Mechanism of adjusting bypass ratio by front variable area bypass injector for a variable cycle engine

Abstract

The Front Variable Area Bypass Injector (FVABI) is a key to bypass ratio adjustment for a Variable Cycle Engine (VCE). In order to study the role of the FVABI with the Core Driven Fan Stage (CDFS) duct, firstly, the engine bypass with the CDFS duct model and the equivalent engine bypass without the CDFS duct model are designed using the concept of a jet boundary line. By comparing the difference between airflow driving forces in the two engine bypass models, the quantitative effects of the injection from the CDFS duct on the mass flow rate of the engine bypass airflow are obtained under different combinations of pressure difference and area ratios. Then, the CDFS duct injection characteristic map is obtained through the typical experiment of the FVABI. Based on this map, the performance model of the FVABI is developed. Finally, the turbofan engine model with the Variable Inlet Guide Vane (VIGV), the First Variable Cycle Engine model (VCE1) with the CDFS duct and without the VIGV, and the Second Variable Cycle Engine model (VCE2) with the CDFS duct and VIGV are built. The gain on the engine bypass ratio adjustment range caused by the injection from the CDFS duct is clarified by comparing the three engine models. It is concluded that the bypass ratio adjustment range of the variable cycle engine with the FVABI is about twice that of the traditional turbofan engine.