Array type cylindrical focusing laser differential interferometer

Abstract

The utility model discloses an array type cylindrical focusing laser differential interferometer, a generated measuring light path comprises a transmitting light path and a receiving light path, an air flow passes through the transmitting light path and the receiving light path, and the measuring light path passes through an area to be measured of the air flow. The optical lens component forming the emitting light path comprises a laser generator, and a first polaroid, a first cylindrical plane convex lens, a beam splitter, a first Wollaston prism, a second cylindrical plane convex lens and a first biconvex lens which are sequentially arranged along the propagation direction of a light beam emitted by the laser; and the receiving light path heating optical lens comprises a second biconvex lens, a third cylindrical surface plano-convex lens, a second Wollaston prism, a second polaroid, a plano-concave lens and a photoelectric detector which are sequentially arranged along the propagation direction of the light beam. The utility model aims to divide a single laser beam emitted by a single laser into a plurality of laser beams by using a diffractive optical element beam splitter, and then the laser beams are focused at a plurality of measuring points in a flat boundary layer to measure density pulsation information.

Description

Technical Field

[0001] The utility model relates to the technical field of fluid mechanics measurement, in particular to an array type cylindrical focusing laser differential interferometer. Background Art

[0002] Wind tunnel test is one of the most important methods in current aerodynamic research, and its method of obtaining flow field state information relies on the support of flow field measurement equipment. At present, quantitative wind tunnel experimental measurement methods include Pitot probe, hot wire anemometer, pulsating pressure sensor, etc. However, the above-mentioned invasive measurement methods are limited by the probe size and low spatial resolution, which will interfere with the flow field itself and affect the measurement accuracy. At present, the density pulsation information of the flow field in the flat plate boundary layer can be obtained through a cylindrical focusing laser differential interferometer, and due to the use of cylindrical lenses, the focusing point of the sheet light can be close to the surface of the flat plate to measure the information of the density pulsation of the flow field inside the flat plate boundary layer, and there is no flat plate shading phenomenon, which has a strong advantage. However, the existing cylindrical focusing laser differential interferometers are all single-point measurements, and can only obtain information from one measuring point each time, and the measurement efficiency is very low. Utility Model Content

[0003] The utility model aims to provide an array type cylindrical focusing laser differential interferometer, which can simultaneously measure the density pulsation information of multiple measuring points in a flat plate boundary layer.

[0004] In order to solve the above technical problems, the utility model specifically provides the following technical solutions: an array cylindrical focusing laser differential interferometer, the generated measurement light path includes a transmitting light path and a receiving light path, the airflow passes through the two, and the measurement light path passes through the area to be measured of the airflow;

[0005] The instrument forming the transmitting optical path includes: an optical signal transmitting unit, a beam splitter and multiple groups of optical lenses, forming multiple groups of test optical paths; the instrument forming the receiving optical path includes: multiple groups of optical lenses and a photoelectric conversion unit, and the photoelectric conversion unit receives the optical signal of the test optical path; multiple groups of photoelectric conversion units are provided, corresponding to the test optical path settings; the above-mentioned optical lenses are arranged in parallel, and the center points of the optical lenses are on the same straight line.

[0006] Further, the optical signal transmitting unit is a laser generator; the multiple groups of optical lenses forming the transmitting light path include a first polarizer, a first cylindrical plano-convex lens, a first Wollaston prism, a second cylindrical plano-convex lens and a first biconvex lens arranged in sequence along the propagation direction of the light beam emitted by the laser, and the beam splitter is arranged between the first cylindrical plano-convex lens and the first Wollaston prism; wherein,

[0007] The laser generator is used to emit a parallel coherent light beam; the first polarizer is used to filter out noise light in the coherent light beam; the convex mirror of the first cylindrical plano-convex lens is set towards the propagation direction of the light beam, and is used to focus the coherent light beam and then expand it to diverge into a fan-shaped light beam; the beam splitter is used to divide a fan-shaped light beam into N identical coherent fan-shaped light beams A; the first Wollaston prism is used to further separate each coherent fan-shaped light beam A into two light beams B with mutually perpendicular polarization directions; the convex mirror of the second cylindrical plano-convex lens is set towards the propagation direction of the light beam, and the second cylindrical plano-convex cylindrical mirror converts the unidirectional divergent light beam B into a parallel light beam B again; the first biconvex lens focuses the parallel light beam B so that the focused light beam B passes through the area to be measured.

[0008] Further, the photoelectric conversion unit is a photodetector; the multiple groups of optical lenses forming the receiving light path include a second biconvex lens, a third cylindrical plano-convex lens, a second Wollaston prism, a second polarizer and a plano-concave lens arranged in sequence along the propagation direction of the light beam, and the photodetector is arranged at the end of the receiving light path; wherein,

[0009] The second double convex lens is used to convert the focused light beam B back into a parallel light beam B; the convex mirror of the third cylindrical plano-convex lens is arranged toward the propagation direction of the light beam, and is used to convert the parallel light beam B into a unidirectional focused light beam B; the second Wollaston prism is used to refocus and merge the two focused light beams B separated by the fan-shaped light beam A into a coherent light beam C; the second polarizer is used to filter the merged coherent light beam C to obtain a focused light beam with a consistent polarization direction, so that the filtered coherent light beam C can perform phase interference; the plano-concave lens is used to expand the filtered coherent light beam C; the photodetector is used to linearly convert the light intensity of the expanded coherent light beam C into a voltage signal, and each coherent light beam corresponds to a photodetector.

[0010] Furthermore, the two fan-shaped beams separated by the first Wollaston prism satisfy the following relationship:

[0011]

[0012] Where ΔX 1 is the separation distance between the two fan-shaped beams, f 2 is the focal length of the second biconvex lens, and σ is the separation angle of the first Wollaston prism.

[0013] Furthermore, the spacing of the above optical lens elements meets the following requirements:

[0014] Among them, L 1is the distance between the first cylindrical plano-convex lens and the second cylindrical plano-convex lens, is the focal length of the first cylindrical plano-convex lens, is the focal length of the second cylindrical plano-convex lens;

[0015] Among them, L 2 is the distance between the first biconvex lens and the second biconvex lens, is the focal length of the first biconvex lens, is the focal length of the second biconvex lens

[0016] Among them, L 3 is the distance between the third cylindrical plano-convex lens and the plano-concave lens, is the focal length of the third cylindrical plano-convex lens;

[0017] L 4 =f V Among them, L 4 is the distance between the plano-concave lens and the photodetector, f V is the focal length of the plano-concave lens.

[0018] Compared with the prior art, the utility model has the following beneficial effects: the array-type cylindrical focusing laser differential interferometer provided by the utility model utilizes a diffraction optical element beam splitter to divide a single laser beam emitted by a single laser into multiple laser beams, which are then focused at multiple measuring points, so that density pulsation information of multiple measuring points in the flat plate boundary layer can be obtained simultaneously each time, which greatly reduces the number of experiments, improves the test efficiency of the wind tunnel, and saves test costs.

[0019] The utility model has good consistency of the test beam of each channel of the interferometer. By performing correlation processing on the experimental data of different measuring points, the correlation of each measuring point can be analyzed, and the understanding of the time coherence and space coherence of the flat plate boundary layer flow field structure can be deepened. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the implementation or the prior art description. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0021] Figure 1 A schematic structural diagram of an array-type cylindrical focusing laser differential interferometer provided in an embodiment of the utility model;

[0022] Figure 2A top view of the focus distribution in the model boundary layer of an array-type cylindrical focusing laser differential interferometer provided in an embodiment of the utility model;

[0023] Figure 3 A front view of the focus distribution in the model boundary layer of an array-type cylindrical focusing laser differential interferometer provided in an embodiment of the utility model.

[0024] The numbers in the figure represent the following:

[0025] P 1 - first polarizer; C 1 -First cylindrical plano-convex lens; E-beam splitter; W 1 -First Wollaston prism; C 2 - Second cylindrical plano-convex lens; S 1 - a first biconvex lens; S 2 - Second biconvex lens; C 3 -Third cylindrical plano-convex lens; W 2 - Second Wollaston prism; P 2 -Second polarizer; V-plano-concave lens; D 1 - a first photodetector; D 2 - Second photodetector; D 3 - A third photodetector; D 4 - A fourth photodetector; D 5 - fifth photodetector; D 6 - A sixth photodetector. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0027] like Figure 1-Figure 3 As shown, the utility model provides an array cylindrical focusing laser differential interferometer, and uses relevant optical lens components to build a measuring interferometer. The measuring light path generated by the measuring interferometer includes a transmitting light path and a receiving light path, and the airflow passes through the two, and the measuring light path passes through the area to be measured of the airflow.

[0028] The optical lens components constituting the emission light path include a laser generator, and a first polarizer, a first cylindrical plano-convex lens, a beam splitter, a first Wollaston prism, a second cylindrical plano-convex lens and a first biconvex lens which are sequentially arranged along the propagation direction of the light beam emitted by the laser;

[0029] The heat-generating optical lens components constituting the receiving light path include a second biconvex lens, a third cylindrical plano-convex lens, a second Wollaston prism, a second polarizer, a plano-concave lens and a photodetector which are sequentially arranged along the propagation direction of the light beam.

[0030] The laser generator emits a parallel coherent beam, which passes through the first polarizer P 1 , filtering out the noise light in the coherent beam.

[0031] The light beam passes through the first plano-convex cylindrical mirror C1, which focuses the coherent light beam and then expands it, diverging the light beam in all directions and allowing the light beam to diverge in a single direction, forming a fan-shaped light beam.

[0032] The fan-shaped light beam passes through the beam splitter E, and a coherent light beam is divided into 6 identical coherent fan-shaped light beams A. The separation angle between the 6 coherent fan-shaped light beams A is adjustable; the separation angle determines the distance between the focal points formed after adjacent coherent light passes through the lens; the separation angle can be adjusted according to the detection points in the area to be tested, and the separation angle determines the distance between adjacent monitoring points.

[0033] Six coherent fan-shaped light beams A pass through the first Wollaston prism W1, and each coherent fan-shaped light beam A is further separated into two fan-shaped light beams B with mutually perpendicular polarization directions, and the separation angle between the two fan-shaped light beams B meets the preset requirements; wherein the mutually perpendicular polarization directions are determined by the characteristics of the first Wollaston prism W1, so that all separated light beams B are in a horizontal plane, so that the airflow passes through perpendicular to the optical axis direction, and passes through the two light beams in sequence.

[0034] Each coherent fan-shaped beam A is separated into two fan-shaped beams B with mutually perpendicular polarization directions, so that there is an optical path difference between the two fan-shaped beams B. The optical path difference further leads to a phase difference, which is reflected as a density difference. The relevant data is used for subsequent voltage inversion of density pulsation information.

[0035] The light beam passes through the second plano-convex cylindrical mirror C 2 , converting the 12 unidirectional divergent light beams B back into parallel light beams B; the parallel light beams B pass through the first biconvex lens S 1 , focus 12 parallel light beams B in various directions; and start the wind tunnel so that the focused light beams B pass through the area of ​​the airflow to be tested.

[0036] The light beam passes through the second biconvex lens S 2 , converting the focused beam B back into a parallel beam B; the beam passes through the third cylindrical convex lens C 3 , converting 12 parallel beams B into a unidirectional focused beam B; the beam passes through the second Wollaston prism W2 , the 12 unidirectional focused beams B are recombined into 6 coherent beams C; the coherent beams C pass through the second polarizer P 2 , filter the combined coherent light beam C to obtain a focused light beam with consistent polarization direction; let the two beams interfere to generate interference light intensity, and the relevant data is used for subsequent voltage inversion of density pulsation information.

[0037] The light beam passes through the concave lens V, which expands the filtered coherent light beam C; the first photodetector D 1 , the second photodetector D 2 , the third photodetector D 3 , the fourth photodetector D 4 , the fifth photodetector D 5 and the sixth photodetector D 6 The corresponding light beam C is received, and the light intensity of the light beam C is linearly converted into a voltage signal.

[0038] The two fan-shaped beams B separated by the first Wollaston prism satisfy the following relationship:

[0039]

[0040] Where ΔX 1 is the separation distance between the two fan-shaped beams B, f 2 is the focal length of the second biconvex lens, and σ is the separation angle of the first Wollaston prism.

[0041] In order to make the light beam pass through the center of the optical lens accurately, the required optical lenses are installed in a coaxial system. This ensures that the center of each optical lens is at the same height. At the same time, the coaxial system can be used to easily adjust the axial position of each lens and the distance between them.

[0042] In this embodiment, the spacing between the optical lens elements must also meet the following requirements:

[0043] Among them, L 1 is the distance between the first cylindrical plano-convex lens and the second cylindrical plano-convex lens, is the focal length of the first cylindrical plano-convex lens, is the focal length of the second cylindrical plano-convex lens;

[0044] Among them, L 2 is the distance between the first biconvex lens and the second biconvex lens, is the focal length of the first biconvex lens, is the focal length of the second biconvex lens

[0045] Among them, L 3 is the distance between the third cylindrical plano-convex lens and the plano-concave lens, is the focal length of the third cylindrical plano-convex lens;

[0046] L 4 =f V Among them, L 4 is the distance between the plano-concave lens and the photodetector, f V is the focal length of the plano-concave lens.

[0047] The interferometer is built with multiple optical lenses. In order to allow the light beam to accurately pass through the center of the optical lens, the required optical components are installed in a coaxial system. This ensures that the center of each optical lens is at the same height. At the same time, the coaxial system can be used to easily adjust the axial position of each lens and the distance between them.

[0048] The formula for the density in the flat plate boundary layer is as follows:

[0049]

[0050] Among them, Δρ is the density gradient at the flow field measurement point; ρ L is the average density of the measuring points; 0 is the laser wavelength; π is the circumference of a circle; L is the length of the sensitive area; K is the Gladstone-Dale constant; V is the voltage output by the photodetector; V 0 =2I 0 RR L , I 0 is the intensity of the single laser beam after being split by the first prism, R is the diode sensitivity of the photodetector; R L is the load resistance of the photodetector.

[0051] According to the Gladstone-Dale formula: Where n is the refractive index; ρ is the density; and K is the Gladstone-Dale constant.

[0052] The change in refractive index leads to a change in the optical path difference, which is:

[0053] ΔOPL=(n 1 -n 2 )L=ΔnL; where L is the size of the sensitive area.

[0054] The change of optical path difference leads to the change of phase difference, which is:

[0055]

[0056] Substituting the optical path difference into the formula, we can get the relationship between phase difference and density change:

[0057]

[0058] The formula for calculating light intensity change is:

[0059]

[0060] Where α is the polarizer angle; β is the phase difference change caused by other factors. (Note: Adjust the polarizer angle to 45 degrees; adjust Wollaston to -90°, at I 1 =I 2 In the case of 1 =I 2 =I 0 ,but:

[0061]

[0062] And because the output voltage U: U = IRR L ;

[0063] The output voltage U of the photodetector when the phase difference caused by the flow is 0 0 :U 0 =I 0 RR L , where R is the diode sensitivity; R L is the load resistance.

[0064] Then the relationship between phase difference and voltage is:

[0065]

[0066] Then the density difference and voltage:

[0067]

[0068] Divide both sides by ρ L , we get:

[0069]

[0070] Therefore, the change of density gradient in the flow field can be reflected by the change of voltage in the photodetector.

[0071] A single laser beam emitted by a single laser is divided into multiple laser beams using a diffractive optical element beam splitter, which are then focused at multiple measuring points. The density pulsation information of multiple measuring points in the flat plate boundary layer can be obtained simultaneously each time, greatly reducing the number of experiments, improving the test efficiency of the wind tunnel, and saving test costs.

[0072] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. An array cylindrical focusing laser differential interferometer, characterized in that: The generated measuring optical path includes a transmitting optical path and a receiving optical path, the airflow passes between the two, and the measuring optical path passes through the area to be measured of the airflow; The instrument forming the emission optical path includes: an optical signal emission unit, a beam splitter and multiple groups of optical lenses, forming multiple groups of test optical paths; The instrument forming the receiving optical path includes: multiple groups of optical lenses and photoelectric conversion units, and the photoelectric conversion units receive the optical signals of the test optical path; the photoelectric conversion units are provided with multiple groups, corresponding to the test optical paths; The optical lenses are arranged in parallel, and the center points of the optical lenses are on the same straight line.

2. The array-type cylindrical focusing laser differential interferometer according to claim 1, characterized in that: The optical signal emitting unit is a laser generator; The multiple groups of optical lenses forming the emission light path include a first polarizer, a first cylindrical plano-convex lens, a first Wollaston prism, a second cylindrical plano-convex lens and a first biconvex lens arranged in sequence along the propagation direction of the light beam emitted by the laser, and the beam splitter is arranged between the first cylindrical plano-convex lens and the first Wollaston prism; wherein, The laser generator is used to emit a parallel coherent light beam; The first polarizer is used to filter out noise light in the coherent light beam; The convex mirror of the first cylindrical plano-convex lens is arranged toward the propagation direction of the light beam, and is used to expand the coherent light beam after focusing, and diverge into a fan-shaped light beam; The beam splitter is used to split a fan-shaped light beam into N identical coherent fan-shaped light beams A; The first Wollaston prism is used to further separate each coherent fan-shaped light beam A into two light beams B with polarization directions perpendicular to each other; The convex mirror of the second cylindrical plano-convex lens is arranged toward the propagation direction of the light beam, and the second cylindrical plano-convex cylindrical mirror converts the unidirectional divergent light beam B back into a parallel light beam B; The first biconvex lens focuses the parallel light beam B so that the focused light beam B passes through the area to be measured.

3. The array-type cylindrical focusing laser differential interferometer according to claim 2, characterized in that: The photoelectric conversion unit is a photoelectric detector; The multiple groups of optical lenses forming the receiving light path include a second biconvex lens, a third cylindrical plano-convex lens, a second Wollaston prism, a second polarizer and a plano-concave lens arranged in sequence along the propagation direction of the light beam, and the photodetector is arranged at the end of the receiving light path; wherein, The second biconvex lens is used to convert the focused light beam B back into a parallel light beam B; The convex mirror of the third cylindrical plano-convex lens is arranged toward the propagation direction of the light beam, and is used to convert the parallel light beam B into a unidirectional focused light beam B; The second Wollaston prism is used to refocus and merge the two focused light beams B separated by the fan-shaped light beam A into a coherent light beam C; The second polarizer is used to filter the combined coherent light beam C to obtain a focused light beam with a consistent polarization direction, so that the filtered coherent light beam C can perform phase interference; The plano-concave lens is used to expand the filtered coherent light beam C; The photoelectric detector is used to linearly convert the light intensity of the expanded coherent light beam C into a voltage signal, and each coherent light beam corresponds to a photoelectric detector.

4. The array-type cylindrical focusing laser differential interferometer according to claim 3, characterized in that: The two fan-shaped beams separated by the first Wollaston prism satisfy the following relationship: Wherein, ΔX1 is the separation distance between the two fan-shaped beams, f2 is the focal length of the second biconvex lens, and σ is the separation angle of the first Wollaston prism.

5. The array-type cylindrical focusing laser differential interferometer according to claim 3, characterized in that: The spacing of optical lens components meets the following requirements: Wherein, L1 is the distance between the first cylindrical plano-convex lens and the second cylindrical plano-convex lens, is the focal length of the first cylindrical plano-convex lens, is the focal length of the second cylindrical plano-convex lens; Wherein, L2 is the distance between the first biconvex lens and the second biconvex lens, is the focal length of the first biconvex lens, is the focal length of the second biconvex lens Wherein, L3 is the distance between the third cylindrical plano-convex lens and the plano-concave lens, is the focal length of the third cylindrical plano-convex lens; L4=f V ; Where L4 is the distance between the plano-concave lens and the photodetector, f V is the focal length of the plano-concave lens.

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