Аналіз точності експериментального визначення ККД вентилятора з використанням вимірювачів крутильного моменту

Abstract

The subject of research in this article is the processes of experimental determination of the characteristics of fans of turbojet bypass engines with a high and ultra-high bypass ratio. 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: determination of the relationship between measurement errors and the accuracy of determining the efficiency and air flow, analysis of the accuracy of alternative methods for organizing measurements and calculating the indicated parameters, comparative study of these methods, and the formation of recommendations for their practical use. For this, analytical methods of error analysis based on the methods of analysis of random variables are used. The following results were obtained: formulas that relate the errors in the calculation of efficiency and consumption with errors in the measured parameters (mathematical models of errors), and determine requirements to the torque measurement precision, which must determine the efficiency with a specified precision. The scientific and practical novelty of the results obtained is as follows: mathematical models of errors in determining the efficiency and flow in the fan have been formed, which relate the errors in the results of calculations with the errors in the measured parameters; because of the use of these models, experimental methods for determining the characteristics of compressors and fans have been developed; for the first time, an analytical expression was obtained that determines the requirements for the measurement error of torque to experimentally determine the efficiency of fans. It is shown that to determine the efficiency with an accuracy of 0.5 %, the accuracy of torque measurement even in the absence of other measurement errors cannot be worse than 0.5 %, and taking into account the perspective of measuring temperatures and pressures with relative standard deviations σδp = 0.02 % and σδT = 0.25 %, the standard deviation of the torque measurement error should not be more than 0.24 %.