Авіаційно-космічна техніка та технологія (Jun 2023)
Analysis of the influence of measurement errors on the absolute errors of the experimental determination of fan efficiency
Abstract
The subject of research in this article is the experimental determination of the characteristics of fans of turbofan engines with a high and ultra-high bypass ratio. Increasing the efficiency of fans of engines of the specified class requires solving many complex interrelated problems, one of which is the determination of characteristics based on test results. The goal is to substantiate the need to use a method based on the determination of torque and the formation of requirements for the accuracy of its measurement. Tasks: clarification of previously obtained relationships between measurement errors and accuracy of determination of efficiency and air flow, formation of universal dependencies that allow analysis of absolute errors of determination of efficiency of any fan or compressor based on known measurement errors, analysis of the accuracy of alternative methods of organization of measurements and calculations the specified parameters, a comparative study of the specified methods and the formation of recommendations for their practical use on the example of the characteristics of a real fan. The following results have been obtained: the formulas that relate the absolute errors of calculating the efficiency and air flow with the absolute errors of the measured parameters (mathematical models of errors) have been clarified, as well as the requirements for the accuracy of the torque measurement necessary to determine the efficiency with the specified accuracy have been specified. The scientific and practical novelty of the results obtained is as follows: the mathematical models of errors in determining the efficiency and air flow in the fan have been clarified, which connect the errors of the calculation results with the errors of the measured parameters, because of the use of these models, experimental methods of determining the characteristics of compressors and fans have been developed; for the first time, the distribution of errors in the entire area of determining the characteristics of a specific fan was analyzed in detail. It is shown that the errors in determining the efficiency of the fan depend significantly on the degree of pressure increase and air flow. At small values of these parameters, the errors increase significantly. In the area of low engine operating modes (close to the area of the low air consumption), the errors in determining the efficiency based on the processing of the measurement results are so large that a reliable determination of the efficiency becomes practically impossible without the involvement of additional information, which can be used as the calculated characteristics of the fan, and as well as the mathematical model of the engine and the results of measuring parameters of the work process in other nodes, except for the fan itself.
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