Novel turbomachinery concepts for highly integrated airframe/propulsion systems

Abstract

Two novel turbomachinery concepts are presented as enablers to advanced flight missions requiring integrated airframe/propulsion systems. The first concept is motivated by thermal management challenges in low-to-high Mach number (4+) aircraft. The idea of compressor cooling combines the compressor and heat exchanger function to stretch turbopropulsion system operational limits. Axial compressor performance with blade passage heat extraction is assessed with computational experiments and meanline modeling. A cooled multistage compressor with adiabatic design point is found to achieve higher pressure ratio, choking mass flow, and efficiency (referenced to an adiabatic, reversible process) at fixed corrected speed, with greatest benefit occurring through front-stage cooling. Heat removal equal to one percent of inlet stagnation enthalpy flux in each of the first four blade rows suggests pressure ratio, efficiency, and choked flow improvements of 23%, 12%, and 5% relative to a baseline, eight-stage compressor with pressure ratio of 5. Cooling is also found to unchoke rear stages at low corrected speed. Heat transfer estimations indicate that surface area limitations and temperature differences favor rear-stage cooling and suggest the existence of an optimal cooling distribution.

(cont.) The second concept is a quiet drag device to enable slow and steep approach profiles for functionally quiet civil aircraft. Deployment of such devices in clean airframe configuration reduces aircraft source noise and noise propagation to the ground. The generation of swirling outflow from a duct, such as an aircraft engine, is conceived to have high drag and low noise. The simplest configuration is a ram pressure driven duct with non-rotating swirl vanes, a so-called swirl tube. A device aerodynamic design is performed using first principles and CFD. The swirl-drag-noise relationship is quantified through scale-model aerodynamic and aeroacoustic wind tunnel tests. The maximum measured stable flow drag coefficient is 0.83 at exit swirl angles close to 500. The acoustic signature, extrapolated to full-scale, is found to be well below the background noise of a well populated area, demonstrating swirl tube conceptual feasibility. Vortex breakdown is found to be the aerodynamically and acoustically limiting physical phenomenon, generating a white-noise signature that is [approx.] 15 dB louder than a stable swirling flow.