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Aerospace Systems Design Laboratory (ASDL)
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ItemDevelopment of a Parametric Drag Polar Approximation for Conceptual Design(Georgia Institute of Technology. School of Aerospace Engineering, 2023-06) Sampaio Felix, Barbara ; Perron, Christian ; Ahuja, Jai ; Mavris, Dimitri N.The present work proposes an efficient parametric approximation of mission drag polars by combining multi-fidelity surrogate models with parametric reduced order modeling techniques. Traditionally, semi-empirical aerodynamic analyses are used to provide drag polars needed for mission analysis during the conceptual design of aircraft. The database needed for these methods is unavailable for unconventional vehicles, and for this reason, many studies rely on higher-fidelity models typical of preliminary design to perform design space exploration for novel vehicle geometries. Due to the high computational cost and evaluation time of these higher-fidelity models, researchers constrain the design space exploration of vehicles by either relying on single discipline optimization or obtaining mission drag polars for a few vehicle geometries within their design loop. The present work demonstrates the application of Hierarchical Kriging surrogate models to obtain mission drag polars for fixed vehicle geometries. Then, the proper orthogonal decomposition reduced order model with Kriging interpolation is used to approximate the coherent structure of mission drag polars. The proposed method is demonstrated on a supersonic commercial aircraft. Experiments showed that both the multi-fidelity surrogate model and the reduced order model are able to emulate vehicle drag polars well for fixed and varying vehicle geometries, respectively.
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ItemSensitivity Analysis of the Overwing Nacelle Design Space(Georgia Institute of Technology, 2022-06-09) Mavris, Dimitri N. ; Ahuja, Jai ; Renganathan, S. AshwinThe overwing nacelle (OWN) concept refers to aircraft designs where the engine is installed above the wing. The OWN configuration offers several advantages over conventional underwing nacelle (UWN) vehicles, which include improved fuel burn and propulsive efficiencies due to the feasibility of ultra high bypass ratio turbofans, and reduced noise. However, a non-optimal OWN design can result in large transonic drag penalties that can potentially outweigh the aforementioned benefits. We study the OWN design problem from an aerodynamics and propulsion perspective, using the NASA common research model, a notional 90,000 pound thrust class turbofan model, and Reynolds–Averaged Navier-Stokes simulations. We first quantify the sensitivity of drag, lift, and pressure recovery to variations in engine location and power setting, and identify trends. Then, we perform aerodynamic design optimization of the wing and nacelle to determine OWN performance improvement from outer mold line refinement at a favorable engine installation location. A 20% reduction in drag is achieved for the optimized OWN configuration, highlighting the sensitivity of OWN aerodynamics to airframe contours. However, compared to the UWN baseline, the optimized OWN drag is 5% higher at the same lift and worsens significantly at higher lift.
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ItemConceptual Design of Boundary Layer Ingesting Aircraft Capturing Aero-Propulsive Coupling(Georgia Institute of Technology, 2022-03-01) Ahuja, Jai ; Mavris, Dimitri N.The impacts of boundary layer ingestion on aircraft performance can be modeled using either a decoupled or a coupled approach. Several studies in literature have adopted the former, while some have shown differences between the two approaches for the performance analysis and design refinement of a sized aircraft. This study quantifies the consequences of ignoring aero-propulsive coupling at the aircraft sizing stage of conceptual design. To do so, a parametric and coupled aero-propulsive design methodology is used that leverages surrogate modeling to minimize the expense of computational fluid dynamics in generating estimates of the boundary layer ingestion performance impacts. The method is applied to the design and analysis of two aircraft in the 150 passenger class, with different engine locations. Discrepancies in block fuel burn estimates, as large as 2.15%, were found to occur by ignoring aero-propulsive interactions.
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ItemA Method for Modeling the Aero-Propulsive Coupling Characteristics of BLI Aircraft in Conceptual Design(Georgia Institute of Technology, 2021-01) Ahuja, Jai ; Mavris, Dimitri N.The impacts of boundary layer ingestion (BLI) on vehicle performance can be modeled using either a decoupled or a coupled approach. Several studies in literature have adopted the former, while some have shown differences between the two approaches for the performance analysis and design refinement of a sized aircraft. This study quantifies the consequences of ignoring aero-propulsive coupling at the aircraft sizing stage of conceptual design. To do so, a parametric and coupled aero propulsive design methodology is used that leverages surrogate modeling to minimize the computational burden of CFD in generating estimates of the BLI performance impacts. The method is applied to the design and analysis of two BLI concepts with engine locations similar to that on the D8 and the NOVA-BLI.
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ItemAssessment of Propulsor On Design and Off Design Impacts on BLI Effects(Georgia Institute of Technology, 2021-01) Ahuja, Jai ; Mavris, Dimitri N.As part of an effort to develop a parametric and coupled aero-propulsive conceptual design methodology for boundary layer ingesting (BLI) aircraft, there is a need to investigate propulsor sizing and off-design impacts on the ingested boundary layer. This study uses 3D CFD analysis to quantify the BLI effects trends as a function of fan annulus area and mass flow rate required, for engine locations similar to those on the the D8, NOVA-BLI and the STARC-ABL concepts. This study extends previous work that relied on CFD analysis of an axisymmetric model for the STARC-ABL concept. The results from this study highlight the propulsor’s contribution to the aero-propulsive coupling inherent in BLI concepts.
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ItemA Methodology for Capturing the Aero-Propulsive Coupling Characteristics of Boundary Layer Ingesting Aircraft in Conceptual Design(Georgia Institute of Technology, 2020-11-11) Ahuja, JaiEconomic 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.
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ItemSensitivity of Boundary Layer Ingestion Effects to Tube and Wing Airframe Design Features(Georgia Institute of Technology, 2020-01) Ahuja, Jai ; Mavris, Dimitri N.Conceptual design of boundary layer ingesting (BLI) aircraft requires a methodology that captures the aero-propulsive interactions in a parametric fashion. This entails modeling the impacts of BLI as a function of the airframe and propulsor design. Previous work has analyzed the sensitivity of these BLI effects to the propulsor size and throttle. This paper assesses the sensitivity of the BLI effects to the airframe design through a series of experiments, using CFD. The scope of this analysis is restricted to tube and wing type BLI concepts. Results from these studies help identify the critical airframe design space that needs to be considered when generating a parametric model of the BLI effects. Guidelines regarding the level of detail required for the airframe geometry model are discussed.