Hybrid-electric aircraft are a potential way to reduce the environmental footprint of aviation Research aimed at this subject has been pursued over the last decade; nevertheless, at this stage, a full overall aircraft design procedure is still an open issue This work proposes to enrich the procedure for the conceptual design of hybrid aircraft found in literature through the definition of a multidisciplinary design optimization (MDO) framework aimed at handling design problems for such kinds of aircraft The MDO technique has been chosen because the hybrid aircraft design problem shows more interaction between disciplines than a conventional configuration, and the classical approach based on multidisciplinary design analysis may neglect relevant features The procedure has been tested on the case study of a single-aisle aircraft featuring hybrid propulsion with distributed electric ducted fans The analysis considers three configurations (with 16, 32, and 48 electric motors) compared with a conventional baseline at the same 2035 technological horizon To demonstrate the framework’s capability, these configurations are optimized with respect to fuel and energy consumption It is shown that the hybrid-electric concept consumes less fuel/energy when it flies on short range due to the partial mission electrification When one increases the design range, penalties in weight introduced by hybrid propulsion overcome the advantages of electrified mission segment: the range for which hybrid aircraft have the same performance of the reference conventional aircraft is named the “breakdown range” Starting from this range, the concept is no longer advantageous compared to conventional aircraft Furthermore, a tradeoff between aerodynamic and propulsive efficiency is detected, and the optimal configuration is the one that balances these two effects Finally, multiobjective optimization is performed to establish a tradeoff between airframe weight and energy consumption

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Multidisciplinary Design Optimization Framework with Coupled Derivative Computation for Hybrid Aircraft

Modern unmanned air vehicles (UAVs) are usually equipped with rotors connected to electric motors that enable them to hover and fly in all directions. The purpose of the paper is to design optimal composite rotor blades for such small UAVs and investigate their aerodynamic performances both computationally and experimentally.,Artificial intelligence method (genetic algorithm) is used to optimize the blade airfoil described by six input parameters. Furthermore, different computational methods, e.g. vortex methods and computational fluid dynamics, blade element momentum theory and finite element method, are used to predict the aerodynamic performances of the optimized airfoil and complete rotor as well the structural behaviour of the blade, respectively. Finally, composite blade is manufactured and the rotor performance is also determined experimentally by thrust and torque measurements.,Complete process of blade design (including geometry definition and optimization, estimation of aerodynamic performances, structural analysis and blade manufacturing) is conducted and explained in detail. The correspondence between computed and measured thrust and torque curves of the optimal rotor is satisfactory (differences mostly remain below 15%), which validates and justifies the used design approach formulated specifically for low-cost, small-scale propeller blades. Furthermore, the proposed techniques can easily be applied to any kind of rotating lifting surfaces including helicopter or wind turbine blades.,Blade design methodology is simplified, shortened and made more flexible thus enabling the fast and economic production of propeller blades optimized for specific working conditions.

Optimal propeller blade design, computation, manufacturing and experimental testing

Experiments were performed using a wall-to-wall unswept and untapered wing with a single slotted flap and a propeller, to obtain a validation dataset and gain insight into primary flow phenomena in propeller-wing-flap interactions. Measurements were taken using pressure taps, a wake rake and oil flow visualization, for several flap deflections (0, 15 and 30 degrees) and thrust settings (unpowered, 𝐽 = 0.8 / 𝑇𝑐 = 1.05 and 𝐽 = 1.0 / 𝑇𝑐 = 0.45). Similarity of the measured data to similar experiments was poor, which was believed to be due to the low Reynolds number of 𝑅𝑒 = 6𝑒5 and sensitivity of local measurements due to occurrence of stall cells. Oil flow visualizations showed significant induction of flow separation from nacelle-wing interactions in unpowered conditions, traced to boundary layer growth. For powered cases it was shown that both sides of the deployed flap are immersed in the part of the slipstream that passes the pressure side of the main element. This part of the slipstream deforms significantly before it reaches the flap and thus results in complex spanwise variations for the flap flow. This stresses the need to investigate slipstream development in propeller-wing-flap systems and the effects on flap flow specifically to gain in-depth understanding of the interactions. The results presented in this paper expose the inherent complexity of investigating propeller-wing-flap systems and gaining viable validation data, and might serve to guide for future investigations of propeller-wing-flap systems. 

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Experimental Investigation of Aerodynamic Interactions of a Wing with Deployed Fowler Flap under Influence of a Propeller Slipstream

In the recent years, aviation is facing with the increasing of fuel price and flights, and the impact is estimated to grow more and more in next years without any action. To reduce its environmental footprint, engineers are trying to design more efficient aircraft, with engines less consuming. However, the classical aircraft’s tube and wing configuration has been developed over half a century, and it still offers small potential gain. A breakthrough in aircraft design is then needed to drastically reduce the problem.

Civil Aircraft Vehicle Design

An accurate estimation of propeller slipstream characteristics is essential to evaluate the performance characteristics of airframe components placed within the propeller slipstream. The complicated vortical structures of the propeller slipstreams necessitate the need of using high-fidelity methods such as computational fluid dynamics (CFD) analysis to estimate the slipstream characteristics. The current investigation deals with comparing the CFD predicted propeller thrust, power and slipstream characteristics with the wind tunnel data for a variable pitch propeller operating at a low Reynolds number of approximately 100,000.
In the current study, the CFD solver used was ANSYS Fluent software. Initial numerical analyses were conducted to evaluate the applicability of intermittency transition model available in the solver, to low Reynolds number flows. For assessment purposes, the Eppler 387 airfoil characteristics obtained using XFOIL (low-fidelity code) and time-accurate CFD calculations were compared with wind tunnel data. When compared to XFOIL drag data, the intermittency model had a better quantitative agreement with wind tunnel data at moderate angles of attack. Subsequently, three-dimensional time-accurate CFD simulations were conducted using the intermittency model to estimate the propeller characteristics. The propeller rotational motion was simulated using the sliding mesh approach. The numerical results for parameters such as thrust and nacelle pressures which are dependent only on pressure fields, have a good agreement with wind tunnel data. Whereas, propeller power and slipstream velocities which are based on both pressure and viscous forces are slightly under predicted in the numerical simulations.

Numerical estimation of slipstream characterisitics for propellers operating at low Reynolds numbers

Conceptual Design of Distributed Propellers Aircraft: Non-Linear Aerodynamic Model Verification of Propeller-Wing Interaction in High-Lifting Configuration

The present investigation addresses two key issues in aerodynamic performance of a propeller–wing configuration, namely linear and nonlinear predictions with low-order numerical models. The develop...

Aerodynamic model of propeller–wing interaction for distributed propeller aircraft concept:

This paper opens an exciting new opportunity of new aircraft concepts specifically targeting to have higher aerodynamic efficiency than conventional designs through the synergistic interaction between the propeller and the wing. Previous literature on propeller and wing performance analysis methods provide a platform on theory description behind the aerodynamic modeling approach selected. The research effort began with attempts to verify previous NASA wind-tunnel tests (TN D-4448) on a medium and short wing span propeller-driven, short take off and landing (STOL) transport aircraft. One prediction is employed on isolated performance of the wing without the propellers and another is to capture one-way coupling, specifically the effect of the propeller slipstream on the wing. For the first decoupled analysis configuration , the vortex lattice model (VLM) technical tools comparison was made with the Athena Vortex Lattice (AVL) and VSPAERO. Next, the propeller and the wing interaction is predicted using three different coupling methods. The first stage of the work is based on VSPAERO solver which combined the actuator disk theory with VLM. The second approach is to compare with the in house code of blade element and lifting line theory (LLT) coupling. Thirdly, to couple the same BET model with VLM to capture the aerodynamics performance and the influence of the propeller on the wing with the aim to determine the lift and induced drag of the configuration. Perhaps the most compelling aspect offered by the technical tools selected is being economic; low computational cost and time. The numerical computation results of the model presented a good correlation with the experimental data. The aerodynamic model developed will be a strong base for more complex analysis and even greater efficiency improvements for a conceptual design studies of future distributed propeller aircraft .

https://hal.archives-ouvertes.fr/hal-01599301/document

Quentin Borlon

Papers

Conceptual Design of Distributed Propellers Aircraft: Non-Linear Aerodynamic Model Verification of Propeller-Wing Interaction in High-Lifting Configuration

Aerodynamic model of propeller–wing interaction for distributed propeller aircraft concept:

Conceptual Design of Distributed Propeller Aircraft: Linear Aerodynamic Model Verification of Propeller-Wing Interaction