CN116106023A - A three-dimensional test device and test method for liquid film fluctuation frequency - Google Patents

Abstract

The invention provides a three-dimensional testing device and testing method for the fluctuation frequency of a liquid film, belonging to the field of gas turbines and internal combustion engines. This method uses a laser generator to emit a continuous laser beam to the surface of the liquid film, and the laser beam is reflected on the surface of the liquid film. Two photodetectors are arranged in space to receive the laser signals reflected by the fluctuations of the liquid film in different directions. During the entire fluctuation cycle, there are only one or two specific positions on the surface of the liquid film that allow the photodetectors to receive the reflected laser light. Signal; the photodetector converts the laser signal into an electrical signal, and uses a computer to convert the electrical signal converted by the photodetector into a frequency domain signal through a fast Fourier transform, and then obtain the fluctuation frequency of a single point and each fluctuation direction of the liquid film . The invention can measure the three-dimensional fluctuation frequency of the liquid film ejected from centrifugal nozzles, pre-film nozzles, direct nozzles and other nozzles, and the measurement results can be used to analyze the initial atomization characteristics of the nozzles and guide the optimal design of the nozzles.

Description

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

technical field

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

Background technique

In order to burn liquid fuel quickly and efficiently, the fuel must be atomized to form a liquid mist. The centrifugal nozzle is a fuel atomization device widely used in the combustion chamber of aero-engines. The atomization process includes the formation of a liquid film, the liquid film generates axial and circumferential unstable fluctuations and separates into liquid strips, and the liquid strips are further broken into droplets. . The pre-film nozzle can enhance the fuel atomization effect and reduce pollutant emissions; its working process is: the fuel passes through the inner pre-film channel to form a liquid film, and the shearing action of the high-speed airflow on both sides makes the liquid film produce different axial and lateral directions. Stable fluctuations, the liquid film forms a liquid ribbon under the action of lateral fluctuations, and the liquid ribbon is further broken to form droplets.

The above-mentioned fluctuation frequency of the liquid film is an important parameter to characterize the characteristics of the initial atomization of the liquid film. At present, the methods for measuring the fluctuation frequency of the liquid film mainly include: 1) Use a high-speed camera to take the corresponding view of the liquid film, and use methods such as POD to analyze the gray scale variation law in the view to obtain the fluctuation frequency of the liquid film. 2) Use the pressure sensor to obtain the acoustic signal related to the liquid film fluctuation, and then perform fast Fourier transform on the obtained acoustic signal to obtain the periodic spectrum signal, so as to obtain the liquid film fluctuation frequency. 3) The frequency of liquid film fluctuations was measured by Plane Induced Fluorescence (PLIF). 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 separately measure the fluctuation frequency of the liquid film along each direction. Therefore, the present invention proposes a method for measuring the fluctuation frequency of the liquid film along various directions by using a laser.

Contents of the invention

In order to measure the three-dimensional fluctuation frequency of the liquid film, the present invention proposes a three-dimensional test method using laser to measure the fluctuation frequency of the liquid film. The method can be used to measure the liquid film in the atomization process of centrifugal nozzles, pre-film nozzles, and direct nozzles. The frequency of membrane fluctuations was tested.

The present invention is achieved like this:

The invention discloses a three-dimensional testing device and testing method for the fluctuation frequency of a liquid film. The device includes a computer in a three-dimensional scene, a three-dimensional coordinate frame, a laser generator, a photoelectric detector, and a liquid film surface.

The test method described is:

1) Using a laser generator as a point light source, a continuous laser beam is emitted to the surface of the liquid film at a certain distance from the nozzle outlet. (In order 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 other The influence of the light source on the measurement signal. In order to avoid the mutual interference of the laser signals reflected by the fluctuation of the liquid film in different directions, it should be avoided that the photodetector receives the laser signals reflected by the peaks and troughs).

2) Two photodetectors are set in the three-dimensional space, one photodetector receives the optical signal reflected by the axial wave of the liquid film, and the other photodetector receives the optical signal reflected by the circumferential/transverse wave of the liquid film, and the general photodetector samples The frequency should be 20 times higher than the fluctuation frequency of the liquid film.

3) Since the positions of the laser generator (incident point) and the photodetector (receiving point) are fixed, the mirror angle of laser reflection changes continuously with the fluctuation of the liquid film, and only one mirror angle in a fluctuation cycle can ensure the reflected light and photoelectric detection. The line connecting the detector and the reflection point on the surface of the liquid film is collinear, and the photodetector can receive the laser signal reflected by the liquid film. At this time, the incident light, reflected light, and the normal three lines 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.

4) The photodetector converts the received optical signal into a corresponding electrical signal.

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 change frequency of the photodetector signal, and further obtain the liquid film at the intersection of the incident light and the liquid film surface (If the intersection point of the incident light and the surface of the liquid film is at half the wavelength of the liquid film fluctuation, and there is no other point on the liquid film surface with the same angle as the reflector at this point within one period, the frequency of the solid-liquid film fluctuation is the same as The change frequency of the photodetector signal is the same. In the rest of the cases, there are two specific positions on the surface of the liquid film that have the same angle as the mirror face angle so that the reflected light, the photodetector and the connection line of the point are collinear, and the fluctuation frequency of the solid-liquid film is photoelectric half of the detector signal change frequency).

6) The laser generator and two photodetectors are fixed on the three-dimensional coordinate frame, and the three-dimensional coordinate frame is driven by a stepping motor, so as to realize the free movement of the position of the liquid film measuring point; repeat steps 1) to 5), and the liquid film The fluctuation frequency of multiple points on the surface is automatically scanned and measured, and finally the overall fluctuation characteristics of the liquid film are obtained.

Compared with the prior art, the present invention has the following advantages: using laser to measure the fluctuation frequency of the liquid film can measure the fluctuation frequency of each fluctuation direction of the liquid film respectively, thereby providing more references for analyzing the initial atomization characteristics of the nozzle; at the same time, the measuring device is fixed on the three-dimensional coordinates On the frame, the three-dimensional coordinate frame is driven by a stepping motor, so as to automatically realize the three-dimensional measurement of the fluctuation frequency of the entire liquid film.

The beneficial effect of the present invention and the prior art is that the three-dimensional test method of the present invention can be used to experimentally measure the liquid film fluctuation frequency in the atomization process of centrifugal nozzles, pre-film nozzles, direct nozzles and other nozzles, so as to reflect the initial The atomization characteristics guide the optimal design of the nozzle.

Description of drawings

Fig. 1 is the schematic diagram of liquid film fluctuation frequency testing system in the embodiment of the present invention;

2 is a schematic diagram of the principle of using laser to measure the fluctuation frequency of liquid film in the embodiment of the present invention;

Fig. 3 is a schematic diagram of testing the axial fluctuation frequency of the centrifugal nozzle liquid film in the embodiment of the present invention;

Fig. 4 is a schematic diagram of testing the circumferential fluctuation frequency of the centrifugal nozzle liquid film in the embodiment of the present invention;

Fig. 5 is a schematic diagram of testing the axial fluctuation frequency of the liquid film of the pre-film nozzle in the embodiment of the present invention;

Fig. 6 is a schematic diagram of testing the lateral fluctuation frequency of the liquid film of the pre-film nozzle in the embodiment of the present invention;

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

Detailed ways

In order to make the object, technical solution and effect of the present invention clearer and clearer, the following examples are given to further describe the present invention in detail. It should be pointed out that the specific implementations described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, the liquid film fluctuation frequency testing system of the present invention comprises a computer 1 in a three-dimensional scene, a three-dimensional coordinate frame 2, a laser generator 3, a first photodetector 4, a second photodetector 5, and a liquid film surface 6. Using the laser generator 3 as a point light source, a continuous laser beam is emitted to the surface of the liquid film 6 at a certain distance from the nozzle outlet, and two photodetectors arranged at different positions in space are used to receive the laser light reflected by the fluctuation of the liquid film in different directions. Signal (generally the photodetector sampling frequency should be 20 times higher than 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 surface of the liquid film can be approximately regarded as a specular reflection. As shown in Figure 2, since the positions of the laser generator (incident point) and the photodetector (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 , only one mirror angle can ensure that the reflected light, the photodetector and the reflection point on the surface of the liquid film are collinear in a fluctuation cycle, and the photodetector can receive the laser signal reflected by the liquid film, and the photodetector cannot receive the laser signal reflected by the liquid film in other cases. Laser signal reflected by the liquid film.

The photodetector converts the received optical 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 to obtain the change frequency of the photodetector signal. Then the fluctuation frequency of the liquid film is obtained (if the intersection point of the incident light and the liquid film surface is at the half wavelength of the liquid film fluctuation, there is no other point on the liquid film surface with the same angle as the mirror at this point within one cycle, and the solid-liquid The film fluctuation frequency is the same as the photodetector signal change frequency. In the rest of the cases, there are two specific positions on the surface of the liquid film with the same angle of reflection mirror in one cycle so that the reflected light, the photodetector and the connection line of the point are collinear, and the solid-liquid film The fluctuating frequency is one-half of the changing frequency of the photodetector signal).

The test schematic diagram of the axial fluctuation frequency of the centrifugal nozzle liquid film is shown in Figure 3. The point light source emits light beams 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 peaks and valleys), the photodetector can just receive the light signal reflected by the surface of the liquid film. . Define the angle between the incident light and the reflected light at this time as β, the angle bisector of the β angle is collinear with the normal line of the liquid film axial wave at the reflection point, and the size of the β angle varies with the incident angle (with the point The position of the light source and the irradiation point of the point light source on the surface of the liquid film are related to changes, and the range of change is 0 to 180 degrees.

The test schematic diagram of the circumferential fluctuation frequency of the liquid film of the centrifugal nozzle is shown in Figure 4, which is a cross-sectional view of a certain axial position. In order to avoid mutual interference between multiple beams of incident light 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 that of the measurement of the axial fluctuation frequency. The second photodetector is used to receive the optical signal reflected by the circumferential wave, and the incident light, the normal line of the circumferential wave at point a, and the connecting line between the second photodetector and point a are in the same plane. Define the included angle between the incident light, the second photodetector and the point a as α, the angle bisector of the α angle is collinear with the normal line of the liquid film circumferential wave at the reflection point, and the size of the α angle varies with the incident angle The change of the temperature ranges from 0 to 180 degrees.

The test schematic diagram of the axial fluctuation frequency of the pre-film nozzle is shown in Figure 5, and the test schematic diagram of the transverse fluctuation frequency is shown in Figure 6. Its principle is the same as the measurement of the fluctuation frequency of the centrifugal nozzle liquid film. The point light source shines on point c on the surface of the liquid film (point c is any point except the peak and valley), the photodetector c is used to receive the optical signal reflected by the axial wave of the liquid film, the incident light, the reflected light, the photodetector c and point c is collinear. When the photodetector receives the reflected signal, the angle between the incident light and the reflected light is γ, the angle bisector of the γ angle is collinear with the normal line of the liquid film axial wave at the reflection point, and the γ angle varies with the incident angle The change varies from 0 to 180 degrees. The photodetector d is used to receive the optical signal reflected by the transverse wave of the liquid film, and the incident light, reflected light, photodetector d and point c are collinear. Define the angle between the incident light and the line connecting the photodetector d and point c as δ, the angle bisector of the δ angle is collinear with the normal line of the liquid film transverse wave at the reflection point, and the change of the δ angle with the incident angle is in 0 ~ 180 degrees change.

A computer is used to perform fast Fourier transform on the signal measured by the photodetector in the above arrangement to obtain the fluctuation frequency of a single point and different fluctuation directions of the liquid film. The laser generator and all photodetectors are fixed on the three-dimensional coordinate frame, and the three-dimensional coordinate frame is driven by the stepping motor, so as to realize the automatic scanning measurement of the fluctuation frequency of multiple measurement points on the liquid film surface. According to the above method, the fluctuation frequency of multiple points on the surface of the liquid film can be measured to analyze the overall fluctuation law of the liquid film, which can be used to support the study of the initial atomization characteristics of the nozzle and guide the optimal design of the nozzle.

The above description is only a preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements can also be made, and these improvements should also be regarded as the present invention. protection scope of the invention.

Claims (5)

1. A three-dimensional testing device and testing method for liquid film fluctuation frequency, characterized in that the device includes a computer (1) in a three-dimensional scene, a three-dimensional coordinate frame (2), a laser generator (3), a photoelectric detector device, The test method described is: Step 1, using the laser generator (3) as a point light source to emit a continuous laser beam to the surface of the liquid film; Step 2, the photodetector receives the laser signal reflected by the fluctuation of the liquid film surface; the laser generator (3) ) as the incident point of the laser beam, and the photodetector as the receiving point of the laser signal, and the positions of the incident point and the receiving point are fixed; Step 3. The surface of the liquid film is equivalent to mirror reflection. When the surface of the liquid film fluctuates, the mirror angle of the laser reflection changes continuously with the fluctuation of the liquid film. Only one mirror angle in a fluctuation cycle can ensure the reflection of light, the photoelectric detector and the liquid. The connecting lines of the reflection points on the surface of the film are collinear, and the photodetector can receive the laser signal reflected by the liquid film. At this time, the three normal lines of the incident light, reflected light, and wave at the intersection of the incident light and the liquid film surface are coplanar, and The angle of incidence is equal to the angle of reflection; Step 4, the photodetector converts the received laser signal into an electrical signal; Step 5, using a computer to perform fast Fourier transform on the electrical signal converted by the photodetector to convert it into a frequency domain signal, and then obtain the fluctuation frequency of the liquid film; Step 6. Move the position of the liquid film measurement point, repeat steps 1 to 5, and automatically scan and measure the fluctuation frequency of multiple points on the liquid film surface, and finally obtain the overall fluctuation characteristics of the liquid film. 2. A three-dimensional test device and test method for liquid film fluctuation frequency according to claim 1, characterized in that the photodetectors are set as the first photodetectors (4) in two different directions, The second photodetector (5); the first photodetector (4) and the second photodetector (5) are respectively used to receive the laser signals reflected by the liquid film surface fluctuations in different directions, so as to detect the liquid film single point, The fluctuation frequency of each fluctuation direction is measured, and the sampling frequency of the photodetector is 20 times higher than the fluctuation frequency of the liquid film; one of the photodetectors in two different directions is used to receive the optical signal reflected by the axial wave of the liquid film, and the other is used to Receive the optical signal reflected by the circumferential/transverse wave of the liquid film. 3. A three-dimensional testing device and testing method for liquid film fluctuating frequency according to claim 1, characterized in that a laser generator (3) is installed at the entrance of the photoelectric detector to emit a laser filter with a corresponding wavelength , to avoid the influence of other light sources on the measurement signal. 4. A three-dimensional test device and test method for liquid film fluctuation frequency according to claim 1, characterized in that, the measurement result of the test method is: if the incident light of the laser generator (3) and the liquid film The intersection point of the surface is at half the wavelength of the liquid film fluctuation, and the liquid film fluctuation frequency is the same as the photodetector signal change frequency; in other cases, the liquid film fluctuation frequency is one half of the photodetector signal change frequency. 5. A three-dimensional testing device and testing method for liquid film fluctuation frequency according to claim 1, characterized in that the laser generator (3) and the photodetector are fixed on the three-dimensional coordinate frame (2), The three-dimensional coordinate frame is driven by the stepping motor to realize the automatic scanning measurement of the three-dimensional fluctuation frequency of multiple measurement points on the surface of the liquid film, and finally obtain the overall fluctuation characteristics of the liquid film.

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