A 3D-PIV measurement device and measurement method based on layered algorithm

Abstract

A 3D-PIV measurement device and method based on a hierarchical algorithm, relating to the technical field of flow field measurement. The laser outputs laser light, and a beam expander and a collimator shape the laser into a sheet of light. The middle position of the two reflectors is the measurement area. The sheet of light is injected into the space between the two reflectors and reflected multiple times to form multiple sheets of light with decreasing energy. Two focusing mirrors are arranged between the two reflectors and on both sides of the measurement area, so that the sheet of light is focused at the center of the measurement area. A high-speed camera is arranged corresponding to the measurement area to capture the scattered image of the tracer particles. Two reflectors are used to form a multi-section, multi-level energy sheet of light in space, and only a single high-speed camera is used to collect the tracer particle scattering signal, which helps to control costs, is simple in calibration, and has high adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of flow field measurement, and in particular to a 3D-PIV measurement device and a measurement method based on a layered algorithm. Background Art

[0002] As an advanced measurement method, PIV (Particle Image Velocimetry) technology has the advantages of non-invasiveness, high temporal and spatial resolution, high sensitivity, and a wide range of applicable scenarios. It is widely used in various flow field measurements. High-speed PIV can "freeze" the flow field, obtain the time evolution process, and further obtain the vorticity and stress distribution of the flow field, providing important measurement basis for flow analysis.

[0003] Traditional 2D-PIV technology can only obtain velocity vectors in a single plane. With the increasing complexity of experiments and in-depth research on scientific issues, 2D-PIV technology can no longer meet the needs of scientific researchers and measurement personnel. Therefore, 3D-PIV is more valued in the field of flow field measurement. 3D-PIV mainly includes tomographic PIV (Tomographic PIV) technology, digital holographic PIV (Digital holographic PIV) technology, and SPIV (Spatial PIV) technology. However, these technologies require the use of multiple cameras and a complex calibration process to achieve 3D-PIV measurement. Not only is the cost huge, but different application scenarios require the system to be rebuilt. It has gradually become difficult to meet the needs of rapid measurement of PIV technology in engineering technology.

[0004] Therefore, in order to achieve low-cost, easy-to-operate, and highly reliable 3D-PIV measurement, the present invention proposes a 3D-PIV measurement device and a measurement method based on an image layering algorithm. The main implementation method of 3D-PIV is to obtain the spatial position of the tracer particles in the measurement area at time t and time t+Δt, and to calculate the spatial three-component velocity field through a three-dimensional cross-correlation algorithm. Considering that the scattered light intensity of the tracer particles is approximately proportional to the energy of the laser, the intensity information of the tracer particle image can be used to approximately distinguish its spatial position. The use of a low-reflectivity reflector can reduce the reflected laser energy, and through multiple reflections, a multi-section sheet light beam with successively reduced energy is formed in space, which further realizes the distinction of tracer particles of different cross sections according to the size of the scattering intensity, thereby realizing the acquisition of the spatial distribution of the tracer particles. Summary of the invention

[0005] In order to address the shortcomings of the background technology, the present invention provides a 3D-PIV measurement device and measurement method based on a hierarchical algorithm, which utilizes two reflectors to form a spatial multi-section, multi-level energy sheet light distribution, and only uses a single high-speed camera to collect tracer particle scattering signals, which helps to control costs, has simple calibration, and high adaptability.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A 3D-PIV measurement device based on a hierarchical algorithm comprises a laser, a beam expander, a collimator, a high-speed camera, two reflectors and two focusing mirrors, wherein the laser outputs laser light, the beam expander and the collimator are sequentially arranged behind the laser to shape the laser into a light sheet, the two reflectors are arranged oppositely in a positive direction behind the light sheet, the middle position of the two reflectors is a measurement area, an angle is left between the arrangement direction of the two reflectors and the incident direction of the light sheet, so that the light sheet can be incident between the two reflectors and reflected multiple times to form multiple light sheets with successively decreasing energy, the two focusing mirrors are arranged between the two reflectors and located on both sides of the measurement area, the two focusing mirrors are confocal, and the light sheet is focused on the center of the measurement area by adjustment, and the high-speed camera is arranged corresponding to the measurement area to capture the scattered image of the tracer particles.

[0008] A 3D-PIV measurement method based on a hierarchical algorithm comprises the following steps:

[0009] Step 1: The laser outputs laser light and is shaped into a light sheet through a beam expander and a collimator in turn, and then introduced between two reflectors. The light sheet has different reflection paths between the two reflectors to form a multi-layer reflection cross section;

[0010] Step 2: Adjust the angle between the incident direction of the sheet light and the arrangement direction of the two reflectors, and then adjust the spacing between the reflection cross sections to form a number of reflection cross sections that meet the measurement requirements between the two reflectors, and ensure that the reflection cross sections in the measurement area are all within the depth of field of the high-speed camera;

[0011] Step 3: Evenly place tracer particles in the measurement area to obtain a scattering image of the tracer particles in the measurement area;

[0012] Step 4: First, use a baffle to block all the light between the two reflectors, then move the baffle to release each light in turn, use a high-speed camera to obtain scattered images in turn, and calibrate the scattered light intensity of each layer of reflection cross section;

[0013] Step 5: According to the reflectivity of the two reflectors and the calibration results of the scattering image, the reflection cross section to which each tracer particle in the scattering image belongs is calculated, and the spatial distribution of the tracer particles is reconstructed;

[0014] Step 6: Repeat the operation to obtain the spatial distribution of the tracer particles in the second frame, and finally calculate the spatial velocity field using the three-dimensional cross-correlation algorithm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention utilizes two reflectors to form a multi-section, multi-level energy sheet light distribution in space, calculates the relative scattering intensity of the tracer particles at the section according to the laser sheet light energy in the spatial section, obtains the three-dimensional spatial distribution of the tracer particles, and realizes the velocity field measurement of the three components in space. Only a single high-speed camera is used to collect the scattering signals of the tracer particles as a whole, which solves the problems of large number of cameras, high cost and complex calibration in traditional three-dimensional particle image measurement. Through the multi-section reflection method, the adaptability of the measurement space area is high, and the number of laser sheet light reflections can be set according to needs to realize wide range measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a front view of the arrangement structure of the 3D-PIV measurement device based on the layered algorithm of the present invention;

[0017] Figure 2 It is a top view of the arrangement structure of the 3D-PIV measurement device based on the layered algorithm of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] like Figure 1-2 As shown, a 3D-PIV measurement device based on a hierarchical algorithm includes a laser 1, a beam expander 2, a collimator 3, a high-speed camera 4, two reflectors 5 and two focusing mirrors 6.

[0020] The laser 1 outputs laser light. The beam expander 2 and the collimator 3 are sequentially arranged behind the laser 1 to shape the laser light into a sheet of light. The two reflectors 5 are arranged opposite to each other in the positive direction behind the light sheet, and the middle position of the two reflectors 5 is the measurement area. There is an angle between the arrangement direction of the two reflectors 5 and the incident direction of the light sheet, so that the light sheet can be incident between the two reflectors 5 and reflected multiple times to form multiple light sheets with decreasing energy. The two focusing mirrors 6 are arranged between the two reflectors 5 and located on both sides of the measurement area. The two focusing mirrors 6 are confocal, and the light sheet is focused at the center of the measurement area by adjustment. The high-speed camera 4 is arranged corresponding to the measurement area to capture the scattered image of the tracer particles.

[0021] Among them, the laser 1 can be a double-pulse laser or a beam of two lasers, and the output laser wavelength is 532nm or 527nm; the reflectivity of the two reflectors 5 is consistent and it is advisable to select a low reflectivity, such as 90% reflectivity, so that the energy of the sheet light decreases successively after multiple reflections, providing a scattered light source for the tracer particles in the measurement area, and the required reflectivity can also be calculated according to actual needs and made according to needs; the actual required sheet light thickness can be formed in the measurement area by adjusting the two focusing mirrors 6; in order to meet the algorithm requirements, the high-speed camera 4 should use a high-bit depth camera, such as 16 bits, which is determined according to the designed number of reflection sections. When the number of reflection sections is low, a low-bit depth camera can also be used to obtain the scattering image of the tracer particles in a single pulse laser, and then according to the relative scattering intensity of the tracer particles at different sections, the tracer particles of the section are extracted using a hierarchical algorithm, and finally the spatial distribution of the tracer particles is formed, and the spatial velocity vector of the measurement area is calculated.

[0022] like Figure 1-2 As shown, a 3D-PIV measurement method based on a hierarchical algorithm includes the following steps:

[0023] Step 1: The laser 1 outputs laser light and is shaped into a light sheet through the beam expander 2 and the collimator 3 in sequence, and then introduced into between the two reflectors 5. The light sheet has different reflection paths between the two reflectors 5 to form a multi-layer reflection cross section;

[0024] Step 2: Adjust the angle between the incident direction of the sheet light and the arrangement direction of the two reflectors 5, and then adjust the spacing between the reflection cross sections to form a number of reflection cross sections that meet the measurement requirements between the two reflectors 5, and ensure that the reflection cross sections in the measurement area are all within the depth of field of the high-speed camera 4. Figure 2 As shown, the figure takes the thirteen-layer reflection cross section as an example;

[0025] Step 3: Evenly place tracer particles in the measurement area to obtain a scattering image of the tracer particles in the measurement area;

[0026] Step 4: First, use a baffle to block all the light between the two reflectors 5, then move the baffle to release each light in turn, use a high-speed camera 4 to obtain scattered images in turn, and calibrate the scattered light intensity of each layer of reflection cross section;

[0027] Step 5: According to the reflectivity of the two reflectors 5 and the calibration results of the scattering image, the reflection cross section to which each tracer particle in the scattering image belongs is calculated, and the spatial distribution of the tracer particles is reconstructed;

[0028] Step 6: Repeat the operation to obtain the spatial distribution of the tracer particles in the second frame, and finally calculate the spatial velocity field using the three-dimensional cross-correlation algorithm.

[0029] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other forms of assembly without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0030] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A 3D-PIV measurement device based on a hierarchical algorithm, characterized in that: The invention comprises a laser (1), a beam expander (2), a collimator (3), a high-speed camera (4), two reflectors (5) and two focusing mirrors (6), wherein the laser (1) outputs laser light, the beam expander (2) and the collimator (3) are arranged in sequence behind the laser (1) to shape the laser light into a light sheet, the two reflectors (5) are arranged in a positive direction opposite to each other behind the light sheet, the middle position of the two reflectors (5) is a measurement area, an angle is left between the arrangement direction of the two reflectors (5) and the incident direction of the light sheet, so that the light sheet can be incident between the two reflectors (5) and reflected multiple times to form multiple light sheets with successively decreasing energy, the two focusing mirrors (6) are arranged between the two reflectors (5) and located on both sides of the measurement area, the two focusing mirrors (6) are cofocal, and the light sheet is focused at the center of the measurement area by adjustment, the high-speed camera (4) is arranged corresponding to the measurement area and is used to capture the scattered image of the tracer particles, and the measurement method comprises the following steps: Step 1: The laser (1) outputs laser light and is shaped into a light sheet through a beam expander (2) and a collimator (3) in sequence and then introduced into between two reflectors (5). The light sheet has different reflection paths between the two reflectors (5) to form a multi-layer reflection cross section; Step 2: adjusting the angle between the incident direction of the sheet light and the arrangement direction of the two reflectors (5), thereby adjusting the spacing between the reflective cross sections, forming a number of reflective cross sections that meet the measurement requirements between the two reflectors (5), and ensuring that the reflective cross sections in the measurement area are all within the depth of field of the high-speed camera (4); Step 3: Evenly place tracer particles in the measurement area to obtain a scattering image of the tracer particles in the measurement area; Step 4: first, use a baffle to block all the light between the two reflectors (5), then move the baffle to release each light in turn, use a high-speed camera (4) to obtain scattered images in turn, and calibrate the scattered light intensity of each layer of reflection cross section; Step 5: Calculate the reflection cross section to which each tracer particle in the scattering image belongs based on the reflectivity of the two reflectors (5) and the calibration result of the scattering image, and reconstruct the spatial distribution of the tracer particles; Step 6: Repeat the operation to obtain the spatial distribution of the tracer particles in the second frame, and finally calculate the spatial velocity field using the three-dimensional cross-correlation algorithm.

2. The 3D-PIV measurement device based on the hierarchical algorithm according to claim 1, characterized in that: The laser (1) is a double-pulse laser or a beam-combined laser of two lasers, and the output laser wavelength is 532nm or 527nm.

3. The 3D-PIV measurement device based on the hierarchical algorithm according to claim 1, characterized in that: The high-speed camera (4) is a 16-bit depth camera.

4. The 3D-PIV measurement device based on the hierarchical algorithm according to claim 1, characterized in that: The reflectivity of the two reflectors (5) is 90%.

Images