Variable Flow Turbofan Engine for an HSCT Application

Abstract

A variable flow fan aircraft propulsion system offers the potential for achieving a low specific thrust with high flow and low jet velocity requirement as specified for takeoff, side-line noise, initial climb, and a high specific thrust requirement for climb and acceleration to supersonic cruise. These requirements are conflicting. To achieve this, the operating envelope of a variable flow fan has to be expanded over existing turbofan engines. The variable flow fan concept (i.e., the Variable Fan Exit or “VFX”) can efficiently operate beyond the usual fan (or compressor) stall operating line using novel methods of designing and scheduling the fan geometry as a function of flight Mach Number, fan pressure ratio and corrected speed. Fan geometry is altered by using variable inlet guide vanes (IGV’s), variable stators, and variable outlet guide vanes (OGV’s).