Plane cascade blade integrated laser camera double-endoscopic PIV (particle image velocimetry) flow field measuring device

Abstract

The invention belongs to the technical field of plane cascade internal flow field test and optical measurement, and relates to a plane cascade blade integrated laser camera double-endoscopic PIV flow field measuring device. The device comprises a laser endoscopic probe, a camera endoscopic probe, a plane blade grid blade, an optical window, a grid plate, an imaging camera, a laser, a light guide arm and the like. A thin and long inner cavity is prefabricated in a blade of a plane blade grid, a plurality of small-size optical windows are formed in a pressure surface or a suction surface of the blade, a laser endoscopic probe is inserted into the blade through an optical interface on a grid plate, and shaped laser sheet light is introduced into an adjacent blade channel through the optical windows to form a target measurement area. The camera endoscopic probe is inserted into the blade through the other interface, the front-end view field of the camera endoscopic probe is aligned with a target measurement area, particle scattered light is guided to an external imaging camera, and synchronous shooting of movement of tracer particles in a blade grid channel is achieved. Particle image sequences of different planes can be obtained under different working conditions in cooperation with a wind tunnel working condition signal and a synchronous control system. Compared with a traditional PIV system depending on a large-size observation window of a test section and external long light path arrangement, only the grid plate and the single blade are locally modified, the structure is compact, disturbance to an original flow field is small, a measurement plane can penetrate into key areas such as a blade near wall, a wake and a corner area, and the measurement precision is high. And the measurement precision and the engineering applicability of a complex flow structure in the plane cascade are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of compressor flow field testing and optical measurement technology, specifically relating to a planar blade integrated laser camera dual-endoscopic PIV flow field measurement device, which is suitable for measuring the velocity field distribution in front of the grating, behind the grating, on the blade surface and inside the blade channel under subsonic and transonic conditions. Background Technology

[0002] Currently, experimental studies of the internal flow field of planar blade cascades still mainly rely on contact measurement methods such as porous aerodynamic probes, wall pressure hole arrays, and hot wire / hot film methods. These methods require probes to be placed through openings in the wall of the blade cascade test section, which inevitably disturbs the original flow field. Furthermore, they can only obtain information from limited measurement points, making it difficult to characterize complex three-dimensional flow structures such as near-wall, wake mixing zone, and corner secondary flow with high spatiotemporal resolution. Particle Image Velocimetry (PIV), as a non-contact, transient, full-field flow field testing method, has been widely used in planar blade cascade wind tunnel tests. However, conventional PIV often uses a combination of external laser sheet light and an external camera, relying on a large transparent window on the side wall of the test section to introduce the light path and arrange the field of view. This results in a long light path with many reflections, making it susceptible to refraction distortion and reflected light. Simultaneously, limited by the space and installation conditions of the test section, the effective field of view that the camera can obtain within the blade cascade passage is limited, and the measurement plane is often confined to areas far from the blade surface, making it difficult to simultaneously measure the velocity field in front of, behind, and near-wall regions.

[0003] Patent CN120294360A discloses a method of introducing an endoscope into the impeller mechanical sleeve to take pictures in conjunction with a camera and sheet light source. However, the endoscope introduces additional obstruction and local disturbances, affecting the representativeness of the measurement results. Therefore, there is currently a lack of a compact device that can achieve PIV measurement without significantly modifying the test section wall. To address this, a planar blade integrated laser camera dual-endoscope PIV flow field measurement device is proposed. By coordinating the laser endoscope probe and the camera endoscope probe inside the blade, sheet light is introduced and particle scattered light is extracted, respectively, constructing a measurement field of view inside the blade channel. This enables high-precision, non-contact, full-field testing of complex flow structures in the areas before, after, and near the wall of the impeller. Summary of the Invention

[0004] The technical problem this invention aims to solve is: addressing the current limitations of planar blade cascade flow field testing, which relies on large sidewall observation windows, long optical path lengths, and numerous folds, making high-precision non-contact full-field measurements difficult within the cascade channel. This invention proposes an integrated laser camera dual-endoscope PIV flow field measurement device for planar blade cascades. By integrating the laser endoscope probe and the camera endoscope probe inside the blade, laser light is directly projected from the optical window to the adjacent channel. The scattered particle light is then guided through the camera endoscope to an external imaging camera, enabling PIV measurements in key areas of the cascade channel. This allows for the acquisition of high spatiotemporal resolution velocity field data for complex structures such as wake mixing, secondary flow, and corner separation, providing reliable experimental support for aerodynamic optimization and numerical simulation verification of planar blade cascades.

[0005] The technical solution of this invention is:

[0006] A planar blade integrated laser camera dual-endoscope PIV flow field measurement device is characterized by comprising a laser endoscope probe (1), a camera endoscope probe (2), a planar blade (3), an optical window (4), a left grating plate (5), a target measurement area (6), a right grating plate (7), an imaging camera (8), a laser (9), a light guide arm (10), and an experimental section wall (11). At least one of the planar blades (3) is an integrated blade, and its interior is provided with a slender inner cavity along the blade span direction or chord direction to accommodate the laser endoscope probe (1) and the camera endoscope probe (2). Several optical windows (4) are opened on the outer surface of the blade pressure surface or suction surface. The right grating plate (7) is machined with a small-sized optical interface that matches the outer diameter of the laser endoscope probe (1) and the camera endoscope probe (2), and is provided with a flange and sealing structure for separating the laser endoscope probe (1) and the camera endoscope probe (2). Do not fix it on the right grating plate (7), and at the same time ensure the airtightness of the experimental section. The laser (9) is connected to the laser endoscope probe (1) through the light guide arm (10). After the laser is shaped by the front end of the laser endoscope probe (1), it is emitted through the optical window (4) at the predetermined position. A laser sheet light with a certain thickness and width is formed in the grating channel between adjacent planar blades (3), which constitutes the target measurement area (6). Tracer particles are evenly scattered at the grating inlet, so that the tracer particles pass through the target measurement area (6) with the airflow. The camera endoscope probe (2) is inserted into the interior of the planar blade (3) through another optical interface. The front field of view is pointed to the target measurement area (6). The scattered light of the tracer particles in the target measurement area (6) is guided to the imaging camera (8) arranged on the outside of the experimental section wall (11). The imaging camera (8) collects the particle image and combines it with the PIV algorithm to reconstruct the velocity field distribution in the planar grating channel.

[0007] Furthermore, the optical window (4) is uniformly opened on the outer surface of the blade along the blade span direction or chord direction of the planar blade (3) with equal diameter and equal spacing. The material of the optical window (4) is sapphire glass or other high pressure resistant and corrosion resistant optical glass. The laser endoscope probe (1) and the camera endoscope probe (2) can move inside the planar blade (3) to adapt to the measurement needs of different positions.

[0008] Furthermore, the diameter of the optical window (4) is 1mm to 12mm, the distance between two adjacent optical windows (4) is 2mm to 200mm, and the outer surface of the optical window (4) and the outline of the pressure surface or suction surface of the planar blade (3) maintain a smooth transition to reduce the interference with the original channel flow field.

[0009] Furthermore, the laser endoscope probe (1) and the camera endoscope probe (2) are located inside the same plane cascade blade (3) or are located in two adjacent plane cascade blades (3). The imaging camera (8) is connected to the synchronous control system with the laser (9) and the wind tunnel working status signal. The particle image sequence in the target measurement area (6) is collected under different incoming flow conditions through the dual-pulse laser and phase-locked triggering method.

[0010] Furthermore, the diameter of the laser endoscope probe (1) and the camera endoscope probe (2) is 1mm to 12mm and the length is 80mm to 500mm. The device can be equipped with two or more imaging cameras (8) with a certain angle between their optical axes, so as to simultaneously capture the target measurement area (6) from different perspectives and realize the three-dimensional PIV measurement of the internal flow field of the compressor.

[0011] The beneficial effects of this invention are:

[0012] Traditional planar blade cascade PIVs often employ a single-channel optical path with an external laser and camera, which suffers from problems such as limited field of view, large distortion, and difficulty in precise measurement of the near-wall region. This invention integrates the illumination and imaging channels into the interior of the blade cascade using a dual-endoscopic laser camera approach, achieving high-quality velocity field measurement of key areas of the blade cascade channel without significantly altering the test section structure.

[0013] Beneficial effect 1:

[0014] The laser endoscope probe and the camera endoscope probe are inserted into the blade through a small optical interface on the grid plate. Illumination and imaging are both arranged in a closed manner within the blade passage. Only small holes and flange sealing structures need to be made locally on the grid plate. There is no need to process large-area transparent windows, which significantly reduces the impact on the test section wall and the overall structural stiffness of the blade grid, while reducing the degree of damage to the original channel profile and flow field.

[0015] Benefit 2:

[0016] The laser beam is shaped inside the blade by a laser endoscope probe and then projected directly into the blade cascade channel through an optical window. Particle-scattered light is guided from inside the channel to an external imaging camera by a camera endoscope probe, forming a compact "endoscope illumination + endoscope imaging" optical path. Compared to traditional external long optical path solutions, the dual-endoscope arrangement significantly shortens the laser and imaging optical paths, reduces geometric distortion and glare caused by multiple refractions and reflections, and improves particle image contrast and related calculation accuracy.

[0017] Benefit 3:

[0018] Laser endoscopes and camera endoscopes can move inside the blade along the blade span or chord direction, so that the laser beam position and the camera field of view are optimally overlapped within the blade passage. This allows for flexible arrangement of measurement planes in different flow regions such as the incoming flow development zone, near-wall secondary flow zone, and wake mixing zone, enabling local magnified observation and multi-section joint measurement, significantly expanding the measurable area and the possible viewing angles.

[0019] Beneficial effect four:

[0020] When two or more camera endoscope channels are deployed, a three-dimensional field of view angle can be formed within the blade cascade channel. Combined with a synchronous control system and dual-pulse laser triggering, multi-view phase-locked acquisition of the same target measurement area can be performed to reconstruct the three-component velocity vector field. Compared to a single-field-of-view scheme, dual-endoscope and multi-endoscope combinations can more accurately resolve the spatiotemporal evolution of typical three-dimensional flow structures in planar blade cascades, such as wake entrainment, corner separation, and near-wall secondary flow, providing more reliable experimental data for aerodynamic optimization and numerical simulation calibration. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating a specific implementation of the integrated laser camera dual-endoscopic PIV inside a planar cascade.

[0022] Figure 2 This is a schematic diagram showing the relationship between the laser endoscope probe, the camera endoscope probe, the planar blade cascade, and the optical window.

[0023] Figure 3 A schematic diagram showing the location of an optical window on a planar blade.

[0024] Figure 4 This is a front view showing the relative positions of the laser endoscope probe, the camera endoscope probe, and the planar blade cascade.

[0025] Wherein: 1-Laser endoscope probe, 2-Camera endoscope probe, 3-Plane cascade blade, 4-Optical window, 5-Left cascade plate, 6-Target measurement area, 7-Right cascade plate, 8-Imaging camera, 9-Laser, 10-Light guide arm, 11-Test section wall. Detailed Implementation

[0026] 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.

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1:

[0029] like Figures 1-4 The diagram shows a planar blade integrated laser camera dual-endoscope PIV flow field measurement device of the present invention, used to measure the unsteady three-dimensional velocity field inside a compressor. It includes a laser endoscope probe (1), a camera endoscope probe (2), planar blades (3), optical windows (4), a left grating plate (5), a target measurement area (6), a right grating plate (7), an imaging camera (8), a laser (9), a light guide arm (10), and an experimental section wall (11). The experimental section has a rectangular cross-section, with a row of planar blades (3) installed inside. The middle blade is designed as an integrated blade, with a slender cavity machined along the blade span direction inside to accommodate the laser endoscope probe (1) and the camera endoscope probe (2). Several optical windows (4) are uniformly opened along the blade span direction on the outer surface of the blade pressure surface. Two small-sized optical interfaces matching the outer diameter of the laser endoscope probe (1) and the camera endoscope probe (2) are pre-processed on the right grid plate (7), and an annular flange and sealing ring are provided to fix the two endoscope probes on the right grid plate (7) respectively, while ensuring the airtightness of the test section. The laser (9) is connected to the laser endoscope probe (1) through the light guide arm (10). The laser beam is transmitted through the light guide arm (10) into the front optical system of the laser endoscope probe (1). After collimation and sheet beam shaping are completed inside the probe, it is emitted from the predetermined optical window (4) on the pressure surface of the integrated blade, forming a laser sheet beam with a certain thickness and width between two adjacent planar blades (3). The coverage area is defined as the target measurement area (6).

[0030] The camera endoscope probe (2) is inserted into the same integrated blade through another optical interface, with its front field of view pointing towards the target measurement area (6), guiding the scattered light of the tracer particles in the area to the imaging camera (8). The imaging camera (8) is connected to the rear end of the camera endoscope probe (2) through a dedicated connection interface, realizing the optical coupling between the endoscope imaging optical path and the external camera. The laser endoscope probe (1) and the camera endoscope probe (2) can move along the blade span inside the blade. By changing their relative positions in the cavity, the height of the laser sheet light in the blade cascade channel and the overlap area between the camera field of view and the sheet light are finely adjusted to adapt to the measurement requirements of different blade height sections and different flow directions. During the experiment, tracer particles are uniformly scattered in the upstream flow of the planar blade cascade, so that the tracer particles enter the blade cascade channel with the airflow and pass through the target measurement area (6). The wind tunnel working status signal, the laser (9) and the imaging camera (8) are all connected to the synchronous control system. Through the dual-pulse laser and phase-locked triggering method, the target measurement area (6) is acquired in a time series of particle images under the set inflow conditions. By using the PIV post-processing algorithm, cross-correlation calculations are performed on the particle images transmitted from the camera's endoscopic channel to obtain the velocity field distribution within the blade cascade channel, thereby enabling the velocity vector reconstruction of typical wake structures, secondary flows, and corner flows within the blade cascade channel.

[0031] Example 2:

[0032] In this embodiment, dual endoscopic probes are arranged inside the blade of the preceding planar cascade to observe the velocity field within the channel of the following planar cascade from the upstream direction. The system includes a laser endoscopic probe (1), a camera endoscopic probe (2), a planar cascade blade (3), an optical window (4), a left cascade plate (5), a target measurement area (6), a right cascade plate (7), an imaging camera (8), a laser (9), a light guide arm (10), and the experimental section wall (11). A slender internal cavity is machined along the blade span direction on the suction side of the preceding planar cascade blade, and several small-sized optical windows (4) are opened on the outer surface of the suction surface. The laser endoscopic probe (1) and the camera endoscopic probe (2) are jointly arranged within this blade, with the optical axes of the front end of the camera endoscopic probe (2) pointing towards the predetermined target measurement area (6) within the channel of the following downstream planar cascade blade. Two optical interfaces matching the outer diameters of the laser endoscopic probe (1) and the camera endoscopic probe (2) are machined on the right cascade plate (7) of the experimental section, and rigid fixation and hermetically sealed are achieved through flanges and sealing structures. The laser (9) is connected to the laser endoscope probe (1) via the light guide arm (10). After the laser beam enters the endoscope probe (1), it is shaped into a sheet beam by the front-end optical system and then emitted downstream through the optical window (4) arranged on the suction surface of the preceding stage blade. A laser sheet beam with a certain thickness and width is formed in the channel between the blades of the following stage planar cascade, and its coverage area is the target measurement area (6). In order to ensure that the sheet beam can sweep through the key area of ​​the following stage cascade channel, the height and incident angle of the sheet beam can be optimized by finely adjusting the movement of the laser endoscope probe (1) in the blade cavity.

[0033] Tracer particles are uniformly seeded upstream of the leading edge of the planar blade cascade, allowing them to pass sequentially through the preceding and following blade cascade channels with the incoming flow, and through the target measurement area (6). The front field of view of the camera endoscope probe (2) is aligned with the target area, guiding the scattered light from the tracer particles to the imaging camera (8) located outside the experimental section. The imaging camera (8) is connected to the camera endoscope probe (2) through an optical coupling interface. The laser (9), the imaging camera (8), and the wind tunnel incoming flow condition signal are connected to the synchronous control system. Through dual-pulse laser and phase-locked triggering, time-series particle images of the target measurement area (6) are acquired under different angles of attack or Mach numbers. The flow characteristics such as wake development, secondary flow structure, and corner separation in the downstream blade cascade channel are analyzed.

[0034] In this embodiment of the invention, by using a dual-endoscope arrangement, laser illumination and imaging field of view are both introduced and extracted from inside the blade with only local modifications to the grating and a single blade. This significantly reduces the distortion and reflection interference caused by the long external optical path to the measurement. At the same time, the measurement plane can be flexibly selected within the narrow blade passage, enabling high spatiotemporal resolution PIV measurements of the complex flow structure in the key area of ​​the planar blade grating.

Claims

1. The technical solution of the present invention is: a planar blade cascade integrated laser camera dual-endoscopic PIV flow field measurement device, characterized in that: The system includes a laser endoscope probe (1), a camera endoscope probe (2), planar blades (3), optical windows (4), a left grating plate (5), a target measurement area (6), a right grating plate (7), an imaging camera (8), a laser (9), a light guide arm (10), and an experimental section wall (11). At least one of the planar blades (3) is an integrated blade, with a slender inner cavity arranged along the blade span direction or chord direction to accommodate the laser endoscope probe (1) and the camera endoscope probe (2). Several optical windows (4) are opened on the outer surface of the blade's pressure or suction surface. The right grating plate (7) is machined with a small-sized optical interface that matches the outer diameter of the laser endoscope probe (1) and the camera endoscope probe (2), and is equipped with a flange and sealing structure to fix the laser endoscope probe (1) and the camera endoscope probe (2) on the right grating plate (7) respectively, while ensuring the experimental section wall. To test the airtightness of the test section, the laser (9) is connected to the laser endoscope probe (1) through the light guide arm (10). After the laser is shaped at the front end of the laser endoscope probe (1), it is emitted through the optical window (4) at a predetermined position. A laser sheet light with a certain thickness and width is formed in the blade channel between adjacent planar blades (3), which constitutes the target measurement area (6). Tracer particles are uniformly scattered at the blade inlet, so that the tracer particles pass through the target measurement area (6) with the airflow. The camera endoscope probe (2) is inserted into the interior of the planar blade (3) through another optical interface. The front field of view is pointed to the target measurement area (6). The scattered light of the tracer particles in the target measurement area (6) is guided to the imaging camera (8) arranged on the outside of the test section wall (11). The imaging camera (8) collects particle images and combines them with the PIV algorithm to reconstruct the velocity field distribution in the planar blade channel. Furthermore, the optical window (4) is uniformly opened on the outer surface of the blade along the blade span direction or chord direction of the planar blade (3) with equal diameter and equal spacing. The material of the optical window (4) is sapphire glass or other high pressure resistant and corrosion resistant optical glass. The laser endoscope probe (1) and the camera endoscope probe (2) can move inside the planar blade (3) to adapt to the measurement needs of different positions. Furthermore, the diameter of the optical window (4) is 1mm to 12mm, the distance between two adjacent optical windows (4) is 2mm to 200mm, and the outer surface of the optical window (4) and the outline of the pressure surface or suction surface of the planar blade (3) maintain a smooth transition to reduce the interference with the original channel flow field. Furthermore, the laser endoscope probe (1) and the camera endoscope probe (2) are located inside the same plane cascade blade (3) or are located in two adjacent plane cascade blades (3). The imaging camera (8) is connected to the synchronous control system with the laser (9) and the wind tunnel working status signal. The particle image sequence in the target measurement area (6) is collected under different incoming flow conditions through the dual-pulse laser and phase-locked triggering method. Furthermore, the diameter of the laser endoscope probe (1) and the camera endoscope probe (2) is 1mm to 12mm and the length is 80mm to 500mm. The device can be equipped with two or more imaging cameras (8) with a certain angle between their optical axes, so as to simultaneously capture the target measurement area (6) from different perspectives and realize the three-dimensional PIV measurement of the internal flow field of the compressor.

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