Ducted Fan System Research Articles

Multi-Objective Design of a Distributed Ducted Fan System

The distributed propulsion system applied to the vertical take-off and landing aircraft must maintain the high performance in both hover and cruise flight. The gap of the power unit has an adverse effect on the distributed ducted fan system, especially in cruise flight. Therefore, a new distributed ducted fan system was proposed, which eliminated the power gap in design, and adjusted the contraction and expansion of the wake through the deflectable induced wing arranged behind the ducted fan to ensure the high efficiency of the distributed ducted fan system in different flight phases. Then, a multi-objective design method of the distributed ducted fan system was proposed, and the feasibility of the design method was verified by designing the inlet and outlet of the duct and the induced wing. Design results show that the performance change of the distributed ducted fan system mainly came from the change of the inlet. By increasing the length and height of the inlet, the flow separation was alleviated and the duct thrust was increased in hove flight, but the cruise drag became larger. The increase of the inlet height made the operating point of the blade far away in hover and cruise flight, which increased the difficulty of the multi-objective design. Compared with the distributed ducted fan system composed of the traditional circular ducted fan, the hovering power load was reduced by 3.703%, but the cruise efficiency was increased by 17.372%, and the spanwise space was reduced by 20% in the final design.

지상 시험과 CFD 시뮬레이션을 통한 덕티드 팬 시스템의 제자리 비행 성능 연구

본 연구에서는 본 연구진에서 설계한 덕티드 팬의 제자리 비행 성능을 확인하기 위해 40% 축소 모델을 이용하여 지상 회전 시험 및 전산 유체 해석을 수행하였다. 본 축소 시험 모델의 블레이드 개수는 6개이며, 팬의 회전속도는 4,000RPM이다. 팬 블레이드의 콜렉티브 피치 각도는 20도에서 36도까지에서 시험을 진행하였다. 지상 시험은 정지 상태에서 1,000RPM씩 증가시키며 4,000RPM까지 성능 데이터를 계측하였다. 전산 유체 해석은 지상 시험과 동일한 조건에서 4,000RPM 시험 조건에 대해 수행하였다. 제자리 비행 성능은 추력, 파워, 덕트 추력 비, FM(Figure of Merit)으로 확인하였다. 시험과 해석 결과 간 비교를 통해 성능 결과의 신뢰성을 확보하였으며, 목표 성능은 콜렉티브 피치각 31도 이상의 조건에서 달성됨을 확인하였다.

An optimization and test method for ducted fans based on CFD

Some unmanned aircrafts with ducted fan systems are characterized by high efficiency, structural safety and good stability. As a major part of such aircrafts, the ducted fan plays an important role in performance. However, changes in the fan blade structure will influence the fan action. First, from a manufacturing point of view, materials and gate positions were selected. The injection molding process parameters were optimized based on an orthogonal testing analysis method, and this optimization process reduced the warpage by 36.4%. Then, the flow fields of the ducted fans in the theoretical and deformed models were compared and analyzed with SolidWorks computational fluid dynamics (CFD). Finally, the wind velocity values at different distances from the nozzle outlet of the ducted fan were obtained using a wind speed measurement experiment system. The results from the model comparisons showed that fan blade deformation reduced the wind speed by approximately 5%.

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.

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.

Noise control for a dipole sound source using micro-perforated panel housing integrated with a Herschel–Quincke tube

This study presents a passive noise control approach for directly suppressing sound radiation from an axial-flow fan, which involves micro-perforated panels (MPPs) backed by cavities and integrated with a hollow tube with the characteristics of a Herschel–Quincke (HQ) tube (MPPHQ housing). Noise suppression is mainly achieved by sound cancellation between the sound fields from the fan with a dipole nature and sound radiation from a vibrating panel via vibro-acoustic coupling. In addition, noise mitigation is supplemented by sound absorption in micro-perforations and acoustic interference at the hollow tube boundaries. A two-dimensional theoretical model is established to investigate the HQ segment housing a sound source. Results show that the HQ segment enhances the sound suppression performance in the passband region of the MPP housing device, and thus, a widened effective working band is obtained. Optimization is conducted to identify the optimal parameters for the MPPHQ housing. The proposed method has the potential to effectively control ducted-fan noise and to enhance the quality of products with a ducted-fan system.

Research on Numerical Calculation for Aerodynamic Characteristics Analysis of Ducted Fan

By taking a typical ducted fan system model as the research object, the unsteady aerodynamics calculation method is established based on slide dynamic mesh technology. After the experimental validation of calculation method, the influence factors of viscous effect, tip clearance and propeller disk location are analyzed based on numerical calculation. The research results show that, the viscous effect embodies the boundary layer interactions between propeller tip and duct, and the calculation accuracy can be improved by considering viscous effect; the tip clearance determines the influence effect of propeller, and the decreasing of tip clearance leads to the increasing of duct thrust; the propeller disk location determines the flow quality and tip clearance, a reasonable location must bring the optimal fairing effect and ensures the tip clearance meeting the design requirements.

Analysis of the effect of ducted fan system variables on ventilation in an empty heading using CFD

Analysis of the effect of ducted fan system variables on ventilation in an empty heading using CFD

Maneuverable Capsule Endoscope Based on Gimbaled Ducted-Fan System: Concept and Simulation Results

Wireless capsule endoscopes are a growing research area because they can be easily swallowed by patients to capture images of the digestive system without pain. However, a drawback of current capsule endoscopes is that most use passive motion. To overcome this drawback, a maneuverable capsule endoscope (MCE) based on a gimbaled ducted-fan (GDF) system is proposed in this study. The system design, prototype development of the GDF system, and associated modeling and simulation are presented. The concept of the GDF is adopted from the thrust-vector control algorithm of a space shuttle. To prevent organ damage, the ducted fan, which generates and controls the thrust required for achieving maneuverability, is mounted on a gimbal structure. A scaled-up prototype of the GDF system was manufactured. The overall conceptual design of the MCE based on the GDF system is presented. A flow simulation and a three-dimensional path-following simulation are performed to evaluate the proposed MCE’s applicability. The mean terminal velocity of the 6:1 scaled-up MCE prototype was calculated from flow simulation to be 0.6047, 0.5941, and 0.9204 m/s for the three postures of the GDF system, respectively, which represented the three translational degrees of freedom. For the 1:1 scale prototype, the mean terminal velocity was calculated to be 0.1147, 0.1127, and 0.1746 m/s for the above three postures, respectively. The proposed MCE dynamic model follows the desired path profile when the Lyapunov stability-based path-following algorithm was applied to it. In summary, the terminal velocity achieved in this research is sufficient for maneuvering inside the stomach organ. The results show that the MCE concept could be used for detecting and diagnosing abnormalities in the digestive system.

Noise control of dipole source by using micro-perforated panel housing

Mitigating low-frequency noise in a small ducted fan system such as hairdryer is still a technical challenge. Traditional duct lining with porous materials work ineffectively due to the limitation of its thickness and length of small domestic product with ducted fans. This study presents a passive approach to directly suppress the sound radiation from the fan housed by a short microperforated panel covered with a shallow cavity backing. The noise suppression is achieved by the sound cancellation between sound fields from a fan of a dipole nature and sound radiation from a vibrating panel via vibro-acoustic coupling and by sound absorption in micro-perforations to widen the stopband. A two-dimensional theoretical model, capable of dealing with strong coupling among the vibrating micro-perforated panel, sound radiation from the dipole source, sound fields inside the cavity and the duct is developed. Through modal analysis, it is found that the even modes of the panel vibration are very important to cancel the sound radiation from the dipole source. Experimental validation is conducted with a loudspeaker to simulate the dipole source, and good agreement between the predicted and measured insertion loss (IL) is achieved.

Numerical Study of Ducted-fan Lip Stall Suppression Based on Inflatable Leading Lip Cell

A novel method using inflatable leading lip cell for suppressing duct lip stall of ducted fan system is presented and numerically simulated using unsteady Reynolds-averaged Navier-Stokes equations. The lip inflatable mechanism consists of an inflatable cell and a faring cell. The inflatable cell size is controllable via inflating or deflating, while the faring cell is basically used to help form a desirable shape of a smooth configuration. The inflatable cell can change the shape of the duct lip, resulting in the change of flow pattern around the duct lip. This method has advantages of no rotating or transmission mechanism, minimum change to the original duct structure, and maximum shape control range. Preliminary results of the numerical simulation demonstrate that the method presented is effective in suppressing the duct lip stall, and it is a promising applicable stall suppression approach.

Tip Clearance Investigation of a Ducted Fan Used in VTOL Unmanned Aerial Vehicles—Part II: Novel Treatments Via Computational Design and Their Experimental Verification

Ducted fan based vertical lift systems are excellent candidates to be in the group of the next generation vertical lift vehicles, with many potential applications in general aviation and military missions. Although ducted fans provide high performance in many “vertical take-off and landing” (VTOL) applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow adversely affects the general aerodynamic performance of ducted fan VTOL unmanned aerial vehicles (UAVs). The current study utilized a three-dimensional Reynolds-averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) model of ducted fan for the development and design analysis of novel tip treatments. Various tip leakage mitigation schemes were introduced by varying the chordwise location and the width of the extension in the circumferential direction. Reduced tip clearance related flow interactions were essential in improving the energy efficiency and range of ducted fan based vehicles. Full and inclined pressure side tip squealers were also designed. Squealer tips were effective in changing the overall trajectory of the tip vortex to a higher path in radial direction. The interaction of rotor blades and tip vortex was effectively reduced and the aerodynamic performance of the rotor blades was improved. The overall aerodynamic gain was a measurable reduction in leakage mass flow rate. This leakage reduction increased thrust significantly. Experimental measurements indicated that full and inclined pressure side tip squealers increased thrust obtained in hover condition by 9.1% and 9.6%, respectively. A reduction or elimination of the momentum deficit in tip vortices is essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing. The novel tip treatments developed throughout this study are highly effective in reducing the adverse performance effects of ducted fan systems developed for VTOL UAVs.

Axial Flow Fan Tip Leakage Flow Control Using Tip Platform Extensions

Performance of an axial flow fan unit is closely related to its tip leakage mass flow rate and level of tip/casing interactions. The present experimental study uses a stereoscopic particle image velocimeter to quantify the three dimensional mean flow observed near the blade tip, just downstream of a ducted fan unit. After a comprehensive description of the exit flow from the baseline fan, a number of novel tip treatments based on custom designed pressure side extensions are introduced. Various tip leakage mitigation schemes are introduced by varying the chordwise location and the width of the extension in the circumferential direction. The current study shows a proper selection of the pressure side bump location and width are the two critical parameters influencing the success of each tip leakage mitigation approach. Significant gains in the axial mean velocity component are observed when a proper pressure side tip extension is used. It is also observed that a proper tip leakage mitigation scheme significantly reduces the tangential velocity component near the tip of the axial fan blade. Reduced tip clearance related flow interactions are essential in improving the energy efficiency of ducted fan systems. A reduction or elimination of the momentum deficit in tip vortices is also essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing.

Superconducting Ducted Fan Design for Reduced Emissions Aeropropulsion

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This article introduces a new conceptual design tool for an environmentally sustainable method of aeropropulsion: a ducted fan system driven by a fully superconducting electrical machine. Such a system could help mitigate aviation's contribution to global climate change by enabling the reduction of greenhouse gas emissions from aircraft. An electro-thermal motor sizing model was coupled with cycle analysis and weight estimation routines to create an automated environment for rapid design trade studies. The resulting parametric cycle analysis and sizing outcomes revealed the system's operational boundaries for a given aspiration space. </para>

Noise-Source Identification for Ducted Fan Systems

Coherence-based source analysis techniques can be used to identify the contribution of combustion noise in the exhaust of a jet engine and to hence enable the design of noise-reduction devices. However, when the combustion noise propagates in a nonlinear fashion, the identified contribution using ordinary coherence methods will be inaccurate. In this paper, an analysis technique is reported that enables the contribution of linear and nonlinear mechanisms to the propagated sound to be identified. An experimental rig is described for studying the propagation ofnoisethrougharotor/statorsetupusingavaneaxialfanmountedinaductsothatnonlinearinteractionsbetweena soundsourceandthefancanbeinvestigated.Thereportedtechniqueisusedtoidentifyanonlineartonegeneratedby the interaction of the rotor and a propagated tone. The identification procedures are then applied to data from fullscaleturbofanengine testsinstrumentedwith pressuretransducers at thecombustor canandinthehot-jet pipewith microphones in the near field. At a particular power setting, the interaction between the combustion noise and the high-pressure turbine is measured in the hot-jet pipe. The analysis techniques enable nonlinear interactions to be identified and enable linear and nonlinear coherent output powers to be determined.

Demonstrating the fundamentals of fan noise

A compact, portable demonstration rig will be shown which lends itself well to demonstrating the dipole nature of fan noise generation. The demonstration apparatus provides a quantitative insight into the interaction of the dipole source distribution and the acoustic impedance presented by the fan duct. The demonstration also brings out some of the factors giving rise to fluctuating blade lift forces which constitute the dipoles responsible for fan noise generation. Implications of the fundamentals demonstrated for the standardization of fan sound measurements and for the design of ducted fan systems will be summarized with reference to a more complete description [P. K. Baade, “Effects of Acoustic Loading on Axial Flow Fan Noise Generation,” Noise Control Eng. (1976) (in press)].