An integrated three-dimensional endoscopic PIV probe for high temperature flow field testing

Abstract

The application belongs to the technical field of aero-engine internal compressor flow field testing and optical measurement, and particularly relates to an integrated three-dimensional endoscopic PIV probe for aero-engine internal flow field measurement, which is suitable for three-dimensional velocity vector measurement of internal flow field of aero-engine, gas turbine and industrial compressor and the like limited space. The probe is characterized by comprising an integrated probe body, a left imaging channel, a laser emission channel, a right imaging channel, an optical window, a spherical lens, a cylindrical lens, an objective lens group, a Littrow prism, a Hopkins cylindrical lens system, an eyepiece group, a blowing channel, an air inlet, an air suction port, an external connecting flange, an external laser interface, an external camera interface, an imaging camera, a laser and a target measurement area. The probe is integrated with the laser emission channel, left and right stereo imaging channels, a cooling system and a blowing system in the high-temperature-resistant cylindrical probe body. Through the synergistic effect of sheet-shaped laser illumination, double-view endoscopic imaging, window cleaning and water-cooling thermal protection, the synchronous measurement of the three-dimensional velocity vector field of the target measurement area in the high-temperature limited internal flow field of the combustion chamber, turbine or casing and the like is realized.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine flow field testing and optical measurement technology, specifically relating to an integrated three-dimensional endoscopic PIV probe for high-temperature flow field testing, suitable for three-dimensional velocity vector measurement of the internal flow field in high-temperature, high-pressure confined spaces such as aero-engine turbines and combustion chambers. Background Technology

[0002] The extremely complex unsteady flow, turbulent structure, and three-dimensional velocity field distribution inside aero-engine gas turbine engines are crucial for evaluating and optimizing their aerodynamic and thermodynamic performance. Particle image velocimetry (PIV), as an advanced non-contact, full-field optical measurement method, has been widely used in fundamental fluid mechanics research. However, applying traditional PIV technology in the confined space and harsh environments of real aero-engines, characterized by high temperature and high pressure, faces insurmountable engineering challenges and technical bottlenecks.

[0003] First, traditional PIV systems typically rely on an "external" optical path layout, requiring large optical windows on the casing wall to illuminate the flow field from an external sheet light source and to capture images of tracer particles from an external camera. However, the aero-engine casing, as a primary load-bearing component, must withstand extremely high mechanical stress and thermal loads. Especially under high-temperature operating conditions, the thermal expansion coefficients of optical glass and metal casing materials differ significantly. Creating large windows would lead to enormous thermal stress concentration, easily causing window cracking or sealing failure, severely compromising the casing's structural strength and fatigue resistance. This not only violates safety regulations for engine testing but also... Second, the internal flow channel design of modern high-performance engines is extremely compact, especially in critical areas such as the compressor interstage, blade passages, and turbine cooling channels, where physical space is limited, making it impossible to install conventional large-field-of-view optical windows.

[0004] Furthermore, the accuracy of optical measurements is limited by the geometric characteristics of the optical interface. Engine flow channel walls are typically complex spatial curved surfaces. If imaging is performed directly through curved walls or windows, severe refraction occurs as light travels through the gas-solid-gas interface, causing laser beam path deflection and nonlinear distortion of the image. This complex optical distortion is difficult to completely eliminate through conventional calibration, significantly reducing the accuracy of cross-correlation calculations and resulting in large errors in the resolved velocity vector field.

[0005] The published patent CN120294360A proposes an endoscopic PIV measurement system. This system uses an endoscope to reduce the window size, which avoids the need for a large window to some extent. However, it adopts a split architecture of "lighting and imaging separation", which means that the laser illumination probe and the imaging probe need to be inserted through different probe holes, which increases the number of openings in the casing and can only realize two-dimensional flow field measurement.

[0006] Meanwhile, the high-temperature environment poses a severe challenge to the survivability and measurement stability of endoscopic PIV measurement systems. If an invasive measurement method is adopted, the probe body must be directly immersed in the high-temperature gas stream. Without effective thermal protection and active cooling design, its internal precision optical components are prone to performance degradation or even permanent damage due to overheating. In addition, thermal expansion and non-uniform thermal deformation caused by high temperature will change the geometric parameters of the internal optical path of the probe, destroy the strict relative positional relationship required for stereo imaging, and cause system calibration failure, thus introducing a non-negligible measurement error.

[0007] Existing technologies lack a compact device capable of extending through a probe into the flow channel, integrating laser illumination and dual-view imaging functions, and possessing reliable thermal protection capabilities, thereby enabling three-dimensional velocity vector measurement in high-temperature environments under single-hole probe conditions. To address this, a three-channel integrated stereo PIV probe for measuring flow fields in aero-engine compressors, turbines, etc., is proposed. This probe achieves single-probe stereo PIV measurement by arranging a laser emission channel and two imaging channels at a certain angle side-by-side within a single probe body, supplemented by an integrated cooling system. Summary of the Invention

[0008] The technical problem this invention aims to solve is as follows: Traditional external PIV probes for aero-engines, such as those for turbines and combustion chambers, face limitations under high temperature, high pressure, and extremely compact space constraints. These limitations include the difficulty in creating large windows, severe optical distortion in curved windows, and the fact that existing endoscopic PIV probes are mostly two-dimensional, unable to acquire three-dimensional velocity components, and lack effective thermal protection technologies. This invention proposes a three-channel integrated stereo PIV probe for flow field measurement in aero-engine compressors, turbines, and other components. This probe integrates laser illumination and left / right parallax imaging optical paths within a single main body, supplemented by an integrated cooling and aerodynamic purging system. It eliminates the need to modify the casing's large window, allowing insertion into the high-temperature flow channel through a single hole, enabling precise measurement of the internal flow field's three-dimensional velocity vector.

[0009] The technical solution of this invention is:

[0010] A three-dimensional endoscopic PIV measurement probe integrating illumination and imaging is characterized by: an integrated probe body (1), a left imaging channel (2), a laser emission channel (3), a right imaging channel (4), optical windows (5), (6), and (7), a spherical lens (8), a cylindrical lens (9), an objective lens group (10) and (11), a Littoral prism (12) and (13), a Hopkins cylindrical lens system (14) and (15), an eyepiece group (16) and (17), a purge channel (18), an air inlet (19), an air suction port (20), a water inlet channel (21), (22), (23), and (24), a drain outlet (25), (26), (27), and (28), an external connecting flange (29), (30), (31), and (32), an external laser interface (33), an external camera interface (34) and (35), an imaging camera (36) and (37), a laser (38), and a target measurement area (39). The integrated probe body (1) is the main support structure of the probe. It is cylindrical in shape, with a diameter of 10~100mm and a length of 100~500mm. The integrated probe body (1) is made of stainless steel or other high-temperature resistant alloys, and its surface is coated with a high-temperature resistant heat-insulating coating.

[0011] Furthermore, the integrated probe body (1) has three parallel and interconnected optical transmission channels precisely machined along the axial direction inside. The laser emission channel (3) is coaxially set on the geometric center axis of the integrated probe body (1) with an aperture of 1~20mm. The left imaging channel (2) and the right imaging channel (4) are symmetrically distributed on both sides of the laser emission channel (3) with an aperture of 1~20mm.

[0012] Furthermore, external connecting flanges (29), (30), (31), and (32) are fixed on the outer wall of the integrated probe body (1) to install and fix the entire probe to the mounting holes on the combustion chamber or turbine casing wall, serving as a rigid connection and sealing interface between the probe and the mounting holes on the combustion chamber casing or turbine casing wall.

[0013] Furthermore, the laser emission channel (3) constitutes the illumination optical path system of the probe. The high-energy pulsed laser beam from the external laser (38) is coupled into the channel through the external laser interface (33) at the tail end of the probe, and is shaped by the combination of cylindrical lens (9) and spherical lens (8) integrated in series inside, completing the beam expansion and focusing. Finally, it is emitted through the optical window (6) sealed and embedded in the center of the front end face of the probe, generating a high-brightness sheet-like illumination light in the flow field in front of the probe, covering the target measurement area (39). The laser shaping optical elements in the laser emission channel (3) are not limited to cylindrical lens (9) and spherical lens (8), but may also include collimating lens, beam expander group, Powell lens, cylindrical lens group, reflector, prism, graded refractive index lens, fiber collimator, fiber coupler, sheet beam shaper or combination thereof; the external laser interface (33) can be directly connected to the free space laser optical path, or it can be connected to the laser (38) through fiber, fiber bundle, fiber connector or fiber collimation module;

[0014] Furthermore, the left imaging channel (2) and the right imaging channel (4) constitute the stereoscopic imaging optical path system of the probe. After passing through their respective optical windows (5) and (7), the optical axes of these two channels converge to the common target measurement area (39), forming a predetermined stereoscopic parallax angle (10°~60°) from the inside out. The scattered light from the excited tracer particles in the target measurement area (39) enters the probe through the optical windows (5) and (7) on both sides of the probe tip.

[0015] Furthermore, the light entering the left imaging channel (2) and the right imaging channel (4) first enters the Littoral prisms (12) and (13) to deflect the line of sight, in order to compensate for the limited observation angle and establish the solid geometric relationship required for three-dimensional reconstruction. Then, the light is collected and initially imaged by the objective lens group (10) and (11) at the front end. Subsequently, the image signal is coupled into the Hopkins cylindrical lens system (14) and (15) to achieve long-distance, low-distortion relay transmission in the slender tubular channel. Finally, the image is output through the eyepiece group (16) and (17) at the rear with focusing function. The line-of-sight deflection element is not limited to a Littoral prism, but can also be a right-angle prism, a roof prism, a reflecting mirror, a wedge prism, an optical steering mirror group, a fiber optic image transfer module, or other optical elements capable of changing the direction of the imaging visual axis; the image transmission system is not limited to a Hopkins cylindrical lens system, but can also be a relay lens group, a gradient refractive index lens group, a rod lens system, a lens array, an imaging fiber bundle, a rigid endoscope image transfer system, a flexible endoscope image transfer system, or a combination thereof; the objective lens group (10), (11) and the eyepiece group (16), (17) can be a fixed focal length structure, or an adjustable focal length, adjustable aperture, or replaceable magnification structure;

[0016] Furthermore, external camera interfaces (34) and (35) physically connect the left imaging channel (2) and the right imaging channel (4) to the high-resolution imaging cameras (36) and (37) respectively, to achieve synchronous acquisition of particle images from dual perspectives. A light-limiting structure can be set in the imaging channel. The light-limiting structure includes an aperture, a light-blocking ring, a limiting hole, an extinction inner wall or a combination thereof, which is used to limit stray light, control the field of view, improve imaging contrast and reduce the influence of high-temperature wall radiation light on particle image acquisition.

[0017] Furthermore, the integrated probe body (1) incorporates a cooling system. The cooling system includes water inlet channels (21), (22), (23), and (24) and drain outlets (25), (26), (27), and (28). The water inlet channels (21), (22), (23), and (24) have a diameter of 5-20 mm, and their shells overlap with the inner wall of the integrated probe body (1), forming an integral design with the probe body (1), and have a certain bend at the probe head. The drain outlets (25), (26), (27), and (28) have a diameter of 3-15 mm.

[0018] Furthermore, the integrated probe body (1) incorporates a purging system. The purging system includes a purging channel (18), an air inlet (19), and an air intake (20). High-pressure gas is sprayed through this channel to the optical windows (5), (6), and (7) at the front end to prevent oil or particles from adhering and affecting the optical transmission performance. Purging can be performed before or during the experiment. The air inlet (19) and the air intake (20) can be interchanged to achieve a better purging effect. The diameter of the air inlet (19) and the air intake (20) is 3~10mm. The radial dimension of the purging channel (18) along the probe is 1~5mm, and the circumferential angle is 20°~60°.

[0019] Furthermore, the materials of the optical windows (5), (6), and (7) are preferably sapphire glass or other high-pressure and corrosion-resistant optical glass, which have the characteristics of high temperature resistance, high pressure resistance and particle erosion resistance, and are sealed and matched with the left imaging channel (2), laser emission channel (3), and right imaging channel (4) of the head of the integrated probe body (1).

[0020] Furthermore, the imaging cameras (36) and (37) are connected to the laser (38) through a synchronous control system. The dual-pulse laser illumination and the phase-locked triggering mode of the camera are used to acquire time-related particle image sequences in the target measurement area (39) and reconstruct the three-dimensional velocity vector field through a three-dimensional cross-correlation algorithm.

[0021] The beneficial effects of this invention are:

[0022] To address the limitations of traditional external PIV probes (Portable Imagers) in handling core components like aero-engine turbines and combustion chambers under high temperature, high pressure, and extremely compact space constraints, which suffer from difficulties in creating large windows, severe optical distortion in curved windows, and the technical bottlenecks of existing endoscopic techniques requiring multiple probe holes and limited to two-dimensional measurements, a three-channel integrated stereo PIV probe with active thermal protection is proposed. This probe employs an integrated design, combining a laser illumination channel, two imaging channels at a specific angle, a high-efficiency circulating cooling system, and a purging system within a single unit. It can penetrate the high-temperature flow channel through a single probe hole, effectively resisting the high-temperature environment thanks to its integrated internal cooling structure. This solves the survival problem of precision optical components under extreme heat loads and the measurement inaccuracies caused by thermal deformation. While maintaining the structural integrity of the casing, this device achieves high-precision measurement of three-dimensional velocity vectors within confined spaces and harsh high-temperature environments.

[0023] Beneficial effect 1:

[0024] The laser illumination path and the dual imaging path with a specific parallax angle are highly integrated into a single probe body, requiring only a standard probe hole in the device wall to operate. This design completely avoids the need for large transparent windows and complex optical path arrangements in the engine load-bearing casing, maintaining the structural strength, airtightness, and overall rigidity of the test section wall. This enables high-precision three-dimensional velocity vector measurement in areas with extremely limited physical space, such as the compressor stage interstage and blade passage of aero-engines.

[0025] Benefit 2:

[0026] Compared to traditional methods that require inserting multiple single-function probes simultaneously to achieve the same three-dimensional measurement purpose, this device only requires small holes and flange sealing structures in localized areas of the wall, eliminating the need for multiple holes. By changing the probe's insertion depth within the flow channel, the device can flexibly traverse and scan flow field regions at different radial positions, no longer limited to a single fixed measurement point, significantly expanding the measurement coverage of a single installation.

[0027] Benefit 3:

[0028] After the laser beam is shaped inside the integrated probe, it is directly injected into the channel of the device under test through the optical window of the probe head. The particle scattered light is then guided from inside the channel by the camera's endoscopic probe to the external imaging camera, forming a compact "endoscopic illumination + endoscopic imaging" optical path. Compared with the traditional external long optical path solution, the integrated endoscopic design effectively reduces geometric distortion and scattering interference caused by multiple refractions and reflections, improves particle image quality and related calculation accuracy, and makes the obtained velocity field information more representative and targeted.

[0029] Beneficial effect four:

[0030] The probe integrates a pneumatic purging system, which directs high-pressure gas to the optical window surface at the probe head via an internal purging channel. The purging channel is completely embedded within the probe body, with no protruding nozzles or conduits at the probe head. This concealed flow channel design effectively removes oil and particles from the optical window surface using high-pressure gas, ensuring optical transmission performance, while maintaining the streamlined and smooth shape of the probe head. It also avoids additional shock waves or wake interference caused by additional purging structures, ensuring the authenticity of the measured flow field and the accuracy of the measurement.

[0031] Benefit 5:

[0032] The probe adopts an integrated design of cooling channel and housing. The water inlet channel has a specific bend at the probe head. This structure allows the cooling medium to provide impact cooling to the laser emission channel and two imaging channel areas at the probe head, specifically enhancing the cooling effect of the three optical channel areas at the probe head. At the same time, the integrated design ensures that the cooling channel housing and the probe body housing are tightly connected, enhancing the cooling effect of the entire probe outer wall surface. This effectively prevents the probe housing from deforming or the internal precision optical components from being damaged in high-temperature environments, significantly improving the reliability and lifespan of the probe when working in the high-temperature core area of ​​aero-engines.

[0033] Benefit 6:

[0034] The complex geometric coupling between the sheet light plane generated by the laser emission channel and the focal planes of the left and right imaging channels has been precisely calibrated and locked during the probe manufacturing and assembly stage. At the test site, only the mechanical installation of the probe and the connection of external cables are required to conduct the test. This completely avoids the time-consuming and challenging coupling adjustment of the laser sheet light and the dual-camera field of view within the confined and complex test bench space of an aero-engine, greatly simplifying the testing process of the 3D PIV system and significantly reducing the technical threshold and time cost of testing. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of an integrated PIV probe according to an embodiment of the present invention.

[0036] Figure 2 This is a top view of an integrated PIV probe according to an embodiment of the present invention.

[0037] Figure 3 This is a sectional view of section AA.

[0038] Figure 4 This is a sectional view of section BB.

[0039] Figure 5 This is a cross-sectional view of section CC.

[0040] Figure 6 This is a sectional view of section DD.

[0041] Figure 7 This is a schematic diagram illustrating a specific implementation of an integrated PIV probe inside the combustion chamber in an embodiment of the present invention.

[0042] Wherein: 1-Integrated probe body, 2-Left imaging channel, 3-Laser emission channel, 4-Right imaging channel, 5, 6, 7-Optical window, 8-Spherical lens, 9-Cylindrical lens, 10, 11-Objective lens group, 12, 13-Littoral prism, 14, 15-Hopkins cylindrical lens, 16, 17-Eyepiece group, 18-Purge channel, 19-Air inlet, 20-Air suction port, 21, 22, 23, 24-Water inlet channel, 25, 26, 27, 28-Drain outlet, 29, 30, 31, 32-External connection flange, 33-External laser interface, 34, 35-External camera interface, 36, 37-Imaging camera, 38-Laser, 39-Target measurement area. Detailed Implementation

[0043] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1 , Figure 2 As shown in the figure, this embodiment introduces a three-dimensional endoscopic PIV measurement probe integrating illumination and imaging, which mainly consists of an integrated probe body (1), a left imaging channel (2), a laser emission channel (3), a right imaging channel (4), optical windows (5), (6), (7), a spherical lens (8), a cylindrical lens (9), an objective lens group (10), (11), a Littoral prism (12), (13), a Hopkins cylindrical lens system (14), (15), an eyepiece group (16), (17), a purge channel (18), an air inlet (19), an air suction port (20), a water inlet channel (21), (22), (23), (24), a drain outlet (25), (26), (27), (28), an external connecting flange (29), (30), (31), (32), an external laser interface (33), and an external camera interface (34), (35). The feature is that the integrated probe body (1) is the main support structure of the probe, and its shape is cylindrical with a diameter of 50 mm and a length of 300 mm. The integrated probe body (1) is made of stainless steel and its surface is coated with a high-temperature resistant heat-insulating coating.

[0046] The relative positions and structures of the probe's internal optical channels, water inlet channels, and purging channels are as follows: Figure 3 As shown. The integrated probe body (1) integrates a laser emission channel (3) and imaging channels (2) and (4) for light transmission, as well as water inlet channels (21), (22), (23), (24) and a purge channel (18) for thermal protection and self-cleaning. In terms of specific layout, the laser emission channel (3) is coaxially set at the geometric center of the cross-section of the integrated probe body (1), with an aperture of 10 mm; the left imaging channel (2) and the right imaging channel (4) are symmetrically distributed on the left and right sides with the central laser channel as the axis of symmetry, close to the probe center line, with an aperture of 8 mm, forming a compact core optical area. The four water inlet channels (21), (22), (23), and (24) are distributed on the upper and lower sides of the above-mentioned optical core area, arranged in a rectangular array around the probe center, with an aperture of 10 mm. The purge channel (18) is embedded in the outer wall of the integrated probe body (1), and its cross-section is an arc-shaped long groove structure extending along the circumference of the probe. The depth of the groove along the radial direction is 1.5 mm, and it covers a sector of about 30° along the circumference.

[0047] The cross-section of the probe inlet pipe drain outlet is as follows Figure 4 As shown. The four drain outlets (25), (26), (27), and (28) are located in the central area of ​​the integrated probe body (1), interspersed between the optical channel and the water inlet channel, and symmetrically distributed around the central laser emission channel (3), with a diameter of 6 mm.

[0048] The probe imaging system, laser system, and purge system, as well as... Figure 5As shown. The laser emission system is located at the central axis of the probe, and the external laser interface (33) is connected to the laser emission channel (3). The laser beam enters from the bottom and passes through the cylindrical lens (9) and spherical lens (8) integrated in series in the channel to complete the beam shaping, beam expansion and focusing. Finally, it is projected onto the flow field to be measured through the optical window (6) sealed in the center of the front end to form a sheet-like illumination light. The imaging subsystem includes two symmetrical optical paths, located on both sides of the laser channel. The front ends of the left imaging channel (2) and the right imaging channel (4) are equipped with optical windows (5) and (7), objective lens groups (10) and (11), and Littoral prisms (12) and (13), respectively. Scattered light from particles within the flow field enters through the window, first passing through the objective lens group (10) and (11) for light collection and preliminary imaging. After the line of sight is refracted by the Littoral prism (12) and (13), it is coupled into the Hopkins cylindrical lens system (14) and (15), which is precisely assembled from multiple lens groups, to achieve long-distance relay transmission of image signals along the slender pipe. Finally, the image is magnified and the focus is adjusted by the eyepiece group (16) and (17) at the bottom before being output. It is then physically connected to the imaging camera through the external camera interface (34) and (35). The purging system is mainly composed of a longitudinally continuous purging channel (18). High-pressure clean gas is introduced through the air inlet (19) at the bottom, transported along the channel to the head, and ejected at high speed from the micro-nozzles around the optical window to achieve the purging cleaning effect. It is then discharged through the negative pressure suction port (20). The diameter of the air inlet (19) and the suction port (20) is 3 mm.

[0049] The probe cooling system is as follows Figure 6 As shown. The water inlet channels (21), (22), (23), and (24) run axially through the entire integrated probe body (1), and their outer walls overlap with the inner walls of the probe body's outer shell, adopting an integrated structural design. This design not only enhances the overall structural rigidity of the probe but also allows the cooling water to directly and effectively cool the outer wall of the probe. In the probe head area, the water inlet channels (21), (22), (23), and (24) are designed with a significant inward bend. This bend guides the cooling medium to change its flow direction, enabling it to directly impact and cool the central area at the top of the probe, specifically enhancing the cooling effect on the head areas of the laser emission channel (3) and the imaging channels (2) and (4) on both sides.

[0050] The specific implementation scheme of the probe inside the combustion chamber is as follows: Figure 7As shown. The integrated probe body (1) extends into the flow channel through a single probe hole opened in the combustion chamber wall, and is tightly fixed and sealed to the casing wall through external connecting flanges (29), (30), (31), and (32). The front end of the integrated probe body (1) is designed with an inward concave arc that matches the inner wall of the casing, so that after the probe is fixed through the external connecting flanges (29), (30), (31), and (32), its head end face can remain flush with the inner wall surface, reducing interference to the flow field. Before the experiment, the air inlet (19) and the air intake (20) are connected to the external air source system to clean the optical windows (5), (6), and (7) of the probe head. The external laser interface (33) at the probe tail is connected to the laser (38) via a light guide arm. The external camera interfaces (34) and (35) are connected to two imaging cameras (36) and (37) respectively via fiber bundles. At the same time, the water inlet channels (21), (22), (23), and (24) are connected to the cooling water source system. During the measurement process, the laser beam is projected through the probe and forms a sheet-like target measurement area (39) at the front end of the probe. This area cuts into the flow field in the mainstream direction inside the combustion chamber. When the tracer particles pass through this sheet area with the mainstream, they are scattered. Under the trigger of the synchronous control system, the two imaging cameras (36) and (37) synchronously acquire particle images through the optical path inside the probe. The obtained images are processed by a three-dimensional cross-correlation algorithm to reconstruct the three-dimensional velocity vector field in the confined space.

[0051] This invention describes a three-dimensional endoscopic PIV measurement probe integrating illumination and imaging. It employs a highly integrated design of laser illumination and dual-view imaging optical paths, tightly sealing the dual imaging channels and laser emission channel within a single probe substrate. An embedded circulating cooling circuit and pneumatic purging system provide active thermal protection and self-cleaning of the optical window. In practical applications such as flow field testing in high-temperature, high-pressure confined spaces like aero-engine combustion chambers or turbines, this probe abandons the traditional approach of using large observation windows or multi-hole arrangements, penetrating deep into the flow channel through a single probe hole in the casing wall. The probe's depth into the measurement area is adjustable, thus enabling more extensive and flexible precise measurement of three-dimensional velocity vectors within confined spaces while ensuring the structural integrity and airtightness of the equipment.

Claims

1. A three-dimensional endoscopic PIV measurement probe integrating illumination and imaging, characterized in that: The integrated probe body (1), left imaging channel (2), laser emission channel (3), right imaging channel (4), optical windows (5), (6), (7), spherical lens (8), cylindrical lens (9), objective lens group (10), (11), Littoral prism (12), (13), Hopkins cylindrical lens system (14), (15), eyepiece group (16), (17), purge channel (18), air inlet (19), air intake (20), water inlet channel (21), (22), (23), (24), drain (25), (26), (27), (28), external connection flange (29), (30), (31), (32), external laser interface (33), external camera interface (34), (35), imaging camera (36), (37), laser (38) and target measurement area (39). The integrated probe body (1) is the main support structure of the probe. It is cylindrical in shape, with a diameter of 10~100mm and a length of 100~500mm. The integrated probe body (1) is made of stainless steel or other high-temperature resistant alloys, and its surface is coated with a high-temperature resistant heat-insulating coating. Furthermore, the integrated probe body (1) has three parallel and interconnected optical transmission channels precisely machined along the axial direction inside. The laser emission channel (3) is coaxially set on the geometric center axis of the integrated probe body (1) with an aperture of 1~20mm. The left imaging channel (2) and the right imaging channel (4) are symmetrically distributed on both sides of the laser emission channel (3) with an aperture of 1~20mm. Furthermore, external connecting flanges (29), (30), (31), and (32) are fixed on the outer wall of the integrated probe body (1) to install and fix the entire probe to the mounting holes on the combustion chamber or turbine casing wall, serving as a rigid connection and sealing interface between the probe and the mounting holes on the combustion chamber casing or turbine casing wall. Furthermore, the laser emission channel (3) constitutes the illumination optical path system of the probe. The high-energy pulsed laser beam from the external laser (38) is coupled into the channel through the external laser interface (33) at the tail end of the probe, and is shaped by the combination of cylindrical lens (9) and spherical lens (8) integrated in series inside, completing the beam expansion and focusing. Finally, it is emitted through the optical window (6) sealed and embedded in the center of the front end face of the probe, generating a high-brightness sheet-like illumination light in the flow field in front of the probe, covering the target measurement area (39). The laser shaping optical elements in the laser emission channel (3) are not limited to cylindrical lens (9) and spherical lens (8), but may also include collimating lens, beam expander group, Powell lens, cylindrical lens group, reflector, prism, graded refractive index lens, fiber collimator, fiber coupler, sheet beam shaper or combination thereof; the external laser interface (33) can be directly connected to the free space laser optical path, or it can be connected to the laser (38) through fiber, fiber bundle, fiber connector or fiber collimation module; Furthermore, the left imaging channel (2) and the right imaging channel (4) constitute the stereoscopic imaging optical path system of the probe. After passing through their respective optical windows (5) and (7), the optical axes of these two channels converge to the common target measurement area (39), forming a predetermined stereoscopic parallax angle (10°~60°) from the inside out. The scattered light from the excited tracer particles in the target measurement area (39) enters the probe through the optical windows (5) and (7) on both sides of the probe tip. Furthermore, the light entering the left imaging channel (2) and the right imaging channel (4) first enters the Littoral prisms (12) and (13) to deflect the line of sight, in order to compensate for the limited observation angle and establish the solid geometric relationship required for three-dimensional reconstruction. Then, the light is collected and initially imaged by the objective lens group (10) and (11) at the front end. Subsequently, the image signal is coupled into the Hopkins cylindrical lens system (14) and (15) to achieve long-distance, low-distortion relay transmission in the slender tubular channel. Finally, the image is output through the eyepiece group (16) and (17) at the rear with focusing function. The line-of-sight deflection element is not limited to a Littoral prism, but can also be a right-angle prism, a roof prism, a reflecting mirror, a wedge prism, an optical steering mirror group, a fiber optic image transfer module, or other optical elements capable of changing the direction of the imaging visual axis; the image transmission system is not limited to a Hopkins cylindrical lens system, but can also be a relay lens group, a gradient refractive index lens group, a rod lens system, a lens array, an imaging fiber bundle, a rigid endoscope image transfer system, a flexible endoscope image transfer system, or a combination thereof; the objective lens group (10), (11) and the eyepiece group (16), (17) can be a fixed focal length structure, or an adjustable focal length, adjustable aperture, or replaceable magnification structure; Furthermore, external camera interfaces (34) and (35) physically connect the left imaging channel (2) and the right imaging channel (4) to the high-resolution imaging cameras (36) and (37) respectively, to achieve synchronous acquisition of particle images from dual perspectives. A light-limiting structure can be set in the imaging channel. The light-limiting structure includes an aperture, a light-blocking ring, a limiting hole, an extinction inner wall or a combination thereof, which is used to limit stray light, control the field of view, improve imaging contrast and reduce the influence of high-temperature wall radiation light on particle image acquisition. Furthermore, the integrated probe body (1) incorporates a cooling system. The cooling system includes water inlet channels (21), (22), (23), and (24) and drain outlets (25), (26), (27), and (28). The water inlet channels (21), (22), (23), and (24) have a diameter of 5-20 mm, and their shells overlap with the inner wall of the integrated probe body (1), forming an integral design with the probe body (1), and have a certain bend at the probe head. The drain outlets (25), (26), (27), and (28) have a diameter of 3-15 mm. Furthermore, the integrated probe body (1) incorporates a purging system. The purging system includes a purging channel (18), an air inlet (19), and an air intake (20). High-pressure gas is sprayed through this channel to the optical windows (5), (6), and (7) at the front end to prevent oil or particles from adhering and affecting the optical transmission performance. Purging can be performed before or during the experiment. The air inlet (19) and the air intake (20) can be interchanged to achieve a better purging effect. The diameter of the air inlet (19) and the air intake (20) is 3~10mm. The radial dimension of the purging channel (18) along the probe is 1~5mm, and the circumferential angle is covered by 20°~60°. Furthermore, the materials of the optical windows (5), (6), and (7) are preferably sapphire glass or other high-pressure and corrosion-resistant optical glass, which have the characteristics of high temperature resistance, high pressure resistance and particle erosion resistance, and are sealed and matched with the left imaging channel (2), laser emission channel (3), and right imaging channel (4) of the head of the integrated probe body (1). Furthermore, the imaging cameras (36) and (37) are connected to the laser (38) through a synchronous control system. The dual-pulse laser illumination and the phase-locked triggering mode of the camera are used to acquire time-related particle image sequences in the target measurement area (39) and reconstruct the three-dimensional velocity vector field through a three-dimensional cross-correlation algorithm.

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