Exploration of acceptable operating range for a compression system in a double bypass engine

Abstract

The variable cycle engine is distinguished by its highly adjustable compression system, whose aerodynamic characteristic is extremely complex. To explore the regulation range of a double bypass engine compression system, a multi-dimensional analysis method is developed, through which the coupling mechanism between the compressor component and the bypass is examined. The operation zones of the compressor components and the bypass system are proposed, and the operation range of the compression system is obtained by calculating the overlapping part of the operation zones. The results show that in the double bypass mode, there exists a minimum mode selector valve area and a minimum core driven fan stage stall margin that ensures a feasible bypass flow, the two parameters correspond to each other. Under the given fan and core driven fan stage conditions, the maximum value of the inner bypass ratio is restricted by the upper limit of the forward variable area bypass injector and the maximum Mach number in the total bypass, while the minimum value of the inner bypass ratio depends on the lower limit of the forward variable area bypass injector geometry and the system recirculation margin. The single bypass mode is a unique condition of the double bypass mode, as the operation zone of the compressor component degenerates from a two-dimensional surface to a straight line. There are multiple bypass states available in the single bypass mode, while the regulation range of the bypass ratio is jointly restricted by the operation range of the high pressure compressor and the aerodynamic boundary of the forward variable area bypass injector.