Aerodynamic Interaction Effects Research Articles

Experimental investigation of wing-propeller aerodynamic interaction in eVTOL configurations

The present study is aimed at the experimental investigation of the effects of wing-propeller aerodynamic interaction in a boom-mounted configuration typically used in eVTOL aircraft. The investigation was focused on the repercussions on wing and propeller performance coming from the variation of angle of attack, advance ratio and blades sense of rotation. Moreover, particular attention was devoted to the evaluation of the effect of the propeller's longitudinal offset. Results of a comprehensive wind tunnel campaign performed on a propeller-mounted wing scaled model confirmed the advantageous effects of an inboard-up rotating propeller on lift generation and drag reduction, while outlined the opposite sensitivity of wing and propeller performances when exposed to a non-zero angle of attack. Propeller's longitudinal offset instead led to slight alterations on wing and propeller aerodynamic performance, while a noteworthy sensitivity on the mounting setup was perceived by propeller aerodynamic performance. Moreover, PIV measurements allowed to evaluate quantitatively the effects of the investigated parameters on propeller slipstream behaviour and blade tip vortices pattern.

The Aerodynamic Interaction Effects between the Rotor and Fuselage on the Drag Performance of a Civil Helicopter in Forward Flight

The aerodynamic interaction between the rotor and fuselage is an important consideration in relation to the drag performance prediction of helicopters. In this paper, based on dynamic patched-grid technology coupled with a three-dimensional N–S equation solver, a numerical study of the aerodynamic interaction effects between the rotor and fuselage on the aerodynamic performance and flow field of the fuselage of a light civil helicopter is carried out under the forward flight condition. The deterioration of the drag performance and the evolution of the flow field structure caused by the rotation of the blades are illustrated. Due to the aerodynamic interaction, the drag of the fuselage is increased by 124.1% while the cycle of drag fluctuation is observed in one full revolution of the rotor with a change in amplitude of ±20%. The comparative results between the rotor-off and rotor-on cases show that the aerodynamic interaction effects between the rotor and fuselage on the drag performance are mainly reflected in the influence of the backward-developing rotor wake on the flow field of the rear part of the fuselage. An additional afterbody vortices system is induced, leading to a large reverse pressure gradient on the rear surface of the helicopter, which contributes to an increase in the pressure drag.

Experimental investigation of the aerodynamic performance of Flettner rotors for marine applications

Flettner rotors are becoming alternative wind-assisted propulsion systems for marine applications. This study experimentally investigated the aerodynamic performance of large-scale Flettner rotors with a diameter D = 350 mm, 0 = α ≤ 4.5, 3.5 = L/D ≤ 6.0, 1.0 ≤ De/D ≤ 2.0, and 9.33 × 104 ≤ Re ≤ 3.15 × 105, where α is the velocity ratio, L is the cylinder span, De is the diameter of the endplate, and Re is the Reynolds number based on D. The initial, increasing, decreasing, and stable areas were defined to describe the variation in the time-averaged lift-to-drag ratio K‾ with an increase in α. Both the aerodynamic performance of Flettner rotors and the range of the four areas were significantly influenced by L/D, De/D, and Re. Based on the measurement of the aerodynamic forces acting on the tested Flettner rotor under the influence of an interfering Flettner rotor with the same α, the effects of aerodynamic interaction for different wind incidence angles β and spacing ratios S/D were studied in detail. In addition, the driving and heeling force coefficients were presented for the combination of two Flettner rotors. Once the arrangement of the two Flettner rotors installed on the deck of a ship was known, both the driving and heeling forces provided by the combination of these rotors depended on α and the apparent wind angle.

Numerical Simulation of Aerodynamic Interaction Effects in Coaxial Compound Helicopters

The so-called coaxial compound helicopter features two rigid coaxial rotors, and possesses high-speed capabilities. Nevertheless, the small separation of the coaxial rotors causes severe aerodynamic interactions, which require careful analysis. In the present work, the aerodynamic interaction between the various helicopter components is investigated by means of a numerical method considering both hover and forward flight conditions. While a sliding mesh method is used to deal with the rotating coaxial rotors, the Reynolds-Averaged Navier-Stokes (RANS) equations are solved for the flow field. The Caradonna & Tung (CT) rotor and Harrington-2 coaxial rotor are considered to validate the numerical method. The results show that the aerodynamic interaction of the two rigid coaxial rotors significantly influences hover’s induced velocity and pressure distribution. In addition, the average thrust of an isolated coaxial rotor is smaller than that of the corresponding isolated single rotor. Compared with the isolated coaxial rotor, the existence of the fuselage results in an increment in the thrust of the rotors. Furthermore, these interactions between the components of the considered coaxial compound helicopter decay with an increase in the advance ratio.

Aeroelastic modeling and analysis of wings in proximity

This study investigates the effects of aerodynamic interaction on the aeroelastic characteristics of wings in proximity which is considered to be aerodynamically more efficient than the single wing case. The structural model of the wing is based on the first-order shear deformation theory and analyzed by the finite element method. The flow surrounding the wings is governed by potential theory and the aerodynamic loads are computed using the unsteady vortex lattice method. The aeroelastic simulation framework is established by integrating the structural and aerodynamic models within the flexible multibody dynamic program to solve the aeroelastic equations of motion in the time domain. Cantilever wings in proximity, arranged in biplane configuration, with different geometric parameters such as gap, sweep angle, dihedral angle, and stagger are considered in the analysis. The numerical results show that the smaller gap between the wings magnifies the aerodynamic interaction effect and decreases the onset of flutter speed. Sweeping the wing backward further reduces the flutter boundaries of the biplane model mainly due to changes in the wing's structural modal whereas the effect of dihedral angles is understated. The effect of stagger is more evident for a smaller gap and mostly leads to an increase in the flutter boundary. The aeroelastic responses are independent of initial disturbance and show a natural tendency to oscillate with a phase difference. This investigation warrants the importance of considering biplane wings as a single system for a gap lower than wing chord length as well as the significance of other geometric parameters in the aeroelastic calculation.

Aeroacoustic and aerodynamic interaction effects between electric vertical takeoff and landing rotors

Electric vertical take-off and landing (eVTOL) aircraft are characterized by their unconventional wing and electric rotor configurations, which involve both side-by-side and tandem rotor configurations. These configurations create unique aerodynamic and acoustic flow-fields. We numerically investigate the interaction effects between rotor pairs as well as their individual and combined acoustic radiation. We examine horizontal and vertical spacing, rotor tilt angles, and forward flight effects. Performance is characterized by thrust coefficient, blade passage frequency (BPF) sound pressure level (SPL), and overall sound pressure level (OASPL). This study is performed with a mid-fidelity aerodynamic solver, Dust, which is used to predict the aerodynamic flow-field. The tonal acoustic pressure at observer positions is predicted via the Farassat F-1A solution of the Ffowcs Williams and Hawkings equation utilizing the aerodynamic flow-field. The configurations studied show strong aerodynamic interaction effects in thrust, as well as out-of-plane acoustic radiation from the aft rotor. Base predictions of thrust and noise are validated via experimental measurement. As rotor separation decreases, we observe that aft rotor thrust decreases and BPF SPL increases. The most forward rotor, however, is marginally impacted by the interactions. [This research is supported by Archer Aviation Inc.]

Genetic algorithm optimization of a horizontal axis wind turbine blade section performance equipped with a single dielectric barrier discharge plasma actuator utilizing a direct regression model

The usage of a single dielectric barrier discharge plasma actuator (SDBD-PA) device for improving a aerodynamic performance of a locally developed horizontal axis wind turbine blade section is studied with one of the most recent electrostatic models. To characterize this blade section behavior over a wide range of operating conditions of SDBD-PA and to advance its performance with a fully automated optimization algorithm, a computationally cost efficient direct regression model is proposed. In this paper, 512 comprehensive numerical simulations are carried out to derive the direct regression model for aerodynamic performance calculation when the PA is in use. However, to obtain highly accurate results, two different models for angle of attacks higher and less than [Formula: see text] are suggested. The proposed mathematical model within the specified boundary limits allows for a rapid linkage between aerodynamic performance and genetic algorithm which canbe made to acquire optimum results for each case without requiring burdensome numerical simulations. It is identified that superimpose input parameters effects onto each other is not explanatory of the final effect on aerodynamic performance and interaction effects should be seriously taken into consideration at the proposed regression model.

Aerodynamic interaction between tandem overlapping propellers in eVTOL airplane mode flight condition

The architecture of new electric aircraft concepts (eVTOLs) for urban air mobility is typically characterised by multi-propellers in tandem configurations with different degrees of rotor disks overlapping. Consequently, the aerodynamic interaction between front propellers slipstream and rear propellers represents one of the key-phenomena which influenced the performance and design of these novel aircraft configurations. A wind tunnel campaign was performed to investigate the aerodynamic interaction between two propellers in tandem with particular focus to airplane mode flight condition of eVTOLs. A systematic series of tests, including thrust and torque measurements and stereoscopic Particle Image Velocimetry (PIV) surveys, were performed on two co-rotating propellers models. The axial distance was fixed during tests while the lateral separation distance was changed to evaluate the effects of aerodynamic interaction on propellers performance and flow field due to different propeller disks overlapping. Load measurements pointed out a remarkable loss of rear propeller thrust occurring when the degree of overlapping between rotors disks is increased. On the other hand, spectral analysis of measured loads signals showed a higher amount of thrust fluctuations amplitude occurring when the degree of overlapping between propeller disks is partial. Stereo PIV results provided insights on the effects of aerodynamic interaction on rear propeller inflow and wake flow physics. Moreover, numerical simulations performed using a mid-fidelity aerodynamic solver based on vortex particle method (VPM) provided enhanced insights to comprehend the interacting flow mechanisms between front propeller slipstream and rear propeller blades responsible for the detrimental effects observed on rear propeller performance.

PERFORMANCE PREDICTION AND DESIGN OF WIND-ASSISTED PROPULSION SYSTEMS

Wind-assisted propulsion is seen as one of the main alternatives to potentially achieve large emission reductions in shipping. However, wind-assisted propulsion introduces new challenges in the design, retrofitting and performance prediction as well as the performance analysis. This paper presents and compares methods to predict the performance of wind-assisted propulsion, using the validated performance prediction model ShipCLEAN. Focus is put on evaluating the difference between 1 degree of freedom (1 DOF) and 4 DOF methods as well as the impact of aerodynamic interaction effects in between multiple sails. Practical design considerations and performance differences are discussed based on an example ship. The study includes a comparison of the performance of different sail types (Flettner rotors, Wing sails and Suction wings) under realistic operational conditions.

Aerodynamic Interaction Effects Between Propellers in Typical eVTOL Vehicle Configurations

Many electric vertical takeoff and landing concepts are characterized by nontraditional vehicle layouts with distributed propellers. Two propeller interaction types were distinguished in this Paper, which investigates how propeller interaction in side-by-side and one-after-another configuration affects performance, in terms of thrust, power, in-plane forces, and out-of-plane moments, and how those performance effects depend on axial and lateral propeller spacing. A wind-tunnel experiment was performed with two propeller units, one instrumented with a force/torque sensor and the other introducing the aerodynamic interaction. Total pressure and planar particle-image velocimetry measurements were taken to investigate slipstream characteristics. A strong dependency of interaction effects on the geometric layout was found. For side-by-side interaction characteristic of vertical takeoff and transition, interaction effects varied from weak at small angle of attack to strong at larger angles. A drop in rear propeller thrust of up to 30% was found at constant advance ratio. Keeping thrust constant resulted in power penalties up to 13% for the two propellers combined. For one-after-another interaction, characteristic of cruise, a maximum reduction of thrust of up to 80% was observed. Thrust compensation led to power penalties up to 30% for the rear propeller alone. An extended blade element momentum model captured most interaction effects with sufficient accuracy.

CFD investigation of interaction effect between hull and accommodation on wind drag of a container ship in head wind

In this paper, we present a research on applying a commercial Computational Fluid Dynamics (CFD) code to determine interaction effect between hull and accommodation on wind drag of a container ship. For the high superstructure and large windward area ships such as container, wind drag acting on hull accounts for a large amount of total resistance. To clearly find aerodynamic performance and interaction effects on wind drag of a container ship, a full scale 1,200 TEU container has been used as a reference model. From results of comparison in the two computed cases of hull with and without accommodation, the interaction effects between hull and accommodation on aerodynamic performance and wind drag have been investigated. The targets of the paper has proposed a new solution to improve aerodynamic performances and reduce wind drag acting on the ship by reducing interaction effects between hull and accommodation.

In-flight Lift and Drag Estimation of an Unmanned Propeller-Driven Aircraft

The high-power density and good scaling properties of electric motors enable new propulsion arrangements and aircraft configurations. This results in distributed propulsion systems allowing to make use of aerodynamic interaction effects between individual propellers and the wing of the aircraft, improving flight performance and thus reducing in-flight emissions. In order to systematically analyze these effects, an unmanned research platform was designed and built at the University of Stuttgart. As the aircraft is being used as a testbed for various flight performance studies in the field of distributed electric propulsion, a methodology for precise identification of its performance characteristics is required. One of the main challenges is the determination of the total drag of the aircraft to be able to identify an exact drag and lift polar in flight. For this purpose, an on-board measurement system was developed which allows for precise determination of the thrust of the aircraft which equals the total aerodynamic drag in steady, horizontal flight. The system has been tested and validated in flight using the unmanned free-flight test platform. The article provides an overview of the measuring system installed, discusses its functionality and shows results of the flight tests carried out.

Study on the Aerodynamic Performance and Internal-External Flow Interaction Effects of Distributed Ducted Fan in the Climbing-Condition

Distributed electric propulsion ducted fans play an important role in saving energy and reducing environmental pollution of the airplanes. In this research, unsteady RANS CFD numerical simulations were used to analyse the possible impact of aerodynamic performance and interaction effects of distributed ducted fan in the climbing condition, which is verified with experimental method. Firstly, this paper will explore the effect of internal/external flow interaction on the flow field of the propulsion system at the same time. Secondly, from the perspective of propulsion efficiency and energy consumption, this paper will find the thrust relationship between the maximum continuous working state and the maximum working state and study the performance of the ducted fan. This paper will aim to reduce energy consumption during the propulsion of ducted fans and obtain longer flight time, and find a balance point between power and propulsion efficiency. The results show that the maximum continuous working state is 85% of the maximum thrust state approximately. By combining the aerodynamic interaction phenomena with the aerodynamic performance of the distributed ducted fan, this research provides an important basis and advice for enhancing the flight time of distributed ducted fans and reducing energy consumption during the process of engineering and flow mechanisms.

Design, operation and analysis of wind-assisted cargo ships

This study presents a novel approach to analytically capture aero- and hydrodynamic interaction effects on wind-assisted ships. Low aspect ratio wing theory is applied and modified to be used for the prediction of lift and drag forces of hulls sailing at drift angles. Aerodynamic interaction effects are captured by analytically solving the Navier-Stokes equation for incompressible, potential flow. The developed methods are implemented to a 4 degrees-of-freedom performance prediction model called “ShipCLEAN”, including a newly developed method for rpm control of Flettner rotors on a ship to maximize fuel savings. The accuracy of the model is proven by model- and full-scale verification. To present the variability of the model, two case study ships, a tanker and a RoRo, are equipped with a total of 11 different arrangements of Flettner rotors. The fuel savings and payback times are assessed using realistic weather from ships traveling on a Pacific Ocean route (tanker) and Baltic Sea route (RoRo). The results verify the importance of using a 4 degrees-of-freedom ship performance model, aero- and hydrodynamic interaction and the importance of controlling the rpm of each rotor individually. Fuel savings of 30% are achieved for the tanker, and 14% are achieved for the RoRo.

Breakdown of aerodynamic interactions for the lateral rotors on a compound helicopter

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.

The effects of the aerodynamic interaction on the performance of two Flettner rotors

Flettner rotors are nowadays becoming a widespread solution for wind-assisted propulsion. To increase the fuel savings of the ship on which they are installed, multiple devices are typically used. However, in the performance estimate of these hybrid ships, it is currently assumed that Flettner rotors operate independently, regardless of the number of devices employed and their relative position on the ship’s deck. The present investigation deals with a wind-tunnel experimental campaign aimed at understanding the aerodynamic interaction effects on the performance of two similar Flettner rotors. The study indicates that the aerodynamic performance of the two Flettner rotors is affected by their interaction, and, generally, this is most noticeable when the devices are set closer to each other and when they are aligned with the wind direction. It is demonstrated that, depending on the apparent wind direction, the layout of the Flettner rotors on the ship’s deck has a remarked influence on the driving and heeling force coefficients of the entire rig. Lastly, the velocity ratio is found to play a key role in the determination of how the interaction affects the Flettner rotor aerodynamic performance.

Aerodynamic Interaction Effects of wingtip-Mounted Propellers

The study presents an aerodynamic analysis of the propeller–wing interaction effects for the wingtip-mounted propeller configuration. The influence of the initial parameters of the propellers, such as the radius, the pitch angle as well as the direction of rotation on the models aerodynamic characteristics, in particular, on the wing span-efficiency factor and the induced drag was determined. In this research a computational simulation of the wingtip flow field was implemented using two different computational models with two different Reynolds numbers.Flow field simulations over computational models with different combinations of initial parameters were performed by means of the computational aerodynamic methods (the panel-vortex method of symmetric peculiarities). The simulation showed a significant positive effect on the aerodynamic characteristics of the computational models due to wingtip-vortex attenuation and swirl recovery by the propeller slipstreams. Analysis of the wing performance pointed out that the aerodynamic benefit of the wingtip-mounted propeller was due to an increase of the effective span-efficiency parameter of the wing.The induced drag coefficients and wing span-efficiency factors of the computational models for different combinations of given initial parameters, such as propellers radius and pitch angles, as well as the direction of rotation are obtained. The dependences between the given initial parameters and the studied aerodynamic characteristics of the computational models are determined. It is established that the character of these dependencies is identical for both computational models with two different Reynolds numbers. The analysis of the obtained dependencies indicates that when the propellers pitch angle φ changes, the highest efficiency zone is observed, that is characterized by the maximum value of the derivative dλef/dφ. The range of expedient change of the propellers pitch angle is determined, as a consequence.The most of the results are presented by diagrams for both computational models. The results obtained are of practical significance and will be useful for the aircraft design, performed according to the studied aerodynamic scheme.

An Experimental Investigation of Rotor–Box Aerodynamic Interaction1

Abstract Multirotor unmanned aerial vehicles (UAVs) are a promising means of package delivery. Such applications generally involve carrying bulky payloads under the vehicle. Understanding the aerodynamic interaction effects of payloads on the vehicle is the key to design such systems, in the low Reynolds number regime of small UAVs. High-speed particle image velocimetry (PIV), force, and torque measurements have been used with a rotor and a cubic box to investigate the rotor–box interactions and configurations typical of multirotor UAVs. The observed rotor and vehicle performance trends are explained by the mean flow field captured through PIV. Conditions similar to ground-effect operation are developed for the rotor at a high level of rotor-box overlap. A slight improvement in the vehicle performance is observed at conditions where the box is just out of the rotor wake. Some basic instantaneous flow phenomena due to rotor–box interaction have been identified. The interactions have been classified into three distinct modes based on observations at a range of box positions relative to the rotor. An empirical tip vortex trajectory model for isolated rotors is found to be instrumental in predicting the interaction mode at a given box position.

A method for optimizing the aerodynamic layout of a helicopter that reduces the effects of aerodynamic interaction

The aerodynamic environment during the flight of a helicopter is complex because of the severe aerodynamic interaction between various components. To fully consider the effect of aerodynamic interaction in the initial stages of helicopter design and to eliminate or reduce its adverse effects, a comprehensive design optimization method for the aerodynamic layout of a helicopter that is capable of reducing the adverse effects of aerodynamic interaction is developed in this paper. To satisfy the requirements for precision and efficiency in the calculation model, an aerodynamic interaction analysis model of various helicopter components was established based on a viscous vortex particle and the unsteady panel hybrid method. To simultaneously consider the influences of the position and shape of the aerodynamic components on the aerodynamic interaction during the optimization process, parameter modeling of the helicopter's shape was performed based on the class function/shape function transformation (CST) method. A Kriging surrogate model of the objective function was further developed and combined with a hybrid sequential quadratic algorithm and genetic algorithm optimization strategy to establish a comprehensive optimization flow for the aerodynamic layout of a helicopter that reduces the adverse effects of aerodynamic interaction. Verification was carried out based on a fuselage shape derived from UH-60 helicopter. The optimization results showed that the use of the comprehensive optimization method for the aerodynamic layout of a helicopter can effectively reduce the adverse effects of aerodynamic interaction. Based on the optimization objectives, the efficiency of hovering increased by 4.7%, the hovering ceiling increased by 3.48%, the speed stability derivative increased by 264.7%, and the angle of attack stability derivative decreased by 26.4%.

Analysis of the Effect of Multirow and Multipassage Aerodynamic Interaction on the Forced Response Variation in a Compressor Configuration—Part I: Aerodynamic Excitation

The aeroelastic prediction of blade forcing is still a very important topic in turbomachinery design. Usually, the wake from an upstream airfoil and the potential field from a downstream airfoil are considered as the main disturbances. In recent years, it became evident that in addition to those two mechanisms, Tyler–Sofrin modes, also called scattered or spinning modes, may have a significant impact on blade forcing. It was recently shown in literature that in multirow configurations, not only the next but also the next but one blade row is very important as it may create a large circumferential forcing variation, which is fixed in the rotating frame of reference. In the present paper, a study of these effects is performed on the basis of a quasi three-dimensional (3D) multirow and multipassage compressor configuration. For the analysis, a harmonic balancing code, which was developed by DLR Cologne, is used for various setups and the results are compared to full-annulus unsteady calculations. It is shown that the effect of the circumferentially different blade excitation is mainly contributed by the Tyler–Sofrin modes and not to blade-to-blade variation in the steady flow field. The influence of various clocking positions, coupling schemes and number of harmonics onto the forcing is investigated. It is also shown that along a speed-line in the compressor map, the blade-to-blade forcing variation may change significantly. In addition, multirow flutter calculations are performed, showing the influence of the upstream and downstream blade row onto aerodynamic damping. The effect of these forcing variations onto random mistuning effects is investigated in the second part of the paper.