Tomography For Two-dimensional Temperature Distribution Based On TDLAS

According to the urgent need for diagnosis of the combustion flow field of the aero-engine combustion chamber,TDLAS measurement system was built,and ART algorithm was introduced to reconstruct the two-dimensional distribution of the temperature field.The main contents and results are as follows:According to the principle of spectral line selection in TDLAS technology,the two absorption lines 7203.89 cm-1 and 7435.61 cm-1 of H2O were selected as the pair of temperature measurement lines.Based on the direct absorption method,TDLAS experimental system was set up.The experiment adopted the time-division method.Two light rays cross vertically through the measured flow field.A program written in Python was used to perform a series of processing on the experimental data to calculate the temperature value.The thermocouples were used to compare the measured temperatures,verifying that the system has a certain degree of accuracy and reliability.The influence of the error was analyzed.In order to achieve the purpose of reconstructing the plane temperature distribution of the combustion field,Algebraic Reconstruction Technique(ART)was introduced.The implementation of the ART algorithm was described in detail.Based on this algorithm,a series of numerical simulations were conducted and the following conclusions were drawn:1)When the number of grids is fixed,the more the number of rays is,the better the reconstruction effect is.2)When the measured area grid is fixed and the number of rays is the same,the more dense the grid is divided,the better the reconstruction effect is.3)When the number of grids is fixed,the reconstruction effect becomes better and better with the increase of the amount of incident light.When the number of light reaches a certain value,the reconstruction effect tends to be the best stable state.4)When the ratio of the light distance to the grid distance is between 0.5 and 1,the reconstruction effect is best.5)In the actual measurement process,due to space and cost constraints,the amount of incident light is small and the reconstruction quality can be improved by increasing the virtual light.TDLAT experimental system was set up.The experiment used 3 horizontal rays and 3 perpendicular rays to intersect.Two-dimensional temperature distribution of the measured area was reconstructed,and the cause of the error was analyzed.The main reasons included:1)Non-uniform etalon peak spacing causes greater relative frequency deviation.2)Voigt fitting bias directly leads to the integral absorption rate value is too large or too small.3)Absorption information of H2O molecules in the normal temperature environment on the selected spectral line is brought into the absorption signal,resulting in larger deviation of the edge temperature value.