BYPASS FLOW PATTERN CHANGES AT TURBO-RAM TRANSIENT OPERATION OF A COMBINED CYCLE ENGINE

Abstract

Turbo-Ramjet Combined Cycle Engine is composed of a turbofan engine and a ramjet engine that is expected to be a candidate of future hypersonic propulsion systems. It can operate as turbofan mode for low speed range (Mach number 0∼3), then changes into ramjet mode for the higher speed range(Mach number 2.5∼5). In order to achieve smooth mode transition, it inevitably employs variable geometry components, so that the latter control sequence has to be carefully scheduled to maintain air flow rate and thrust at cruise condition during the mode transition. The present study therefore examines the flow pattern changes due to ram air mixing with fan bypass air, that are not available from the transient engine thermo-cycle simulation. CFD calculation showed that such flow patterns be feasible, yielding rather good agreement between the thermo-cycle and flow simulations with respect to total engine air flow rate and thrust.