Research On Overall Performance Of Super High Bypass Ratio Engine With Tip-jet Self-driven Fan

Economic demand makes the bypass ratio of turbofan engine increase continuously,but the increase of bypass ratio will bring about the problem that the speed between fan and low-pressure compressor and low-pressure turbine does not match.At present,the main solutions are three-rotor structure scheme and gear transmission structure scheme.The three-rotor scheme will lead to the complexity of engine structure and control law,which makes it difficult to realize.However,the cooling and reliability of gearbox in gear transmission structure still need to be tested.Therefore,this paper conceives a new type of jet self-driving fan scheme,which draws air from the low-pressure turbine to the fan tip area.Through the hoop-ring nozzle structure arranged at the fan tip,the gas ejects at a higher speed,and drives the fan to rotate by the reaction force obtained from the high-speed gas ejection.Firstly,this paper establishes the calculation model of the fan's jet driving force.Under the given air total temperature,air total pressure and tip hoop nozzle area,the jet driving force can be obtained.Then,the model of turbofan engine with large bypass ratio and jet self-driving fan is established by using object-oriented method and C++ program,and the fan air intake,engine thrust and fuel consumption under design state are determined.In the calculation of engine non-design point state,the method of component characteristics scaling and Newton-Raphson iteration is adopted.Seven initial guesses are given.Seven equilibrium equations are established by using the constraint conditions of engine components working together.In the flight envelope of civil aviation passenger aircraft,some typical working points are selected to calculate the thrust and fuel consumption of the engine in the non-design state,and the working lines of fans,supercharged stages and high-pressure compressors are given.Gasturb software is used to calculate the design and non-design points of conventional turbofan engines with large bypass ratio.By comparing the thrust and fuel consumption of the engines under the jet self-driving scheme with those under the conventional scheme,the following conclusions are drawn:Under the condition that the thrust and fuel consumption of the engine are basically unchanged,the series of the low-pressure turbine of the engine is successfully reduced,the weight of the engine is further reduced,and the thrust-weight ratio of the engine is increased.