A pressure-sensitive paint-based correction method for film cooling effectiveness measurement

Abstract

The application discloses a kind of pressure-sensitive paint-based air film cooling efficiency measurement correction method, comprising the following steps: by calibration, the relationship model between light intensity and oxygen partial pressure is obtained;According to the demand, configure specific oxygen-containing mixed gas;Pressure-sensitive paint is sprayed on the surface of the model to be measured;The specific oxygen-containing mixed gas is combined with the model to be measured to obtain the model to be measured under four specific environments;Collect the surface of the model to be measured under each specific environment to obtain the corresponding light intensity image of the surface of the model to be measured;Based on the light intensity image, the air film cooling efficiency of the surface of the model to be measured is obtained by calculation.The application corrects the deviation caused by pressure assumption in the process of measuring air film cooling efficiency by pressure-sensitive paint by using specific oxygen-containing mixed gas, and improves the accuracy of air film cooling efficiency measurement.

Description

Technical Field

[0001] This invention belongs to the field of cooling efficiency measurement technology for hot-end components of aero-engines, and particularly relates to a method for measuring and correcting the air film cooling efficiency based on pressure-sensitive paint. Background Technology

[0002] Gas turbine engines, based on the Brayton cycle, are widely used in ground-based gas turbines and aero engines. Increasing the turbine inlet temperature directly improves cycle efficiency. Currently, turbine inlet temperatures have already exceeded the temperature resistance limit of turbine blades, making efficient cooling technology indispensable. Film cooling (FSC) technology involves creating discrete holes on the turbine blade surface to draw cooling gas from the inside of the blade to the outer wall, and is one of the important cooling methods for hot-end components. Under the influence of the mainstream gas flow, the cooling gas forms a film on the blade surface, isolating the high-temperature gas. Film cooling efficiency (FSC) is an important evaluation parameter for FSC, characterizing the temperature after the mainstream combustion gas and cool gas mix under adiabatic wall conditions. A value of 1 indicates that the temperature near the wall is equal to the cool gas temperature, indicating the best cooling effect; a value of 0 indicates that the temperature near the wall is equal to the mainstream temperature, with no cooling effect. The main methods for measuring FSC efficiency are thermal measurement methods and mass transfer analogy methods. Thermal measurement methods are inevitably affected by thermal conductivity and are often contact-based. Pressure-sensitive paint (PSP) is widely used in mass transfer analogy methods. Due to the oxygen quenching effect, pressure-sensitive paint can obtain the oxygen partial pressure on the surface of an object by measuring light intensity. This characteristic has been utilized in numerous film cooling efficiency measurement experiments. Before using a PSP to measure film cooling efficiency, calibration is required to determine the relationship between light intensity and oxygen partial pressure. When measuring film cooling efficiency, the pressure-sensitive paint needs to be sprayed onto the surface to be tested, and the model under test is photographed in four specific environments. In the measurement process, previous researchers used the pressure field measurement results obtained in the third environment with air as the jet to replace the pressure field in the fourth environment with a heterogeneous gas jet to measure the film cooling efficiency. However, under high-speed, complex flow conditions, when the density of the heterogeneous gas differs from that of air, there will be a significant difference between the pressure distribution in the third environment with air as the jet and the pressure distribution in the fourth environment with a heterogeneous gas jet, which will lead to deviations in the measurement results. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a correction method for measuring the gas film cooling efficiency based on pressure-sensitive paint. This method corrects the deviation caused by the pressure assumption during the measurement of gas film cooling efficiency using a specific oxygen-containing mixed gas, thereby improving the accuracy of the gas film cooling efficiency measurement.

[0004] To achieve the above objectives, the present invention provides a method for correcting the measurement of film cooling efficiency based on pressure-sensitive paint, comprising:

[0005] By calibration, a model relating light intensity and oxygen partial pressure is obtained;

[0006] Configure specific oxygen-containing gas mixtures according to requirements;

[0007] Pressure-sensitive paint was sprayed onto the surface of the model to be tested;

[0008] By combining the specific oxygen-containing gas mixture with the test model, test models under four specific environments are obtained;

[0009] For each specific environment, the surface of the model under test is sampled to obtain the corresponding light intensity image of the surface of the model under test.

[0010] Based on the light intensity image, the air film cooling efficiency of the surface of the model under test is calculated.

[0011] Optionally, the four specific environments include a first specific environment, a second specific environment, a third specific environment, and a fourth specific environment;

[0012] The first specific environment is a dark and motionless environment;

[0013] The second specific environment is a light-filled, non-flowing environment;

[0014] The third specific environment is an environment with light, flow, and a specific oxygen-containing gas mixture in the jet;

[0015] The fourth specific environment is an environment with light, flow, and a jet of dissimilar gas.

[0016] Optionally, the specific oxygen-containing gas mixture is composed of a certain proportion of oxygen, argon, and sulfur hexafluoride.

[0017] Optionally, the density of the specific oxygen-containing gas mixture used in the third specific environment is the same as the density of the opposite gas in the fourth specific environment, and the oxygen mole fraction of the specific oxygen-containing gas mixture used in the third specific environment is the same as the oxygen mole fraction in the air.

[0018] Optionally, a model for the relationship between light intensity and oxygen partial pressure can be obtained through calibration, including:

[0019] A reference condition is selected, wherein the oxygen partial pressure and temperature of the reference condition are the same as those of the second specific environment. The light intensity under the reference condition is used as the reference light intensity. The relationship model between light intensity and oxygen partial pressure is calibrated as follows:

[0020]

[0021] Among them, I refI is the reference light intensity; I1 is the light intensity on the surface of the model under test in a dark, non-flowing environment; x is the environmental intensity that changes during the calibration process. x To calibrate the light intensity on the model surface under the x environment; The oxygen partial pressure is under reference conditions; To calibrate the oxygen partial pressure on the model surface under environment x; T ref This is a reference temperature.

[0022] Optionally, acquiring the light intensity image of the test model surface under each specific environment includes:

[0023] Based on the first specific environment, a first type of light intensity image is obtained;

[0024] Based on the second specific environment, a second type of light intensity image is obtained;

[0025] Based on the third specific environment, a third type of light intensity image is obtained;

[0026] Based on the fourth specific environment, a fourth light intensity image is obtained.

[0027] Optionally, the method for calculating the film cooling efficiency of the surface of the model under test based on the light intensity image is as follows: perform image conversion on the light intensity image to obtain a two-dimensional matrix of oxygen partial pressure;

[0028] Based on the two-dimensional matrix of oxygen partial pressure, the gas film cooling efficiency of the surface of the model under test is obtained by calculation.

[0029] Optionally, the method for calculating the film cooling efficiency of the surface of the model under test based on the two-dimensional matrix of oxygen partial pressure is as follows:

[0030]

[0031] Where η is the film cooling efficiency, W fg W represents the molecular weight of the heterogeneous gas. air The molecular weight of air. The oxygen partial pressure on the surface of the model under test in the third specific environment. This refers to the oxygen partial pressure on the surface of the model under test in the second specific environment. This represents the oxygen partial pressure on the surface of the model under test in the fourth specific environment.

[0032] Technical effects of the invention: The invention discloses a method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint. By using a specific oxygen-containing mixed gas, a pressure field that is closer to the fourth environment than the original method is created in the third environment. This corrects the measurement deviation caused by the difference between the pressure distribution of the third environment with air as the jet and the pressure distribution of the fourth environment with heterogeneous gas as the jet under high-speed and complex flow conditions. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0034] Figure 1 This is a schematic diagram of the measurement steps of the correction method for measuring the film cooling efficiency using pressure-sensitive paint according to an embodiment of the present invention; where 1 is the pressure-sensitive paint coating, 2 is the model to be tested, 3 is the film pore, 4 is the jet, 5 is the main stream, 6 is the light source, and 7 is the scientific camera.

[0035] Figure 2 The deviation distribution of the measurement of the blade tip film cooling efficiency caused by the original method of using air as a jet in a third environment in the embodiments of the present invention;

[0036] Figure 3 This embodiment of the invention uses an improved method to measure the deviation distribution of the blade tip film cooling efficiency;

[0037] Figure 4 This is the average distribution of the absolute values ​​of the deviation of the blade tip air film cooling efficiency measured using pressure-sensitive paint before and after the improved method in this embodiment of the invention;

[0038] Figure 5 This is a schematic flowchart of the method for measuring and correcting the air film cooling efficiency based on pressure-sensitive paint according to an embodiment of the present invention. Detailed Implementation

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0041] like Figure 5 As shown, this embodiment provides a method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint, including the following steps:

[0042] By calibration, a model relating light intensity and oxygen partial pressure is obtained;

[0043] Configure specific oxygen-containing gas mixtures according to requirements;

[0044] Pressure-sensitive paint was sprayed onto the surface of the model to be tested;

[0045] By combining the specific oxygen-containing gas mixture with the test model, test models under four specific environments are obtained;

[0046] For each specific environment, the surface of the model under test is sampled to obtain the corresponding light intensity image of the surface of the model under test.

[0047] Based on the light intensity image, the air film cooling efficiency of the surface of the model under test is calculated.

[0048] The four specific environments include the first specific environment, the second specific environment, the third specific environment, and the fourth specific environment;

[0049] The first specific environment is a dark, non-moving environment;

[0050] The second specific environment is a light-filled, non-flowing environment;

[0051] The third specific environment is one with light, flow, and a specific oxygen-containing gas mixture in the jet;

[0052] The fourth specific environment is one with light, flow, and a jet of dissimilar gas.

[0053] A specific oxygen-containing gas mixture is composed of a certain proportion of oxygen, argon, and sulfur hexafluoride.

[0054] The density of the specific oxygen-containing gas mixture used in the third specific environment is the same as the density of the opposite gas in the fourth specific environment, and the oxygen mole fraction of the oxygen-containing gas mixture is the same as the oxygen mole fraction in the air.

[0055] Models for obtaining the relationship between light intensity and oxygen partial pressure include:

[0056] The calibration process will select reference conditions, where the oxygen partial pressure and temperature are the same as those of the second specific environment. The light intensity under the reference conditions will be used as the reference light intensity. The calibration will then yield a model showing the relationship between light intensity and oxygen partial pressure.

[0057]

[0058] Among them, I ref I is the reference light intensity; I1 is the light intensity on the surface of the model under test in a dark, non-flowing environment; x is the environmental intensity that changes during the calibration process. xTo calibrate the light intensity on the model surface under the x environment; The oxygen partial pressure is under reference conditions; To calibrate the oxygen partial pressure on the model surface under environment x; T ref This is a reference temperature.

[0059] The light intensity image of the test model surface under each specific environment is acquired, including:

[0060] Based on the first specific environment, acquire the first type of light intensity image;

[0061] Based on the second specific environment, acquire the second type of light intensity image;

[0062] Based on a third specific environment, acquire a third type of light intensity image;

[0063] Based on the fourth specific environment, a fourth light intensity image is obtained.

[0064] The method for calculating the film cooling efficiency of the surface of the model under test based on light intensity images is as follows: perform image transformation on the light intensity images to obtain a two-dimensional matrix of oxygen partial pressure.

[0065] Based on a two-dimensional matrix of oxygen partial pressure, the gas film cooling efficiency of the surface of the model under test is obtained by calculation.

[0066] The method for calculating the film cooling efficiency of the surface of the model under test based on a two-dimensional matrix of oxygen partial pressure is as follows:

[0067]

[0068] Where η is the film cooling efficiency, W fg W represents the molecular weight of the heterogeneous gas. air The molecular weight of air. The oxygen partial pressure on the surface of the model under test in the third specific environment. This refers to the oxygen partial pressure on the surface of the model under test in the second specific environment. This represents the oxygen partial pressure on the surface of the model under test in the fourth specific environment.

[0069] like Figure 1 As shown, this embodiment provides a measurement device for a method of correcting the gas film cooling efficiency based on pressure-sensitive paint. The testing device includes a pressure-sensitive paint coating 1, a model to be tested 2, gas film pores 3, a jet 4 (which is a heterogeneous gas or air in the original method, and a heterogeneous gas or a specific oxygen-containing mixture in the correction method), a main stream 5, a light source 6, and a scientific camera 7.

[0070] like Figure 1 As shown, this embodiment provides a measurement method for a pressure-sensitive paint-based gas film cooling efficiency correction method, including:

[0071] Step 1: Prepare a specific oxygen-containing gas mixture using argon, sulfur hexafluoride, and oxygen, such that the density of this gas is the same as that of the heterogeneous gas, and the mole fraction of oxygen in this gas is the same as that of air. The following table shows the mixture ratios for densities 1.5 and 2.0 with air, as shown in Table 1.

[0072] Table 1

[0073]

[0074] Step 2: Spray pressure-sensitive paint 1 onto the surface of the model to be tested 2.

[0075] Step 3: As Figure 1 Set up a scientific camera 7, set a filter in front of the camera lens, and take a light intensity image J1 under conditions of no light source.

[0076] Step 4: As Figure 1 The surface of the model under test 2 is illuminated by a light source 6 of a specific wavelength, which excites the pressure-sensitive paint to emit fluorescence. The light intensity image J2 is captured by a scientific camera 7. This operating condition is also called the reference condition. At this time, the ambient temperature is T. ref .

[0077] Step 5: As Figure 1 Open the main air stream 5 and the specific oxygen-containing mixed gas jet 4, set the flow parameters, use a light source 6 of a specific wavelength to illuminate the surface of the model under test 2, and take a light intensity image J3 through a scientific camera 7.

[0078] Step 6: As Figure 1 Turn on the main air stream 5 and the heterogeneous gas jet 4, set the flow parameters, use a light source 6 of a specific wavelength to illuminate the surface of the model under test 2, and take a light intensity image J4 through a scientific camera 7.

[0079] Step 7: The gas film cooling efficiency is obtained by processing the acquired fluorescence intensity images J1 to J4.

[0080] The processing method in step 7 includes the following steps:

[0081] Step 71: First, use MATLAB or other programs to read the light intensity images J1 to J4 and convert them into two-dimensional light intensity matrices I1 to I4 with light intensity values;

[0082] Step 72: Substitute the two-dimensional light intensity matrix corresponding to the above fluorescence intensity image into the following formula to calculate the ratio data of oxygen partial pressure on the surface of the model to be tested 2. and

[0083]

[0084]

[0085] in, Obtained through prior calibration experiments.

[0086] Step 73: Using the oxygen partial pressure ratio data, calculate the film cooling efficiency using the following formula:

[0087]

[0088] Among them, W fg W represents the molecular weight of the heterogeneous gas. air The molecular weight of air.

[0089] The gas film cooling efficiency was measured using pressure-sensitive paint, and the measurement deviation was corrected using a specific oxygen-containing mixed gas, thus solving the problem of deviation caused by pressure distribution under different jet working fluids during the measurement of gas film cooling efficiency using pressure-sensitive paint.

[0090] This embodiment evaluates the correction effect of a measurement method for a pressure-sensitive paint-based film cooling efficiency correction method:

[0091] In fact, the formula for film cooling efficiency is:

[0092]

[0093] Where η is the film cooling efficiency, W fg W represents the molecular weight of the heterogeneous gas. air The molecular weight of air. The partial pressure of oxygen in the mainstream air, P air It is the pressure of the mainstream air. P4 represents the oxygen partial pressure on the surface of the model under test in the fourth specific environment, and P4 is the pressure on the surface of the model under test in the fourth specific environment.

[0094] In the experiment, a certain gas was introduced into a third specific environment, whose oxygen mole fraction was the same as that of the mainstream air. Therefore, the oxygen mole fraction was the same as that of air throughout the entire flow field.

[0095]

[0096] in, P3 is the oxygen partial pressure on the surface of the model under test in the third specific environment, and P3 is the pressure on the surface of the model under test in the third specific environment.

[0097] Therefore, the formula for calculating the film cooling efficiency is:

[0098]

[0099] Conclusion:

[0100]

[0101] The formula for the film cooling efficiency used in the experiment is as follows:

[0102]

[0103] Therefore, the deviation between the two is:

[0104]

[0105] It can be seen that the deviation originates from the difference in pressure fields between the third and fourth specific environments. According to the mass transfer analogy to heat transfer theory, if the tracer gas is considered a heterogeneous gas, then:

[0106]

[0107] Among them, C w C represents the mass fraction of the heterogeneous gas near the wall. ∞ The mass fraction of heterogeneous gases in the mainstream air is taken as 0; C C The mass fraction of the heterogeneous gas at the jet inlet is taken as 1. When the jet is a heterogeneous gas, the mass fraction of the heterogeneous gas near the wall is used as the film cooling efficiency value.

[0108] This embodiment focuses on the film cooling system at the blade tip, using a mixture of sulfur hexafluoride and argon as the heterogeneous gas with a density ratio of 2.0. Using CFX software, numerical simulations were performed to obtain the pressure fields for three different jet configurations: air, heterogeneous gas, and a specific oxygen-containing mixture with a density of 2.0. The mass fraction of the heterogeneous gas near the wall was obtained as the film cooling efficiency when the jet was heterogeneous gas, to evaluate the impact of different pressure distributions on the film cooling efficiency measured using pressure-sensitive paint.

[0109] Figure 2 The numerical simulation in this embodiment shows the measurement deviation distribution of the blade tip film cooling efficiency caused by the original method of using air as a jet in the third environment. Due to the leakage flow at the blade tip, the film flow direction is generally from the pressure side to the suction side. Figure 3 This is the measurement deviation distribution of the blade tip film cooling efficiency obtained from numerical simulation in this embodiment when using the improved method. Figure 2 and Figure 3 The mainstream blade pressure ratio is 1.5, and the blowing ratio (M = ρ) is... c u c / ρ ∞ u ∞The value is 2.0. It is evident that in the traditional method, measurement deviations occur throughout the entire test area due to the different pressure distributions between the third and fourth environments mentioned in this invention. Specifically, a positive deviation region exists near the pressure surface, upstream of the air film orifice flow direction; a negative deviation region exists near the air film orifice; and a smaller positive deviation region exists near the suction surface. (Comparison) Figure 2 and Figure 3 It can be clearly concluded that using a specific oxygen-containing gas mixture in the third environment will significantly reduce the deviation of the entire measurement area, and the correction method is very effective. Figure 4 For different blowing ratios, the average distribution of the absolute value of the deviation of the blade tip film cooling efficiency was measured using pressure-sensitive paint before and after the improvement in this embodiment. It can be seen that the flow parameters have an impact on the deviation distribution, and in all cases, the correction method of the present invention can control the deviation to a low value.

[0110] This invention discloses a method for correcting the measurement of film cooling efficiency based on pressure-sensitive paint. By using a specific oxygen-containing mixed gas, a pressure field that is closer to the fourth environment than the original method is created in the third environment. This corrects the measurement deviation caused by the difference between the pressure distribution of the third environment with air as the jet and the pressure distribution of the fourth environment with heterogeneous gas as the jet under high-speed and complex flow conditions.

[0111] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for measuring and correcting the film cooling efficiency of pressure-sensitive paint, characterized in that, Includes the following steps: By calibration, a model relating light intensity and oxygen partial pressure can be obtained. Configure specific oxygen-containing gas mixtures according to requirements; Pressure-sensitive paint was sprayed onto the surface of the model to be tested; By combining the specific oxygen-containing gas mixture with the test model, test models under four specific environments are obtained; For each specific environment, the surface of the model under test is sampled to obtain the corresponding light intensity image of the surface of the model under test. Based on the light intensity image, the air film cooling efficiency of the surface of the model under test is obtained by calculation; The four specific environments include the first specific environment, the second specific environment, the third specific environment, and the fourth specific environment; The first specific environment is a dark and motionless environment; The second specific environment is a light-filled, non-flowing environment; The third specific environment is an environment with light, flow, and a specific oxygen-containing gas mixture in the jet; The fourth specific environment is an environment with light, flow, and a jet of dissimilar gas; The specific oxygen-containing gas mixture is composed of a certain proportion of oxygen, argon, and sulfur hexafluoride; The density of the specific oxygen-containing gas mixture used in the third specific environment is the same as the density of the opposite gas in the fourth specific environment, and the oxygen mole fraction of the specific oxygen-containing gas mixture used in the third specific environment is the same as the oxygen mole fraction in the air.

2. The method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint as described in claim 1, characterized in that, The relationship model between light intensity and oxygen partial pressure was obtained through calibration, including: A reference condition is selected, wherein the oxygen partial pressure and temperature of the reference condition are the same as those of the second specific environment. The light intensity under the reference condition is used as the reference light intensity. The relationship model between light intensity and oxygen partial pressure is calibrated as follows: in, I ref It is the reference light intensity; I 1 x represents the light intensity on the surface of the model under test in a dark, stagnant environment; x represents the environmental changes during the calibration process. I x To calibrate the light intensity on the model surface under the x environment; The oxygen partial pressure is under reference conditions; To calibrate the oxygen partial pressure on the model surface under environment x; This is a reference temperature.

3. The method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint as described in claim 1, characterized in that, Acquiring light intensity images of the test model surface under each specific environment includes: Based on the first specific environment, a first type of light intensity image is obtained; Based on the second specific environment, a second type of light intensity image is obtained; Based on the third specific environment, a third type of light intensity image is obtained; Based on the fourth specific environment, a fourth light intensity image is obtained.

4. The method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint as described in claim 3, characterized in that, The method for calculating the film cooling efficiency of the surface of the model under test based on the light intensity image is as follows: perform image transformation on the light intensity image to obtain a two-dimensional matrix of oxygen partial pressure. Based on the two-dimensional matrix of oxygen partial pressure, the gas film cooling efficiency of the surface of the model under test is obtained by calculation.

5. The method for measuring and correcting the film cooling efficiency based on pressure-sensitive paint as described in claim 4, characterized in that, The method for calculating the film cooling efficiency of the surface of the model under test based on the two-dimensional matrix of oxygen partial pressure is as follows: in, For film cooling efficiency, The molecular weight of the opposite gas is... The molecular weight of air. The oxygen partial pressure on the surface of the model under test in the third specific environment. This refers to the oxygen partial pressure on the surface of the model under test in the second specific environment. This represents the oxygen partial pressure on the surface of the model under test in the fourth specific environment.

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