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Jai Ahuja
(Advisor: Prof. Dimitri Mavris)
will defend a doctoral thesis entitled,
A Methodology for Capturing the Aero-Propulsive Coupling Characteristics of Boundary Layer Ingesting Aircraft in Conceptual Design
On
Friday, October 9 at 08:00 a.m.
https://bluejeans.com/620783318
Abstract
Economic and environmental benefits of fuel efficient aircraft have driven research towards unconventional configurations and technologies. Boundary Layer Ingesting (BLI) concepts appear to be a promising solution, relying on a synergistic interaction between the airframe and propulsor for improved fuel efficiency. Maximizing benefits of BLI while minimizing the risks not only involves careful design of the propulsor, but also the airframe given that the embedded propulsor performance is dependent on the ingested boundary layer flow, which in turn is affected by the airframe. The highly coupled nature of the propulsion system with the airframe for BLI concepts requires a Multidisciplinary Design Analysis and Optimization (MDAO) approach.
Majority of the modeling approaches in literature, however, have treated the BLI problem in a decoupled fashion, especially at the vehicle sizing stage. On the other hand, coupled aero-propulsive methodologies proposed are better suited for point design refinement at the preliminary design stage. Decoupled methods fail to capture aero-propulsive interactions. The impacts of BLI may be overestimated or underestimated, and thus, there is a risk that the sized vehicle will not be satisfactory or even feasible. Quantifying the consequences of ignoring BLI aero-propulsive coupling at the aircraft sizing stage is the primary motivation of this research effort. To address this aspect, a parametric and coupled aero-propulsive design and analysis methodology that is appropriate for conceptual design BLI vehicle sizing and corresponding trade studies is necessary.
A MDAO methodology for BLI aircraft in conceptual design is proposed, allowing for design space exploration and simultaneous optimization of the airframe and propulsor cycle. BLI effects on vehicle performance are identified using the Power Balance formulation. Studies are devised to identify the critical airframe and propulsor design space influencing these BLI effects. Through physics based reasoning, these studies provide rule of thumb guidelines for concept designers to focus on certain design parameters over others. High fidelity aerodynamic analysis, through CFD, is used strategically for constructing parametric semi-empirical models of the BLI effects, which are then integrated with a cycle analysis code, an aircraft sizing and mission analysis tool, and other analysis modules in a MDAO environment. A fine balance is thus achieved between high fidelity requirements for modeling complex physics and the need for expedited MDAO in conceptual design.
The proposed method is applied to the design and analysis of two tube and wing BLI configurations with different engine locations, similar to the D8 and NOVA-BLI concepts. These vehicles are also designed using a decoupled approach that is reflective of similar methods in literature. A design space exploration involving engine cycle and airframe design parameters is conducted, using the decoupled and coupled approaches, followed by optimization to find the best designs within the specified constraints. The studies show noteworthy differences in performance and design trends between the two BLI modeling approaches. Additionally, the wing influence on the ingested airflow is observed to affect the BLI aero-propulsive coupling strength. The top-mounted engine configuration like the D8 exhibits stronger coupling compared to the side-mounted engine variant like the NOVA-BLI. In general, the results support use of coupled and parametric methodologies for BLI concept design.
Committee
