A three-dimensional testing device and testing method for liquid film fluctuation frequency

Abstract

This invention provides a three-dimensional testing device and method for measuring the fluctuation frequency of liquid films, belonging to the field of gas turbines and internal combustion engines. The method uses a laser generator to emit a continuous laser beam onto the surface of the liquid film, which is reflected. Two photodetectors are arranged in space to receive the laser signals reflected from the fluctuations of the liquid film in different directions. Throughout the fluctuation period, only one or two specific locations on the liquid film surface allow the photodetectors to receive the reflected laser signals. The photodetectors convert the laser signals into electrical signals. Using a computer, a fast Fourier transform is used to convert the electrical signals obtained from the photodetectors into frequency domain signals, thereby obtaining the fluctuation frequency of the liquid film at a single point in each fluctuation direction. This invention can measure the three-dimensional fluctuation frequency of liquid films ejected from nozzles such as centrifugal nozzles, pre-filming nozzles, and direct-fire nozzles. The measurement results can be used to analyze the initial atomization characteristics of the nozzles and guide the optimized design of the nozzles.

Description

Technical Field

[0001] The invention belongs to the field of gas turbines and internal combustion engines, and relates to a three-dimensional testing device and a testing method for liquid film fluctuation frequency. Background Art

[0002] In order to make liquid fuel burn quickly and efficiently, the fuel must be atomized to form liquid mist. Centrifugal nozzles are currently widely used in fuel atomization devices in aircraft engine combustion chambers. The atomization process includes the formation of a liquid film, the separation of the liquid film into liquid strips due to axial and circumferential unstable fluctuations, and the further breaking of the liquid strips into droplets. The pre-filming nozzle can enhance the fuel atomization effect and reduce pollutant emissions; its working process is as follows: the fuel forms a liquid film through the inner pre-filming channel, and the shearing effect of the high-speed airflow on both sides causes the liquid film to produce unstable fluctuations in the axial and lateral directions. The liquid film forms a liquid band under the action of lateral fluctuations, and the liquid band is further broken into droplets.

[0003] The fluctuation frequency of the above-mentioned liquid film is an important parameter to characterize the initial atomization characteristics of the liquid film. At present, the main methods for measuring the fluctuation frequency of the liquid film are: 1) Use a high-speed camera to shoot the corresponding view of the liquid film, and use POD and other methods to analyze the grayscale change law in the view to obtain the fluctuation frequency of the liquid film. 2) Use a pressure sensor to obtain the sound signal related to the fluctuation of the liquid film, and then perform a fast Fourier transform on the obtained sound signal to obtain a periodic spectrum signal, thereby obtaining the fluctuation frequency of the liquid film. 3) Use the plane induced fluorescence technology (PLIF) to measure the fluctuation frequency of the liquid film. 4) Study the attenuation law of the laser beam after passing through the liquid film to measure the fluctuation frequency of the liquid film. The above methods can only measure the overall fluctuation frequency of the liquid film, but cannot measure the fluctuation frequency of the liquid film in each direction separately. Therefore, the present invention proposes a method for measuring the fluctuation frequency of the liquid film in each direction using a laser. Summary of the invention

[0004] In order to measure the three-dimensional fluctuation frequency of the liquid film, the present invention proposes a three-dimensional testing method for measuring the fluctuation frequency of the liquid film using laser. The method can be used to test the fluctuation frequency of the liquid film in the atomization process of centrifugal nozzles, pre-film nozzles, direct nozzles, etc.

[0005] The present invention is achieved in that:

[0006] The present invention discloses a three-dimensional testing device and method for liquid film fluctuation frequency. The device comprises a computer, a three-dimensional coordinate frame, a laser generator, a photoelectric detector and a liquid film surface in a three-dimensional scene.

[0007] The test method described is:

[0008] 1) Use a laser generator as a point light source to emit a continuous laser beam to the surface of the liquid film at a certain distance from the nozzle outlet. (To avoid mutual interference between different incident light rays and simplify the test system, only one point light source is set; at the same time, the light source is a laser of a certain wavelength, and a filter of the wavelength laser is installed at the entrance of the photodetector to avoid the influence of other light sources on the measurement signal. To avoid mutual interference between laser signals reflected by fluctuations in different directions of the liquid film, the photodetector should avoid receiving laser signals reflected from the peaks and troughs).

[0009] 2) Two photodetectors are set in three-dimensional space, one photodetector receives the light signal reflected by the axial wave of the liquid film, and the other photodetector receives the light signal reflected by the circumferential / lateral wave of the liquid film. Generally, the sampling frequency of the photodetector should be 20 times higher than the fluctuation frequency of the liquid film.

[0010] 3) Since the laser generator (incident point) and the photodetector (receiving point) are fixed in position, the mirror angle of laser reflection changes continuously with the fluctuation of the liquid film. In one fluctuation cycle, only one mirror angle can ensure that the lines connecting the reflected light, the photodetector and the reflection point on the liquid film surface are collinear, and the photodetector can receive the laser signal reflected by the liquid film. At this time, the three lines of the incident light, the reflected light and the normal line of the wave at the intersection of the incident light and the liquid film surface are coplanar, and the incident angle is equal to the reflection angle.

[0011] 4) The photodetector converts the received light signal into a corresponding electrical signal.

[0012] 5) Using a computer, through fast Fourier transform, the electrical signal converted by the photodetector is converted into a frequency domain signal to obtain the changing frequency of the photodetector signal, and further obtain the fluctuation frequency of the liquid film at the intersection of the incident light and the liquid film surface (if the intersection of the incident light and the liquid film surface is at half the wavelength of the liquid film fluctuation, there is no other point on the liquid film surface with the same mirror angle as that point within one cycle, and the solid-liquid film fluctuation frequency is the same as the photodetector signal changing frequency. In other cases, there are two specific positions on the liquid film surface with the same mirror angle within one cycle, so that the line connecting the reflected light, the photodetector and the point is collinear, and the solid-liquid film fluctuation frequency is half of the photodetector signal changing frequency).

[0013] 6) The laser generator and two photodetectors are fixed on a three-dimensional coordinate frame, which is driven by a stepper motor to achieve free movement of the liquid film measuring point position; steps 1) to 5) are repeated to automatically scan and measure the fluctuation frequency of multiple points on the liquid film surface, and finally the overall fluctuation characteristics of the liquid film are obtained.

[0014] The present invention has the following advantages over the prior art: by using laser to measure the fluctuation frequency of the liquid film, the fluctuation frequency of each fluctuation direction of the liquid film can be measured respectively, thereby providing more references for analyzing the initial atomization characteristics of the nozzle; at the same time, the measuring device is fixed on a three-dimensional coordinate frame, and the three-dimensional coordinate frame is driven by a stepping motor, thereby automatically realizing three-dimensional measurement of the entire liquid film fluctuation frequency.

[0015] The beneficial effect of the present invention over the prior art is that the three-dimensional testing method of the present invention can be used to experimentally measure the liquid film fluctuation frequency during the atomization process of nozzles such as centrifugal nozzles, pre-film nozzles, and direct-injection nozzles, thereby reflecting the initial atomization characteristics of the nozzle and guiding the optimal design of the nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a liquid film fluctuation frequency testing system in an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the principle of measuring the liquid film fluctuation frequency by using laser in an embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the centrifugal nozzle liquid film axial fluctuation frequency test in an embodiment of the present invention;

[0019] Figure 4 Schematic diagram of the test of the circumferential fluctuation frequency of the liquid film of the centrifugal nozzle in the embodiment of the present invention;

[0020] Figure 5 Schematic diagram of the test of axial fluctuation frequency of the liquid film of the pre-filming nozzle in an embodiment of the present invention;

[0021] Figure 6 Schematic diagram of the test of the lateral fluctuation frequency of the liquid film of the pre-filming nozzle in an embodiment of the present invention;

[0022] Among them, 1-computer, 2-three-dimensional coordinate frame, 3-laser generator, 4-first photodetector, 5-second photodetector, 6-liquid film surface DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail by enumerating examples below. It should be noted that the specific implementation described here is only used to explain the present invention and is not used to limit the present invention.

[0024] like Figure 1As shown, the liquid film fluctuation frequency test system of the present invention includes a computer 1, a three-dimensional coordinate frame 2, a laser generator 3, a first photodetector 4, a second photodetector 5, and a liquid film surface 6 in a three-dimensional scene. The laser generator 3 is used as a point light source to emit a continuous laser beam to the liquid film surface 6 at a certain distance from the nozzle outlet, and two photodetectors arranged at different positions in space are used to respectively receive laser signals reflected by the fluctuations of the liquid film in different directions (generally, the sampling frequency of the photodetector should be higher than 20 times the fluctuation frequency of the liquid film). Since the local small area of ​​the liquid film is approximately smooth, the reflection of the laser on the liquid film surface can be approximately regarded as mirror reflection. Figure 2 Since the positions of the laser generator (incident point) and the photoelectric detector (receiving point) are fixed, the surface of the liquid film is equivalent to mirror reflection. When the liquid film fluctuates, the mirror angle of the laser reflection changes continuously with the fluctuation of the liquid film. In one fluctuation cycle, only one mirror angle can ensure that the line connecting the reflected light, the photoelectric detector and the reflection point on the surface of the liquid film is collinear, and the photoelectric detector can receive the laser signal reflected by the liquid film. In other cases, the photoelectric detector cannot receive the laser signal reflected by the liquid film.

[0025] The photodetector converts the received light signal into a corresponding electrical signal, and uses a computer to perform fast Fourier transform on the electrical signal converted by the photodetector to convert it into a frequency domain signal, thereby obtaining the changing frequency of the photodetector signal, and then obtaining the fluctuation frequency of the liquid film (if the intersection of the incident light and the liquid film surface is at half the wavelength of the liquid film fluctuation, and there is no other point on the liquid film surface with the same reflection mirror angle as that point within one cycle, the solid-liquid film fluctuation frequency is the same as the photodetector signal change frequency. In other cases, there are two specific positions on the liquid film surface with the same reflection mirror angle within one cycle, so that the line connecting the reflected light, the photodetector and the point are collinear, and the solid-liquid film fluctuation frequency is half of the photodetector signal change frequency).

[0026] The test diagram of the axial fluctuation frequency of the centrifugal nozzle liquid film is as follows: Figure 3 As shown. A point light source emits a light beam to the surface of the liquid film. When the point light source irradiates point a on the surface of the liquid film (point a is any point on the surface of the liquid film except the crests and troughs), the photoelectric detector can just receive the light signal reflected from the surface of the liquid film. The angle between the incident light and the reflected light is defined as β. The bisector of angle β is collinear with the normal of the axial wave of the liquid film at the reflection point. The size of angle β changes with the change of the incident angle (related to the position of the point light source and the irradiation point of the point light source on the surface of the liquid film), and the range of change is 0 to 180 degrees.

[0027] The test diagram of the circumferential fluctuation frequency of the centrifugal nozzle liquid film is shown in the figure. Figure 4The figure shows a cross-sectional view at a certain axial position. In order to avoid mutual interference between multiple incident light beams and simplify the test system, the measurement of the circumferential fluctuation frequency and the measurement of the axial fluctuation frequency share a point light source, and the test principle is the same as the measurement of the axial fluctuation frequency. The second photodetector is used to receive the light signal reflected by the circumferential wave. The incident light, the normal of the circumferential wave at point a, and the line connecting the second photodetector and point a are coplanar. The angle between the incident light, the line connecting the second photodetector and point a is defined as α, and the bisector of angle α is colinear with the normal of the circumferential wave of the liquid film at the reflection point. The size of angle α varies from 0 to 180 degrees with the change of the incident angle.

[0028] The test diagram of the axial fluctuation frequency of the pre-filming nozzle is shown in the figure. Figure 5 As shown, the test diagram of the lateral fluctuation frequency is as follows Figure 6 As shown. Its principle is the same as the measurement of the fluctuation frequency of the liquid film in a centrifugal nozzle. A point light source is irradiated to point c on the surface of the liquid film (point c is any point except the peak and trough of the wave), and the photodetector c is used to receive the light signal reflected by the axial wave of the liquid film. The incident light, the reflected light, the photodetector c and the line connecting point c are collinear. It is defined that the angle between the incident light and the reflected light when the photodetector receives the reflected signal is γ, and the bisector of the γ angle is collinear with the normal of the axial wave of the liquid film at the reflection point. The γ angle changes from 0 to 180 degrees with the change of the incident angle. The photodetector d is used to receive the light signal reflected by the transverse wave of the liquid film. The incident light, the reflected light, the photodetector d and the line connecting point c are collinear. It is defined that the angle between the incident light, the photodetector d and the line connecting point c is δ, and the bisector of the δ angle is collinear with the normal of the transverse wave of the liquid film at the reflection point. The δ angle changes from 0 to 180 degrees with the change of the incident angle.

[0029] The signal measured by the photoelectric detector in the above arrangement is fast Fourier transformed by a computer to obtain the fluctuation frequency of a single point of the liquid film and in different fluctuation directions. The laser generator and all photoelectric detectors are fixed on a three-dimensional coordinate frame, and the three-dimensional coordinate frame is driven by a stepper motor to realize automatic scanning measurement of the fluctuation frequency of multiple measurement points on the surface of the liquid film. By measuring the fluctuation frequency of multiple points on the surface of the liquid film according to the above method, the overall fluctuation law of the liquid film can be analyzed to support the study of the initial atomization characteristics of the nozzle and guide the optimization design of the nozzle.

[0030] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A testing method for a three-dimensional testing device of a liquid film fluctuation frequency, characterized in that: The device comprises a computer (1) in a three-dimensional scene, a three-dimensional coordinate frame (2), a laser generator (3), and a photoelectric detector. The test method described is: Step 1: using a laser generator (3) as a point light source to emit a continuous laser beam to the surface of the liquid film; Step 2: a photoelectric detector receives a laser signal reflected by the fluctuation of the surface of the liquid film; the laser generator (3) is used as the incident point of the laser beam, and the photoelectric detector is used as the receiving point of the laser signal, and the positions of the incident point and the receiving point are fixed; Step 3: The liquid film surface is equivalent to mirror reflection. When the liquid film surface fluctuates, the mirror angle of laser reflection changes continuously with the fluctuation of the liquid film. In one fluctuation cycle, only one mirror angle can ensure that the lines connecting the reflected light, the photoelectric detector and the reflection point on the liquid film surface are collinear. The photoelectric detector can receive the laser signal reflected by the liquid film. At this time, the incident light, the reflected light and the normal line of the wave at the intersection of the incident light and the liquid film surface are coplanar, and the incident angle is equal to the reflection angle. Step 4: The photodetector converts the received laser signal into an electrical signal; Step 5: Use a computer to perform fast Fourier transform on the electrical signal converted by the photodetector to convert it into a frequency domain signal, thereby obtaining the fluctuation frequency of the liquid film; Step 6: Move the measuring point of the liquid film, repeat steps 1 to 5, automatically scan and measure the fluctuation frequency of multiple points on the surface of the liquid film, and finally obtain the overall fluctuation characteristics of the liquid film.

2. The testing method of a three-dimensional testing device for liquid film fluctuation frequency according to claim 1, characterized in that: The photoelectric detector is configured as a first photoelectric detector (4) and a second photoelectric detector (5) in two different directions; the first photoelectric detector (4) and the second photoelectric detector (5) are respectively used to receive laser signals reflected by the fluctuations on the surface of the liquid film in different directions, thereby respectively measuring the fluctuation frequencies of a single point of the liquid film and in each fluctuation direction, and the sampling frequency of the photoelectric detector is 20 times higher than the fluctuation frequency of the liquid film; one of the photoelectric detectors in the two different directions is used to receive the light signal reflected by the axial wave of the liquid film, and the other is used to receive the light signal reflected by the circumferential / lateral wave of the liquid film.

3. The testing method of a three-dimensional testing device for liquid film fluctuation frequency according to claim 1, characterized in that: The laser generator (3) is installed at the entrance end of the photoelectric detector to emit a filter for laser light of corresponding wavelength, so as to avoid the influence of other light sources on the measurement signal.

4. The testing method of a three-dimensional testing device for liquid film fluctuation frequency according to claim 1, characterized in that: The measurement result of the test method is: if the intersection point of the incident light of the laser generator (3) and the liquid film surface is at half the wavelength of the liquid film fluctuation, the liquid film fluctuation frequency is the same as the photoelectric detector signal change frequency; in other cases, the liquid film fluctuation frequency is half the photoelectric detector signal change frequency.

5. The testing method of a three-dimensional testing device for liquid film fluctuation frequency according to claim 1, characterized in that: The laser generator (3) and the photoelectric detector are fixed on the three-dimensional coordinate frame (2), and the three-dimensional coordinate frame is driven by a stepping motor to realize automatic scanning measurement of the three-dimensional fluctuation frequency of multiple measurement points on the surface of the liquid film, and finally obtain the fluctuation characteristics of the entire liquid film.

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