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This work presents the effect of wingtip-mounted propellers on the aircraft drag polar, identified from in-flight measurements. In previous wind-tunnel experiments, significant reductions in drag a...

Because of their potential to reduce aircraft emissions, counter-rotating open rotors (CRORs) have seen a renewed interest in applications, from civil aviation to urban air mobility. However, there...

A general formulation for the fluid–structure interaction of an airfoil undergoing prescribed pitching and passive heave and deformation about an arbitrary axis is given in the linearized potential...

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.

An experimental study is conducted to advance the understanding of flow physics associated with a boundary-layer ingesting, distributed propulsion system. The influence of incoming boundary-layer t...

Air vehicle sizing requires the ability to estimate the propulsive power and energy requirements of a flight vehicle as well as its weight. Existing tools and methods for aircraft sizing typically ...

A novel model is proposed to estimate the optimal propulsive efficiency and the optimal dimensionless heaving velocity of a flapping foil based on a lift–drag ratio under the assumption of negligib...

This study describes the aerodynamic efficiency of a forebody–inlet configuration and computational investigation of a drone system, capable of sustainable supersonic cruising at Mach 1.60. Because the whole drone configuration is formed around the induction system and the design is highly interrelated to the flow structure of forebody and inlet efficiency, analysis of this section and understanding its flow pattern is necessary before any progress in design phases. The compression surface is designed analytically using oblique shock patterns, which results in a low drag forebody. To study the concept, two inlet–forebody geometries are considered for Computational Fluid Dynamic simulation using ANSYS Fluent code. The supersonic and subsonic performance, effects of angle of attack, sideslip, and duct geometries on the propulsive efficiency of the concept are studied by solving the three-dimensional Navier–Stokes equations in structured cell domains. Comparing the results with the available data from other sources indicates that the aerodynamic efficiency of the concept is acceptable at supersonic and transonic regimes.

Advances in aerodynamic and propulsive efficiency of future aircraft can be achieved by strategic installation of propellers near the airframe. This paper presents a robust and computationally efficient engineering method to estimate the load distribution of a propeller operating in arbitrary nonuniform flow that is induced by the airframe and by different flight conditions. The time-resolved loading distribution is computed by determining the local blade section advance ratio and using the sensitivity distribution along the blade, which is a property of the propeller in isolated conditions. The method is applied to four representative validation cases by comparing to full-blade computational fluid dynamics (CFD) simulations and experimental data. For the evaluated cases, it is shown that the changes in the propeller loads due to the nonuniform inflow are predicted with errors ranging from 0.5 up to 12% compared to the validation data. By extending the quasi-steady approach with a correction to account for unsteady effects, the time-resolved blade loading is also well approximated, without adding computational cost. The proposed method provided a time-resolved solution within several central processing unit seconds, which is seven orders of magnitude faster compared to full-blade CFD computations.

Boundary-layer ingestion (BLI) promises increased aircraft efficiency, but excessive inlet distortion must be avoided to prevent fans that are too heavy or structurally infeasible. We propose a new...

Electric aircraft technology has enabled the use of multiple rotors in novel concepts for urban air mobility. However, multirotor configurations introduce strong aerodynamic and aeroacoustic intera...

Lack of flexibility limits the performance enhancement of man-made flapping wing Micro Air Vehicles (MAVs). Active chordwise deformation (bending) is introduced into the flapping wing model at low Reynolds number of Re = 200 in the present study. The lattice Boltzmann method with immersed boundary is adopted in the numerical simulation. The effects of the bending amplitude, bending frequency and phase lag between bending and flapping on the propulsive performance are analysed. The numerical results show that all the chordwise deformation parameters including the bending amplitude, bending frequency and phase lag have a great influence on the flow field, Leading-Edge Vortex (LEV), Trailing-Edge Vortex (TEV) and previous Leading-Edge Vortex (pLEV) of the deformable flapping wing, which leads to the variation of the propulsive performance. With decreasing bending amplitude and increasing bending frequency, both the thrust and energy dissipation coefficients increase. The highest thrust coefficient and highest energy dissipation coefficient occur at a phase lag of 180°. On the other hand, strong dependence of the propulsive efficiency on the vortex tangle is found. The highest propulsive efficiency is obtained for the present model at a dimensionless bending amplitude of 0.2, bending frequency of 0.7Hz, and phase lag of 0°.

Wake ingestion has been studied in order to develop a physics-based understanding of its effect on engine power and propulsive efficiency. A combination of analysis and testing has been employed. A...

Turbo-electric propulsive fuselage aircraft featuring Boundary-Layer Ingestion (BLI) are considered promising candidates to achieve the emissions reduction targets set for aviation. This paper presents an analytical method capable of estimating the BLI benefit at aircraft level, enabling a quick exploration of the propulsive fuselage design space. The design space exploration showed that the assumptions regarding the underwing turbofans and BLI fan mass estimation can have an important impact on the final fuel burn estimation. The same applies to the total efficiency assumed for the electric transmission, the range of the aircraft mission, and the propulsive efficiency of the engines used as benchmark. The regional jet and short- to medium-range aircraft classes seem to be the most promising as the ingested drag and power saving are among the largest, with long-range aircraft being just behind. The future introduction of advanced technologies, which target the reduction of vortex and wave dissipation at aircraft level, could increase the potential benefit of propulsive fuselage BLI. On the other hand, the potential benefit would be decreased if more efficient and lighter ultra high bypass ratio engines were used as benchmark.

General expressions are derived in this paper for the aerodynamic force and moment on an arbitrary set of pitching and heaving foils from the vortical impulse theory in the limit of linearized pote...

Made available in DSpace on 2022-04-28T19:44:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-01 National Science Foundation National Cancer Institute Migratory birds have the ability to save energy during flight by arranging themselves in a V-formation. This arrangement enables an increase in the overall efficiency of the group because the wake vortices shed by each of the birds provide additional lift and thrust to every member. Therefore, the aerodynamic advantages of such a flight arrangement can be exploited in the design process of micro air vehicles. One significant difference when comparing the anatomy of birds to the design of most micro air vehicles is that bird wings are not completely rigid. Birds have the ability to actively morph their wings during the flapping cycle. Given these aspects of avian flight, the objective of this work is to incorporate active bending and torsion into multiple pairs of flapping wings arranged in a V-formation and to investigate their aerodynamic behavior using the unsteady vortex lattice method. To do so, the first two bending and torsional mode shapes of a cantilever beam are considered and the aerodynamic characteristics of morphed wings for a range of V-formation angles, while changing the group size in order to determine the optimal configuration that results in maximum propulsive efficiency, are examined. The aerodynamic simulator incorporating the prescribed morphing is qualitatively verified using experimental data taken from trained kestrel flights. The simulation results demonstrate that coupled bending and twisting of the first mode shape yields the highest propulsive efficiency over a range of formation angles. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a five-body V-formation incorporating coupled bending and twisting of the first mode at a formation angle of 140 degrees. These results indicate the potential improvement in the aerodynamic performance of the formation flight when introducing active morphing and bioinspiration. Department of Mechanical and Aerospace Engineering New Mexico State University Department of Mechanical Engineering American University of Sharjah Campus of São João da Boa Vista São Paulo State University (UNESP) Campus of São João da Boa Vista São Paulo State University (UNESP) National Science Foundation: OAC-2019000 National Cancer Institute: U54 CA132383

Made available in DSpace on 2022-04-28T19:42:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-01 New Mexico State University Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) National Science Foundation National Cancer Institute Many research studies have investigated the characteristics of bird flights as a source of bioinspiration for the design of flapping-wing micro air vehicles. However, to the best of the authors’ knowledge, no drone design targeted the exploitation of the aerodynamic benefits associated with avian group formation flight. Therefore, in this work, a conceptual design of a novel multi-flappingwing drone that incorporates multiple pairs of wings arranged in a V-shape is proposed in order to simultaneously increase the propulsive efficiency and achieve superior performance. First, a mission plan is established, and a weight estimation is conducted for both 3-member and 5-member configurations of the proposed air vehicle. Several wing shapes and airfoils are considered, and aerodynamic simulations are conducted, to determine the optimal planform, airfoil, formation angle, and angle of attack. The simulation results reveal that the proposed bioinspired design can achieve a propulsive efficiency of 73.8%. A stability analysis and tail sizing procedure are performed for both 3-member and 5-member configurations. In addition, multiple flapping mechanisms are inspected for implementation in the proposed designs. Finally, the completed prototypes’ models of the proposed multi-flapping-wing air vehicles are presented, and their features are discussed. The aim of this research is to provide a framework for the conceptual design of bioinspired multi-flapping-wing drones and to demonstrate the sizing, weight estimation, and design procedures for this new type of air vehicles. This work establishes the first multi-flapping-wing drone design which exploits the aerodynamic features of the V-formation flight observed in birds to achieve superior performance in terms of payload and endurance. Department of Mechanical and Aerospace Engineering New Mexico State University Department of Mechanical Engineering American University of Sharjah São Paulo State University (UNESP), Campus of São João da Boa Vista São Paulo State University (UNESP), Campus of São João da Boa Vista CAPES: 88881.302889/2018-01 National Science Foundation: OAC-2019000 National Cancer Institute: U54 CA132383

[EN] Distributed electric propulsion and boundary layer ingestion are two attractive technologies to reduce the power consumption of fixed wing aircraft. Through careful distribution of the propulsive system elements, higher aerodynamic and propulsive efficiency can be achieved, as well as a lower risk of total loss of aircraft due to foreign object damage. When used on the wing, further reductions of the bending moment on the wing root can even lead to reductions of its structural weight, thus mitigating the expected increase of operating empty weight due to the extra components needed. While coupling these technologies in fixed-wing aircraft is being actively studied in the big aircraft segment, it is also an interesting approach for increasing the efficiency even for aircraft with maximum take-off masses as low as 25 kg, such as the A3 open subcategory for civil drones from EASA. This paper studies the effect of changing the propellers' position in the aerodynamic performance parameters of a distributed electric propulsion with boundary layer ingestion system in a 25 kg fixed-wing aircraft, as well as in the performance of the propellers. The computational results show the trade-offs between the aerodynamic efficiency and the propeller efficiency when the vertical position is varied., This research was funded by the Agencia Estatal de Investigacion of Spain through grant number PID2020-119468RA-I00/AEI/10.13039/501100011033.

We consider the propulsive performance of an unsteady heaving and pitching foil, experimentally studying an extensive parameter space of motion amplitudes, frequencies, and phase offsets between the heave and pitch motions. The phase offset $\phi$ between the heaving and pitching motions proves to be a critical parameter in determining the dynamics of the foil and its propulsive performance. To maximize thrust, the heave and pitch motions need to be nearly in phase ($\phi=330^\circ$), but to maximize efficiency, the pitch motion needs to lag the heave motion ($\phi=270^\circ$), corresponding to slicing motions with a minimal angle of attack. We also present scaling relations, developed from lift-based and added mass forces, which collapse our experimental data. Using the scaling relations as a guide, we find increases in performance when foil amplitudes (specifically pitch) increase while maintaining a modest angle of attack.

The effects of the phase difference between fore- and hindwings are experimentally investigated on the aerodynamic force, aerodynamic efficiency, and longitudinal control forces for tandem flapping...

The aerodynamic performance of four 12-inch diameter propellers was investigated at propeller disk angles-of-attack ranging from 0° to 90° and at advance ratios ranging from 0 to 0.55. Aerodynamic load measurements using a six-axis load cell showed that the thrust of all four propellers increased with an increasing disk angle-of-attack, for all the advance ratios investigated. On the other hand, power consumption demonstrated lower sensitivity to variations in the propeller angle-of-attack. The load difference between the advancing and retreating blades caused pitch and yaw moments, which increased with an increasing propeller angle-of-attack. When plotted as a function of the inflow advance ratio, the thrust, power and propulsive efficiency plots overlapped for the range of disk angle-of-attacks. Analytical prediction of the performance of the rotor was carried out using blade element theory. Comparisons of the experimental data acquired and the predictions using different inflow models was made. The evaluation showed that the Glauert [15] and Coleman et al. [16] inflow models are capable of predicting propeller performance at a wide range of non-zero disk angle-of-attack with maximum discrepancy of 15%.

The aerodynamic performance of the exhaust system is becoming more important in the design of engines for civil aircraft applications. To increase propulsive efficiency and reduce specific fuel consumption, it is expected that future engines will operate with higher bypass ratios, lower fan pressure ratios and lower specific thrust. At these operating conditions, the net thrust and the specific fuel consumption are more sensitive to losses in the exhaust. Thus the performance of the exhaust needs to be accurately assessed as early as possible during the design process. This research investigates low-order models for the prediction of the performance of separate-jet exhaust systems, as a function of the free-stream Mach number, the fan nozzle pressure ratio and the extraction ratio (fan to core pressure ratio). In the current practice the two nozzles are typically considered in isolation and the performance is modelled as a function of their pressure ratio. It is shown that the additional degrees of freedom have a substantial impact on the metrics describing the performance of the exhaust system. These models can be employed at a preliminary design stage coupled with engine performance models, which require as input the characteristics of the exhaust system. Two engines, which are representative of current and future large turbofan architectures are studied. The low-order models investigated, generalized Kriging and radial basis functions, are constructed based on data obtained with computational fluid dynamics simulations. The data represents the characteristics of the exhaust of each engine, and they are provided for the first time for a wide operational envelope. The influence on accuracy of the type of surragate model and its settings have been quantified. Furthermore, the trade-off between the accuracy of the model and the number of samples has been identified. It is found that the exhaust performance metrics can be modelled using a low-order model with sufficient accuracy. Recommendations on the best settings of the model are also provided.

Traditionally, computational design optimization of commercial aircraft is performed by considering a small number of representative operating conditions. These conditions are based on the design M...

This paper addresses the design of swirl recovery vanes for propeller propulsion in tractor configuration at cruise conditions using numerical tools.Amultifidelity optimization framework is formulated for the design purpose, which exploits low-fidelity potential flow-based analysis results as input for high-fidelity Euler equation-based simulations. Furthermore, a model alignment procedure between low- and high-fidelity models is established based on a shapepreserving response prediction algorithm. Two cases of swirl recovery are examined. The first is the swirl recovery by the trailing wing, which leads to a reduction of the lift-induced drag. This is achieved by the optimization of the wing twist distribution. The second case is swirl recovery by a set of stationary vanes, which leads to production of additional thrust. In the latter case, four configurations are evaluated by locating the vanes at different azimuthal and axial positions relative to the wing. An optimum configuration is identified where the vanes are positioned on the blade-downgoing side downstream of the wing. For the configuration and conditions examined, the wing twist optimization reduces the induced drag by 3.9 counts (5.9% of wing-induced drag), whereas the optimized 4-bladed SRVs lead to an induced-drag reduction of 6.1 counts (9.2% of wing-induced drag).

This study aims to characterize the complex propulsive-airframe and cross-propulsor interactions that occur on an overwing distributed propulsion system with boundary-layer ingestion. Wind tunnel e...

Propulsors with boundary layer ingestion (BLI) generate a propulsive force with lower flow power input than conventional engines. This aerodynamic benefit can be traced back to its sources: reducti...

The system-level capabilities and component-level sensitivities of hybrid-electric propulsion systems were analyzed by modeling a twin-engine general-aviation aircraft. The flight-performance model...

A parametric numerical study is conducted to assess the effect of trajectory nature on the propulsive performances of a NACA0014 flapping airfoil. Sinusoidal and non-sinusoidal plunging and pitching trajectories are combined to achieve sought flapping trajectories. To this aim, the effect of kinematic parameters such as oscillation frequency, plunging amplitude, pitching amplitude, and phase angle between pitch and plunge is evaluated on thrust and propulsive efficiency behavior at a low Reynolds number, $$Re=1.1$$ x $$ 10^4$$ . It is found that the best propulsive efficiency is obtained for sinusoidal paths, while non-sinusoidal ones are found to slightly improve thrust and lift forces. Furthermore, thrust coefficient maximum values are obtained for non-sinusoidal trajectories when flatness coefficients $$S>1$$ . The highest lift coefficient values are found however for flapping trajectories when flatness coefficients $$S

It is envisaged that the next generation of civil aero-engines will employ high bypass ratios to lower specific thrust and improve propulsive efficiency. This trend is likely to be accompanied with the integration of compact nacelle and exhausts in podded under-wing installation positions that are close coupled to the airframe. This leads to the requirement for a comprehensive methodology able to predict aerodynamic performance for combined airframe-engine architectures. This paper presents a novel thrust and drag accounting approach for the aerodynamic analysis of integrated airframe-engine systems. An integral metric is synthesised based on the concept of net vehicle force. This is accomplished through the consolidation of aerodynamic coefficients, combined with the engine cycle characteristics obtained from a thermodynamic matching model. The developed approach is coupled with an in-house tool for the aerodynamic design and analysis of installed aero-engines. This framework is deployed to quantify the impact of engine installation position on the aerodynamic performance of a future large turbofan installed on a commercial wide-body airframe. The governing flow mechanisms are identified and their influence is decomposed in terms of the impact on airframe, nacelle, and exhaust performance. It is shown that it is essential to include the impact of installation on the exhaust for the correct determination of overall airframe-engine performance. The difference in net vehicle force for a close coupled position can reach up to -0.70% of nominal standard net thrust relative to a representative baseline engine location.

Counter Rotating Open Rotors (CROR) have the potential to reduce environmental emissions thanks to their high propulsive efficiency. However, there are a number of concerns surrounding their acoustic emissions. This contribution presents a novel multi-configuration CROR that offers considerable noise reductions. In particular, we consider locking either fore or aft rotor during take-off, with the running rotor providing the required thrust. Duringcruise, both rotors are operated to retain the high efficiency of the CROR. A coupled Computational Fluid Dynamics-Computational Aeroacoustics analysis (CFD-CAA) has shown the potential of this multi-configuration concept to offer substantial noise reductions when compared to a baseline CROR. During a simulated constant-altitude flyover at take-off conditions, reductions of 3.5 dBA and 7.9 dBA have been demonstrated when either fore or aft row is locked, respectively. Using the EPNL metric, this result corresponded to7 EPNLdB and 12EPNLdB, respectively, for the same flyover.

International audience; 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.

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×10^3 and 3.4×10^4, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0º to 10º. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored., Fundação para a Ciência e a Tecnologia e Santander-UBI, Fundação para a Ciência e Tecnologia (FCT) through the project number UIDB/50022/2020, the Grant co-sponsored by Santander-UBI BID/FE/2019 and the grant sponsored by Fundação para a Ciência e a Tecnologia 2020.04648.BD

Auxiliary lift and/or thrust on a compound helicopter can introduce complex aerodynamic interactions between the auxiliary lift and thrust components and the main rotor. In this study high-fidelity computational fluid dynamics analyses were performed to capture the various aerodynamic interactions which are occurring for the Airbus RACER compound helicopter, featuring a box-wing design for auxiliary lift in cruise and wingtip-mounted lateral rotors in pusher configuration for auxiliary thrust in cruise and counter-torque in hover. Although the study was limited to a specific geometry, the effects and phenomena are expected to be to some extent applicable in general for compound helicopters and wingtip-mounted rotors in pusher configuration. A quantitative indication of the aerodynamic interaction effects could be established by leaving away different airframe components in the simulations. The downwash of the main rotor was found to cause a small negative angle of attack in cruise for the wings and lateral rotors and impinged directly on the lateral rotors in hover, resulting in moderate to very significant sinusoidally varying blade loading. The wing increased lateral rotor propulsive efficiency in cruise through its wingtip rotational flowfield and to a lesser extent through its wake. An upstream effect of the lateral rotors on the wing loading was also found. In hover the wing caused a net increase in left lateral rotor thrust as the deflection of the main rotor flow towards the rotor resulted in a local thrust decrease and the low momentum inflow to the rotor from the wake of the wing resulted in a local thrust increase. A small thrust decrease for the right lateral rotor was found due to the wing disturbing its slipstream as this rotor produced reversed thrust. In general, very significant aerodynamic interaction effects can be expected when a main rotor, lateral rotors and wing are in proximity to each other.

Until electric energy storage systems are ready to allow fully electric aircraft, the combination of combustion engine and electric motor as a hybrid-electric propulsion system seems to be a promis...

Simulations are reported on the behavior of two tandem symmetric foils in an in-line configuration undergoing pitching motion. The Reynolds number was varied between 1000 and 4000, whereas the pitching Strouhal number ranged from 0.2 to 0.5 and the amplitude of pitching varied from 4 to 8 deg. The streamwise separation distance between the foils was fixed at one chord length. The performance of the downstream foil was significantly worsened (up to 80% in efficiency) by the tandem effects. The Strouhal number, Reynolds number, and pitching amplitude had substantial impact on the performance of the downstream foil. For the upstream foil, however, the performance improved by up to 147% in efficiency at all ranges of Reynolds number, Strouhal number, and pitching amplitude. The scaling of the individual foil performance metric and the system collective performance metric were investigated for tandem foils. The scaling developed for isolated foils does hold for tandem foils in the in-line configuration with modified empirical coefficients that depend on reduced frequency and Reynolds number in a range of St and Re. However, the leading foil behavior at lower St is more scattered compared to higher St, which suggests more significant wake interactions that influence the scaling and performance of the leading foil. © 2020 by the American Institute of Aeronautics and Astronautics,., T14-Q01, This study has received support from Canada First in Research Excellence through the University of Alberta Future Energy Systems Institute, grant number T14-Q01. The simulations were carried out using the Compute Canada computational clusters.

For the past few decades flapping wing aerodynamics has attracted a great deal of research interest from both the aeronautical and biological communities pertaining to the development of MAVs. The objective of this study is to examine and understand the effect of non-dimensional plunge amplitude and reduced frequency on propulsive performance of NACA 4-digit airfoil series and to examine the performance characteristics of square plunge motion and trapezoidal plunge motion. Two dimensional flow simulations around plunging symmetric aerofoils were performed using FLUENT. The simulations were carried out at Reynolds number of 20000 using incompressible laminar, NS solver. The reduced frequency (k) was varied from 0.5–5 and the plunging amplitude (h) was varied from 0.25–1.5. The plunging motions to the aerofoils were provided through UDFs. The effect of variation of k and h on the thrust coefficient ( C T ), power-input coefficient ( C P ) and propulsive efficiency (η) is studied. C T value is maximum for square plunge profile for all the airfoils. However, for a given value of h, with the increase in k, C T increases with increasing thickness of the airfoil and reaches a maximum value for airfoil thickness of NACA0018 and then starts decreasing. With varying h and k, it was observed that the propulsive efficiency reached a peak value and the peak shifts to higher h and k with increasing airfoil thickness. From the above study, it was concluded that airfoil thickness played a major part in influencing the thrust generation at low Strouhal number. However, at high Strouhal numbers airfoils showed diverse trends with respect to thrust generation. Sinusoidal plunging motion was more efficient but generated less thrust when compared to square and trapezoidal plunging motions.

Ongoing engine developments require advanced thermal management technologies to handle the increasing demand of refrigeration and lubrication. As the thermal capacity of the oil lubricant and coolant circuits becomes saturated, conventional fuel-based oil cooling systems need to be supplemented with additional cooling sources. Finned heat exchangers integrated in the core/bypass-flow splitter surface of a turbofan provide enhanced oil heat removal capabilities. For a positive impact in the overall engine efficiency, the surface heat exchangers need to be designed to maximize heat transfer while minimizing the impact in the propulsive efficiency. This work focuses on the sensitivity of the complex transonic and three-dimensional turbofan bypass-flow to arrays of fins embedded on the splitter, which determines the aerodynamic penalty that can be incurred at the benefit of increased oil heat capacity. We present an experimental study of a turbofan bypass-flow and asses the flow modifications introduced by two different fin heat exchanger designs, with “continuous” and “interrupted” fins, both aligned with the mean flow direction. Experiments were performed in a ground test facility that reproduces the flow in the bypass duct of turbofan at the design point characterized by cruise velocities and take-off atmospheric conditions. Different measurement techniques were adapted to the flow and wind tunnel requirements to provide an accurate characterization of the flow developing over the splitter surface. Results are reported in terms of flow velocity and orientation, turbulence intensity and temperature with and without the arrays if fins present in the flow. This work demonstrates the importance of aerodynamically optimized designs to minimize detrimental effects on propulsive efficiencies, and provides estimate values of flow disturbances in realistic engine conditions that can be incorporated into simplified engine performance models.

A vortex-based method is presented for the hydroelastic analysis of a hydrofoil in flapping motion, operating as a biomimetic thruster. The system performs combined heaving and pitching motion with appropriate phase difference. As a first approximation, the foil is assumed to be very thin permitting to neglect thickness effects as higher-order contributions to the hydrodynamics. Moreover, the flapping thruster is considered to be flexible, free to deform under inertia and reactive forces caused by its forced motion and hydrodynamic pressure, respectively. The proposed method is validated through a series of comparisons with other models, as well as experimental results, for the case where the foil is clamped at its leading edge, while its trailing edge acts as a free end. It is illustrated that chordwise flexibility can significantly improve the propulsive efficiency. For demonstration purposes, a realistic propulsion problem concerning an autonomous underwater vehicle (AUV) is studied, indicating an efficiency increase almost 10% in comparison with the rigid case. The present method can serve as a useful tool for the preliminary design, as well as for the assessment and dynamic control of such biomimetic systems for marine propulsion and energy recovery.

The development of cheaper, more efficient access to space is fundamental to the viability of many current and future ambitions for space exploitation and exploration. Vehicle concepts that combine...

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the second part of a two part paper, we apply the fan gas path and body force model design process from Part 1 to the problem of predicting flow separation over an engine nacelle lip caused by crosswind. The inputs to the design process are based on NASA Stage 67. A body force model using the detailed Stage 67 geometry is also used to enable assessment of the accuracy of the design process based approach. In uniform flow, the model produced by the design process recreates the spanwise loading distribution of Rotor 67 with a 7% RMS error. Both models are then employed to predict crosswind separation velocity. The two approaches are found to agree in their prediction of the crosswind separation velocity to within 5%.

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the first part of a two part paper, we present a design process that produces a fan gas path and body force model with performance representative of modern high bypass ratio turbofan engines. The target users are those with limited experience in turbomachinery design or limited access to fan geometry. We employ quasi-1D analysis and a series of simplifying assumptions to produce a gas path and the body force model inputs. Using a body force model of the fan enables steady computational fluid dynamics simulations to capture fan&ndash, distortion interaction. The approach is verified for the NASA Stage 67 transonic fan. An example of the design process is also included, the model generated is shown to meet the desired fan stagnation pressure ratio and thrust to within 1%.

A blended-wing-body aircraft with distributed propulsion system is a new design concept proposed in recent years to achieve the N + 3 goal. Distributed engines can be embedded on different positions on the upper surface of the aircraft due to its smaller size compared with the traditional engines. Different installation positions can influence not only the aerodynamic characteristics but also the engine performance, especially during the off-design conditions such as takeoff condition. Thus, a propulsion/airframe integration analysis method was developed to calculate the performance of several configurations with different engine positions at takeoff condition. We found that there is strong coupling between the aerodynamics and propulsion efficiency, and that the span position of the propulsion system has more significant effects on the performance of the aircraft compared with its chord position.

Controlling and directing the boundary layer on the surfaces of a flight vehicle are two of the most demanding challenges in advanced aerodynamic designs. The design of highly integrated and submerged inlets with a large offset between the entrance and compressor face is particularly challenging because of the need for controlling or reducing the adverse effects of the boundary layer on propulsive efficiency. S-duct diffusers are used widely in flight vehicles when the compressor face needs to be hidden, and their performance is generally sensitive to the quality of ingested boundary layer from the fuselage. Passive or active flow control mechanisms are needed to prevent flow separations at the bends. In this paper, a new method is presented for optimal inlet/body integration based on a pair of ridges ahead of the inlet and its effects on the performance of a semicircular S-duct inlet integrated on a flat surface using CFD. In this design, the ridge changes an inefficient inlet concept to one with acceptable performance. The new method of integration is practicable for top-mounted inlet configurations where the use of diverters and other mechanisms results in higher amounts of drag, weight, and complexity.

Comparisons are made for propulsion systems for unmanned flights with several hundred kilowatts of propulsive power at moderate subsonic speeds up to 50 h in duration. Gas-turbine engines (turbofan...

The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for Computational Fluid Dynamics (CFD) analyses. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown, and improvements between subsequent BLI designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet, with Reynolds number of 40 million based on mean aerodynamic chord and an angle of attack of 2° for all geometries. Results indicate an 8% reduction in engine power requirements at cruise for the BLI configuration compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using CDISC has been shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately twelve counts over the baseline geometry.

Electroaerodynamic thrust has been proposed as a means for aircraft propulsion, potentially enabling near-silent and solid-state flight. Studies to date have experimentally quantified electroaerody...

Analysis was performed to assess the impact of atmospheric-breathing supersonic retropropulsion as a technology solution for Mars descent. Vehicle models were developed for three architectures, emp...

International audience; The electrohydrodynamic thrust generated by wire–cylinder electrodes under high dc voltage is experimentally analyzed. Some recent experimental studies have shown that electrohydrodynamic thrusters produced by corona discharge and ionic wind are able to deliver high thrust-to-power ratio, which reopens prospects for electrohydrodynamic propulsion. From simple considerations based on ultralight aircraft mass, aerodynamics, battery mass, and experimental electrohydrodynamic thrust densities, their potential for applications is showcased. Furthermore, an experimental study is performed, for which the experimental observations are presented in terms of electric field and thrust density. This allows a simplified and synthetic presentation of propulsive properties. Various experimental biases have been identified and corrected. The measure of time-periodic oscillations of the airflow in the back of the thruster pinpoints a possible wake effect due to the impact of ionic wind on electrodes. The variations of the associated drag are studied when varying the position of the collecting electrodes. It is shown that aerodynamic losses can be significant in experimental electrohydrodynamic thrusters.