A Reconstruction Method for the End Wall of a Cascade in Gas Turbine Transient and Steady State Experiments

Abstract

The present invention discloses a method for reconstructing the end wall of a gas turbine transient and steady-state experimental cascade, comprising the following steps: Step (1): Arrange multiple groups of calibration points in the end wall region of the experimental cascade, and respectively determine the coordinate points of the calibration points in the three-dimensional space and the coordinates in the two-dimensional pixel plane of the infrared camera; Step (2): Based on the geometry of the experimental cascade, divide the cascade profile types and divide the three-dimensional structured / unstructured grids, and then output the grid nodes and grid profile information; Step (3): Select the shooting perspective for the initial experiment; Step (4): Extract the end wall experimental data; Step (5): Reconstruct the end wall region with the obtained turbine cascade end wall grid nodes and grid profile information; Step (6): Determine whether the reconstruction of the complete end wall region is completed. The present invention improves the reliability and accuracy of the end wall reconstruction method, reduces the experimental operation difficulty and obtains more accurate experimental data.

Description

Technical Field

[0001] The present invention relates to the technical field of gas turbine aerodynamic heat transfer and integrated cooling, and specifically relates to a method for reconstructing the end wall of a gas turbine transient and steady-state experimental cascade. Background Technique

[0002] As an important work component in aero-engines and heavy gas turbines, increasing the inlet temperature of a gas turbine can effectively improve its thermal efficiency. Under this background, the inlet temperature of gas turbines has been increasing year by year. Among them, the inlet temperature of advanced heavy gas turbine turbines has exceeded 1600K, and the inlet gas temperature of military aero-engine turbines can reach 2000K, far exceeding the environmental working temperature (1300K) that the current materials used to manufacture turbines (such as nickel-based superalloys) can withstand. To ensure the normal operation of gas turbines, it is necessary to combine advanced cooling technologies, high-temperature-resistant materials, and thermal barrier coatings to design more reliable blade solutions.

[0003] Due to the complex flow and strong mixing inside the turbine cascade passage, it greatly increases the design difficulty of the turbine cascade. Conducting in-depth research on the flow, heat transfer, and cooling characteristics of the gas turbine cascade passage has important industrial significance for the development of modern advanced cooling scheme designs. Transient and steady-state experiments are important means for conducting mechanistic research on the cascade passage. Among them, infrared thermography (IRT) technology has been widely used in various domestic and foreign experimental studies on heat transfer and cooling. Limited by the processing size of the infrared window, the images captured by the infrared camera often do not contain the complete end wall area. And most of the experiments on the end wall area of the cascade avoid the influence of the blade body and blade tip. Therefore, the test piece model is often designed with a relatively high blade height, which further increases the occlusion of the end wall area of the cascade. And the above problems cannot be solved by simply adjusting the shooting angle, which greatly increases the operation difficulty of the researchers' experiments and further restricts the quantitative analysis of the experimental data by the researchers and the extended research based on the experimental data. Summary of the Invention

[0004] In order to overcome the defects existing in the above technologies, the purpose of the present invention is to provide a method for reconstructing the end wall of a gas turbine transient and steady-state experimental cascade, which improves the reliability and accuracy of the end wall reconstruction method, reduces the experimental operation difficulty and obtains more accurate experimental data, and better meets the needs of gas turbine experimenters.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for reconstructing the end wall of a gas turbine transient and steady-state experimental cascade, comprising the following steps:

[0007] Step (1): Modify or design the experimental model according to the experimental requirements, and deploy multiple groups of calibration points in the endwall region of the experimental cascade. Determine the coordinate points of the calibration points in the three-dimensional space and the coordinates in the two-dimensional pixel plane of the infrared camera, that is, the three-dimensional space point coordinates and two-dimensional image point coordinates of the calibration points.

[0008] Step (2): Based on the geometry of the experimental cascade, divide the cascade profile types (such as endwall, blade body, blade tip, etc.), and divide the three-dimensional structured or unstructured grids. Then output the grid nodes and grid profile information of the cascade profile (such as endwall, blade body, blade tip, etc.).

[0009] Step (3): Select the shooting perspective for the initial experiment.

[0010] Step (4): Based on the experimental results of Step (3), extract the endwall experimental data.

[0011] Step (5): Reconstruct the endwall region based on the turbine cascade endwall grid nodes and grid profile information obtained in Step (2).

[0012] Step (6): Based on the turbine blade endwall grid nodes and grid profile information in Step (2), determine whether the reconstruction of the complete endwall region is completed.

[0013] Limited by the processing size of the infrared window, the images captured by the infrared camera often do not contain the complete endwall region. And for most experiments on the cascade endwall region, to avoid the influence of the blade body and blade tip, the test piece model is often designed with a relatively high blade height, which further increases the occlusion of the cascade endwall region.

[0014] To solve the above problems, in Step (1), multiple groups of calibration points need to be deployed in the endwall region of the test piece before the experiment, and ensure that they are clearly visible in the images captured by the infrared camera, and extract the coordinates of the calibration points in the three-dimensional space.

[0015] In Step (2), divide the profiles of the turbine cascade three-dimensional model (such as endwall, blade body, blade tip, etc.), and then divide the three-dimensional structured / unstructured grids. On this basis, export the grid node coordinates and grid surface information of each profile grid respectively.

[0016] In Step (3), since the present invention aims to reconstruct the entire endwall region through multi-view, there is no need to deliberately avoid the occlusion of the blade tip and infrared window on the cascade endwall during each perspective shooting. It is only necessary to ensure that the calibration points deployed on the test piece are within the depth of field of the infrared camera, that is, the calibration points are clearly visible in the infrared image.

[0017] In step (4), the experimental data of the endwall region is extracted based on the extraction method of the cascade profile data in the transient and steady-state experiments of the gas turbine. In particular, different from the blade and blade tip regions, the blade and blade tip regions are not covered or interfered by other profiles and can be directly reconstructed and data-extracted, while the endwall region is blocked by the blades and blade tips of adjacent experimental cascades. Therefore, when reconstructing the endwall region, it is necessary to ensure the integrity of the reconstructed endwall for further post-processing, and at the same time, avoid mis-extracting the data of the blade or blade tip region to the endwall region due to line-of-sight occlusion;

[0018] First, it is necessary to preprocess the captured images using the profile information of the blade tip and blade regions, that is, project the profile information of the blade tip and blade onto the image plane, and mask the pixel points within the blade tip or blade profile so that they cannot be mis-extracted by the grid profile of the endwall region.

[0019] In step (5), the grid nodes and grid profile information of the endwall region obtained in step (2) are projected onto the pixel plane, and the projection of each grid node is traversed in turn; if the grid node is located in the endwall region, the pixel value is updated, that is, the average value of the pixel values obtained from each shooting angle; if the grid node is not located in the endwall region, that is, the grid node is in the masked area, the extraction of the pixel value of this point is abandoned.

[0020] In step (6), traverse the grid nodes in the endwall region in turn to determine whether the reconstruction of the complete endwall region is completed: if pixel values exist for all nodes, the three-dimensional reconstruction and experimental data extraction of the complete endwall region are completed; if there are nodes without pixel values, it means that this region is blocked by the blade or infrared window, and the shooting angle needs to be updated to supplement the endwall information.

[0021] The beneficial effects of the present invention:

[0022] (1) The present invention has strong applicability and can be used in any gas turbine heat transfer and cooling test bench with an infrared window without any modification to the test bench;

[0023] (2) The reconstruction algorithm of the present invention has a feedback function, that is, it can characterize the occluded region, which is convenient for scientific research and testing personnel to correct the view;

[0024] (3) The present invention can accurately and reliably reconstruct the complete endwall region, reducing the operation difficulty brought by scientific research and testing personnel in pursuit of a larger viewing angle during the experiment, and at the same time facilitating the post-processing of measurement parameters by scientific research and testing personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flowchart of a method for reconstructing the endwall of a gas turbine transient and steady-state experimental cascade of the present invention.

[0026] Figure 2 It is a schematic diagram of the end wall being blocked by adjacent blades in this embodiment.

[0027] Figure 3 It is the structured grid in the end wall region of this embodiment.

[0028] Figure 4 It is a schematic diagram of the division of the cascade profile in the pixel plane in this embodiment.

[0029] Figure 5 It is a schematic diagram of multi - perspective shooting in the end wall region of this embodiment. Detailed implementation manners

[0030] The present invention will be further described in detail below in conjunction with embodiments.

[0031] Figure 1 It is a flowchart of the reconstruction method for the end wall of the gas turbine transient and steady - state experimental cascade. According to the experimental requirements, the experimental model is modeled or designed, and multiple groups of calibration points are arranged in the end wall region of the experimental cascade. The coordinate points of the calibration points in the three - dimensional space and the coordinates in the two - dimensional pixel plane of the infrared camera are determined respectively, that is, the three - dimensional space point coordinates and two - dimensional image point coordinates of the calibration points; according to the geometry of the experimental cascade, the cascade profile types (such as end wall, blade body, blade tip, etc.) are divided, and three - dimensional structured / unstructured grids are divided, and then the grid surface information is output; a shooting perspective with good visibility is selected for the initial experiment; the end wall region images are extracted according to the initial captured images; the end wall region is reconstructed through the grid in the gas turbine end wall region; each grid node is traversed to determine whether the reconstruction and data extraction of the complete end wall region are completed.

[0032] The reconstruction method for the end wall of the gas turbine transient and steady - state experimental cascade includes the following steps:

[0033] Step (1): According to the experimental requirements, the experimental model is modeled or designed, and multiple groups of calibration points are arranged in the end wall region of the experimental cascade. The coordinate points of the calibration points in the three - dimensional space and the coordinates in the two - dimensional pixel plane of the infrared camera are determined respectively, that is, the three - dimensional space point coordinates and two - dimensional image point coordinates of the calibration points;

[0034] Step (2): Based on the geometry of the experimental cascade, the cascade profile types (such as end wall, blade body, blade tip, etc.) are divided, and three - dimensional structured / unstructured grids are divided, and then the grid node and grid profile information are output;

[0035] Step (3): Select a shooting perspective for the initial experiment;

[0036] Step (4): Based on the experimental results of step (3), the end wall experimental data are extracted;

[0037] Step (5): Reconstruct the endwall region based on the turbine cascade endwall grid nodes and grid surface information obtained in step (2);

[0038] Step (6): Determine whether the reconstruction of the complete endwall region is completed based on the turbine blade endwall grid nodes and grid surface information in step (2).

[0039] Limited by the processing size of the infrared window, the images captured by the infrared camera often do not contain the complete endwall region; and for most experiments on the cascade endwall region, in order to avoid the influence of the blade body and blade tip, the test piece model is often designed with a relatively high blade height, which further increases the occlusion of the cascade endwall region;

[0040] To solve the above problems, in step (1), multiple sets of calibration points need to be arranged in the endwall region of the test piece before the experiment, and ensure that they are clearly visible in the images captured by the infrared camera, and extract the coordinates of the calibration points in the three-dimensional space.

[0041] In step (2), the surfaces of the turbine cascade three-dimensional model (such as endwall, blade body, blade tip, etc.) are divided, and then three-dimensional structured / unstructured grids are divided; and on this basis, the grid node coordinates and grid surface information of each surface grid are exported respectively.

[0042] In step (3), since the present invention aims to reconstruct the entire endwall region through multi-view, there is no need to deliberately avoid the occlusion of the blade tip and infrared window on the cascade endwall when shooting from each perspective. It is only necessary to ensure that the calibration points arranged on the test piece are within the depth of field of the infrared camera, that is, the calibration points are clearly visible in the infrared images.

[0043] In step (4), the endwall region experimental data is extracted based on the extraction method of the cascade surface data in the gas turbine transient and steady-state experiments. In particular, different from the blade body and blade tip regions, the blade body and blade tip regions are not covered or interfered by other surfaces and can be directly reconstructed and data extracted, while the endwall region is blocked by the blade body and blade tip of the adjacent experimental cascade. Therefore, when reconstructing the endwall region, it is necessary to ensure the integrity of the reconstructed endwall for further post-processing, and at the same time, avoid mis-extracting the data of the blade body or blade tip region to the endwall region due to line-of-sight occlusion;

[0044] First, it is necessary to preprocess the captured images using the surface information of the blade tip and blade body regions, that is, project the surface information of the blade tip and blade body onto the image plane, and mask the pixel points belonging to the blade tip or blade body surface, so that they cannot be mis-extracted by the grid surface of the endwall region.

[0045] In step (5), project the grid nodes and grid surface information in the endwall region obtained in step (2) onto the pixel plane, and sequentially traverse the projections of each grid node; if the grid node is located in the endwall region, update the pixel value, that is, the average value of the pixel values obtained in each shooting perspective; if the grid node is not located in the endwall region, that is, the grid node is in the mask area, discard the extraction of the pixel value of this point.

[0046] In step (6), sequentially traverse the grid nodes in the endwall region to determine whether the reconstruction of the complete endwall region is completed: if pixel values exist for all nodes, the three-dimensional reconstruction of the complete endwall region and the extraction of experimental data are completed; if there are nodes for which pixel values are not obtained, it indicates that there is a phenomenon of occlusion by the blade body or infrared window in this region, and it is necessary to update the shooting perspective to supplement the endwall information.

[0047] In an embodiment of the present invention, a certain gas turbine moving blade is used to conduct a transient experiment on the heat transfer cooling of the endwall, and the test piece is preprocessed and experimental data is extracted based on the present invention.

[0048] Refer to Figure 1 , this example provides a method for reconstructing the endwall of a gas turbine transient and steady-state experimental cascade, which specifically includes the following steps:

[0049] Example:

[0050] 1. Modify or design the experimental model and arrange calibration points

[0051] In this embodiment, the main concerned area is the performance index of the cascade endwall. Therefore, it is necessary to design a relatively high blade height to avoid the influence of the flow in the blade body and blade tip regions on the flow field in the endwall region. For this reason, in this embodiment, the blade height of the experimental model is set to 80 mm. However, the relatively high blade height further exacerbates the occlusion of the endwall region, resulting in partial loss of the endwall region in the infrared image, as Figure 2 shown.

[0052] 2. Grid division of the turbine cascade endwall

[0053] In this embodiment, it is necessary to perform surface division on the cascade model, such as the blade tip, blade body, endwall, etc. Particularly, to achieve the complete reconstruction of the endwall region, the endwall region of the cascade model cannot exceed the endwall region of the test piece model, and three-dimensional structured grids are divided on this basis, as Figure 3 shown.

[0054] 3. Initial perspective shooting

[0055] As Figure 5 shown in Perspective 1, select an initial perspective to shoot the endwall region, and adjust the aperture so that the endwall region is within the depth of field of the infrared camera.

[0056] 4. Extraction of Endwall Experimental Data

[0057] Based on the extraction method of cascade profile data from gas turbine transient and steady-state experiments, the experimental data in the endwall region is extracted. In particular, different from the blade body and blade tip regions, the blade body and blade tip regions are not covered or interfered by other profiles and can be directly reconstructed and data-extracted. However, in the endwall region, there is a phenomenon that it will be blocked by the blade body and blade tip of adjacent experimental cascades. Therefore, when reconstructing the endwall region, it is necessary to ensure the integrity of the reconstructed endwall for further post-processing, and at the same time, it is necessary to avoid mis-extracting the data of the blade body or blade tip region to the endwall region due to line-of-sight occlusion. To solve the above problems, first, project the profile information of the blade tip and blade body into the image plane to perform profile segmentation on the image information, and sequentially segment the image into the inlet section, blade tip region, blade body region, outlet section through the profile lines of each profile, and the remaining region is the endwall region, as Figure 4 shown. Then, perform mask processing on the pixel points in the inlet section, blade tip region, blade body region, and outlet section to prevent them from being mis-extracted by the grid profile of the endwall region. Finally, only extract the endwall pixel values located in the non-masked region to complete the extraction of the initial experimental data.

[0058] 5. Update Reconstructed Data

[0059] Before the initial shooting, the numerical values of the grid projection points in the endwall region are all assigned zero. After the first shooting, assign the results of the experimental data extraction to the grid projection points. For the second and subsequent shootings, update the grid projection points with the average value of the pixel values obtained from each perspective. When completing each data extraction, the endwall region image will be automatically updated to display the data extraction effect, and the missing data region will be feedback through the gray region, so as to select a suitable perspective for the next shooting to complete the data extraction of the entire endwall region.

[0060] 6. Determine Whether 3D Reconstruction is Completed

[0061] Traverse each grid projection point. If the pixel values of all grid projection points have been updated, then the 3D reconstruction of the endwall region is completed;

[0062] If there are still some grid projection points with zero values (i.e., the gray region mentioned in step 5), then it is necessary to update the perspective and shoot again, as Figure 5 shown in Perspective 2.

[0063] The present invention is used to process the experimental data obtained from gas turbine transient and steady-state experiments, in which a complete cascade endwall is reconstructed based on the endwall surface information and the endwall experimental data is extracted.

Claims

1. Reconstruction method for the end wall of a cascade in gas turbine transient and steady state experiments, characterized in that, It includes the following steps: Step (1): Modify or design the experimental model according to the experimental requirements, and arrange multiple groups of calibration points in the end wall area of the experimental cascade. Determine the coordinate points of the calibration points in the three-dimensional space and the coordinates in the two-dimensional pixel plane of the infrared camera, that is, the three-dimensional space point coordinates and two-dimensional image point coordinates of the calibration points; Step (2): Divide the cascade profile type based on the geometry of the experimental cascade, and divide the three-dimensional structured or unstructured grid, and then output the grid nodes and grid profile information of the cascade end wall; Step (3): Select the shooting perspective for the initial experiment; Step (4): Extract the end wall experimental data based on the experimental results of Step (3); Step (5): Reconstruct the end wall area based on the grid nodes and grid profile information of the turbine cascade end wall; Step (6): Judge whether the reconstruction of the complete end wall area is completed based on the grid nodes and grid profile information of the gas turbine cascade end wall; In Step (4), extract the end wall area experimental data by using the extraction method of the gas turbine transient and steady-state experimental cascade profile data; Use the profile information of the blade tip and blade body areas to preprocess the captured images, that is, project the profile information of the blade tip and blade body into the image plane, and mask the pixel points belonging to the blade tip or blade body profile to prevent them from being mis-extracted by the grid profile of the end wall area; In Step (5), project the grid nodes and grid profile information of the end wall area obtained in Step (2) onto the pixel plane, and traverse the projections of each grid node in turn; if the grid node is located in the end wall area, update the pixel value, that is, the average value of the pixel values obtained at each shooting perspective; If the grid node is not located in the end wall area, that is, the grid node is in the masked area, give up the extraction of the pixel value of this point; In Step (6), traverse the grid nodes of the end wall area in turn to judge whether the reconstruction of the complete end wall area is completed: if pixel values exist for all nodes, the three-dimensional reconstruction and experimental data extraction of the complete end wall area are completed; if there are nodes without pixel values, it means that there is a phenomenon of being blocked by the blade body or infrared window in this area, and the shooting perspective needs to be updated to supplement the end wall information.

2. The reconstruction method of the cascade end wall for gas turbine transient and steady state experiments according to claim 1, characterized in that In Step (1), multiple groups of calibration points need to be arranged in the end wall area of the test piece before the experiment, and ensure that they are clearly visible in the images captured by the infrared camera, and extract the coordinates of the calibration points in the three-dimensional space.

3. The reconstruction method of the cascade end wall for gas turbine transient and steady state experiments according to claim 1, characterized in that, In Step (2), divide the profile of the three-dimensional model of the turbine cascade, and then divide the three-dimensional structured / unstructured grid; and on this basis, export the grid node coordinates and grid surface information of each profile grid respectively.

4. The method for reconstructing the end wall of the cascade for gas turbine transient and steady-state experiments according to claim 1, characterized in that, When shooting at each perspective, there is no need to deliberately avoid the occlusion of the blade tip and infrared window on the cascade end wall, only need to ensure that the calibration points arranged on the test piece are within the depth of field of the infrared camera, that is, the calibration points are clearly visible in the infrared image.

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