An optical test system and test method for measuring the total temperature of a supersonic combustion flow field

Abstract

The present invention discloses an optical test system and test method for measuring the total temperature of a supersonic combustion flow field, which relates to the field of combustion flow field measurement. The system includes: a supersonic combustion incoming flow, a timing synchronizer, a first laser, a first focusing lens, a first total reflection flat mirror, a second laser, a second focusing lens, a sheet light lens, a second total reflection flat mirror, a computer, an ICCD, a tunable laser diode, a laser controller, a photodetector, an industrial control computer, and a signal monitor. Based on non-contact optical testing technology, the present invention obtains the local total temperature by simultaneously measuring the flow velocity and static temperature of the combustion flow field without destroying the flow structure and combustion state of the combustion flow field, will not cause obvious influence on the structure of the supersonic combustion flow field, will not cause unnecessary oblique shock waves, and will not affect the local and downstream flow and combustion states of the measured combustion flow field.

Description

Technical Field

[0001] The present invention relates to the field of combustion flow field measurement, and specifically, to an optical test system and test method for measuring the total temperature of a supersonic combustion flow field. Background Art

[0002] The total temperature can be used to reflect the important parameter of combustion efficiency in the field of supersonic combustion. For an engine, it can further reflect the performance of the combustion chamber. Therefore, the total temperature is a key test parameter in the fields of combustion basic science and engineering applications. Nowadays, the main method for measuring the total temperature is the contact measurement technology of the total temperature probe. For example, the next-generation wind tunnel test facility (NG-Turb) reported by the German Aerospace Center (DLR) in 2023 reflects all the boundary conditions of the facility with three parameters: mass flow rate, total temperature, and total pressure. The total temperature measurement method mentioned therein is still the immersion pneumatic probe. For detailed information, see the literature Andreas Pahs, Anna-Samira Franz-Xaver Torsten Wolf, Turbine operation and measurement at DLRs next generation turbine test facility[C], Proceedings of ASME Turbo Expo 2023, GT2023-102118. This contact method of the pneumatic probe has a very obvious impact on the supersonic flow field structure, which will cause unnecessary oblique shock waves, and then affect the flow and combustion states at the local and downstream positions of the probe. Summary of the Invention

[0003] Based on the non-contact optical test technology, the present invention obtains the local total temperature by simultaneously measuring the flow velocity and static temperature of the combustion flow field without destroying the flow structure and combustion state of the combustion flow field, providing a new idea for measuring the total temperature of the supersonic combustion flow field, and further providing a new test device and method for quantifying the combustion efficiency and evaluating the performance of the engine combustion chamber.

[0004] To achieve the above-mentioned invention purpose, the present invention provides an optical test system for measuring the total temperature of a supersonic combustion flow field, and the system includes:

[0005] Supersonic combustion incoming flow, timing synchronizer, first laser, first focusing lens, first total reflection flat mirror, second laser, second focusing lens, sheet light lens, second total reflection flat mirror, computer, ICCD, tunable laser diode, laser controller, photodetector, industrial control computer, and signal monitor;

[0006] Among them, the supersonic combustion incoming flow forms a measured combustion flow field in a preset area to provide an object for test measurement; a timing synchronizer is used to control the timing relationship among various components in the system; a first laser is used to generate a first pulsed laser, and the first pulsed laser is focused by a first focusing lens and then irradiated onto a first total reflection flat mirror, and the laser after being reflected by the first total reflection flat mirror is irradiated into the measured combustion flow field; a second laser is used to generate a second pulsed laser, and the second pulsed laser is focused by a second focusing lens and then irradiated onto a sheet light lens, and the sheet light lens processes the focused laser into sheet light, and the sheet light is irradiated into the measured combustion flow field after being reflected by a second total reflection flat mirror; a tunable laser diode is used to generate a laser that scans at a fixed frequency within a preset range; a laser controller is used to control the output wavelength and frequency of the tunable laser diode; a photodetector is used to receive the signal after the laser emitted by the tunable laser diode passes through the measured combustion flow field; an industrial control computer is used to control the laser controller, collect and store the signal information transmitted by the photodetector, and process the near-infrared band absorption spectrum test data in the signal information; a signal monitor is used to monitor the near-infrared band absorption spectrum test data.

[0007] Among them, the principle of the present invention is as follows: water molecules in the combustion flow field can be laser-marked, and after marking, the flow velocity of the combustion flow field is calculated by recording the displacement of the marked molecules within a known time; water molecules can absorb the energy of a laser in a certain infrared band, and the static temperature of the combustion flow field in the absorption region can be calculated through the absorption intensity of the absorbed infrared light; after obtaining the static temperature and flow velocity of the combustion flow field, the two key parameters of the Mach number and total temperature of the supersonic combustion flow field, namely the Mach number and total temperature of the combustion flow field, can be obtained according to the relationship among the static temperature, flow velocity, sound speed, Mach number, and total temperature of the combustion flow field.

[0008] Among them, in the embodiment of the present invention, the system further includes: an oscilloscope, and the oscilloscope is used to check the timing relationship among the first laser, the second laser, the ICCD, and the tunable laser diode.

[0009] Among them, in the embodiment of the present invention, a timing synchronizer is used to control the timing relationship among various components in the system. Specifically, the timing synchronizer is used to control the first laser and the tunable laser diode to be turned on simultaneously at time t0 and turned off simultaneously at time t1, and is used to control the second laser and the ICCD to be turned on simultaneously at time t2 and turned off simultaneously at time t3. The order along the time axis is t0, t1, t2, and t3 in sequence.

[0010] Among them, in the embodiment of the present invention, the first laser is used to generate a pulsed laser with a wavelength of 193 nm, and the pulsed laser is used to crack H2O in the measured combustion flow field into OH and H.

[0011] Among them, in the embodiments of the present invention, the second laser is used to generate pulsed laser with a wavelength of 282 nm, and the pulsed laser is used to excite the OH groups in the measured combustion flow field to a preset state, and the ICCD is used to record the fluorescence radiation generated during the regression process of the OH groups from the preset state to the initial state.

[0012] Among them, in the embodiments of the present invention, the computer is used to determine the positions of the marked OH groups based on the recording results of the ICCD.

[0013] The present invention also provides a test method for an optical test system for measuring the total temperature of a supersonic combustion flow field as described above. The test method includes:

[0014] Step 1: Build an optical test system;

[0015] Step 2: Connect the components in the optical test system;

[0016] Step 3: Turn on the equipment in the optical test system;

[0017] Step 4: Adjust the positions and directions of the devices in the optical test system;

[0018] Step 5: Turn on the combustion flow field;

[0019] Step 6: Turn on the optical test system and perform corresponding control on the equipment in the optical test system according to the preset timing relationship;

[0020] Step 7: Turn off the optical test system and the combustion flow field in sequence after a period of time;

[0021] Step 8: Result processing, obtaining the total temperature of the combustion flow field based on the flow velocity of the combustion flow field and the static temperature of the combustion flow field.

[0022] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0023] The present invention can obtain the local total temperature by measuring the flow velocity and static temperature of the combustion flow field simultaneously based on non-contact optical testing technology without destroying the flow structure and combustion state of the combustion flow field precursor, will not cause obvious influence on the supersonic combustion flow field structure, will not cause unnecessary oblique shock waves, and will not affect the local and downstream flow and combustion states of the measured combustion flow field. Description of the Drawings

[0024] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of the present invention, and do not limit the embodiments of the present invention;

[0025] Figure 1 It is a schematic diagram of the principle of the optical test system for measuring the total temperature of the supersonic combustion flow field in the present invention;

[0026] Figure 2 Schematic diagram of the timing relationship of each component within one pulse time in the present invention;

[0027] Figure 3 Schematic diagram of the measurement positions at the test site;

[0028] Figure 4 Schematic diagram of the test results of the velocity at the measurement positions;

[0029] Figure 5 Schematic diagram of the test results of the change of the temperature at the measurement positions over time;

[0030] Among them, 1 - supersonic combustion incoming flow, 2 - timing synchronizer, 3 - first laser, 4 - first focusing lens, 5 - first total reflection flat mirror, 6 - second laser, 7 - second focusing lens, 8 - light sheet lens, 9 - second total reflection flat mirror, 10 - oscilloscope, 11 - computer; 12 - ICCD, 13 - tunable laser diode, 14 - laser controller, 15 - photodetector, 16 - industrial control computer, 17 - signal monitor. Specific embodiments

[0031] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0032] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0033] Embodiment 1;

[0034] Please refer to Figure 1 , the principle of the total temperature measurement test device and method proposed by the present invention is as Figure 1As shown in the figure, α represents the angle between the 193nm laser and the infrared laser when they pass through the measured combustion flow field; λ represents the specific length at which the 193nm laser can be used to mark the water molecules for velocity measurement after being focused in the measured area. The finally obtained total temperature is the average total temperature within the rectangular area along the flow direction. The entire system includes several components and necessary accessories such as fiber optic connectors. The names and main functions of each component are as follows: Supersonic combustion incoming flow 1, providing the test measurement object; Timing synchronizer 2, controlling the timing relationship between components; First laser 3, used to generate pulsed laser with a wavelength of 193nm. This laser is used to break down H2O in the combustion flow field into OH and H. This process can be regarded as marking OH at a specific position with a laser of 193nm wavelength; First focusing lens 4, focusing the laser emitted by the 193nm laser, increasing the laser energy per unit space and improving the breakdown rate of H2O; First total reflection flat mirror 5, changing the transmission direction of the 193nm laser so that the laser enters the measured combustion flow field at a suitable position and direction; Second laser 6, used to generate pulsed laser with a wavelength of 282nm. This laser is used to excite the OH groups in the combustion flow field to a high energy state. The high energy state OH groups are unstable and will return to the low energy state. The return process is accompanied by fluorescence radiation, which can be recorded by ICCD, and then the position of the marked OH groups can be determined; Second focusing lens 7, focusing the laser emitted by the 282nm laser, increasing the laser energy per unit space and improving the excitation rate of OH; Sheet light lens 8, stretching the focused 282nm wavelength laser in a single direction, shaping the laser into a thin sheet laser; Second total reflection flat mirror 9, reflecting the thin sheet laser into the position to be measured; Oscilloscope 10, used to check the timing relationship between components 3, 6, 12 and 13; Computer 11; ICCD 12; Tunable laser diode 13, used to generate laser that can be scanned at a fixed frequency within a certain range. This range and frequency are controlled by the laser controller 14 according to the specific test object. The laser in this band can be absorbed by H2O, thereby causing changes in the signals collected by the photodetector 15. The combustion flow field parameters can be inversely calculated through the specific change amount; Laser controller 14, controlling the output wavelength and frequency of the tunable laser diode 13; Photodetector 15, receiving the signals of the laser emitted by the tunable laser diode 13 after passing through the combustion flow field; Industrial control computer 16, controlling the laser controller 14, collecting and storing the information of the photodetector 15, processing the near-infrared band absorption spectrum test data, and obtaining the average static temperature under line-of-sight integration; Signal monitor 17, the visualization medium of the near-infrared band absorption spectrum test control program. Among them, components 3-9, 11 and 12 are used to measure the flow velocity of a small line segment (assuming the length is λ) in the focused area of the line segment after passing through the combustion flow field after component 5. After obtaining the flow velocity of the line segment, its average value is calculated. Components 13-17 are used to measure the static temperature under line-of-sight integration on the optical path.Then, calculate the average Mach number and average total temperature within the rectangular region covered by a length of λ and an angle of ɑ in the combustion flow field region using the relationships between various physical quantities.

[0035] Figure 2 It is the timing relationship of each component within a pulse time. Figure 2 In it, the 193nm laser and the near-infrared laser simultaneously emit pulsed lasers at time t0, and then simultaneously end at time t1. The near-infrared detector synchronously records the near-infrared laser. The 282nm laser and the camera are simultaneously turned on at time t2 and simultaneously turned off at time t3.

[0036] The present invention Figure 3 carried out measurement tests on the shown test object. Figure 3 In it, a is the original diagram of the object to be measured, b is the schematic diagram of the measured position. The vertically upward arrow represents the region where the 193nm laser acts, the arrow from the lower right to the upper left represents the region where the near-infrared laser acts, and the parallelogram represents the region where the 282nm sheet laser acts; at the central position of a space limited in the up, down, front, and back directions, there is a stream of gas jetting from left to right. From the brightness distribution of the gas, it can be found that there is a strong discontinuous combustion flow field similar to an oblique shock wave. Thus, it can be judged that the gas is a supersonic gas. Due to the combustion chemical reaction, Figure 3 H2O exists at the middle measured position shown in (b). Figure 3 In it, the 193nm laser from bottom to top dissociates H2O into OH and H ( Figure 2 at time t0 shown). Figure 3 In it, the 282nm sheet light from the lower left to the upper right excites OH to a state that can be recorded by the ICCD ( Figure 2 at time t1 shown); simultaneously when the 193nm laser is triggered, Figure 3 in (b), the mid-infrared band laser from the lower right to the upper left (with an included angle of 15° with the direction of the 193nm laser in the experiment) absorbs the signal of H2O and is recorded by the photodetector ( Figure 2 at time t0 shown).

[0037] Figure 4 gives the velocity of the measured combustion flow field within the time period from t1 to t0 recorded by the 193nm laser and the 282nm laser. At time t0, the 193nm laser acts on H2O to generate OH, and at time t1, the 282nm laser records the position of OH. The velocity can be calculated through the time difference and the displacement at the two moments. During the experiment, the velocity within the region from 14.9mm to 23.3mm in the vertical direction was recorded. The velocity distribution is as Figure 3 shown, and the average velocity of the combustion flow field is 1000m / s. Figure 4 shown.

[0038] Figure 5The line-averaged temperature on the optical path recorded by the mid-infrared band laser absorption of H2O is given. Figure 5 What is given in is the variation of the line-averaged temperature with time. Since the temperature fluctuates relatively greatly with time under supersonic combustion, Figure 5 only the temperature data within a relatively stable period of time is intercepted, and this data is time-averaged to obtain an average temperature of 1125 K.

[0039] Among them, after obtaining the flow velocity and static temperature of the combustion flow field, the speed of sound is calculated through the relationship between the static temperature of the combustion flow field and the speed of sound, the Mach number of the combustion flow field is calculated through the relationship between the speed of sound, the flow velocity of the combustion flow field and the Mach number of the combustion flow field, and the total temperature of the combustion flow field is calculated through the relationship between the Mach number of the combustion flow field, the static temperature of the combustion flow field and the total temperature of the combustion flow field.

[0040] According to the formula for calculating the speed of sound, the formula for calculating the Mach number, and the relationship between the total temperature and the static temperature of the combustion flow field, the calculation process of the total temperature of the measured area is as follows:

[0041]

[0042] T * = T·(1 + 0.165·Ma 2 ) = 1125·(1 + 0.165·1.52 2 ) = 1554 K (3)

[0043] In formula (1), c is the speed of sound, T is the static temperature. In formula (2), Ma is the Mach number, V is the velocity. In formula (3), T * is the total temperature. Through calculation, it is obtained that the total temperature of the supersonic combustion area with a height of 8.5 mm and a width of 2.3 mm in the measured area is approximately 1554 K.

[0044] Among them, based on the above embodiments, the embodiments of the present invention also provide a test method for an optical test system for measuring the total temperature of a supersonic combustion flow field. The test method includes:

[0045] Step 1: Build an optical test system;

[0046] Step 2: Connect each component in the optical test system;

[0047] Step 3: Turn on the equipment in the optical test system;

[0048] Step 4: Adjust the position and direction of each equipment in the optical test system;

[0049] Step 5: Turn on the combustion flow field;

[0050] Step 6: Turn on the optical test system and perform corresponding control on the equipment in the optical test system according to the preset timing relationship.

[0051] Step 7: After a period of time, turn off the optical test system and the combustion flow field in sequence.

[0052] Step 8: Result processing, obtaining the total temperature of the combustion flow field based on the flow velocity of the combustion flow field and the static temperature of the combustion flow field.

[0053] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0054] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. An optical test system for measuring the total temperature of a supersonic combustion flow field, characterized in that: The system comprises: Supersonic combustion flow, timing synchronizer, first laser, first focusing lens, first total reflection plane mirror, second laser, second focusing lens, sheet light lens, second total reflection plane mirror, computer, ICCD, tunable laser diode, laser controller, photoelectric detector, industrial computer and signal monitor; Among them, the supersonic combustion flow flows to the preset area to form the combustion flow field to be measured, which is used to provide the test measurement object; the timing synchronizer is used to control the timing relationship between the various components in the system; the first laser is used to generate a first pulse laser, which is focused by the first focusing lens and then emitted to the first total reflection plane mirror, and the laser reflected by the first total reflection plane mirror is emitted into the combustion flow field to be measured; the second laser is used to generate a second pulse laser, which is focused by the second focusing lens and then emitted to the sheet light lens, and the sheet light lens processes the focused laser into a sheet light, which is reflected by the second total reflection plane mirror and then emitted into the combustion flow field to be measured; the ICCD records the displacement of the marked substance within a known time, and the results of the ICCD and the oscilloscope are viewed and recorded by a computer; it can A tunable laser diode is used to generate a near-infrared laser that scans at a fixed frequency within a preset range; a laser controller is used to control the output wavelength and frequency of the tunable laser diode; a photodetector is used to receive the signal after the laser emitted by the tunable laser diode passes through the combustion flow field to be measured; an industrial computer is used to control the laser controller, as well as to collect and store the signal information transmitted by the photodetector, and to process the near-infrared band absorption spectrum test data in the signal information; a signal monitor is used to monitor the near-infrared band absorption spectrum test data; a computer calculates the combustion flow field flow velocity based on the results recorded by the ICCD and the oscilloscope; the industrial computer and the signal monitor are used to obtain the combustion flow field static temperature; the combustion flow field total temperature is obtained based on the combustion flow field flow velocity and the combustion flow field static temperature.

2. The optical test system for measuring total temperature of supersonic combustion flow field according to claim 1, characterized in that: The system further comprises an oscilloscope for checking the timing relationship among the first laser, the second laser, the ICCD and the tunable laser diode.

3. The optical test system for measuring total temperature of supersonic combustion flow field according to claim 2, characterized in that: The timing synchronizer is used to control the timing relationship between the components in the system, specifically: the timing synchronizer is used to control the first laser and the tunable laser diode to be turned on at time t0 and turned off at time t1 at the same time, and to control the second laser and the ICCD to be turned on at time t2 and turned off at time t3 at the same time.

4. The optical test system for measuring total temperature of a supersonic combustion flow field according to claim 1, characterized in that: The first laser is used to generate a pulse laser with a wavelength of 193 nm, and the pulse laser is used to decompose H2O in the measured combustion flow field into OH and H.

5. The optical test system for measuring total temperature of supersonic combustion flow field according to claim 1, characterized in that: The second laser is used to generate a pulsed laser with a wavelength of 282nm, which is used to excite the OH groups in the measured combustion flow field to a preset state. The ICCD is used to record the fluorescence radiation generated by the OH groups in the process of regression from the preset state to the initial state.

6. The optical test system for measuring total temperature of supersonic combustion flow field according to claim 5, characterized in that: A computer is used to determine the position of the labeled OH groups based on the ICCD recordings.

7. The optical test system for measuring total temperature of a supersonic combustion flow field according to claim 1, characterized in that: The total temperature of the combustion flow field is calculated as follows: the speed of sound is calculated through the relationship between the static temperature of the combustion flow field and the speed of sound; the Mach number of the combustion flow field is calculated through the relationship between the speed of sound, the flow velocity of the combustion flow field and the Mach number; the total temperature of the combustion flow field is calculated through the relationship between the Mach number of the combustion flow field, the static temperature of the combustion flow field and the total temperature of the combustion flow field.

8. A test method of an optical test system for measuring total temperature of a supersonic combustion flow field based on any one of claims 1 to 7, characterized in that: The test method includes: Step 1: Build an optical test system; Step 2: Connect the components in the optical test system; Step 3: Turn on the equipment in the optical test system; Step 4: Adjust the position and direction of each device in the optical test system; Step 5: Start the combustion flow field; Step 6: Start the optical test system and control the equipment in the optical test system accordingly according to the preset timing relationship; Step 7: After a period of time, turn off the optical test system and the combustion flow field in turn; Step 8: Result processing: obtaining the total temperature of the combustion flow field based on the combustion flow field velocity and the combustion flow field static temperature.

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