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Title:Experimental and computational investigation of the transonic aero-propulsive interactions of an overwing ducted fan
Author(s):Lauer, Matthew G
Advisor(s):Ansell, Phillip J
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
propulsion-airframe integration
flow physics
aerospace engineering
Abstract:Propulsion-airframe integration (PAI), or the coupling of propulsors into aerodynamic surfaces, is a key component of electric aircraft design to take advantage of the differences in system configurations from conventional (gas turbine engine) aircraft. Advantages gained by embedding the propulsors include wake-filling, boundary layer ingestion benefits, differential yaw control, and noise reduction (if propulsors are embedded in the upper surfaces of the aircraft). However, PAI significantly complicates the physics of the flowfield over the aerodynamic surfaces. Some research has been done in the subsonic context for PAI, but not much experimental or computational transonic PAI research has been done. This work takes a hybrid approach to transonic PAI, using both experiments and computation to validate each other and to unveil a new understanding of the coupled interactions observed between normal shock wave, boundary layer, and thrust on a transonic wing. A number of important results were found from both the experimental and computational transonic PAI studies. The first is the shift in local normal shock wave position with the static implementation of a nacelle into an airfoil section. By increasing the induced mass flow rate into the nacelle, there was a further shift in the normal shock wave position, as well as a growth of the airfoil's supersonic zone and strengthening of the terminating shock wave. For the slightly compressible case tested, the boundary layer height of the nacelle-integrated airfoil decreased uniformly with increasing induced mass flow rate into the nacelle. However, this was not the case for the transonic nacelle-integrated airfoil, in which the shock wave-induced boundary layer growth overtook the decrease in boundary layer height due to the favorable pressure gradient introduced by the mass flow induction and reversed the trend. The kinetic energy defect, a key parameter utilized in the study of propulsive efficiency for boundary-layer ingesting propulsion systems, was found to increase uniformly at the nacelle highlight with increased induced mass flow rate for all cases, with the largest increase coming at both slightly compressible and supercritical freestream Mach numbers. These results, while coming from a canonical test case that does not represent an applied design appropriate for an actual wing, capture the salient physics of transonic PAI and would likely apply to all aerodynamic-surface-integrated propulsors. The results also have important implications for propulsive efficiency and wave drag. The increased kinetic energy defect ingestion should increase propulsive efficiency with increased thrust, but the increased shock strength would introduce a wave drag penalty. A trade study between these two output parameters may be a subject for future research. Ultimately, this study showed the complexities of transonic aero-propulsive interactions and some of the important flow phenomena that should be considered as this field develops.
Issue Date:2021-04-27
Rights Information:Copyright 2021 Matthew G. Lauer
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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