On Intake-Compressor Interactions Within an Integrated Propulsion System

The integration of a propulsion system into the airframe can contribute to the overall aircraft performance and is beneficial for military applications due to a reduction of the aircraft radar cross-section. On the other hand, engine integration calls for serpentine engine intake systems in which generally combined pressure-swirl distortions are provoked, which affect the performance of the propulsion system. The Military Engine Intake Research Duct (MEIRD) was designed to provoke a large-scale flow separation as well as a combined pressure-swirl distortion. The serpentine research duct is tested in both a remote- and close-coupled setup with the Larzac 04 turbofan engine to assess the aerodynamic interactions between the flow within the intake duct and the compression system. The upstream effect of the compression system on the steady-state duct flow is within the range of expectations. Less is known from the open literature with regards to the unsteady character of the flow in such a setup. Three distinct unsteady flow phenomena caused by the serpentine shape of the duct are identified up- and downstream of the low pressure compressor in the remote-coupled setup. An additional distinct low frequency unsteadiness is provoked with a configuration which features vortex generators for flow control. All phenomena are largely attenuated by the upstream effect of the compressor in the close-coupled setup. Nonetheless, the surge margin is massively reduced due to the inflow distortion and stall cells within the first stage of the low pressure compressor are visualized at high thrust settings of both the remote- and close-coupled setup, which are expected to impact the durability of the compression system.