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Aerospace Systems Design Laboratory (ASDL)
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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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ItemModeling Framework for Identification and Analysis of Key Metrics for Trajectory Energy Management of Electric Aircraft(Georgia Institute of Technology, 2021-08) Beedie, Seumas M. ; Harris, Caleb ; Verberne, Johannes ; Justin, Cedric Y. ; Mavris, Dimitri N.To prepare for the upcoming entry into service of electric and hybrid-electric aircraft, regulators may have to update or develop new regulations and standards to ensure safe operations of these new vehicles. To ensure public acceptance, these vehicles need to demonstrate an equivalent level of safety consistent with existing regulations. However, the ability to fly in different modes (forward flight, vertical flight) and the different powertrain elements may require significant changes to regulations to ensure that an insightful representation of the usable energy is provided to flight crews. This requires an understanding of the major operational differences between conventional and electric aircraft, and how these differences impact the trajectories a vehicle can fly. For instance, there is no simple analog to fuel gauges for measuring the extractable energy available on board electric aircraft, as energy related metrics can vary with a range of variables, such as component temperatures, battery health, and environmental conditions. It is thus more complex for flight crews to gauge in real-time how much usable energy is available and to figure out which trajectories are feasible with respect to both energy and power. To assess the feasibility of trajectories and quantify the adequacy of novel energy tracking metrics and methodologies, a trajectory energy management simulation environment is implemented allowing the simulation of various energy metrics across a range of vehicles and missions. This allows decision makers and regulators to assess the importance of these metrics for safe operation across a wide variety of missions. The impact of ambient air temperature, battery state of health, and initial battery, motor, and inverter temperatures are assessed for a typical flight mission. It is concluded that state of health, ambient temperature, and initial battery temperature all had significant impacts on the final state of charge and amount of extractable energy. Additionally, at high ambient temperatures and in aggressive climbs, motor temperature limits and inverter temperature limits can sometimes be reached, further complicating the assessment of what can be done with the amount of energy stored on board. Proper management of these constraints is therefore crucial for optimizing trajectories with respect to energy metrics. Future work is proposed regarding further expansion of the framework simulating aircraft with vertical takeoff and landing capability, and flight-dynamics algorithms that will enable simulation of optimal energy mission profiles.
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ItemAircraft Performance Model Calibration and Validation for General Aviation Safety Analysis(Georgia Institute of Technology, 2020-03) Puranik, Tejas G. ; Harrison, Evan D. ; Chakraborty, Imon ; Mavris, Dimitri N.Performance models facilitate a wide range of safety analyses in aviation. In an ideal scenario, the performance models would show inherently good agreement with the true performance of the aircraft. However, in reality, this is rarely the case: either owing to underlying simplifications or due to the limited fidelity of applicable tools or data. In such cases, calibration is required to fine-tune the behavior of the performance models. For point-mass steady-state performance models, challenges arise due to the fact that there is no obvious, unique metric or flight condition at which to assess the accuracy of the model predictions, as well as because a large number of model parameters may potentially influence model accuracy. This work presents a two-level approach to aircraft performance model calibration. The first level consists of using manufacturer-developed performance manuals for calibration, whereas the second level provides additional refinement when flight data are available. The performance models considered in this work consist of aerodynamic and propulsion models (performance curves) that are capable of predicting the non-dimensional lift, drag, thrust, and torque at any given point in time. The framework is demonstrated on two representative general aviation aircraft. The demonstrated approach results in models that can predict critical energy-based safety metrics with improved accuracy for use in retrospective safety analyses.