Electrolytic hydrogen bubble-based tracer PIV boundary layer flow field test system and test method

Abstract

The application discloses a kind of based on electrolytic hydrogen bubble's PIV boundary layer flow field test system and test method of satellite, including integrated optical measurement module and tracer particle generation module;Optical measurement module is located in UUV interior, including laser emitter assembly, sapphire prism and the two imaging cameras of symmetrical arrangement, laser sheet light is refracted after sapphire prism and forms sheet light area on the outer surface of UUV;Tracer particle generation module includes cathode, anode and power supply unit, cathode is the platinum wire array of several platinum wires arranged along the axis of UUV, each platinum wire is located at different height from the wall surface of UUV;Power supply unit selectively energizes platinum wire and independently adjusts voltage, control the number and frequency of hydrogen bubbles generated, realize the synchronous measurement of flow field information at different thickness positions of boundary layer.The application realizes boundary layer flow field in-situ satellite measurement and synchronous fine measurement at different thickness positions under the condition of not changing the appearance of UUV, with the advantages of high integration, small flow field disturbance, high measurement efficiency.

Description

A system and method for testing the boundary layer flow field of a portable PIV based on hydrogen electrolysis bubbles. Technical Field

[0001] This invention relates to the field of fluid dynamics testing, and in particular to a portable PIV boundary layer flow field testing system and method based on electrolytic hydrogen bubbles. Background Technology

[0002] Particle image velocimetry (PIV) has become a key method for obtaining flow field information in fluid mechanics research due to its advantages such as non-contact and interference-free operation and transient full-field measurement. Its basic principle involves seeding tracer particles in the fluid, illuminating the area to be measured with laser light, recording particle images with a high-speed camera, and then obtaining the velocity distribution of the flow field through relevant algorithms.

[0003] In the development of underwater vehicles, especially unmanned underwater vehicles (UUVs), obtaining body-fit boundary layer flow field information during navigation is crucial for revealing flow resistance mechanisms, optimizing shape design, and verifying hydrodynamic characteristics. However, under current technological conditions, applying PIV technology to in-situ measurements of UUV boundary layers still faces many challenges:

[0004] First, existing PIV measurement devices are mostly suitable for laboratory environments and are difficult to implement in-situ measurements under real-world conditions. For example, patent document CN117949170A discloses a "Bionic UUV Self-propelled Model Natural Water Area PIV Flow Field Testing Device," which integrates core components such as lasers and cameras onto an independent underwater PIV truss and deploys it in natural water areas via a barge. While this solution achieves tracking and measurement of the self-propelled model, its measurement system is still an external device independent of the vehicle, guiding the UUV into the measurement area via a navigation probe. This approach is essentially "the vehicle enters the measurement field" rather than "the measurement field follows the vehicle," making it impossible to achieve continuous, in-situ monitoring of the flow field of the UUV during actual navigation. Furthermore, the presence of the large truss structure also poses a potential impact on the vehicle's maneuverability and the real flow field environment.

[0005] Secondly, existing hydrogen bubble flow visualization technologies have limitations for precise measurements at different thicknesses within the boundary layer. Hydrogen bubble technology is a classic flow visualization and measurement method, using hydrogen bubbles generated on a cathode platinum wire via water electrolysis as tracer particles. For example, patent document CN102426092A discloses a "Boundary Layer Visualization Test Device Based on Hydrogen Bubble Flow Visualization Technology," which details a method for observing the boundary layer in a laboratory pipe environment using single or multiple platinum wires to generate hydrogen bubbles. However, in this existing technology and conventional hydrogen bubble applications, the cathode platinum wires are typically arranged in a single or multiple configuration perpendicular to the wall. This arrangement has the following inherent drawbacks: firstly, it is difficult to achieve independent control among multiple parallel platinum wires, usually only generating bubbles within the same plane, making it impossible to selectively and precisely measure the flow field at different normal heights (i.e., different velocity layers) within the boundary layer; secondly, the support structure perpendicular to the wall inevitably disturbs the flow within the minute boundary layer, affecting the accuracy of the measurement results. Although literature CN102426092A uses a precise height adjustment device to move the position of a single platinum wire to achieve measurements at different heights, this is a "time-division" measurement method, which cannot simultaneously acquire flow field information at different boundary layer heights at the same time, making it difficult to capture the spatial correlation of transient flow structures.

[0006] Furthermore, although micro- and nano-bubbles have been proposed as tracer particles in existing technologies (such as patent document CN116296247A), their generation methods are complex, and they are mostly used for displaying the overall flow field, lacking a mature solution that combines them with UUV body measurement and fine control within the boundary layer.

[0007] In summary, the existing technology lacks a testing system that can achieve in-situ measurement with UUV and simultaneously and precisely acquire flow field information at different thicknesses within the boundary layer. Summary of the Invention

[0008] The technical problem to be solved:

[0009] Existing technologies mainly suffer from the following technical problems: Traditional PIV measurement systems are mostly independent, external laboratory equipment, which cannot be highly integrated into the UUV, making it difficult to achieve in-situ, body-attached boundary layer observation during actual navigation. Moreover, when using hydrogen bubble technology for boundary layer measurement, there is a lack of means to selectively and synchronously acquire transient flow field information at different normal heights within the boundary layer without disturbing the flow field.

[0010] Therefore, how to deeply integrate the PIV system with the UUV body and combine it with a novel, finely controllable multilayer tracer particle generator to achieve in-situ, body-based, multi-dimensional measurement of the UUV boundary layer flow field is a technical problem that urgently needs to be solved by those skilled in the art.

[0011] Technical solution:

[0012] To address the problems existing in the prior art, this invention proposes a portable PIV boundary layer flow field testing system and method based on electrolytic hydrogen bubbles. This system enables real-time observation and analysis of boundary layer flow without significantly altering the shape of the UUV, and is suitable for fundamental research on the fluid dynamics of UUVs and engineering experiments.

[0013] On one hand, this invention proposes a body-based PIV boundary layer flow field testing system based on electrolytic hydrogen bubbles, comprising:

[0014] An integrated optical measurement module, located inside the UUV, is used to form a sheet light region in the vicinity of the outer surface of the UUV and to image that region;

[0015] The tracer particle generation module is used to generate hydrogen bubbles upstream of the sheet light region as tracer particles, so that the hydrogen bubbles flow into the sheet light region.

[0016] The integrated optical measurement module includes:

[0017] Optical support frame, fixedly connected to the internal skin of the UUV;

[0018] A laser emitter assembly, mounted on the optical support frame, is used to emit shaped sheet light;

[0019] A sapphire prism is encapsulated in an optical window at a corresponding position on the UUV skin, used to refract the sheet light to a region adjacent to the outer surface of the UUV to form a sheet light region;

[0020] The first imaging camera and the second imaging camera are mounted on the optical support frame and symmetrically arranged on both sides of the sapphire prism for synchronous imaging of the sheet light area from different perspectives.

[0021] The tracer particle generation module includes:

[0022] The cathode is disposed on the UUV skin surface upstream of the sheet light region;

[0023] The anode is located on the UUV skin surface downstream of the sheet light region;

[0024] The power supply unit, located inside the UUV, is electrically connected to the cathode and anode and is used to generate hydrogen bubbles at the cathode by electrolyzing water.

[0025] The cathode is a multi-layered platinum wire array composed of several platinum wires arranged at intervals along the UUV axis. Each platinum wire is located at a different height from the UUV wall to correspond to different thicknesses of the boundary layer. Adjacent platinum wires have a preset spacing in the height direction to avoid interfering with the flow field on the UUV wall. The power supply unit can selectively energize one or more platinum wires in the platinum wire array and control the number and frequency of hydrogen bubbles generated by each platinum wire by adjusting the voltage applied to different platinum wires, thereby realizing the synchronous measurement of flow field information at different thicknesses within the boundary layer.

[0026] In a further preferred embodiment, the total height of the platinum wire array is less than the boundary layer thickness of the flow field adjacent to the UUV surface.

[0027] In a further preferred embodiment, the platinum wire array is fixed to the surface of the UUV skin by an insulating bracket. The insulating bracket is made of high-strength engineering plastic and has mounting grooves corresponding to the number of platinum wires. After the platinum wires pass through the mounting grooves, they are fixed by spot welding or conductive adhesive.

[0028] In a further preferred embodiment, the power supply unit includes a multi-channel electronic switch array, with each channel independently connected to a platinum wire. Different channels are selected to conduct by a control signal, thereby achieving selective energization of one or more platinum wires.

[0029] In a further preferred embodiment, the power supply unit is configured to supply power to the cathode in a pulsed manner; the operating timing of the laser emitter assembly, the first imaging camera, and the second imaging camera is synchronized with the pulsed power supply timing of the power supply unit.

[0030] In a further preferred embodiment, the power supply unit has a built-in timing controller that can precisely control the delay time of laser emission and camera exposure relative to the electrolysis pulse, and capture images of hydrogen bubbles at different motion moments after they are generated by adjusting the delay time.

[0031] In a further preferred embodiment, the sapphire prism has an inverted trapezoidal cross-section, with its short side facing the laser emitter assembly, its two inclined sides facing the first imaging camera and the second imaging camera respectively, and its long side flush with the outer surface of the UUV or embedded in the skin.

[0032] In a further preferred embodiment, the anode is a graphite electrode.

[0033] On the other hand, based on the above system, this invention also proposes a method for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles, comprising the following steps:

[0034] Step S1: Form a sheet light region in the vicinity of the outer surface of the UUV using an integrated optical measurement module;

[0035] Step S2: Selectively energize one or more platinum wires in the multilayer platinum wire array through the power supply unit, so that the selected platinum wire is electrolyzed to generate hydrogen bubbles, and the hydrogen bubbles flow into the sheet light region as tracer particles.

[0036] Step S3: Simultaneously image the hydrogen bubbles in the sheet light area using the first imaging camera and the second imaging camera.

[0037] Step S4: Perform particle image velocimetry processing based on the acquired image to obtain flow field velocity information at different thickness locations within the boundary layer.

[0038] In a further preferred embodiment, in step S2, the number and frequency of hydrogen bubbles generated by each platinum wire are controlled by adjusting the voltage applied to different platinum wires, so as to achieve synchronous measurement of different boundary layer thickness positions.

[0039] Beneficial effects:

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] First, this invention highly integrates the PIV optical measurement module inside the UUV, and uses a sapphire prism to guide the laser light from the sheet to the outer surface of the UUV. Without changing the shape of the UUV or adding external loads, it enables in-situ and continuous observation of the flow field of the vehicle's own body boundary layer during actual navigation, solving the technical problem that existing external PIV systems are difficult to achieve body-mounted measurement.

[0042] Secondly, this invention employs a multi-layer platinum wire array arranged along the UUV axis as the electrolytic cathode, and independently controls the on / off state and voltage regulation of each platinum wire layer through a power supply unit. This enables the selective generation of hydrogen bubble tracer particles at different normal heights within the boundary layer simultaneously. This overcomes the limitations of traditional hydrogen bubble technology, which only allows for "time-division" measurements via mechanically moving the platinum wire. It achieves simultaneous and refined measurement of flow field information at different thicknesses within the boundary layer, providing a crucial means for studying the transient flow structure and pseudo-sequential characteristics of the boundary layer.

[0043] Third, in this invention, the platinum wire array is arranged along the UUV axis, with adjacent platinum wires maintaining a preset spacing. The total height of the platinum wire array is less than the boundary layer thickness. Compared to the cathode insertion method perpendicular to the wall in traditional hydrogen bubble technology, this arrangement causes less disturbance to the flow within the boundary layer, ensuring that the measurement results are closer to the actual flow state. Simultaneously, by controlling the distribution height of the platinum wires within the boundary layer, the generation and movement of hydrogen bubbles within the boundary layer can be ensured, accurately reflecting the velocity distribution of the fluid within the boundary layer.

[0044] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0045] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0046] Figure 1 is a schematic diagram of the overall layout of the present invention.

[0047] Figure 2 is a partially enlarged schematic diagram of the main device of the present invention.

[0048] Figure 3 is a schematic diagram of the working state of the present invention.

[0049] Figure 4 is a schematic diagram of the near-wall boundary layer velocity distribution and hydrogen bubble tracer measurement principle of the present invention.

[0050] Reference numerals and names in the attached figures: 1. Integrated optical measurement module; 2. Tracer particle generation module; 11. Optical support frame; 12. Laser emitter assembly; 13. Sapphire prism; 14. First imaging camera; 15. Second imaging camera; 21. Cathode; 22. Anode; 23. Power supply unit; 3. Hydrogen bubble; 4. Camera field of view; 5. Sheet light area; 6. UUV skin. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0052] Example 1:

[0053] As shown in Figures 1 to 4, this embodiment provides a portable PIV boundary layer flow field testing system based on electrolytic hydrogen bubbles to overcome the technical defects of existing PIV measurement systems that are difficult to achieve in-situ portable UUV measurement and existing hydrogen bubble technology that cannot simultaneously and finely measure flow field information at different thicknesses within the boundary layer; the testing system includes an integrated optical measurement module 1 and a tracer particle generation module 2.

[0054] 1. Structure and layout of the integrated optical measurement module:

[0055] An integrated optical measurement module 1 is located inside the UUV and is used to form a sheet light area in the vicinity of the outer surface of the UUV and to image the area. It includes an optical support frame 11, a laser emitter assembly 12, a sapphire prism 13, a first imaging camera 14, and a second imaging camera 15.

[0056] The optical support frame 11 is made of aluminum alloy, which has good strength and corrosion resistance. It is fixed to the internal skin of the UUV by bolts or screws. The structural design of the optical support frame 11 fully considers the internal space constraints of the UUV and adopts a lightweight design to ensure that a stable mounting base is provided for each optical component without affecting the original structural strength of the UUV.

[0057] The laser emitter assembly 12 is mounted on the optical support frame 11 and is used to emit the shaped sheet laser light. In this embodiment, the laser emitter assembly 12 uses a solid-state laser with an output wavelength of 532nm, adjustable power, and a maximum output power of 200mW. The laser emitter assembly 12 integrates a shaping optical system, which shapes the point light source into a thin sheet laser beam of approximately 1mm thickness using a cylindrical lens, forming the sheet laser light. The operating timing of the laser emitter assembly 12 is controlled by an external trigger signal, enabling precise synchronization with the imaging camera.

[0058] The UUV skin 6 has optical windows at corresponding positions, which are formed by encapsulating sapphire prisms 13. The sapphire prism 13 has an inverted trapezoidal cross-section, as shown in Figure 2. Its short side faces the laser emitter assembly 12, its two inclined sides face the first imaging camera 14 and the second imaging camera 15 respectively, and its long side is flush with or slightly embedded in the skin of the UUV. Sapphire material has excellent optical transmittance, extremely high hardness, and compressive strength, enabling it to withstand the high-pressure environment underwater while ensuring low-loss transmission of laser light.

[0059] The sapphire prism 13 is packaged as follows: First, a stepped window matching the shape of the sapphire prism 13 is machined on the UUV skin, and a sealing groove is set on the edge of the window; then, the sapphire prism 13 is embedded in the window, with its long side flush with the outer surface of the UUV; finally, waterproof sealant is filled into the sealing groove or an O-ring is installed, and the sapphire prism 13 is fixed to the inside of the skin by a clamping ring to ensure the sealing reliability of the optical window in deep water environment.

[0060] The shaping sheet light emitted by the laser emitter assembly 12 enters from the short side of the sapphire prism 13 and is refracted inside the prism. Since the refractive index of the sapphire prism 13 is higher than that of water, by precisely designing the prism angle, the sheet light can exit from the long side of the sapphire prism 13 at a specific angle, forming a sheet light region near the outer surface of the UUV that substantially coincides with the longitudinal section plane of the UUV. This sheet light region is close to the outer surface of the UUV and is used to illuminate the boundary layer flow field flowing across the UUV surface.

[0061] The first imaging camera 14 and the second imaging camera 15 are both mounted on the optical support frame 11 and symmetrically arranged behind the beveled sides of the sapphire prism 13. In this embodiment, both the first imaging camera 14 and the second imaging camera 15 are high-speed CMOS cameras with a resolution of no less than 1920×1080 pixels and a maximum frame rate of 1000fps. The lens axes of the two cameras pass perpendicularly through the beveled sides of the sapphire prism 13 and point towards the sheet light area, ensuring that the cameras can clearly capture images of tracer particles within the sheet light area through the sapphire prism 13.

[0062] This symmetrical dual-camera setup allows the two cameras to simultaneously capture images of the same illuminated area from different perspectives, achieving stereoscopic imaging. Utilizing binocular stereo vision, the position and trajectory of the tracer particles in three-dimensional space can be reconstructed, enabling the measurement of the three-dimensional transient flow field of the body-fitted boundary layer. The synchronization trigger signal for both cameras is provided by an external controller, ensuring consistent exposure times.

[0063] 2. Structure and layout of the tracer particle generation module:

[0064] The tracer particle generation module 2 is used to generate hydrogen bubbles as tracer particles upstream of the sheet light region, so that the hydrogen bubbles flow into the sheet light region. It includes a cathode 21, an anode 22 and a power supply unit 23.

[0065] The cathode 21 is positioned on the surface of the UUV skin 6 upstream of the sheet-light region, approximately 20-50 mm from the center of the sheet-light region, to ensure that hydrogen bubbles can smoothly flow into the sheet-light region after generation. In this embodiment, the cathode 21 is a multi-layer platinum wire array composed of several platinum wires arranged at intervals. The platinum wire diameter is selected as 20 μm to ensure sufficient mechanical strength while minimizing disturbance to the flow.

[0066] As shown in Figure 4, the arrangement of the platinum wire array is one of the key innovations of this invention. Unlike the arrangement in traditional hydrogen bubble technology where the platinum wires are perpendicular to the carrier plane (i.e., perpendicular to the wall and parallel to the flow direction), the platinum wire array of this invention is arranged along the UUV axis. Specifically, the length direction of each platinum wire is parallel to the water flow direction, and both ends of the platinum wires are fixed to the surface of the UUV skin by insulating supports. This arrangement ensures that the platinum wires do not obstruct the flow as they would with a vertical arrangement, minimizing interference with the boundary layer flow field.

[0067] Furthermore, the platinum wire array in this invention features a layered distribution along its height. As shown in Figure 4, the platinum wire array comprises multiple platinum wires, each located at a different height from the UUV wall to correspond to different thicknesses of the boundary layer. For example, starting from the wall and moving outwards, the first layer of platinum wires is positioned at a height of [missing information - likely a specific height or value]. The second layer is The third layer is And so on. Adjacent platinum wires have a predetermined spacing in the height direction. h, in this embodiment h is set to 0.5 mm, and the specific value can be adjusted according to the boundary layer thickness and measurement resolution requirements.

[0068] The total height of the platinum wire array (i.e., the height of the outermost platinum wire from the UUV wall) is designed to be less than the boundary layer thickness of the flow field adjacent to the UUV surface. The boundary layer thickness δ can be estimated based on the UUV's speed and fluid properties, ensuring that the platinum wire array is completely located within the boundary layer. This design aims to ensure that when hydrogen bubbles are generated through platinum wire electrolysis, the generated hydrogen bubbles always move within the boundary layer and do not penetrate it into the external mainstream region, thus accurately reflecting the velocity distribution characteristics of the fluid within the boundary layer.

[0069] The platinum wire array is fixed to the UUV skin surface via an insulating bracket. The bracket is made of high-strength engineering plastic, offering excellent insulation and mechanical strength. Mounting slots corresponding to the number of platinum wires are machined into the bracket; the wires pass through these slots and are secured by spot welding or conductive adhesive, ensuring reliable electrical connections. The bottom of the bracket is fixed to the skin surface by bolts or adhesive, and the mounting position can be adjusted as needed.

[0070] The anode 22 is a chemically stable graphite electrode, installed on the UUV skin 6 downstream of the sheet-firing area, approximately 30-60 mm from the center of the sheet-firing area. The graphite electrode has good conductivity and corrosion resistance, and does not generate ions that pollute the water during electrolysis, making it suitable for long-term underwater use. The anode 22 is connected to the power supply unit 23 via a watertight cable.

[0071] The power supply unit 23 is located inside the UUV, typically installed in a sealed electrical compartment. The positive and negative terminals of the power supply unit 23 are connected to the anode 22 and cathode 21 respectively via watertight cables. In this embodiment, the core component of the power supply unit 23 is a programmable pulse power supply, capable of outputting pulse currents with adjustable amplitude, adjustable pulse width, and adjustable frequency.

[0072] The key function of the power supply unit 23 is its ability to selectively energize one or more platinum wires in the platinum wire array. This allows the operator to select a specific height within the boundary layer to generate hydrogen bubbles, thereby enabling visualization of flow profiles with different thicknesses within the boundary layer. Specifically, the power supply unit 23 integrates a multi-channel electronic switch array, with each channel independently connected to a platinum wire. By selecting different channels to conduct using control signals, selective energizing of one or more platinum wires can be achieved. When a channel is activated, the pulsed current output by the power supply unit 23 is applied to the corresponding platinum wire, electrolyzing and generating hydrogen bubbles on the surface of that wire.

[0073] The power supply unit 23 can also independently control the number and frequency of hydrogen bubbles generated by each platinum wire by adjusting the voltage applied to different platinum wires. The higher the voltage, the greater the electrolysis current, and the more hydrogen bubbles are generated; the higher the pulse frequency, the more obvious the periodicity of hydrogen bubble generation. By independently adjusting the voltage and pulse parameters of each channel, hydrogen bubbles of different densities and frequencies can be generated on platinum wires at different heights to meet the needs of different flow field measurements.

[0074] The power supply unit 23 is configured to supply power to the cathode in a pulsed manner, with a pulse frequency typically between 50 and 200 Hz, matching the dual-frame exposure mode of PIV measurements. The operating timing of the laser emitter assembly 12, the first imaging camera 14, and the second imaging camera 15 is synchronized with the pulsed power supply timing of the power supply unit 23. Specifically, while outputting a pulsed current, the power supply unit 23 sends a synchronization trigger signal to the laser emitter assembly 12 and the camera, triggering laser emission and camera exposure to ensure precise synchronization between particle image capture and hydrogen bubble generation.

[0075] In practical applications, the test system in this embodiment is assembled and debugged according to the following steps:

[0076] First, fix the optical support frame 11 at a predetermined position inside the UUV, ensuring that it is securely installed and accurately positioned. Then, install the laser emitter assembly 12, the first imaging camera 14, and the second imaging camera 15 onto the optical support frame 11 according to the design positions, and adjust the orientation of each component to ensure that the laser emission direction and the camera optical axis meet the design requirements.

[0077] Secondly, an optical window is machined on the UUV skin, and the sapphire prism 13 is sealed and encapsulated in the window. During installation, it is necessary to ensure that the long side of the sapphire prism 13 is flush with the outer surface of the UUV, and that the seal between the prism and the skin is reliable.

[0078] Next, cathode 21 and anode 22 are installed on the skin surfaces upstream and downstream of the sheet light region, respectively. When installing the platinum wire array, a dedicated positioning fixture must be used to ensure that each platinum wire is precisely positioned at the designed height. The platinum wires are fixed to the insulating support by spot welding to ensure reliable electrical connections and sufficient mechanical strength. After installation, the actual height coordinates of each platinum wire are measured and recorded for subsequent data processing.

[0079] Next, connect all electrical lines, including the power supply and control lines for the laser emitter assembly 12, the data and control lines for the camera, and the connection lines between the power supply unit 23 and the cathode anode. All through-cabin cables must be connected via watertight connectors and undergo rigorous sealing checks.

[0080] Finally, system integration and calibration are performed. The UUV is placed in a still water environment, the system is started, and it is checked whether the laser beam accurately illuminates the predetermined area, whether the camera image is clear, and whether the platinum wire generates hydrogen bubbles normally. A calibration target is used to perform three-dimensional calibration of the measurement area, obtaining the camera's internal and external parameters to prepare for subsequent three-dimensional flow field reconstruction. Special attention must be paid to the overlap between the calibration target plane and the laser beam plane during calibration to ensure calibration accuracy.

[0081] In practical use, when a UUV travels underwater at a set speed, water flows over the surface of the UUV, forming a boundary layer. The test system of this invention is then activated, and the operation process is as follows:

[0082] The power supply unit 23 selects the platinum wires to be energized according to a preset measurement scheme. For example, if it is necessary to measure the flow field information at different heights within the boundary layer, multiple platinum wires at different heights are energized simultaneously; if it is necessary to measure the flow field at a specific height, only a single platinum wire at the corresponding height is energized. After selection, the power supply unit 23 applies voltage to the selected platinum wire in a pulse manner.

[0083] Under the influence of voltage, an electrolysis reaction occurs on the surface of the selected platinum wire, generating hydrogen bubbles. Because the platinum wire is located inside the boundary layer, the generated hydrogen bubbles are extremely small (typically tens of micrometers in diameter) and exhibit excellent fluid following properties. Once generated, the hydrogen bubbles are immediately carried downstream by the water flow within the boundary layer.

[0084] While outputting pulsed current, power supply unit 23 sends synchronous trigger signals to laser emitter assembly 12, first imaging camera 14, and second imaging camera 15. Upon receiving the trigger signal, laser emitter assembly 12 immediately emits a laser pulse, which, after refraction by sapphire prism 13, forms a sheet-like region near the outer surface of the UUV. Simultaneously, the two cameras are synchronously exposed under the control of the trigger signal to image the hydrogen bubbles within the sheet-like region.

[0085] Because the hydrogen bubbles move with the flow, the images captured by the two cameras record the position information of the hydrogen bubbles at the moment of exposure. By using two consecutive pulse exposures (dual-frame mode), the displacement information of the hydrogen bubbles within a very short time interval can be obtained.

[0086] After the synchronized images acquired by the two cameras are transmitted to the computer, they are processed using particle image velocimetry software. The processing includes: preprocessing the images (such as background subtraction and contrast enhancement); performing cross-correlation analysis to calculate particle displacement within each analysis window; calculating the velocity vector by combining calibration parameters and the time interval between the two frames; and fusing the image data from the two cameras to reconstruct the three-dimensional velocity field using a stereo vision algorithm.

[0087] Since platinum wires at different heights have definite height coordinates in space, the hydrogen bubbles they generate can be distinguished in images by their distribution characteristics along the height direction. By identifying the height information of the bubbles using image processing software, velocity information at different boundary layer heights can be obtained. Combining this velocity information yields the velocity distribution profile along the normal direction within the boundary layer.

[0088] Example 2:

[0089] This embodiment further optimizes the synchronous control method of the power supply unit based on embodiment 1.

[0090] In this embodiment, the power supply unit 23 not only outputs pulsed current and synchronous trigger signal, but also has a built-in timing controller, which can precisely control the delay time of laser emission and camera exposure relative to the electrolysis pulse. By adjusting the delay time, images of hydrogen bubbles at different motion moments after generation can be captured, thereby enabling more precise study of the boundary layer flow field on the outer surface of the UUV.

[0091] Specifically, the timing controller uses the rising edge of the electrolytic pulse as the time zero point, and after a preset delay time... After t, laser emission and camera exposure are triggered. By changing By acquiring multiple sets of images, a sequence of images can be obtained showing the entire process of hydrogen bubbles from generation to movement to different positions within the sheet light region, providing richer information for studying the flow characteristics of the near-wall region within the boundary layer.

[0092] Furthermore, the power supply unit 23 in this embodiment also supports a "scanning" power-on mode. In this mode, the power supply unit 23 sequentially energizes each platinum wire in the multilayer platinum wire array according to a preset order, applying a pulse voltage to only one platinum wire at a time, while simultaneously triggering the camera to acquire images. By controlling the time interval between energizing adjacent platinum wires to be extremely short (e.g., less than 1 ms), it can be assumed that the flow field does not change significantly within this time interval. Therefore, the flow field velocity profile across the entire thickness of the boundary layer can be obtained through a single scan measurement. This method avoids the problem of mutual interference of bubbles that may occur when multiple platinum wires are energized simultaneously, and is particularly suitable for high-precision measurement of boundary layer velocity profiles.

[0093] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A system for testing the flow field of a portable PIV boundary layer based on hydrogen bubble electrolysis, characterized in that: include: An integrated optical measurement module, located inside the UUV, is used to form a sheet light region in the vicinity of the outer surface of the UUV and to image that region; A tracer particle generation module is used to generate hydrogen bubbles upstream of the sheet light region as tracer particles, allowing the hydrogen bubbles to flow into the sheet light region. The integrated optical measurement module includes: an optical support frame, fixedly connected to the inner skin of the UUV; a laser emitter assembly, mounted on the optical support frame, for emitting the shaped sheet light; a sapphire prism, encapsulated in an optical window at a corresponding position on the UUV skin, for refracting the sheet light to a region adjacent to the outer surface of the UUV to form a sheet light region; a first imaging camera and a second imaging camera, mounted on the optical support frame and symmetrically arranged on both sides of the sapphire prism, for synchronously imaging the sheet light region from different perspectives; the tracer particle generation module includes: a cathode, disposed on the surface of the UUV skin upstream of the sheet light region. The anode is located on the UUV skin surface downstream of the sheet light region; the power supply unit is located inside the UUV and electrically connected to the cathode and anode, used to generate hydrogen bubbles at the cathode by electrolyzing water; the cathode is a multi-layer platinum wire array composed of several platinum wires arranged at intervals along the UUV axis, with each platinum wire located at a different height from the UUV wall to correspond to different thicknesses of the boundary layer, and adjacent platinum wires having a preset spacing in the height direction to avoid interfering with the flow field on the UUV wall; the power supply unit can selectively energize one or more platinum wires in the platinum wire array, and control the number and generation frequency of hydrogen bubbles generated by each platinum wire by adjusting the voltage applied to different platinum wires, thereby achieving synchronous measurement of flow field information at different thicknesses within the boundary layer.

2. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The total height of the platinum wire array is less than the boundary layer thickness of the flow field adjacent to the UUV surface.

3. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The platinum wire array is fixed to the surface of the UUV skin by an insulating bracket. The insulating bracket is made of insulating material that meets the strength requirements and has mounting grooves corresponding to the number of platinum wires. After the platinum wires pass through the mounting grooves, they are fixed by spot welding or conductive adhesive.

4. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The power supply unit includes a multi-channel electronic switch array, with each channel independently connected to a platinum wire. Different channels are selected to conduct by control signals, thereby achieving selective energization of one or more platinum wires.

5. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The power supply unit is configured to supply power to the cathode in a pulsed manner; the operating timing of the laser emitter assembly, the first imaging camera, and the second imaging camera is synchronized with the pulse power supply timing of the power supply unit.

6. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 5, characterized in that: The power supply unit has a built-in timing controller that can precisely control the delay time of laser emission and camera exposure relative to the electrolysis pulse, and capture images of hydrogen bubbles at different motion moments after they are generated by adjusting the delay time.

7. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The sapphire prism has an inverted trapezoidal cross-section, with its short side facing the laser emitter assembly, its two sloping sides facing the first imaging camera and the second imaging camera respectively, and its long side flush with the outer surface of the UUV or embedded in the skin.

8. The system for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles according to claim 1, characterized in that: The anode is a graphite electrode.

9. A method for testing the flow field of a portable PIV boundary layer based on electrolytic hydrogen bubbles, using the testing system described in any one of claims 1 to 8, characterized in that: Including the following Steps: Step S1: Form a sheet-like region near the outer surface of the UUV using an integrated optical measurement module; Step S2: Selectively energize one or more platinum wires in the multilayer platinum wire array using a power supply unit, causing the selected platinum wire to electrolyze and generate hydrogen bubbles, which then flow into the sheet-like region as tracer particles; Step S3: Simultaneously image the hydrogen bubbles in the sheet-like region using a first imaging camera and a second imaging camera; Step S4: Perform particle image velocimetry processing based on the acquired images to obtain flow field velocity information at different thickness locations within the boundary layer.

10. The method according to claim 9, characterized in that: In step S2, the number and frequency of hydrogen bubbles generated by each platinum wire are controlled by adjusting the voltage applied to different platinum wires, so as to achieve synchronous measurement of different boundary layer thickness positions.

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