Propellers have gained traction in recent years and are subsequently being integrated into unconventional airframe configurations as part of conceptual designs for developing sustainable aircraft. Close coupling of the propeller and airframe enhances the non-uniformity of the inflow to the propeller. This non-uniform inflow introduces unsteady loading, affecting the propeller's performance. This paper investigates the impact of accounting for installation effects during propeller blade design within an optimization toolchain. This toolchain is applied to a propeller mounted at the rear of a fuselage utilizing Boundary Layer Ingestion (BLI). The proposed design methodology utilizes existing analysis methods to assess the installed aerodynamic and structural performance of the propeller. A gradient-based optimizer is coupled to these analysis methods to design two distinct blades for a multi-segment mission with the objective to maximize the aerodynamic performance. The geometry of the first propeller blade is optimized for the uniform inflow and consequently optimized to operate in the non-uniform inflow. The second blade is from the outset designed for the non-uniform inflow condition. The implementation of the proposed design methodology captures the sensitivity of the inflow field within the design loop, resulting in two distinct blade designs. Upon comparing these blades in BLI inflow conditions to meet identical performance requirements, it was observed that the blade designed to account for installation effects featured a higher inboard chord distribution and consumed 1.58% less energy compared to the blade optimized for uniform inflow for the considered mission profile.@en

Fuselage Boundary-Layer Ingestion (BLI) is a promising example of synergistic design and propulsion-airframe integration to reduce fuel burn. For a BLI configuration, the aero propulsive performance of the aircraft is a result of the complex aerodynamic interaction between the fuselage airframe and the BLI propulsor. This paper presents a design method for the aft fuselage including the propulsor shrouding to minimize the required shaft power of an aft-mounted propulsor in the conceptual design phase. First, a global aerodynamic design space exploration is carried out using Computational Fluid Dynamics (CFD) to identify the key design parameters and their influence to the aerodynamic performance of the propulsive fuselage. An optimization study is subsequently carried out to improve the aerodynamic performance of a baseline design. The optimization was performed for a turbo-electric BLI configuration and within representative design constraints. The optimization achieved a decrease of approximately 10% of the isentropic shaft power required for the aft-mounted propulsor for a constant net force acting on the propulsive fuselage. The presented methodology and the resulting design practices can be effectively applied to other advanced aircraft configurations.@en

Boundary-layer ingestion (BLI) is a propulsor–airframe integration technology that promises substantial fuel consumption benefits for future civil aircraft. This paper discusses an experimental study, conducted within the European Union–funded Horizon 2020 CENTRELINE project, on the aerodynamic performance of an aircraft with a BLI propulsor integrated at the aft-fuselage section (known as the Propulsive Fuselage Concept). The low-speed wind-tunnel experiments were carried out at Reynolds and Mach numbers of 460,000 and 0.12, whereas the Reynolds and Mach numbers are 40,000,000 and 0.82 at full-flight scale. Aerodynamic loads measurements show that the BLI propulsor affects the longitudinal and lateral-directional equilibrium of the aircraft in off-cruise conditions. Moreover, velocity and total pressure measurements characterize the flowfield around the BLI propulsor in cruise and off-cruise conditions. The analysis of the momentum and power fluxes in the flowfield shows that, while around 20% of the total aircraft drag is due to the fuselage body, only less than 5% of the total aircraft drag power is dissipated in the fuselage wake. Furthermore, the BLI propulsor recovers around 50% the axial kinetic energy flux in the fuselage boundary layer (the so-called wake-filling effect), suggesting an increased propulsive efficiency.@en

The AeroCity is a new form of transportation concept that has been developed to provide high-speed ground transportation at a much lower cost than the existing high-speed railway. Utilizing the Wing-in-Ground (WIG) effect, the AeroCity vehicle does not require complex infrastructures like other contemporary concepts, such as the Hyperloop or Maglev trains. In the current work, the aerodynamic characteristics of the AeroCity vehicle are examined through a Computational Fluid Dynamics (CFD) analysis. The results from the CFD analysis qualitatively match with the findings of wind tunnel experiments. Surface streamlines and boundary layer measurements correspond well with the numerical data. However, the force measurements show a discrepancy. It is found that the separation bubble over the side plates is not captured by the CFD, and this is responsible for an under-prediction of the drag at higher free-stream velocities. The Transition SST model improved the matching between the experiments and numerical simulations. The influence of the moving ground is numerically investigated, and the effect of non-moving ground on the vehicle aerodynamics was found not to be significant. Finally, the inclusion of the track wall is examined. It is found that the merging of the wingtip vortices is responsible for a significant drag increase and, therefore, an alternative track geometry should be investigated. @en

Boundary-layer ingestion (BLI) has been proposed as one of the novel airframe–engine integration technologies to reduce aircraft fuel consumption. The current numerical analysis involves the evaluation of the effect of fuselage design on the power consumption of a boundary-layer ingesting propulsor modeled as an actuator volume without nacelle. An axisymmetric fuselage model is used as a canonical case to study BLI in transonic flight conditions. The flowfield is investigated through the power balance and the exergy analysis methods. Results show that the fuselage geometry and flight conditions only have a minor effect on the BLI power saving benefit when compared to the effect on the drag power of the fuselage. This indicates that, for the range of fuselage geometries and flight conditions studied, the isolated fuselage drag can be used for a qualitative performance assessment of different fuselage designs even for BLI configurations. Also, the power saving results obtained based on the power balance and the exergy analysis methods show similar qualitative trends for the fuselage geometries and flight conditions considered. Furthermore, the BLI propulsor has a negligible effect on the upstream anergy generation rate. Turbulence and temperature gradients within the flow are the important reasons for the deterioration of the BLI propulsor performance as expected.

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Key results from the EU H2020 project CENTRELINE are presented. The research activities undertaken to demonstrate the proof of concept (technology readiness level-TRL 3) for the so-called propulsive fuselage concept (PFC) for fuselage wake-filling propulsion integration are discussed. The technology application case in the wide-body market segment is motivated. The developed performance bookkeeping scheme for fuselage boundary layer ingestion (BLI) propulsion integration is reviewed. The results of the 2D aerodynamic shape optimization for the bare PFC configuration are presented. Key findings from the high-fidelity aero-numerical simulation and aerodynamic validation testing, i.e., the overall aircraft wind tunnel and the BLI fan rig test campaigns, are discussed. The design results for the architectural concept, systems integration and electric machinery pre-design for the fuselage fan turbo-electric power train are summarized. The design and performance implications on the main power plants are analyzed. Conceptual design solutions for the mechanical and aerostructural integration of the BLI propulsive device are introduced. Key heuristics deduced for PFC conceptual aircraft design are presented. Assessments of fuel burn, NOx emissions, and noise are presented for the PFC aircraft and benchmarked against advanced conventional technology for an entry-into-service in 2035. The PFC design mission fuel benefit based on 2D optimized PFC aero-shaping is 4.7%.

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View Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2467.vid

Boundary Layer Ingestion (BLI) is a technology that promises fuel consumption benefits for future civil aircraft. However, it introduces detrimental aerodynamic interactions between the propulsor and the airframe. In particular, the inflow to the BLI propulsor is affected by the flow around the airframe elements. The non-uniform inflow can influence the fan aerodynamic, aeroacoustic and aeroelastic performance. As a consequence, the fan design needs to tolerate the inlet distortions in all the flight phases. This paper discusses an experimental study of the aerodynamic performance of an aircraft with a BLI propulsor integrated at the aft-fuselage section, representative of a Propulsive Fuselage Concept (PFC) aircraft. Aerodynamic load measurements show that the BLI propulsor affects the longitudinal and lateral-directional equilibrium of the aircraft in off-cruise conditions. Flow measurements at the BLI propulsor inlet indicate that the fuselage boundary layer induces the strongest total pressure distortion. However, particularly at a non-zero sideslip angle, the vertical tail plane strongly affects the inflow to the BLI propulsor, introducing non-symmetric total pressure and velocity distortions. The analysis of the momentum and power fluxes in the flowfield show that around 20% of the total aircraft drag is produced in the fuselage boundary layer, while around 5% of the total aircraft drag power is dissipated in the fuselage wake. Furthermore, the BLI propulsor substantially reduces the axial kinetic energy flux in the fuselage boundary layer (the so-called ``wake-filling'' effect), suggesting an increased propulsive efficiency.@en

Boundary Layer Ingestion (BLI) is a promising propulsion integration technology capable of enhancing aircraft propulsive efficiency. The Propulsive Fuselage Concept (PFC), a tube-and-wing configuration with an aft-fuselage-mounted BLI propulsor, is particularly suited for BLI. Although extensively studied on a system level, the aerodynamic performance of the PFC, resulting from the complex interaction between the airframe and the propulsor, is still largely uncharted. In this paper, the results of wind-tunnel tests on a simplified PFC model are presented. The model featured an axisymmetric fuselage body with an integrated BLI shrouded fan. Flowfield measurements were performed through particle image velocimetry to analyze the key aerodynamic phenomena and to assess the distribution of momentum and mechanical energy around the aft-fuselage propulsor. Results show that the BLI fan alters the surrounding flowfield by increasing the mass flow in the inner part of the fuselage boundary layer and by reducing the boundary-layer thickness. Moreover, the power analysis indicates that the potential benefit of BLI is strongly dependent on the fan setting. Increasing the fan shaft power leads to a higher amount of power dissipated in the near wake. However, an increasing share of the energy flux is associated with the momentum excess contained in the wake.

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The paper discusses optimality constellations for the design of boundary layer ingesting propulsive fuselage concept aircraft under special consideration of different fuselage fan power train options. Therefore, a rigorous methodical approach for the evaluation of the power saving potentials of propulsive fuselage concept aircraft configurations is provided. Analytical formulation for the power-saving coefficient metric is introduced, and, the classic Breguet–Coffin range equation is extended for the analytical assessment of boundary layer ingesting aircraft fuel burn. The analytical formulation is applied to the identification of optimum propulsive fuselage concept power savings together with computational fluid dynamics numerical results of refined and optimised 2D aero-shapings of the bare propulsive fuselage concept configuration, i.e. fuselage body including the aft–fuselage boundary layer ingesting propulsive device, obtained during the European Union-funded DisPURSAL and CENTRELINE projects. A common heuristic for the boundary layer ingesting efficiency factor is derived from the best aero-shaping cases of both projects. Based thereon, propulsive fuselage concept aircraft design optimality is parametrically analysed against variations in fuselage fan power train efficiency, systems weight impact and fuselage-to-overall aircraft drag ratio in cruise. Optimum power split ratios between the fuselage fan and the underwing main fans are identified. The paper introduces and discusses all assumptions necessary in order to apply the presented evaluation approach. This includes an in-depth explanation of the adopted system efficiency definitions and drag/thrust bookkeeping standards.

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