Ducted Fan Research Articles

Reduced-order analysis of the acoustic near field of a ducted axial fan

Spatio-temporal and modal analyses of the tip-vortex system of a ducted axial fan are performed based on highly resolved large-eddy simulations by proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). The Reynolds number based on the tip speed of the blade and the diameter of the fan Do is Re=9.36×105, the Mach number is M=0.136, and the rotational speed Ω=3000 rpm. The tip clearances s/Do=0.001,0.005, and 0.01 are investigated for the design and off-design operating conditions. Only at the off-design condition, a blade-tip-vortex interaction is observed for s/Do=0.01 and s/Do=0.005 while further reduction of the tip clearance to s/Do=0.001 prevents the cyclic interaction of the neighboring blades tip vortex with the current blade and a fully transitional region develops on the suction side of the blade. The POD results capture the narrowband cyclic interaction of the blade wake at the off-design condition. The first two energetic mode pairs can be linked to the interaction of the blades with the incoming wakes of the preceding blades. Compared to the POD results, the DMD modes corroborate the findings of blade-wake interactions. Furthermore, they highlight the connection to boundary layer transition on the suction side of the blades. The spatio-temporal DMD analyses at the characteristic frequencies of the blade-wake interaction reveal the generation of pressure waves which evolve in the azimuthal direction like isolated bubbles and propagate upstream of the blade. It causes two peaks in the spectrum of the acoustic pressure in the near field acoustics in agreement with the experimental sound spectra for s/Do=0.01 and s/Do=0.005 at the off-design condition.

Parameter Optimization of a Bi-copter Type Unmanned Aerial Vehicle to Avoid Propeller-induced Vibrations During Hovering

The vibration parameters of a bi-copter-type unmanned aerial vehicle is optimized by considering operational vibration with payloads. The double electric ducted fan loads, which transmit excitations to the fuselage, are predicted and compared using optimization methods. While the minimum vibration amplitude for stress will be achieved at 7.69 Hz, it will be 9.80 Hz. for minimum deformation without sacrificing safety factor requirement. It ensures sensitive vertical acceleration. It is not seen significant differences on results from screening and genetic algorithm methods. Correlations between frequencies and structural responses are determined. It is observed that the stress and deformation amplitudes of the structure decreases at increasing frequencies up to the next natural frequency. While the highest amplitude is seen at the first frequency, it decreases in increasing modes. The airframe structural model’s operational frequency must be 7.69 or 9.80 Hz to achieve sensitive vertical acceleration. Subsequently, it is aimed to develop an autonomous task by the implemented system controlled by various algorithm as a future work.

Aerodynamic analysis and control for a novel coaxial ducted fan aerial robot in ground effect

Modeling and control for a novel coaxial ducted fan aerial robot in-ground-effect is presented in this article. Based on experiments using the ducted fan bench test, the fitting curve of the ground effect thrust of the ducted fan aerial robot at different heights is obtained. In addition, the flow field simulation results of the prototype with ground effect at different heights can be obtained using computational fluid dynamics software. A simplified model of the prototype for control can be designed based on several reasonable hypotheses that are established using blade element and momentum theory. To compensate for the disturbance associated with ground effect, a nonlinear disturbance observer is designed to estimate the disturbance, and control structure of the closed-loop system is composed of a nonlinear disturbance observer combined with a double-loop proportion–integration–differentiation controller. The results of several numerical simulations and experiments demonstrate the effectiveness of this controller structure. The performances of tracking trajectory and system stability are improved significantly, compared to the situation that the ground effect is not compensated for.

Multidisciplinary Design Optimization Framework with Coupled Derivative Computation for Hybrid Aircraft

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.

Analysis of fixed-wing VTOL aircraft with gas-driven fan propulsion system

This paper presents a new concept of vertical take-off and landing (VTOL) propulsion system based on gas-driven fan. This system has a simple mechanical actuation mechanism and enables high cruising efficiency. However, compared with the traditional ducted fan propulsion system, the concept may have disadvantages, such as large total pressure loss due to the intake and small installation thrust caused by internal and external flow coupling. An overall performance analysis model of a fixed-wing VTOL aircraft that combines the characteristics of propulsion system components is established to clarify the influences of such factors on the propulsion system. The comprehensive performance of the existing VTOL propulsion system and the new concept is compared. A sensitivity analysis of key aerodynamic parameters is performed for the new propulsion system. Results indicate that the new propulsion system can balance the contradiction between VTOL and flight and obtain a large range and an effective load when the speed requirement is low. Nevertheless, this system is sensitive to the aerodynamic parameters. The energy loss coefficient of the propulsion system should be less than 0.2 to ensure that the propulsion system can be at an efficient operating point.

Aerodynamic performance assessment of a ducted fan UAV for VTOL applications

The aerodynamic performance of a recent developed ducted fan Unmanned Aerial Vehicle (UAV) was experimentally assessed by means of force, pressure and PIV measurements. Experiments were conducted on the UAV for both hover and forward flight configurations. Particular attention was given to the in-ground-effect which is important for the take-off and landing modes of the UAV during flight. Variations included rotational speed of the contra-rotating fan, incident angle, forward flight speed and the exit-to-ground distance were examined, allowing a comprehensive understanding of the overall aerodynamic characteristics of the ducted fan UAV. Wind tunnel measurement has successfully defined an initial operation region of the ducted fan UAV. The inlet velocity distortion at the inlet of the UAV during forward flight can significantly influence the inlet circumferential pressure distribution and therefore in principle affect the overall aerodynamic performance. The presence of the ground during take-off and landing can enhance the total lift generation with slightly sacrificing propulsive efficiency. In addition, when the UAV flies in proximity of the ground the back pressure at exit will be increased and thus alleviates the lift production by the duct lip. The outcomes can provide essential information in design and optimization of ducted fan type flight vehicles.

Flight and Interaction Control of an Innovative Ducted Fan Aerial Manipulator.

An innovative aerial manipulator with ducted fans is proposed to achieve side-on aerial manipulation tasks in a confined environment, such as canopy sampling in dense forests. The dynamic model of the novel design is studied, and on this basis a composite controller is proposed to address the challenges of arm extension and physical interaction during the manipulation process. An adaptive controller is proposed for the aerial platform to achieve good stability and tracking performance under the manipulator motion, and an impedance controller is designed for the manipulator to ensure compliance and stability during physical contact. The experimental tests validate the effectiveness of the proposed prototype structure and controller design.

On the role of acoustic reflections from duct boundaries in fan flutter

The role that acoustic reflections from duct boundaries play in aeroengine fan flutter is theoretically investigated. To make a systematic parametric study attainable, a three-dimensional semi-analytical approach is employed. Based on the transfer element method combined with a boundary integral equation method, this approach effectively captures the acoustic coupling effect of an annular rotor undergoing incipient oscillation and a finite-length non-rigid duct in subsonic flow. For a given vibration mode, the disturbances generated both inside and outside the duct are determined by a simultaneous solution. The flutter likelihood is subsequently evaluated through the energy method. Results reveal that near the flutter boundary, the aeroelastic impact of duct boundary reflections becomes evident and critical when propagating (cut-on or weakly damped) acoustic modes exist in the flow duct. Under such condition the aerodynamic interaction between both duct openings strongly affects the sound field distribution, thus contributing to the notable installation effect on aeroelastic stability. Moreover, the flutter-driven acoustic field is also susceptible to the sound reflection effect of the partially lined duct wall. It is found that the variation of the blade aerodynamic damping with the liner impedance is markedly different when the duct end reflections come into play. Under appropriate conditions the mutual effect of the lined wall and the duct openings significantly strengthens their acoustic couplings with the ducted fan, where a reasonable estimate of aeroelastic stability can only be provided with an adequate consideration of the realistic acoustic boundary conditions for the entire duct.

Limitations and Challenges in Designing an All-Electric Aircraft: Analytical Study

Driven by rapid depletion of non-renewable energy resources, emission reduction of combustion engine exhaust, noise reduction and in-efficiency of combustion engine demand and production of electric vehicle has seen a significant growth in recent years. However, when it comes to electrification of the aircraft technology, there are a number of challenges and technological limitations faced by the designer such as vicious weight cycle, in-sufficient energy density and power constraints in batteries. This paper outlines those challenges in design and manufacturing of a manned electric aircraft. Using MATLAB, a mathematical model of the electric aircraft is created considering parameters like power required, battery capacity, battery weight and total weight of the aircraft. Range and endurance of an electric aircraft for different variations in payload or passenger capacity will be determined. This detailed study will give a picture on what is achievable using current technology (battery energy density, combustion free jet propulsion etc.) and what can be achieved based on the limitations in developing a electric ducted fan engines. This paper also outlines design challenges being faced in combustion free jet propulsion namely electric ducted fan engines which is needed for propelling the electric aircraft. This paper is concluded with design recommendations and parameters to be considered during design process for a fully electric aircraft.

Numerical investigation on aerodynamic performance of a ducted fan under interferences from the ground, static water and dynamic waves

Ducted fans have been widely applied in various VTOL (vertical takeoff and landing) vehicles due to their high efficiency and low noise. By using the sliding mesh technique to simulate propeller rotation, a ducted fan system is chosen and the effects of the ground, static water and dynamic waves on its aerodynamic performance are evaluated, thereby exploring the adaptability of the system to complicated environments. The ground is set to slip wall moving with the same speed as the free stream and the static water surface is identified by using the VOF model. To generate dynamic waves, the open channel wave boundary is investigated to simulate a Stokes wave combined with the VOF model. A series of calculation cases consisting of free space, the ground effect, the static water effect and the wave effect are observed and analyzed in detail. The results indicate that ground, water surface and wave can strongly affect the aerodynamic performance of the ducted fan, as they interrupt the jet flow from the outlet of the duct and further pull the rebounded flow into the system. A decrease in the height between the system and the surface leads to a greater influence on the ducted fan. The strong effect obtained by the rigid ground benefits the lift of the propeller the most but also greatly weakens the lift of the duct; ultimately, the total lift of the system is lost. The torque changes by a law similar to that of the lift. The soft water surface is impacted to form a “drainage area”, which can be considered to increase the distance between the system and the water. Therefore, the water effect is not as strong as the ground effect. However, the change rules of the lift and the torque are nearly the same as those for the ground effect. The dynamic wave has the most complicated effect on the system. The periodic wave causes unpredictable periodic changes on the lift and the torque of the duct and the propeller, which may be related to numerical wave attenuation and the real-time changes in the soft wave surface. A larger wave height and a shorter distance between the wave and the system lead to a greater influence on the ducted fan. Moreover, the dynamic wave can induce “dynamic uplift” and hysteresis phenomena on the aerodynamic performance of the system.

Review on ducted fans for compound rotorcraft

ABSTRACTThis paper presents a survey of published works on ducted fans for aeronautical applications. Early and recent experiments on full- or model-scale ducted fans are reviewed. Theoretical studies, lower-order simulations and high-fidelity CFD simulations are also summarised. Test matrices of several experimental and numerical studies are compiled and discussed. The paper closes with a summary of challenges for future ducted fan research.

Wire-Suspended Device Control Based on Wireless Communication With Multirotor for Long Reach-Aerial Manipulation

In this study, we propose a long-reach aerial manipulation system with a wire-suspended device that allows the airframe to maintain its position at the desired distance away from the target. We implemented a feedback communication between the multirotor and wire-suspended device to maintain the position of the wire-suspended device directly below the multirotor while maintaining a constant distance from the target. The multirotor communicates its velocity and relative position to the wire-suspended device to control the ducted fans, whereas the wire-suspended device transmits the attitude and distance from the ground to the multirotor to control the winch. The designed controller for the ducted fans allows the wire-suspended device to behave like a long rigid robotic arm. The performance of the designed controller was verified by navigating the multirotor over stepped surfaces while the wire-suspended device was being lowered.

Neural-Networks Control for Hover to High-Speed-Level-Flight Transition of Ducted Fan UAV With Provable Stability

In this paper, we focus on the transition control of a ducted fan vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV). To achieve a steady transition from hover to high-speed flight, a neural-networks-based controller is proposed to learn the system dynamics and compensate for the tracking error between the aircraft dynamics and the desired dynamic performance. In prior, we derive the nonlinear system model of the aircraft full-envelope dynamics. Then, we propose a novel neural-networks-based control scheme and apply it on the underactuated aircraft system. Key features of the proposed controller consist of projection operator, state predictor and dynamic-formed adaptive input. It is proved and guaranteed that the tracking errors of both state predictor and neural-networks weights are upper bounded during the whole neural-networks learning procedure. The very adaptive input is formed into a dynamic structure that helps achieve a reliable fast convergence performance of the proposed controller, especially in high-frequency disturbance conditions. Consequently, the closed-loop system of the aircraft is able to track a certain trajectory with desired dynamic performance. Satisfactory results are obtained from both simulations and practical flight test in accomplishing the designed flight course.

Conceptual Design of Electrical Ducted Fan (EDF)

Electric Ducted Fan (EDF) is an electric propulsion consist of duct, fan and electric motor with main power source is from battery which generates compression air for thrust. EDF is used as an alternative propulsion for high speed UAV especially for target UAV or “bomb” controlled UAV. It’s design is very simple and no need extra maintenance compared to jet engine. Design process of an EDF is more simple than a jet engine, nevertheless it could obtain enough thrust for high speed flying. The aim of this research is to design an EDF as an alternative propulsion for high speed UAV and performance analyzing of EDF using analitical approach. Design of EDF produce an EDF with inlet and outlet diameter are 70mm and 60mm. Total length of EDF is 116,1mm. Performance analysis of EDF shows that by 700W of motor power could reach 16N of thrust which is accepted performace for 70mm EDF.

Low speed longitudinal aerodynamic, static stability and performance analysis of a hypersonic waverider

Hypersonic waveriders have the potential to significantly reduce travel times on long haul civilian transport routes. The design of hypersonic aircraft is heavily influenced by the aerodynamic efficiency at the cruise Mach number, resulting in less than ideal geometries for subsonic flight. Waverider aerodynamics and stability in the low speed regime is rarely investigated and not well understood, but is crucial for horizontal take-offs and landings. This paper presents a combination of numerical simulation results and experimental data for the low speed variant of the Mach 8 HEXAFLY-INT waverider. Aerodynamic, control and stability testing was conducted in the University of Sydney 4 foot by 3 foot low speed facility, while propulsion testing of the vehicle-integrated electric ducted fan was completed in the 7 foot by 5 foot tunnel. Motor thrust settings were tested for 8 lithium polymer cells connected serially drawing between 5 and 25 amperes. Computational fluid dynamics simulations are compared with wind tunnel tests for angles of attack between −5 and 25 degrees and elevon deflections between −10 and 10 degrees. Results show the aerodynamics is dominated by leading edge flow separation and vortex lift. At a centre of gravity location of 44.4% of the vehicle length, stability is observed up to 22 degrees angle of attack. Past this point, instability occurs due to vortex breakdown. The centre of gravity aft stability limit was found at 53.1% of the vehicle length. Overall, good agreement is seen between simulation and tunnel data, validating the modelling methods used. The low speed demonstrator can achieve trimmed flight from 12 m/s, but is only speed stable above 19 m/s. A cruise speed of 19 m/s is selected and can be attained with approximately −9.2 degrees of elevon and 7.1 degrees AoA for a centre of gravity location of 44.4%. Shifting the centre of gravity aft can reduce the trim angle of attack to below 6 degrees with −4 degrees elevon deflection. Take-off and landing can be achieved at 15 m/s between 9.8 and 12 degrees angle of attack, depending on centre of gravity configuration. A maximum climb rate of 2.1 m/s is predicted at 16.3 m/s based on the power settings tested. Overall, the results show the aircraft satisfies stability and performance requirements in the longitudinal axis.

Assessment of statistical sampling methods and approximation models applied to aeroacoustic and vibroacoustic problems

The effect of multiple process parameters on a set of continuous response variables is, especially in experimental designs, difficult and intricate to determine. Due to the complexity in aeroacoustic and vibroacoustic studies, the often-performed simple one-factor-at-a-time method turns out to be the least effective approach. In contrast, the statistical Design of Experiments is a technique used with the objective to maximize the obtained information while keeping the experimental effort at a minimum. The presented work aims at giving insights on Design of Experiments applied to aeroacoustic and vibroacoustic problems while comparing different experimental designs and approximation models. For this purpose, an experimental rig of a ducted low-pressure fan is developed that allows gathering data of both, aerodynamic and aeroacoustic nature while analysing three independent process parameters. The experimental designs used to sample the design space are a Central Composite design and a Box-Behnken design, both used to model a response surface regression, and Latin Hypercube sampling to model an Artificial Neural network. The results indicate that Latin Hypercube sampling extracts information that is more diverse and, in combination with an Artificial Neural network, outperforms the quadratic response surface regressions. It is shown that the Latin Hypercube sampling, initially developed for computer-aided experiments, can also be used as an experimental design. To further increase the benefit of the presented approach, spectral information of every experimental test point is extracted and Artificial Neural networks are chosen for modelling the spectral information since they show to be the most universal approximators.

Rapid and optimal design of a tail-sitter VTOL ducted fan using a neural network and PSO algorithm

Considering the optimal performance and new applications of the ducted fans, especially in UAV missions, this paper aims to provide an optimal and rapid method for designing the UAVs based on new mathematical and analytical tools which improved and accelerated many of the long engineered processes. In this design method, an initial design is carried out based on the momentum theory and the first size approximation of different sections of the duct fan, such as the inlet and outlet diameter, the power and the duct thrust, is determined. Then by connecting the MATLAB and a ducted fan design software called the ducted fan design code (DFDC), several optimal design schemes for the duct are extracted by the particle swarm optimization algorithm. The parameters search domain in the algorithm is obtained from the initial design with the Momentum theory method and the various results of DFDC software, in the case. Finally, in order to obtain the final duct design, according to the optimized information, a multilayer perceptron neural network using an error-back propagation algorithm is trained. In the redesign loops, without a time-consuming optimization, the trained neural model can extract the duct parameters very quickly, based on the constraints of structure, control design, and missions targets.

Effects of tip-jet on the performance of a ducted fan

Tip-jet technology has potential value for application in vertical take-off and landing or short take-off and landing concept aircraft. The main objective of this current work is to investigate the effects of the tip-jet on the performance of a ducted fan in hover. The overall flow field of the ducted fans with tip-jet was simulated by using the shear-stress transport k-omega turbulence model with a refined high-quality structured grid at various rotational speeds. The comparative analysis of the performances of the ducted fans with different tip-jet locations was carried out. The results indicate that the circulation of the blade with tip-jet is affected by the flow blockage, Coanda effect, and edge-shed vortex. These flow features were formed by the tip-jet. The fan’s thrust could be augmented when the nozzle was a little farther from the blade trailing edge. However, a higher jet flow utility efficiency could be achieved when the nozzle was close to the blade trailing edge.

Aerodynamic Characteristics of a Ducted Fan System Based on Momentum Source Method

Ducted fan systems have received a considerable attention due to their potential for wide application in both civil and military missions. Compared with isolated fans, the presence of duct can substantially weaken the contraction of fan wake and gives the potential to fly efficiently with high security, compact structure and low noise. Based on the momentum source method (MSM) and the S-A turbulence model, a computational fluid dynamics (CFD) simulation model is established and validated as a reliable tool by comparing with calculation results based on sliding mesh technique. The effect of the revolution speed, flight velocity and angle of attack on the aerodynamic characteristics of the ducted fan system is evaluated in detail. The calculation results show that the thrust of the ducted fan system shows an approximate quadratic increase with the increasing revolution speed; As the vertical velocity increases, the thrust of the ducted fan system increases first and then decreases; As the forward velocity increases, the lift and drag of the ducted fan system increase; As the angle of attack increases, the drag of the ducted fan system increases and the lift first increases and then decreases.

Low‐frequency dynamics of a floating wind turbine in wave tank–scaled experiments with SiL hybrid method

AbstractThe design of floating wind turbines needs the validation of numerical models against measurements obtained from experiments that accurately represent the system dynamics. This requires solving the conflict in the scaling of the hydrodynamic and aerodynamic forces that arises in tests with wind and waves. To sort out this conflict, we propose a hybrid testing method that uses a ducted fan to replace the rotor and introduce a force representing the aerodynamic thrust. The force is obtained from a simulation of the rotor coupled in real time with the measured platform displacements at the basin. This method is applied on a test campaign of a semisubmersible wind turbine with a scale factor of 1/45. The experimental data are compared with numerical computations using linear and non‐linear hydrodynamic models. Pitch decays in constant wind show a good agreement with computations, demonstrating that the hybrid testing method correctly introduces the aerodynamic damping. Test cases with constant wind and irregular waves show better agreement with the simulations in the power spectral density's (PSD's) low‐frequency region when non‐linear hydrodynamics are computed. In cases with turbulent wind at rated wind speed, the low‐frequency platform motions are dominated by the wind, hiding the differences from hydrodynamic non‐linearities. In these conditions, the agreement between experiments using the proposed hybrid method and computations is good in all the frequency range both for the linear and the non‐linear hydrodynamic models. Conversely, for turbulent winds producing lower rotor thrust, non‐linear hydrodynamics are relevant for the simulation of the low‐frequency system dynamics.