New insights into component matching mechanism in the compression system of double bypass engine

Variable cycle engine(VCE)is one of the most promising technologies for the next-generation aircraft,the matching of different components in the compression system is a key difficulty VCE faced.To investigate the component matching mechanisms in the VCE compression system,an advanced throughflow program is employed to calculate the characteristic lines of each component,and a zero-dimensional method is developed to cap-ture the component performance deviation during the coupling working process.By setting the compressor stall and choke conditions as the boundary,the operation range of the compression system isfirst clarified,and the aerodynamic performance in the operation zone is discussed,thus providing a theoretical basis for optimization of the engine operating con-trol scheme.Results show that the efficiency of the coreflow is optimum at the left-bottom corner of the operation region,while the total pressure ratio peaks at the right-top area,hence a balance is needed when deciding the matching point.Regulations of component control pa-rameters will change the position of the operation zone,as well as the corresponding aerody-namic performance.Decreasing the core driven fan stage rotating speed can improve the total bypass ratio,yet the total pressure ratio of the coreflow will be decreased.Closing the core driven fan stage inlet guide vane can increase the total bypass ratio without changing the core flow aerodynamic performance significantly.The bypass ratio of the compression system can also be increased by increasing the fan stall margin or decreasing its rotating speed,both ways will decrease the total pressure ratio of the core flow.Results of the study will benefit the variable cycle engine design process in operation point evaluation and thermodynamic cycle optimization.

Numerical analysis for the matching of the core driven compression system in a double bypass engine

The numerical analysis for the matching of the core driven compression system in a double bypass variable cycle engine was presented in this paper.The system consists of a one-stage-core driven fan stage(CDFS),an inner bypass duct and a five-stage high pressure compressor(HPC),providing two basic operating modes: the single bypass mode and the double bypass mode.Variable vanes are necessary to realize the mode switch of the system.The correct matching in the double bypass mode requires a proper combination of the mass flow,total pressure ratio and blade speed.The work capacity of the system decreases in the double bypass mode and the pressure ratio tends to decrease more for the CDFS and the front stages of the HPC.The overall system efficiency is higher in the double bypass mode.The radial distributions of aerodynamic parameters are similar in different modes.The notable redistribution of mass flow downstream the CDFS in the single bypass mode leads to strong radial flows and additional mixing losses.The absolute flow angles into the inner bypass increase for the inner span and decrease for the outer span when the system is switched from the single bypass mode to the double bypass mode.