Person:

Mavris, Dimitri N.

Permanent Link

https://hdl.handle.net/1853/71501

Associated Organization(s)

Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

Organizational Unit

Aerospace Systems Design Laboratory (ASDL)

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Publication Search Results

Now showing 1 - 10 of 12

Development 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.
Sensitivity Analysis of the Overwing Nacelle Design Space

(Georgia Institute of Technology, 2022-06-09) Mavris, Dimitri N. ; Ahuja, Jai ; Renganathan, S. Ashwin

The 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.
Conceptual 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.
A 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.
Assessment 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.
Sensitivity 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.
Conceptual Design of a BLI Propulsor Capturing Aero-Propulsive Coupling and Distortion Impacts

(Georgia Institute of Technology, 2019) Pokhrel, Manish ; Shi, Mingxuan ; Ahuja, Jai ; Gladin, Jonathan ; Mavris, Dimitri N.

Boundary Layer Ingestion (BLI) appears to be a promising solution to meet aggressive aviation fuel burn and environmental goals defined by NASA and other entities. Propulsion-airframe integration plays a critical role in BLI vehicle design given the strong coupling between the airframe and the propulsion system. Several studies have focused on flow field impacts on the propulsion system performance, but have ignored the effect of the propulsor on the flow field. Recent studies, however, have focused on both aspects, highlighting the need for capturing this interdisciplinary coupling. Multidisciplinary analyses (MDA), especially those involving CFD, are computationally expensive and are not suitable in the conceptual design of BLI propulsion systems. This paper aims to provide a less expensive approach by developing a parametric formulation for the effect of the propulsion system on the flow field, which can then be used in BLI propulsor conceptual design. This paper quantifies the sensitivity of the changes in the flow field due to the on-design and off-design parameters of the propulsion system. In addition, it also illustrates the difference in propulsion system design and performance when the throttle dependent effects on the flow field is captured, to the case where it is not. Distortion impacts on engine sizing and performance are also considered in this paper.
CFD Study of an Over-Wing Nacelle Configuration

(Georgia Institute of Technology, 2018-10-05) Berguin, Steven H. ; Renganathan, Sudharshan Ashwin ; Ahuja, Jai ; Chen, Mengzhen ; Perron, Christian ; Tai, Jimmy C. M. ; Mavris, Dimitri N.

Engine bypass ratio (BPR) has grown significantly over the years, due to a desire for increased efficiency, and the large fan diameters that have resulted are forcing the engines so close to the wing that there is no room left for them to grow any larger due to ground clearance constraints. As BPR increases even further in the future, conventional Under-Wing Nacelle (UWN) installations will therefore no longer be possible without drastic modification of the wing and landing gear. Over-Wing nacelle concepts solve this problem by offering a convenient installation for high BPR turbofans and, additionally, offer the potential to mitigate community noise through engine noise shielding using the wing as a shield. However, OWN has historically warranted concern about unacceptably high drag levels at transonic speeds and the purpose of this research was to determine whether or not drag can be improved enough to take advantage of the aforementioned cross-disciplinary benefits. To do so, three studies were conducted: study 1 conducted a simple nacelle sweep in order to identify and visualize the physical mechanisms driving the configuration, study 2 then conducted a sensitivity analysis in order to understand important design variables and, finally, study 3 performed single point optimization for a trailing edge OWN concept. Overall, results suggests that OWN drag can be improved to levels commensurate with its Under-Wing Nacelle (UWN) counterpart. However, limitations of the analysis tools employed for this research (in the area of shape optimization) were insufficient to outperform the UWN baseline. Such limitations were successfully overcome by modern OWN concepts, such as the Honda Business Jet and the military Lockheed HWB for air mobility missions. Overall, it is therefore the authors' opinion that either leading-edge or trailing-edge mounted OWN configurations are concepts worth investigating further for civil transport applications.
Sensitivity Analysis of Aero-Propulsive Coupling for Over-Wing-Nacelle Concepts

(Georgia Institute of Technology, 2018) Berguin, Steven H. ; Renganathan, Sudharshan Ashwin ; Ahuja, Jai ; Chen, Mengzhen ; Tai, Jimmy C. M. ; Mavris, Dimitri N.

A sensitivity analysis is performed to quantify the relative impact of perturbing a set of design variables representing an airplane configuration with Over-Wing Nacelles (OWN), operating at transonic cruise. The goal is to study the impact of perturbing the engine's XYZ position and power setting on installation drag, engine inlet pressure recovery, and lift curve characteristics. High- fidelity Reynolds Averaged Navier-Stokes (RANS) simulations of the Common Research Model (CRM) modified with powered, over-wing nacelles are performed and dominant main effects and interactions are identified. The most dominant effect was by far the engine's X position, but it was also found that podded OWN configurations exhibit statistically significant, aero-propulsive coupling. Specifically, certain engine locations cause changes in the flow-field that deteriorate inlet pressure recovery and, vice versa, a change in engine boundary conditions can affect installation drag. It is therefore recommended to simulate OWN concepts using a coupled MDA or MDAO approach to capture interdependencies between aerodynamics and propulsion.
Multidisciplinary Analysis of Aero-Propulsive Coupling for the OWN Concept

(Georgia Institute of Technology, 2018) Ahuja, Jai ; Renganathan, Sudharshan Ashwin ; Berguin, Steven ; Mavris, Dimitri N.

The Over Wing Nacelle (OWN) concept enables the installation of turbofans with high bypass ratios for improved effciency in commercial transport vehicles, in addition to offering other advantages in the form of (i) mitigation of jet noise, (ii) foreign object damage avoidance and (iii) jet-powered lift. While these benefits can be offset by the large transonic drag rise, aerodynamic shape optimization of the wing and nacelle outer mold lines can help realize the full aerodynamic potential of the OWN concept. However, if coupling between the airframe aerodynamics and the propulsion system is strong, multidisciplinary optimization may need to be conducted. In this paper, the aerodynamics-propulsion coupling in the OWN concept is studied. A high fidelity Reynolds Averaged Navier Stokes (RANS) model along with a low fidelity engine thermodynamic cycle analysis model are used to represent the aerodynamic and propulsion systems respectively. The necessary coupling variables are identified and the coupled system is solved for disciplinary feasibility using the Fixed Point Iteration technique. The Common Research Model (CRM) wing and nacelle are used as the baseline geometry to carry out the study. The study reveals that for the OWN concept, aerodynamics-propulsion coupling is not significant enough to warrant multi-disciplinary shape optimization. While airframe aerodynamics has a strong effect on the propulsion system, the reverse interaction is weaker.