governing equations (such as the Navier-Stokes equations). Homogeneous flow models greatly simplify computational complexity and are currently the mainstream method in engineering applications. However, their fundamental limitation lies in the artificial assumption that the gas and liquid phases have the same velocity at any location, completely neglecting the interphase slip effect. This simplification leads to the model's inability to accurately reflect the momentum transfer process between phases. Studies have shown that neglecting slip velocity introduces non-physical numerical dissipation, resulting in insufficient accuracy in predicting cavitation flow structure evolution, pulsating pressure, and cavitation risk areas. To improve the physical realism and predictive accuracy of cavitation numerical models, developing experimental methods that can directly measure and quantify actual slip velocity, thereby providing data support for introducing accurate interphase momentum exchange correction terms into the model, has become an urgent and crucial research need in this field.
[0004] At the experimental measurement level, obtaining the slip velocity of the gas-liquid two-phase flow in unsteady cavitation flow faces significant technical challenges. Traditional optical flow field measurement techniques, such as particle image velocimetry (PIV) or laser Doppler velocimetry (LDV), rely on the scattering signal of incident laser light by tracer particles in the fluid. These techniques are very mature in single-phase flow. However, when applied to gas-liquid two-phase flow such as cavitation, the situation becomes extremely complex: on the one hand, to measure the liquid phase velocity, tracer particles need to be seeded in the liquid; on the other hand, the cavitation bubbles themselves also generate strong scattered light signals to the laser. These two signals are highly coupled and interfere with each other in time and space.
[0005] Existing techniques often fail to effectively separate these two types of signals, resulting in inherent defects in the measurement results: (1) If a conventional PIV system is used, the strong scattered light from the bubbles will form bright spots or large bright areas, severely obscuring or interfering with the tracer particle image, causing the liquid phase velocity calculation based on the cross-correlation of the particle image to fail or have extremely large errors; (2) If attempts are made to separate the bubble signal through image processing or filtering to analyze the gas phase motion, the tracer particle signal will be treated as noise and filtered out. Therefore, most existing experimental studies can only estimate the velocity of a certain phase, and cannot directly, synchronously, and independently obtain the precise three-dimensional velocity vectors of the gas and liquid phases at the same time and space point. The core physical quantity of gas-liquid two-phase slip velocity has long lacked reliable direct experimental observation data, forming a key technological gap.
[0006] Furthermore, to achieve accurate measurement of complex three-dimensional cavitation flow fields, stereo PIV / PTV technology is required. This necessitates that the observation window possess excellent optical transmittance and minimize refraction of light as it passes through the interface between different media (water-observation window-air), otherwise, it will lead to serious errors in the reconstruction of three-dimensional spatial coordinates. Existing experimental section designs often struggle to balance optical compatibility, targeted structural design to reduce refraction errors, and modular maintenance convenience.
[0007] In summary, these shortcomings in existing technologies collectively hinder a deeper understanding of the interphase interaction mechanism in cavitation flows and the development of high-fidelity numerical models. Summary of the Invention
[0008] To address the shortcomings of existing technologies, this invention provides a measurement system and method for the slip velocity of unsteady cavitation flow gas and liquid phases, enabling simultaneous measurement of transient gas phase velocity and liquid phase velocity, thereby accurately calculating the slip velocity and providing reliable experimental data support for the correction of cavitation numerical models.
[0009] The present invention achieves the above-mentioned technical objectives through the following technical means.
[0010] A measurement system for the slip velocity of unsteady cavitation flow gas-liquid two-phase flow includes a Venturi-type experimental section and a gas-liquid two-phase synchronous imaging velocimetry system.
[0011] The Venturi-type experimental section is used to create unsteady cavitation flow within it.
[0012] The gas-liquid two-phase synchronous imaging velocimetry system includes an illumination system, a first imaging unit, a second imaging unit, and a synchronizer. The illumination system generates and guides a sheet laser to illuminate the target measurement section within the Venturi-type experimental section. The first imaging unit includes two first CCD cameras arranged on the first side of the Venturi-type experimental section, each with an optical filter lens in front of its lens for selectively transmitting fluorescence signals from liquid-phase tracer particles, used to acquire images of liquid-phase motion. The second imaging unit includes two second CCD cameras arranged on the second side of the Venturi-type experimental section opposite to the first side, each with a density filter lens in front of its lens for attenuating light intensity and suppressing fluorescence signals, used to acquire images of the gas phase structure. The synchronizer controls the pulse emission of the sheet laser to synchronize with the exposure actions of the first and second CCD cameras.
[0013] Furthermore, the Venturi-type experimental section includes a main frame, a plug-in assembly, and a sealing and fixing assembly; the main frame has flange structures at both ends for connecting external pipelines, and its interior forms a stepped cavity; the plug-in assembly includes an upper wall plug, a lower wall plug, a front wall plug, and a rear wall plug made of transparent material, the upper wall plug, the lower wall plug, the front wall plug, and the rear wall plug are respectively installed in the stepped cavity of the main frame through the sealing and fixing assembly, and the inner surface of the lower wall plug, the outer surface of the front wall plug, and the outer surface of the rear wall plug are respectively provided with trapezoidal bosses; the inner surfaces of each plug in the plug-in assembly together form a Venturi-type flow channel.
[0014] Furthermore, the trapezoidal protrusions on the outer sides of the front and rear wall inserts are configured as observation interfaces; the shooting direction of the first CCD camera is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the front wall insert; the shooting direction of the second CCD camera is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the rear wall insert.
[0015] Furthermore, the lighting system includes a dual-pulse laser, a reflecting plane mirror, and a cylindrical lens; the laser beam emitted by the dual-pulse laser is reflected by the reflecting plane mirror and then incident on the cylindrical lens, where it is expanded into a sheet-like laser.
[0016] Furthermore, the optical filter lens is configured to block the wavelength light of the sheet laser and allow the fluorescent wavelength light emitted by the stimulated emission of the liquid-phase tracer particles to pass through.
[0017] Furthermore, the first CCD camera and the second CCD camera constitute two independent stereo vision systems, which are used to reconstruct the three-dimensional transient velocity fields of the liquid phase and the gas phase, respectively.
[0018] A measurement method for a gas-liquid two-phase slip velocity measurement system based on unsteady cavitation flow includes the following steps:
[0019] S01: Unsteady cavitation flow is formed in the Venturi-type experimental section;
[0020] S02: Add a refractive index matching liquid to the flow medium so that the refractive index of the flow medium matches the refractive index of the material of the transparent insert constituting the wall of the Venturi-type experimental section, and incorporate fluorescent tracer particles into the flow medium.
[0021] S03: Adjust the lighting system so that the sheet laser illuminates the target measurement section of the Venturi-type experimental section;
[0022] S04: The illumination system, the first imaging unit and the second imaging unit are synchronously triggered by the synchronizer to acquire liquid phase tracer particle image sequence and gas phase structure image sequence respectively;
[0023] S05: While keeping the position of the optical elements unchanged, perform three-dimensional spatial calibration on the measurement system and establish the stereo vision mapping relationship between the cameras in the first imaging unit and the second imaging unit respectively.
[0024] S06: Based on the calibration results, perform three-dimensional reconstruction and velocity calculation on the liquid phase tracer particle image sequence and the gas phase structure image sequence respectively to obtain the liquid phase three-dimensional transient velocity field and the gas phase three-dimensional transient velocity field.
[0025] S07: The three-dimensional transient velocity field of the liquid phase and the three-dimensional transient velocity field of the gas phase are spatiotemporally aligned, and the velocity vector difference between the two phases is calculated point by point to obtain the gas-liquid two-phase slip velocity field.
[0026] Furthermore, in step S02, the refractive index matching solution is a sodium iodide solution.
[0027] Furthermore, in step S05, the specific steps for three-dimensional spatial calibration include: removing part of the wall inserts of the Venturi-type experimental section, placing the three-dimensional calibration plate on the plane where the target measurement section is located, taking pictures of the calibration plate using the first CCD camera and the second CCD camera, and calculating stereo vision parameters based on the captured images.
[0028] Furthermore, in step S06, when performing three-dimensional reconstruction and velocity calculation on the liquid phase tracer particle image sequence and the gas phase structure image sequence, a three-dimensional volume velocimetry technique based on image cross-correlation is adopted.
[0029] The beneficial effects of this invention are as follows:
[0030] 1. The unsteady cavitation flow gas-liquid two-phase slip velocity measurement system of this invention, by designing a synchronous imaging velocimetry system including four high-speed CCD cameras and utilizing optical filtering technology for signal separation, achieves synchronous, independent, and interference-free imaging of the gas phase structure and liquid phase tracer particles within the same measurement volume at the same time point. This fundamentally solves the bottleneck problem of mutual interference and inability to separate gas-liquid two-phase signals in existing technologies, making it possible to extract pure gas phase image sequences and liquid phase image sequences separately.
[0031] 2. The measurement system for the gas-liquid two-phase slip velocity of unsteady cavitation flow described in this invention achieves a breakthrough from indirect estimation to direct measurement by independently acquiring two sets of image sequences and applying the principle of dual-camera stereo vision to reconstruct the three-dimensional velocity field. It can independently and accurately calculate the three-dimensional transient velocity fields of both the gas and liquid phases in cavitation flow. This is something that existing single-system PIV or conventional imaging techniques cannot achieve.
[0032] 3. The measurement system for the unsteady cavitation flow gas-liquid two-phase sliding velocity of the present invention comprises a venturi-type experimental section assembled from a stainless steel main frame and detachable transparent plexiglass inserts. By setting trapezoidal protrusions on the outside of the inserts, the flow channel shape can be flexibly adjusted by replacing the inserts, greatly enhancing the versatility and maintainability of the experimental device. Secondly, it provides an optically optimized vertical incident interface for a high-speed CCD camera, allowing the camera's optical axis to be arranged perpendicular to the working surface, thereby minimizing the refraction effect of light passing through the multi-layer medium interface and laying a solid foundation for high-precision three-dimensional particle image velocimetry.
[0033] 4. The method for measuring the slip velocity of the gas-liquid two-phase in unsteady cavitation flow described in this invention, by aligning the spatiotemporal coordinates and performing point-by-point vector calculations on the three-dimensional transient velocity fields of the gas and liquid phases obtained separately, can directly and quantitatively obtain the complete spatiotemporal distribution of the slip velocity field of the gas-liquid two-phase in unsteady cavitation flow. Moreover, the obtained slip velocity data is real and reliable, providing an unprecedented direct experimental observation means for the study of the momentum and energy exchange mechanism between phases in cavitation flow.
[0034] 5. The method for measuring the slip velocity of unsteady cavitation gas-liquid two-phase flow described in this invention, through refractive index matching and in-situ spatial calibration, not only further eliminates systematic errors and ensures high accuracy and reliability of measurement results, but also forms a complete technical solution from experimental preparation, data acquisition to result output, making the measurement technology have good scalability and engineering application potential. Attached Figure Description
[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For those skilled in the art, it is obvious that other drawings can be obtained from these drawings without creative effort.
[0036] Figure 1 This is a schematic diagram of the measurement system for the slip velocity of the unsteady cavitation flow gas-liquid two-phase system described in this invention.
[0037] Figure 2 This is a three-dimensional structural diagram of the Venturi-type experimental section described in this invention.
[0038] Figure 3 This is a schematic cross-sectional view of the Venturi-type experimental section at the middle section of the present invention.
[0039] Figure 4 This is a three-dimensional structural diagram of the main frame described in this invention.
[0040] Figure 5 This is a three-dimensional structural diagram of the upper wall insert and the lower wall insert described in this invention.
[0041] Figure 6 This is a three-dimensional structural diagram of the front wall insert and the rear wall insert described in this invention.
[0042] Figure 7 This is a diagram illustrating the shooting angle of a CCD camera.
[0043] In the picture:
[0044] 1-Venturi-type experimental section; 101-Main frame; 102-Upper wall insert; 103-Lower wall insert; 104-Front wall insert; 105-Rear wall insert; 106-Sealing plate; 2-First CCD camera; 3-Second CCD camera; 4-Dual pulse laser; 5-Reflecting plane mirror; 6-Cylindrical lens; 7-Synchronizer. Detailed Implementation
[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0047] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0048] like Figure 1 As shown, the measurement system for the unsteady cavitation flow gas-liquid two-phase slip velocity of the present invention includes a Venturi-type experimental section 1 and a gas-liquid two-phase synchronous imaging velocimetry system.
[0049] The Venturi-type experimental section 1 is used to create unsteady cavitation flow within it; such as... Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the Venturi-type experimental section 1 includes a main frame 101, a plug-in assembly, and a sealing and fixing assembly. The main frame 101, serving as the load-bearing and connecting foundation for the entire experimental section, is precision-machined from stainless steel. Flange interfaces are provided at both ends of the frame for sealing connection with the circulating water tunnel pipeline. The main frame 101 is constructed with a stepped annular cavity around its perimeter. Threaded holes and annular grooves for accommodating O-ring seals are machined on the inner stepped surface of this cavity, facilitating the installation, positioning, and sealing of the transparent plug-in.
[0050] The plug-in assembly includes an upper wall plug-in 102, a lower wall plug-in 103, a front wall plug-in 104, and a rear wall plug-in 105, all made of high-transmittance acrylic glass (such as PMMA). The upper wall plug-in 102, lower wall plug-in 103, front wall plug-in 104, and rear wall plug-in 105 are respectively installed in the stepped cavity of the main frame 101 via sealing and fixing components. The inner surfaces of the upper wall plug-in 102 and the lower wall plug-in 103 respectively form the top cover and bottom wall of the flow channel. The inner surface of the lower wall plug-in 103 (i.e., the side facing the interior of the flow channel) is machined with a trapezoidal boss structure. The trapezoidal boss on the inner surface of the lower wall plug-in 103 constitutes the characteristics of a Venturi tube flow channel, constructing the contour from the contraction section to the throat and then to the diffusion section. The inner surfaces of the upper wall insert 102 and the lower wall insert 103 respectively form the front and rear observation windows of the flow channel; the outer surfaces of the front wall insert 104 (i.e., the side facing away from the flow channel and towards the external camera) and the rear wall insert 105 are respectively provided with trapezoidal protrusions, and the inclined sides of the trapezoidal protrusions are constructed as observation interfaces. After the four inserts are assembled and embedded into the main frame 101, the inner surfaces of the inserts together form a complete Venturi-type flow channel. The throat region of this flow channel is a specific location for inducing unsteady cavitation phenomena. By adjusting the operating conditions of the circulating water tunnel, unsteady cavitation flow phenomena can be induced in the throat region.
[0051] The sealing and fixing assembly includes a stainless steel sealing plate 106 and matching bolts. During assembly, each acrylic insert is first accurately placed into the stepped cavity of the main frame 101. Then, the sealing plate 106 is placed over the outside of the insert, and bolts are screwed through the plate into the threaded holes of the frame. By evenly tightening the bolts, the plate compresses the insert and compresses the O-ring pre-placed in the sealing groove, thereby achieving a reliable static seal in a flow field with high operating pressure. This structure facilitates the individual disassembly of the upper wall insert 102, providing convenience for subsequent in-situ calibration operations.
[0052] The gas-liquid two-phase synchronous imaging velocimetry system includes an illumination system, a first imaging unit, a second imaging unit, and a synchronizer 7. The illumination system generates and guides a sheet-like laser to illuminate the target measurement section within the Venturi-type experimental section 1. The illumination system includes a dual-pulse laser 4, a reflecting plane mirror 5, and a cylindrical lens 6. In this embodiment, the dual-pulse laser 4 emits a short-pulse-width green laser (wavelength 532 nm). The cylindrical lens 6 expands the point-like laser beam into a sheet-like laser with a thickness of approximately 1 mm. The laser beam emitted by the dual-pulse laser 4 is reflected by the reflecting plane mirror 5 and then incident on the cylindrical lens 6, where it is expanded into a sheet-like laser. The sheet-like laser is incident perpendicularly from the upper wall insert 102 and illuminates the central section (i.e., the XY plane) to be measured at the throat of the Venturi channel.
[0053] like Figure 7As shown, the first imaging unit includes two first CCD cameras 2, arranged on the first side of the Venturi-type experimental section 1. Each camera has an optical filter in front of its lens for selectively transmitting the fluorescence signal of the liquid-phase tracer particles, used to acquire images of liquid-phase motion. The shooting direction of the first CCD camera 2 is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the front wall insert 104. This perpendicular incident arrangement minimizes the refraction effect when light passes through the interfaces of multiple media such as water, plexiglass, and air, thereby significantly improving the spatial positioning accuracy of three-dimensional particle image velocimetry. An optical filter is installed in front of the lens of each first CCD camera 2. This filter has high transmittance for the fluorescence wavelength of the liquid-phase tracer particles, while strongly blocking laser wavelengths.
[0054] like Figure 7 As shown, the second imaging unit includes two second CCD cameras 3, arranged on the second side of the Venturi-type experimental section 1 opposite to the first side. Each camera has a density filter in front of its lens to attenuate light intensity and suppress fluorescence signals, used to acquire images of the gas phase structure. The shooting direction of the second CCD camera 3 is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the rear wall insert 105 to obtain a gas phase image without refraction distortion. A density filter (neutral density filter) is installed in front of the lens of the second CCD camera 3, mainly used to uniformly attenuate the incident light intensity and prevent strong scattered light from the gas phase structure from saturating the camera sensor.
[0055] The synchronizer 7 is connected to and controls the dual-pulse laser 4 and four high-speed CCD cameras via cables. The synchronizer 7 ensures that the dual-pulse emission of the laser is synchronized with the two exposures of all cameras on a microsecond time scale, thereby providing an accurate time reference for transient velocity measurement.
[0056] Working principle:
[0057] During the experiment, fluorescent microparticles were dispersed into the water flow. Under laser illumination, the particles absorbed 532nm green light and emitted yellow fluorescence (wavelength 584nm); simultaneously, cavitation bubbles strongly scattered the 532nm laser light. The optical filter in front of the first CCD camera 2 effectively blocked the strong scattered light from the bubbles, recording only the particle fluorescence, thus obtaining a pure liquid-phase motion image. The density filter in front of the second CCD camera 3, after overall attenuating the light intensity, allowed the higher-intensity bubble scattered light signal to be clearly recorded, while the weak particle fluorescence was suppressed, thus obtaining an image dominated by the gas phase structure. Synchronous control ensured that both sets of images were captured at the same instant.
[0058] The measurement method of the gas-liquid two-phase slip velocity measurement system based on unsteady cavitation flow described in this invention includes the following steps:
[0059] S01: Install the Venturi-type experimental section 1 in the circulating water tunnel. Start the water tunnel and adjust the flow rate and inlet pressure until periodic unsteady cloud-like cavitation flow is observed in the throat region of the Venturi channel;
[0060] S02: To reduce refractive interference at the observation window interface, optical matching of the working fluid is required. An appropriate amount of sodium iodide solution is added to the working medium of the circulating water tunnel. By adjusting the concentration of the sodium iodide solution, the refractive index of the mixed liquid is made to be basically matched with the refractive index of the plexiglass insert material. Simultaneously, an appropriate amount of fluorescent particles with an average diameter of 20 μm are uniformly seeded into the working medium as liquid-phase tracer particles.
[0061] S03: Turn on the low-power indicator light of the dual-pulse laser 4, and sequentially adjust the angle and position of the reflecting plane mirror 5 and the cylindrical lens 6 so that the formed laser sheet light penetrates the upper wall insert 102 perpendicularly and completely covers the central section to be measured at the throat of the flow channel. Adjust the spatial pose, pitch angle, and lens focal length of the four CCD cameras to ensure that their field of view completely covers the area illuminated by the laser sheet light and obtains a clear initial image;
[0062] S04: Set the trigger frequency of synchronizer 7, start synchronizer, and dual-pulse laser 4 emits a series of paired high-energy short pulses. Four cameras simultaneously perform double exposure, thereby capturing a series of time-correlated transient image pairs. During this process, the first CCD camera 2 acquires the liquid phase fluorescent particle image sequence, and the second CCD camera 3 acquires the gas phase structure scattered light image sequence. All images are strictly time-stamped.
[0063] S05: After image acquisition, keep all optical components in their original positions and remove the upper wall insert 102. Place the 3D calibration plate into the flow channel, positioning it within the same XY plane illuminated by the previous laser sheet light. Use the four cameras, which remain stationary, to photograph the calibration plate. Based on the obtained calibration plate images, apply a mature stereo vision calibration algorithm to calculate and establish the 3D mapping relationship of the stereo vision system formed by the two front CCD cameras 2 and the 3D mapping relationship of the stereo vision system formed by the two rear CCD cameras 3. This step provides the necessary transformation parameters for subsequent inversion of 3D spatial coordinates from 2D image coordinates.
[0064] S06: Using the calibration parameters obtained in step 5, process the two sets of image sequences independently.
[0065] For the liquid phase particle image sequence acquired by the first CCD camera 2, a three-dimensional particle image velocimetry algorithm is adopted. First, stereo matching and three-dimensional coordinate reconstruction are performed on the fluorescent particles in the views of the two cameras at the same time. Then, cross-correlation analysis is performed on the three-dimensional positions of the particles in two consecutive frames of laser pulse images to calculate the three-dimensional transient velocity vector of the liquid phase at each position within the measurement volume. Finally, the liquid phase velocity field is synthesized.
[0066] For the gas phase structure image sequence acquired by the second CCD camera 3, a three-dimensional volume velocimetry technique based on image cross-correlation is applied. The three-dimensional spatial displacement of the bubble swarm texture or structural pattern between continuous pulses is analyzed to calculate the three-dimensional transient velocity field of the gas phase.
[0067] S07: The obtained liquid and gas phase velocity fields of the cavitation flow are aligned in time and space. The corresponding gas and liquid phase velocity vectors are extracted at the same spatial grid locations, and point-by-point calculations are performed to obtain the transient gas-liquid two-phase slip velocity vector at that location, thus obtaining the gas-liquid two-phase slip velocity distribution throughout the entire measurement area. By calculating the entire time series, the spatiotemporal evolution of the slip velocity field is obtained, providing crucial data for cavitation model correction.
[0068] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.
[0069] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.
Claims
1. A measurement system for the slip velocity of a gas-liquid two-phase flow in unsteady cavitation, characterized in that, Including the Venturi-type experimental section (1) and the gas-liquid two-phase synchronous imaging velocimetry system; The Venturi-type experimental section (1) is used to generate unsteady cavitation flow within it; The gas-liquid two-phase synchronous imaging velocimetry system includes an illumination system, a first imaging unit, a second imaging unit, and a synchronizer (7). The illumination system is used to generate and guide a sheet laser to illuminate the target measurement section within the Venturi-type experimental section (1). The first imaging unit includes two first CCD cameras (2), which are arranged on the first side of the Venturi-type experimental section (1), and each camera is equipped with an optical filter lens for selectively transmitting the fluorescence signal of the liquid phase tracer particles, for acquiring liquid phase motion images. The second imaging unit includes two second CCD cameras (3), which are arranged on the second side of the Venturi-type experimental section (1) opposite to the first side, and each camera is equipped with a density filter lens for attenuating light intensity and suppressing fluorescence signals, for acquiring gas phase structure images. The synchronizer (7) is used to control the pulse emission of the sheet laser and the exposure actions of the first CCD camera (2) and the second CCD camera (3) to achieve synchronous triggering.
2. The measurement system for the slip velocity of unsteady cavitation flow gas-liquid two-phase flow according to claim 1, characterized in that, The Venturi-type experimental section (1) includes a main frame (101), a plug-in assembly, and a sealing and fixing assembly; the main frame (101) has flange structures at both ends for connecting external pipelines, and a stepped cavity is formed inside; the plug-in assembly includes an upper wall plug-in (102), a lower wall plug-in (103), a front wall plug-in (104), and a rear wall plug-in (105) made of transparent material. The upper wall plug-in (102), lower wall plug-in (103), front wall plug-in (104), and rear wall plug-in (105) are respectively installed in the stepped cavity of the main frame (101) through the sealing and fixing assembly. The inner surface of the lower wall plug-in (103), the outer surface of the front wall plug-in (104), and the outer surface of the rear wall plug-in (105) are respectively provided with trapezoidal bosses; the inner surfaces of each plug-in in the plug-in assembly together form a Venturi-type flow channel.
3. The measurement system for the slip velocity of unsteady cavitation flow gas-liquid two-phase flow according to claim 2, characterized in that, The trapezoidal protrusions on the outer sides of the front wall insert (104) and the rear wall insert (105) are configured as observation interfaces with their inclined sides; the shooting direction of the first CCD camera (2) is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the front wall insert (104); the shooting direction of the second CCD camera (3) is perpendicular to the observation interface of the trapezoidal protrusion on the outer side of the rear wall insert (105).
4. The measurement system for the gas-liquid two-phase slip velocity of unsteady cavitation flow according to claim 2, characterized in that, The lighting system includes a dual-pulse laser (4), a reflecting plane mirror (5), and a cylindrical lens (6); the laser beam emitted by the dual-pulse laser (4) is reflected by the reflecting plane mirror (5), then incident on the cylindrical lens (6) and expanded into a sheet-like laser.
5. The measurement system for the slip velocity of unsteady cavitation flow gas-liquid two-phase flow according to claim 2, characterized in that, The optical filter is configured to block the wavelength of the sheet laser and allow the fluorescent wavelength of the liquid-phase tracer particles to pass through.
6. The measurement system for the gas-liquid two-phase slip velocity of unsteady cavitation flow according to claim 1, characterized in that, The first CCD camera (2) and the second CCD camera (3) constitute two independent stereo vision systems, which are used to reconstruct the three-dimensional transient velocity fields of the liquid phase and the gas phase, respectively.
7. A method for measuring the gas-liquid two-phase slip velocity of an unsteady cavitation flow based on any one of claims 1-6, characterized in that, Includes the following steps: S01: Unsteady cavitation flow is formed in the Venturi-type experimental section (1); S02: Add a refractive index matching liquid to the flow medium so that the refractive index of the flow medium matches the refractive index of the material of the transparent plug that constitutes the wall of the Venturi-type experimental section (1), and add fluorescent tracer particles to the flow medium. S03: Adjust the lighting system so that the sheet laser illuminates the target measurement section of the Venturi-type experimental section (1); S04: The lighting system, the first imaging unit and the second imaging unit are synchronously triggered by the synchronizer (7) to acquire liquid phase tracer particle image sequence and gas phase structure image sequence respectively; S05: While keeping the position of the optical elements unchanged, perform three-dimensional spatial calibration on the measurement system and establish the stereo vision mapping relationship between the cameras in the first imaging unit and the second imaging unit respectively. S06: Based on the calibration results, perform three-dimensional reconstruction and velocity calculation on the liquid phase tracer particle image sequence and the gas phase structure image sequence respectively to obtain the liquid phase three-dimensional transient velocity field and the gas phase three-dimensional transient velocity field. S07: The three-dimensional transient velocity field of the liquid phase and the three-dimensional transient velocity field of the gas phase are spatiotemporally aligned, and the velocity vector difference between the two phases is calculated point by point to obtain the gas-liquid two-phase slip velocity field.
8. The measurement method according to claim 7, characterized in that, In step S02, the refractive index matching solution is a sodium iodide solution.
9. The measurement method according to claim 7, characterized in that, In step S05, the specific steps for three-dimensional spatial calibration include: removing part of the wall inserts of the Venturi-type experimental section (1), placing the three-dimensional calibration plate on the plane where the target measurement section is located, taking pictures of the calibration plate using the first CCD camera (2) and the second CCD camera (3), and calculating stereoscopic vision parameters based on the captured images.
10. The measurement method according to claim 7, characterized in that, In step S06, when performing three-dimensional reconstruction and velocity calculation on the liquid phase tracer particle image sequence and the gas phase structure image sequence, a three-dimensional volume velocimetry technique based on image cross-correlation is adopted.