A method for improving the precision of infrared thermal imaging transition test of boundary layer of an impeller machine

Abstract

The application discloses a method for improving the precision of boundary layer infrared thermal imaging transition test of a turbomachinery. The surface of a turbomachinery blade is heated by a transient laser pulse, and the temperature distribution of different regions of the blade surface is sensed by an infrared high-speed camera according to the different heat exchange coefficients of the laminar flow / turbulent flow region, so that the transition interval is determined. An analysis model between the thickness d and the thermal conductivity λ of the heat insulation coating and the temperature drop degree ΔT lam‑turb of the laminar flow-turbulent flow region is derived. On this basis, an infrared thermal imaging test signal-to-noise ratio maximization scheme is provided, the optimal effect of wall surface heat exchange enhancement is achieved by optimizing the physical property parameters of the heat insulation coating, and the temperature drop amplitude ΔT lam‑turb of the laminar flow-turbulent flow region is increased by 10-20 times. The method significantly improves the precision of infrared thermal imaging transition test, and provides an advanced diagnosis technology for the blade surface transition flow of a turbomachinery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of impeller mechanical testing, and relates to impeller mechanical blade flow testing and boundary layer transition diagnosis, in particular to a method for improving the accuracy of impeller mechanical boundary layer infrared thermal imaging transition testing based on wall surface reinforced heat exchange. BACKGROUND

[0002] In the design and performance optimization process of modern aero-engines and various high-performance impeller machines, accurate diagnosis of the internal flow field of impeller components is crucial. The transition flow phenomenon, i.e., the evolution of fluid from laminar flow to turbulent flow, especially when the inlet Reynolds number of a compressor / turbine component decreases to a critical value (2x10 5 ) or below, will produce significant laminar separation and transition process on the surface of the blade / end wall. This process leads to a sharp thickening of the three-dimensional boundary layer, intensifying turbulent mixing, which results in a sharp decline in compressor / turbine component efficiency, an increase in engine fuel consumption, and a downward shift in stable working boundary.

[0003] Generally, the transition flow inside the impeller machine can be diagnosed by means of wire, hot wire, surface hot film, oil flow display, etc. However, most of the related methods are invasive measurements that have a non-negligible impact on the local flow field, and the test scheme is generally complex and time-consuming. Taking oil flow display as an example, when testing under multiple working conditions, the oil flow trace of the previous working condition needs to be completely removed. However, in actual operation, it may be difficult to completely remove it, and on the other hand, it may damage the surface of the blade. Both of the above factors can cause the transition to be advanced. Hot film testing can only obtain the quasi-wall shear force at a certain blade height section, and it is difficult to reflect the transition characteristics at different blade height positions. Moreover, the laying and installation of the hot film are extremely complex.

[0004] As a non-invasive diagnostic method, infrared thermal imaging technology uses a transient laser pulse to heat the surface of the impeller machine blade. According to the different heat transfer coefficients in the laminar / turbulent flow area, the temperature distribution of different areas on the blade surface is sensed by a high-speed infrared camera, and the transition interval is determined. Compared with traditional methods, infrared thermal imaging technology has the advantages of not interfering with the flow field, simple test scheme, and being able to realize accurate measurement of the temperature distribution of the entire surface of the blade. Especially when there are flow separation, transition, and shock wave-boundary layer interference on the surface of the impeller machine blade, the local heat transfer coefficient and recovery temperature will produce obvious differences, which can be captured by infrared thermal imaging technology, providing intuitive and accurate information for the diagnosis of flow characteristics.

[0005] However, although infrared thermal imaging technology has unique advantages in transition flow diagnosis, it still faces some challenges in practical application. One of the main technical difficulties is that the determination of the transition interval is heavily dependent on the temperature difference between the laminar and turbulent flow regions. At low flow rates (low speed / subsonic speed), it is difficult to accurately determine the position of the transition interval due to the small temperature difference between the laminar and turbulent flow regions, which affects the accuracy and reliability of the test. Therefore, how to increase the temperature drop amplitude between the laminar and turbulent flow regions through technical innovation to enhance the signal-to-noise ratio of infrared thermal imaging transition test technology has become a key issue to improve the test accuracy of complex transition flow inside turbomachinery. This not only involves the improvement of the test technology itself, but also includes the optimization of the test environment and conditions. Solving this problem will provide important technical support for the fine aerodynamic design of turbomachinery, and further promote the performance improvement of aeroengines. SUMMARY

[0006] (I) Invention purposes

[0007] In view of the defects and deficiencies of the existing infrared thermal imaging technology in the boundary layer transition test of turbomachinery, especially the low test accuracy and difficulty in accurately determining the transition interval position due to the small temperature difference between the laminar and turbulent flow regions at low flow rates, in order to solve the above problems in the prior art, the purpose of the present application is to provide a scheme for increasing the temperature drop degree of laminar-turbulent flow region in infrared test by strengthening the wall heat transfer, thereby improving the accuracy of transition interval determination. The present application uses a one-dimensional analysis model to establish a correlation model of the physical parameters (thickness d and thermal conductivity λ) of the thermal insulation material and the temperature drop of the laminar and turbulent flow regions to optimize the configuration of the physical parameters of the thermal insulation material and strengthen the wall heat transfer, significantly increase the temperature drop amplitude of the laminar-turbulent flow region under the same working conditions, maximize the signal-to-noise ratio of infrared thermal imaging test, improve the accuracy of transition interval determination, and provide important technical support for the fine aerodynamic design and performance optimization of turbomachinery.

[0008] (II) Technical solutions

[0009] To achieve the purpose of the present application and solve its technical problems, the present application adopts the following technical solutions:

[0010] A method for improving the accuracy of infrared thermal imaging transition test of boundary layer of turbomachinery is used in the boundary layer test of key components such as compressors and turbines of turbomachinery, which improves the accuracy of transition interval determination of boundary layer of turbomachinery by increasing the temperature difference between the laminar and turbulent flow regions. In the implementation of the method, at least the following steps are included:

[0011] SS1. A coating of thermal insulation material is applied to the surface of the blade of the impeller machine to be tested, and the physical parameters d and λ of the thermal insulation material are selected and adjusted according to the required test accuracy and the thermal response characteristics of the blade surface, wherein d and λ are the thickness and thermal conductivity of the thermal insulation material, respectively;

[0012] SS2. Based on a one-dimensional analysis model that comprehensively considers the effects of heat conduction and convective heat transfer, a correlation between the temperature drop amplitude ΔT lam-turb between the laminar and turbulent regions of the blade surface and the physical parameters d and λ of the thermal insulation material is established, wherein ΔT lam-turb = |T w,lam -T w,turb |, T w,lam and T w,turb are the wall temperatures of the laminar and turbulent regions of the blade surface, respectively.

[0013] SS3. According to the correlation between the temperature drop amplitude ΔT lam-turb between the laminar and turbulent regions of the blade surface and the physical parameters d and λ of the thermal insulation material, the optimal parameter values of the physical parameters d and λ of the thermal insulation material are determined to maximize the temperature drop amplitude ΔT lam-turb between the laminar and turbulent regions of the blade surface under the test conditions, thereby enhancing the heat transfer effect of the blade wall to be tested.

[0014] SS4. The surface of the blade to be tested is heated using a transient laser pulse, and the surface temperature is controlled to rapidly rise to a set temperature value T sub and uniformly distribute.

[0015] SS5. The blade wall temperature T w at different flow direction positions after heating is captured by an infrared high-speed camera, so as to facilitate subsequent temperature difference analysis and determination of the transition region.

[0016] SS6. According to the difference ΔT lam-turb between the laminar region wall temperature T w，lam and the turbulent region wall temperature T w，turb of the blade surface, the position of the boundary layer transition region of the blade surface of the impeller machine to be tested is determined.

[0017] Preferably, in the one-dimensional analysis model in step SS2, the blade to be tested is regarded as a base material, and its surface is covered with a coating of thermal insulation material with a thickness d and a thermal conductivity λ. The surface temperature of the blade is uniformly raised to T sub by a transient laser pulse, and the heat conduction inside the thermal insulation coating and the convective heat transfer outside the thermal insulation coating and the fluid are considered. Based on the energy conservation equation, the temperature T w of the surface of the thermal insulation coating is derived, and T sub , the free stream temperature T 0,∞The relationship between the convective heat transfer coefficient h and the physical properties d and λ of the insulation material, and the difference in convective heat transfer coefficient between the laminar and turbulent regions leading to the corresponding wall temperature T. w,lam T w,turb They are also different, and the difference is the required ΔT. lam-turb .

[0018] Furthermore, in step SS2 above, the expression for the energy conservation equation established based on the one-dimensional analysis model is as follows:

[0019]

[0020] In the formula, T is the heat flux density per unit area. sub T represents the temperature reached by the blade substrate material after being heated by a transient laser pulse. w T represents the temperature of the surface of the thermal insulation material coating. rec To restore the temperature and make it approximately equal to the free-flow temperature T 0,∞ h is the convective heat transfer coefficient of the coating surface of the insulation material;

[0021] Based on the above energy conservation equation, the temperature T on the surface of the thermal insulation material coating is derived. w With T sub Free flow temperature T 0∞ The relationship between the convective heat transfer coefficient h and the physical properties d and λ of the insulation material:

[0022]

[0023] in, B is dimensionless i The number is used to characterize the relative magnitude of the wall's thermal conductivity resistance and the surface's convective thermal transfer resistance.

[0024] Furthermore, in step SS2 above, the convective heat transfer coefficient h is based on the laminar and turbulent regions. lam h turb And the corresponding B i Numbers _lam Bi _turb The wall temperatures T in the laminar and turbulent regions were calculated respectively. w,lam T w,turb The difference between the two is the required ΔT. lam-turb The corresponding calculation formula is as follows:

[0025]

[0026]

[0027]

[0028] In the formula, B represents the laminar and turbulent flow regions, respectively. i The number is used to characterize the relative importance of wall-to-wall convective heat transfer and internal conductive heat transfer within the insulation material coating in laminar and turbulent flow regions. h is the convective heat transfer coefficient between the turbulent and laminar regions near the transition point. turb h lam The ratio reflects the difference in convective heat transfer intensity between the turbulent and laminar flow regions.

[0029] Furthermore, in step SS2 above, based on the same physical property parameters d and λ of the same insulation layer material, the B values ​​in the laminar and turbulent regions are the same. i The difference in the number depends on the difference in their convective heat transfer coefficient h, that is:

[0030]

[0031] Thus, ΔT lam-turb The calculation formula can be further transformed into the following calculation formula:

[0032]

[0033] Under different test conditions, Bi was adjusted by optimizing the physical properties d and λ of the insulation material. _lam To achieve ΔT lam-turb This maximizes the signal-to-noise ratio of infrared testing and improves the accuracy of transition diagnosis.

[0034] Furthermore, in step SS2 above, under different test conditions, the temperature drop ΔT between the laminar and turbulent regions on the blade surface is considered. lam-turb With laminar flow region Bi _lam Fitting the relationship between the numbers to obtain Bi in different laminar flow regions _lam ΔT under number configuration lam-turb The distribution curve is used to determine the optimal laminar flow region Bi under the corresponding operating conditions. _lam The parameters d and λ of the thermal insulation material are configured and then optimized to achieve the desired ΔT under the corresponding test conditions. lam-turb Maximize.

[0035] Furthermore, in step SS2 above, under different test conditions, the ratio k of the convective heat transfer coefficient between the laminar and turbulent regions is analyzed, and the optimal laminar region Bi under the corresponding conditions is determined based on this ratio. _lam Number configuration Then, the physical property parameters d and λ of the thermal insulation material are optimized and determined, thereby achieving ΔT under the corresponding test conditions. lam-turb Maximize.

[0036] Further, in the step SS2, the optimal configuration parameters are determined by extremum solving to quickly obtain the thermal insulation material property parameters d, λ that maximize the temperature drop amplitude in various working conditions.

[0037] Preferably, in the step SS4, the transient laser pulse heating process is controlled by adjusting the laser power and pulse width to adapt to the thermal insulation material coating with different thickness d and thermal conductivity λ, ensuring that the blade surface temperature uniformly rises to T sub .

[0038] Preferably, in the step SS5, the capture frequency of the infrared high-speed camera is adjusted according to the speed of the blade surface temperature change to ensure that sufficient temperature distribution data is captured for subsequent temperature difference analysis and determination of the transition region.

[0039] (Three) Technical effects

[0040] Compared with the prior art, the method for improving the accuracy of infrared thermal imaging transition test of the boundary layer of a turbomachinery by wall surface heat transfer enhancement provided by the present application has the following characteristics:

[0041] (1) The present application significantly increases the temperature difference between the laminar and turbulent regions by optimizing the configuration of the property parameters of the thermal insulation material coating on the surface of the turbomachinery blade, greatly improving the accuracy of determining the boundary layer transition region. By adjusting the thickness and thermal conductivity of the thermal insulation material, the heat transfer on the blade surface can be effectively controlled, enabling the infrared thermal imaging technology to more sensitively and accurately capture the temperature change in the transition region, which is of great significance for the performance evaluation and optimization of turbomachinery.

[0042] (2) Based on the analysis model of one-dimensional heat conduction and convective heat transfer effect, the present application establishes a correlation model between the thickness d and thermal conductivity λ of the thermal insulation coating and the temperature drop amplitude ΔT lam-turb between the laminar and turbulent regions, providing a theoretical basis for maximizing the signal-to-noise ratio of infrared thermal imaging by wall surface heat transfer enhancement, ensuring that the parameters can be adjusted according to the specific working condition requirements in actual application to achieve the best test results, not only enhancing the reliability of the method, but also improving its applicability and flexibility.

[0043] (3) The present application optimizes the configuration of the property parameters of the thermal insulation coating and proposes a signal-to-noise ratio maximization scheme for infrared thermal imaging, increasing the temperature drop amplitude in the laminar / turbulent region by 10-20 times, significantly increasing the signal-to-noise ratio of infrared testing, and providing a solution for fine transition flow testing in the confined space of turbomachinery.

[0044] (4) The application significantly improves the accuracy and reliability of the boundary layer transition test of the impeller machine by comprehensively applying the thermal insulation material coating, transient laser pulse heating and high-speed infrared thermal imaging technology, and provides important technical support for performance optimization and reliability evaluation of the impeller machine. The method improves the sensitivity and accuracy of the infrared thermal imaging test by accurately controlling the thermal response characteristics of the blade surface, and has important application value in the fields of aerodynamic design and fault diagnosis of the impeller machine. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0046] Figure 1 The flow chart of the method for improving the accuracy of the infrared thermal imaging transition test of the boundary layer of the impeller machine is shown.

[0047] Figure 2 The schematic diagram of the one-dimensional analysis model of convective heat transfer is shown.

[0048] Figure 3 The schematic diagram of the ΔT distribution under different enhanced heat transfer parameter configurations is shown. lam-turb

[0049] Figure 4 The schematic diagram of the enhanced heat transfer scheme and the temperature drop amplitude ΔT lam-turb / T sub -T 0,∞ contrast. DETAILED DESCRIPTION

[0050] In order to better understand the present application, the content of the present application will be further illustrated below in combination with the embodiments. In the drawings, the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The described embodiments are part of the embodiments of the present application, not all. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The structure and technical solutions of the present application will be further described in detail below in combination with the drawings, and an embodiment of the present application is given.

[0051] Embodiment 1

[0052] ​The present application provides a method for improving the accuracy of infrared thermal imaging transition test of the boundary layer of a turbomachinery, which is used in the boundary layer test of key components of turbomachinery such as compressors and turbines, and improves the accuracy of determining the transition zone of the boundary layer of the turbomachinery by increasing the temperature difference between the laminar flow region and the turbulent flow region. As a specific example, as shown in Figure 1 The method mainly includes the following steps when implemented:

[0053] SS1. A heat insulation material coating is applied to the surface of the blade of the turbomachinery to be tested, and the physical parameters d and λ of the heat insulation material are selected and adjusted according to the required test accuracy and the thermal response characteristics of the blade surface, wherein d and λ are the thickness and thermal conductivity of the heat insulation material, respectively;

[0054] SS2. Based on a one-dimensional analysis model considering the effects of heat conduction and convective heat transfer, the temperature drop amplitude ΔT lam-turb between the laminar flow region and the turbulent flow region on the surface of the blade is established in relation to the physical parameters d and λ of the heat insulation material, wherein ΔT lam-turb = |T w,lam -T w,turb |, T w,lam and T w,turb are the wall temperatures of the laminar flow region and the turbulent flow region on the surface of the blade, respectively;

[0055] SS3. According to the established relationship between the temperature drop amplitude ΔT lam-turb between the laminar flow region and the turbulent flow region on the surface of the blade and the physical parameters d and λ of the heat insulation material, the optimal configuration parameter values of the physical parameters d and λ of the heat insulation material are determined to maximize the temperature drop amplitude ΔT lam-turb between the laminar flow region and the turbulent flow region on the surface of the blade under the test working conditions, and to further enhance the heat transfer effect of the blade wall to be tested;

[0056] SS4. The surface of the blade to be tested is heated using a transient laser pulse, and the surface temperature is controlled to rapidly rise to a set temperature value T sub and uniformly distribute;

[0057] SS5. The blade wall temperature T w at different flow direction positions after heating is captured by an infrared high-speed camera, so as to facilitate subsequent temperature difference analysis and determination of the transition zone;

[0058] SS6. According to the difference ΔT lam-turb between the wall temperature T w，lam of the laminar flow region and the wall temperature T w，turb of the turbulent flow region on the surface of the blade, the position of the boundary layer transition zone on the surface of the blade of the turbomachinery to be tested is determined.

[0059] The method shown in the present application effectively increases the temperature difference between the laminar flow region and the turbulent flow region by applying a thermal insulation coating with optimized physical parameters on the blade surface of the turbomachinery, combines a one-dimensional heat conduction analysis model and infrared thermal imaging technology, significantly improves the accuracy of the transition test, and is suitable for fine diagnosis of the complex flow characteristics inside the turbomachinery.

[0060] As a preferred example, Figure 2 A one-dimensional analysis model for testing the convective heat transfer on the surface of the blade thermal insulation material in step SS2 is given. The test blade serves as a substrate, on which a layer of thermal insulation material with a thickness of d and a thermal conductivity of λ is covered. The test blade is heated by a transient laser pulse to a temperature of T sub , and is uniformly distributed. Then, the wall surface temperature T w at different flow direction positions is obtained by an infrared high-speed camera. According to the difference ΔT w,lam between the wall surface temperature T w,turb of the laminar flow region and the wall surface temperature T lam-turb of the turbulent flow region, the blade surface boundary layer transition interval is determined. The theoretical analysis process is as follows:

[0061]

[0062] In the expression of the above energy conservation equation, is the heat flux density per unit area, T sub is the temperature of the blade substrate after being heated by a transient laser pulse, T w is the temperature of the surface of the thermal insulation material coating, T rec is the recovery temperature and is approximately equal to the free stream temperature T 0,∞ , and h is the convective heat transfer coefficient of the surface of the thermal insulation material coating.

[0063] The B i number is defined as follows to characterize the relative size of the wall surface heat conduction thermal resistance and the surface convective heat transfer thermal resistance:

[0064]

[0065] Then:

[0066]

[0067] Let T rec =T 0,∞ , T sub be a constant, then the wall surface temperature T w of the laminar / turbulent flow region completely depends on B i . B ih is related to the local flow (such as Reynolds number), and d and λ are determined by the insulator. Therefore, under the same flow conditions, the temperature difference between the laminar flow and turbulent flow area obtained by infrared testing is completely determined by the physical parameters d and λ of the insulator. First, consider two extreme cases, which are analyzed as follows:

[0068] (1) If the insulator is very thin and has a large thermal conductivity, B i → 0, then T w → T sub , that is, the surface temperature of the entire insulator is the same as the temperature of the test piece, and cannot reflect the temperature difference caused by the transition process, that is, ΔT lam-turb → 0.

[0069] (2) If the insulator is very thick and has a small thermal conductivity, B i → ∞, then T w → T rec ≈ T 0,∞ . Similarly, it cannot reflect the temperature difference caused by the transition process, that is, ΔT lam-turb → 0.

[0070] The above results show that by optimizing the selection of the physical parameters d and λ of the insulator (corresponding to different wall surface enhanced heat transfer schemes), it is expected to maximize the target ΔT i under the best B lam-turb configuration.

[0071] The best effect of wall surface enhanced heat transfer is achieved by parameter configuration, and the theoretical analysis is as follows:

[0072] Let T rec = T 0,∞ , then:

[0073]

[0074]

[0075] Then ΔT lam-turb can be expressed as:

[0076]

[0077] Since the physical parameters of the same insulator are the same, the difference between B i in the laminar flow area and the turbulent flow area depends on h, that is:

[0078]

[0079] Then we have:

[0080]

[0081] Given a specific k value, then ΔT lam-turb Depends on B i_lam , the optimal enhanced heat exchange scheme corresponds to B i_lam , which can be expressed as:

[0082]

[0083] h turb / h lam is the ratio of heat transfer coefficients in the turbulent region and the laminar region near the transition point. The ratio is related to the incoming flow Reynolds number, and also related to factors affecting the growth characteristics of the boundary layer, such as roughness, turbulence, presence or absence of separation bubbles, etc., but its value is generally between 2 and 4.

[0084] Figure 3 ΔT lam-turb distribution under different enhanced heat exchange parameter configurations is given. For a specific flow condition (k value determined), ΔT lam-turb rapidly rises with the increase of B i . When B i increases to a certain value, ΔT lam-turb remains at a relatively high level and maintains a relatively flat development trend, and is no longer sensitive to B i . The above results show that when configuring the enhanced heat exchange parameters, the heat insulation material should be as thick as possible and the thermal conductivity should be as good as possible to avoid the influence of low B i on the test results. Moreover, the optimal enhanced heat exchange scheme corresponds to B i , which depends on h turb / h lam under the working condition. The larger h turb / h lam , the smaller the optimal B i . Therefore, by reasonably optimizing the physical parameters of the heat insulation material (i.e., determining the optimal B i corresponding to the working condition), the heat exchange can be enhanced, which can effectively increase the temperature drop amplitude of the laminar region / turbulent region and improve the diagnostic precision of the infrared thermal imaging transition region.

[0085] In the preferred embodiment of the application, in the step SS2, the optimal configuration parameter value is obtained by extreme value solving to quickly obtain the physical parameters d and λ of the heat insulation material with the maximum temperature drop amplitude under multiple working conditions.

[0086] In the preferred embodiment of the application, in the step SS4, the transient laser pulse heating process is controlled by adjusting the laser power and pulse width to adapt to the heat insulation material coating with different thickness d and thermal conductivity λ, and ensure that the blade surface temperature uniformly rises to T sub .

[0087] In a preferred embodiment of the present invention, in step SS5 above, the capture frequency of the infrared high-speed camera is adjusted according to the rate of change of the blade surface temperature to ensure that sufficient temperature distribution data is captured for subsequent temperature difference analysis and determination of transition intervals.

[0088] The above-described embodiment 1 details the implementation process of the present invention. By precisely controlling and optimizing the physical properties of the thermal insulation material, combined with transient laser heating technology and high-speed infrared thermal imaging, the present invention can significantly improve the temperature difference between laminar and turbulent flow regions, thereby accurately determining the boundary layer transition region. It is readily apparent that this method not only improves the accuracy of transition testing but also possesses the advantages of simple testing procedures and low cost, providing strong support for the refined diagnosis of complex flow characteristics within turbomachinery.

[0089] Example 2

[0090] To further verify the applicability and effectiveness of the method of the present invention under different working conditions, based on the above embodiment 1, this embodiment 2 demonstrates through specific working condition tests that by optimizing the parameters of the insulation material to enhance wall heat transfer, the accuracy of infrared thermal imaging transition testing can be improved.

[0091] Taking a specific operating condition as an example, this study verifies the feasibility of improving the diagnostic accuracy of infrared thermal imaging transition zones by enhancing heat transfer through the wall surface. Under this condition, h... lam =10W·m -2 ·K -1 h turb / h lam =3, limited by material temperature, temperature difference T sub -T 0,∞ The temperature is set to 20K. Optimizing the physical properties of the insulation material directly determines the temperature drop in the laminar-turbulent flow region.

[0092] (1) Thermal insulation material A:

[0093] The thermal conductivity of the insulation material is: λ = 0.2 W·m -1 ·K -1 If the thickness d is 0.1mm, then B i，lam =0.005, ΔT lam-turb 0.2K corresponds to ΔT lam-turb / T sub -T 0,∞ =0.01.

[0094] (2) Thermal insulation material B:

[0095] The thermal conductivity of the insulation material is: λ = 0.2 W·m -1 ·K -1 If the thickness d is 2mm, then B i，lam =0.1, ΔTlam-turb It is 2.8K, corresponding to ΔT lam-turb / T sub -T 0,∞ =0.14.

[0096] (3) Thermal insulation material C:

[0097] The thermal conductivity of the insulation material is: λ=0.04W·m -1 ·K -1 If the thickness d is 2mm, then B i，lam =0.5 (close to the optimal value at this point), ΔT lam-turb The maximum temperature drop achievable under this condition is 5.3K. The corresponding ΔT is... lam-turb / T sub -T 0,∞ =0.265.

[0098] By comparing the ΔT corresponding to insulation materials A, B, and C lam-turb / T sub -T 0,∞ It can be seen that by reasonably optimizing the physical properties of insulation materials, wall heat transfer can be significantly enhanced, and the temperature drop in the laminar / turbulent flow region can be increased by 10 to 20 times (e.g., Figure 4 As shown in the figure, it significantly increases the infrared test signal-to-noise ratio and improves the transition test accuracy.

[0099] Through a detailed comparative analysis of Example 2, the crucial role of optimizing the design of thermal insulation material properties to maximize the temperature drop in the laminar and turbulent flow regions is clearly revealed, thus verifying the performance of the method of this invention in improving the accuracy of infrared thermal imaging transition testing. This method not only enhances the wall heat transfer effect but also provides a more accurate method for boundary layer transition diagnosis of turbomachinery, demonstrating the broad potential and practical value of this invention in real-world applications.

[0100] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for improving the accuracy of infrared thermography transition test of the boundary layer of turbomachinery, by increasing the temperature difference between the laminar and turbulent flow regions to improve the accuracy of the determination of the transition region of the boundary layer of turbomachinery, characterized in that, The method comprises at least the following steps when implemented: SS1. A thermal insulation material coating is applied to the surface of the blade of the turbomachinery to be tested, and the physical parameters d and λ of the thermal insulation material are selected and adjusted according to the required test accuracy and the thermal response characteristics of the blade surface, wherein d and λ are the thickness and thermal conductivity of the thermal insulation material, respectively; SS2. Based on a one-dimensional analysis model considering the heat conduction and convection effects, the temperature drop range ΔT between the laminar flow region and the turbulent flow region on the blade surface is established lam-turb and the correlation between the thermal insulation material physical parameters d and λ, wherein ΔT lam-turb = |T w,lam -T w,turb |, T w,lam , T w,turb are the wall temperatures of the laminar flow region and the turbulent flow region on the blade surface, respectively SS3. According to the established temperature drop range ΔT between the laminar flow region and the turbulent flow region of the blade surface layer lam-turb The correlation between the thermal insulation material physical parameters d and λ, and the optimal configuration parameter value of the thermal insulation material physical parameters d and λ are determined to maximize the temperature drop range ΔT between the laminar flow region and the turbulent flow region of the blade surface layer under the test working condition lam-turb , and further strengthen the heat exchange effect of the blade wall surface to be tested; SS4. The surface of the blade under test is heated using transient laser pulses and the surface temperature is controlled to rise rapidly to a set temperature value T sub and is evenly distributed; SS5. The blade wall surface temperature T at different streamwise positions after heating is captured by an infrared high-speed camera w for subsequent temperature difference analysis and determination of the transition region. SS6. Based on the wall temperature T of the laminar flow zone on the blade surface w，lam and the wall temperature T in the turbulent region w，turb Difference ΔT lam-turb The location of the boundary layer transition zone on the surface of the impeller blade under test is determined.

2. The method of claim 1, wherein, In the one-dimensional analysis model, the blade to be measured is regarded as a substrate material, the surface of which is covered with a coating of thermal insulation material with thickness d and thermal conductivity λ, and the surface temperature of the blade is uniformly raised to T sub , the temperature T w at the surface of the coating of thermal insulation material is derived based on the energy conservation equation, taking into account the heat conduction inside the coating of thermal insulation material and the convective heat exchange outside the coating with the fluid sub , the free stream temperature T 0,∞ , the convective heat exchange coefficient h, and the physical parameters d and λ of the thermal insulation material w,lam , T w,turb are not the same, and the difference between them is the required ΔT lam-turb .

3. The method of claim 2, wherein the method is characterized by, In the step SS2, the expression of the energy conservation equation established based on the one-dimensional analysis model is as follows: wherein q is the heat flux per unit area, T sub T is the temperature of the blade substrate material after heating by a transient laser pulse, T w T is the temperature of the surface of the thermal barrier coating, T rec T is the recovery temperature and is approximately equal to the free stream temperature 0,∞ h is the convective heat transfer coefficient at the surface of the thermal barrier coating. Based on the above energy conservation equation, the temperature T of the surface of the thermal insulation material coating is derived w The relationship between T sub , the free stream temperature T 0,∞ , the convective heat transfer coefficient h, and the physical parameters d, λ of the thermal insulation material is derived. wherein, is dimensionless B i a number to represent the relative magnitude of the wall conduction thermal resistance and the surface convection heat transfer thermal resistance.

4. The method of claim 3, wherein the method is characterized by, In the step SS2, the convection heat transfer coefficient h lam , h turb of the laminar flow region and the turbulent flow region are calculated respectively based on the laminar flow region and the turbulent flow region i , Bi _lam , Bi _turb , and the wall surface temperature T w,lam , T w,turb of the laminar flow region and the turbulent flow region are calculated respectively based on the laminar flow region and the turbulent flow region lam-turb : wherein B is the ratio of the convective heat transfer coefficient in the laminar region and the turbulent region i N is the number of layers of the thermal barrier coating, and h is the convective heat transfer coefficient in the turbulent region turb h is the convective heat transfer coefficient in the laminar region lam The ratio of h and h reflects the difference in the convective heat transfer intensity in the turbulent region and the laminar region.

5. The method of claim 4, wherein the method further comprises: In the step SS2, based on the same physical parameters d, λ of the same thermal insulation layer material, the laminar flow region and the turbulent flow region B i The difference in the number depends on the difference in the convective heat transfer coefficient h: Thus, ΔT lam-turb is further transformed into the following calculation formula: In different test conditions, the physical parameters d and λ of the thermal insulation material are optimized to adjust Bi _lam to achieve the maximization of ΔT lam-turb , thereby improving the signal-to-noise ratio of infrared testing and the accuracy of transition diagnosis.

6. The method of claim 5, wherein the method further comprises: In step SS2 above, under different test conditions, the temperature drop ΔT between the laminar and turbulent regions on the blade surface is considered. lam-turb With laminar flow region Bi _lam Fitting the relationship between numbers, Bi in different laminar flow regions _lam ΔT under number configuration lam-turb The distribution curve is used to determine the optimal laminar flow region Bi under the corresponding operating conditions. _lam The parameters d and λ of the thermal insulation material are configured and then optimized to achieve the desired ΔT under the corresponding test conditions. lam-turb Maximize.

7. The method of claim 5, wherein the method further comprises: In step SS2, the ratio k of the convection heat transfer coefficient in the laminar flow region and the turbulent flow region is analyzed under different test conditions, and the optimal laminar flow region Bi under the corresponding test condition is determined based on the ratio _lam Numerical configuration Then, the physical parameters d and λ of the thermal insulation material are optimized and determined, so as to maximize ΔT lam-turb under the corresponding test condition.

8. The method of claim 5, wherein the method further comprises: In the step SS2, the optimal configuration parameters are determined by simple extreme value solving to quickly obtain the physical parameters of the thermal insulation material that maximize the temperature drop amplitude under multiple working conditions.

9. The method of claim 1, wherein the method is used to improve the accuracy of infrared thermography boundary layer transition testing of an impeller of a turbomachinery. In the above step SS4, the transient laser pulse heating process is controlled by adjusting the laser power and pulse width to accommodate the thermal barrier coating of different thickness d and thermal conductivity λ, ensuring the blade surface temperature is uniformly raised to T sub . ​ 10. The method of claim 1, wherein the method is used to improve the accuracy of infrared thermography boundary layer transition testing of an impeller of a turbomachinery. In the step SS5, the capture frequency of the infrared high-speed camera is adjusted according to the speed of the temperature change of the blade surface to ensure that sufficient temperature distribution data is captured for subsequent temperature difference analysis and determination of the transition region.

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