Shevchenko M. Determination Method of the Most Advantageous Composition of Propulsion for a Supersonic Cruising Aircraft

The analysis of the problem of composition and parameters chosen for the supersonic aircrafts propulsion was performed. It was found that this problem is solved on the basis of an approach of choosing the propulsion composition and parameters according to a given efficiency criterion at a given flight speed. Herewith, a limited range of propulsions in a narrow range of flight speeds is considered. This problem formulation does not allow obtaining the dependence of the propulsion composition and parameters on the speed of supersonic cruising flight. Thus, the establishment of patterns of change of the propulsion composition and parameters from the speed of supersonic cruising is a vital problem. Substantiation of the use of the approach of choosing the most advantageous propulsion composition and parameters by the criterion of minimum relative mass of fuel and propulsion for establishing the patterns of change of the propulsion composition and parameters from the supersonic cruising speed was performed. Ways for improving this approach have been selected. The list of mathematical models and methods necessary for development of a method of choosing propulsion composition and parameters for aircraft with the supersonic cruising speed was defined. Effective in terms of calculation results optimizing and processing the method of choosing the most advantageous propulsion composition and parameters by the criterion of the minimum mass of fuel and propulsion taking into account profile and the mode of the flight, geometric characteristics and the variation of mass and aerodynamic parameters of the supersonic cruising speed aircraft has been developed. In the developed method, the mathematical models and methods, which are needed for solving the problem of choosing the propulsion composition and parameters, were comprehensively structured. Necessity of improvement of mathematical models of the working process of combustion chamber and propulsion with combined turboramjet engines was substantiated, namely turboramjet engine without energy transfer to the external duct (TJER), afterburning turbofan engine (TFEA) and duct-burning turbofan engine (TFEDB) that have ramjet modes. The mathematical model of the combustion chamber working process has been improved taking into account the influence of the chemical composition of the working substance on the different operating modes of the combustor on the enthalpy, which allows to increase the calculation accuracy of specific fuel consumption. The mathematical models of working process of the propulsion with TJER, TFEA and TFEDB on ramjet modes have been improved considering the total pressure losses which are caused by presence in the external duct flowpath adjustable-blade fan setting up in feathering, sudden expansion of the flow at the entrance to the mixing chamber and bottom drag at zero gas flow through the internal duct. The adequacy of improved mathematical models of the propulsion and its elements was carried out by comparing the calculation results with General Electric experimental data and calculation data performed by M. N Bondaryuk. Satisfactory results coincidence of the modeling of the combustion chamber working process and the speed characteristics of the ramjet engine was obtained. Verification of the mathematical model of aircraft aerodynamic characteristics was carried out by comparing the calculation results with NASA data. The error of comparison is less than 2%. Substantiation of the reliability of the mathematical modeling results of aircraft motion was performed by comparing the results of modeling with NASA data. The difference between obtained simulation parameters of the aircraft for cruising flight and NASA data is less than 0.5%. Using the developed method for aircraft with given flight profile with transoceanic range, aircraft mass and aerodynamic characteristics, the relative mass of fuel and propulsion for different propulsion composition were calculated. The propulsions with turbojet engines (TJE), turbofan and mixed flows turbofan engines, and propulsions with TFEA, TFEDB and TJER on ramjet mode were considered. Patterns of change of relative mass of fuel and propulsion in Mach numbers range M = 1.5…4 were established for the given propulsion compositions. The dependences of the propulsion working process optimal parameters for takeoff mode on the speed of supersonic cruising flight, providing minimum of relative mass of fuel and propulsionwere obtained.