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Flowfield and acoustic measurements from a model tiltrotor in hover

JOURNAL OF AIRCRAFT 1998年第6期35卷 921-929页

作者： Polak, DR George, AR United Technol Res Ctr E Hartford CT 06108 USA Cornell Univ Ithaca NY 14853 USA

rotor inflow aerodynamics and noise measurements were made on three configurations of an 8% scale model of the XV-15 tiltrotor in hover: 1) single Isolated rotor, 2) two rotors with no fuselage, and 3) complete tiltrotor aircraft. For the tiltrotor aircraft configuration and for the configuration of two rotors without the fuselage, the mean inflow velocity was higher at psi = 270 deg compared with the rest of the rotor disk, leading to reduced blade angle of attack and blade loading in this region. This azimuthally varying blade loading caused an impulsive noise that radiated preferentially behind the model. For the complete tiltrotor configuration, the turbulence ingested by the rotors was intermittent and depended on the instantaneous position of the fountain now, which shifted from side to side across the longitudinal plane of the model. The fountain turbulence had a higher velocity scale, smaller length scale, and was closer to isotropic than the ingested ambient turbulence. The tiltrotor configuration radiated less harmonic noise, but more broadband noise than the configuration with two rotors and no fuselage. Diagonal fences on the wings of the tiltrotor reduced the inflow turbulence intensity in the fountain region by a factor of about 3, and reduced the noise by 4.1 dBA behind the model. Scaling relations were derived to extrapolate the model measurements to the full-scale XV-15.

关键词： Tilt rotor Noise Turbulence fountain rotor disks Blade loading blade angle rotors INFLUX Tiltrotor aircraft Acoustic measurements Impulse noise Turbulent Flow model measurement Noise measurement Hovering

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Non-linear bearing stiffness parameter extraction from random response in flexible rotor-bearing systems

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JOURNAL OF SOUND AND VIBRATION 1997年第3期203卷 389-408页

作者： Tiwari, R Vyas, NS Department of Mechanical Engineering Indian Institute of Technology Kanpur India

A procedure for estimation of non-linear stiffness parameters of rolling element bearings supporting a flexible rotor, based on analysis of the random response signals picked up from the bearing caps, is developed. The non-linear multi-degree-of-freedom equations, governing the motion of a flexible shaft carrying a disc and experiencing random excitations due to imperfections of the bearing surfaces and assembly, are subjected to co-ordinate transformation and subsequently modelled as multi-dimensional Markov process through the Fokker-Planck equation. The solution procedure for the Fokker-Planck equation and the assumptions involved are outlined. The vibrations experienced at the bearings are processed through a curve fitting algorithm to obtain the necessary bearing stiffness parameters. The technique has an advantage over other existing ones in that it does not require an estimate of the excitation forces and measurements of vibrations at the rotor disc and works directly on the response signals from the bearing caps. The algorithm is illustrated for a laboratory rotor-bearing test rig and the result are compared with those obtained through an existing analytical model. The developed algorithm is tested by numerical simulation. (C) 1997 Academic Press Limited.

关键词： Rolling element bearings Vibrations Contact Vibration flexible rotor OSCILLATING FORCE flexible shaft rolling bearings Contact Information Markov chain Fokker-Planck equation rotor disks Bearings Response Signal

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Design and analysis of high-speed coreless axial flux permanent magnet generator with circular magnets and coils

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IET ELECTRIC POWER APPLICATIONS 2010年第9期4卷 739-747页

作者： Fei, W. Luk, P. C. K. Jinupun, K. Cranfield Univ Dept Engn Syst & Management Shrivenham SN6 8LA England

A high-speed coreless surface mounted axial flux permanent magnet generator with circular magnets and coils is proposed and studied. The performances of the machine are estimated and optimised by approximate theoretical analysis and comprehensive three-dimensional (3D) electromagnetic finite element analysis (FEA). Mechanical stresses in the rotor disc developed at high rotational speed are analysed and evaluated by 3D mechanical FEA to ensure the rotor's integrity. Finally, a prototype machine is constructed and tested. Both the experimental and predicted results have shown that the proposed generator possesses distinct advantages such as simple structure and high efficiency. The prototype also demonstrates its utility as a very low-cost generator.

关键词： Magnetoelectric generators Axial flow Theoretical analysis simple structures Magnetic materials Finite element method machine rotor disks High rotating speed MAGNETS

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Torque characteristics enhancement of ring winding axial flux permanent magnet generator for direct-drive wind turbine

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IET ELECTRIC POWER APPLICATIONS 2020年第9期14卷 1584-1591页

作者： Gharehseyed, Saber Vahedi, Abolfazl Nobahari, Amin Darjazini, Amir Iran Univ Sci & Technol IUST Dept Elect Engn Ctr Excellence Power Syst Automat & Operat Tehran 16846 Iran

Ring winding axial flux permanent magnet (PM) machine (RWAFPM) has recently been introduced, which is beneficial in terms of manufacturability and fault tolerability. This study aims to examine the use of RWAFPM for a small-scale direct-drive wind generator. The structural features of the RWAFPM make it subjected to remarkable cogging torque. Accordingly, the main efforts of this study are focused on finding a proper solution for its torque profile challenges. In this regard, extensive investigations are carried out on rotor design improvements. First, several schemes are analysed, separately, including pole skewing, pole arc ratio modifying, pole grouping and rotor disks shifting. Then an optimum combination of selected schemes is calculated by the Taguchi method and considering the mean torque value as well as the PM usage. It is demonstrated that significantly improved results could be achieved mainly through cost-effective modified fabrication. The 3D finite element models are employed throughout the study along with some experimental measurements to verify the results.

关键词： machine windings Taguchi methods torque wind turbines permanent magnet generators finite element analysis rotors fault tolerance wind power plants direct-drive wind turbine fault tolerability direct-drive wind generator structural features cogging torque torque profile rotor design improvements pole grouping rotor disks mean torque value axial flux permanent magnet generator pole skewing ring winding axial flux permanent magnet machine PM RWAFPM pole arc ratio modification Taguchi method cost-effective modified fabrication 3D finite element models torque characteristics enhancement

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Aerodynamics of Airfoils at High and Reverse Angles of Attack

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JOURNAL OF AIRCRAFT 2011年第6期48卷 2012-2023页

作者： Smith, Marilyn J. Liggett, Nicholas D. Koukol, Benjamin C. G. Georgia Inst Technol Daniel Guggenheim Sch Aerosp Engn Atlanta GA 30332 USA

Current rotorcraft research to increase flight speed or to alleviate adverse physical phenomena expand the Mach/angle-of-attack envelope in which the rotor blades operate. For example, rotor blades will experience large areas over the rotor disk where reverse-flow effects cannot be neglected during the design and analysis of an efficient rotor at high advance ratios. A cost-effective alternative to extensive experimental analyses is the use of computational fluid dynamics codes to quantify the behavior of airfoils at high and reverse angles of attack, as well as to add to the knowledge of the behavior of airfoils when they are immersed in these flows. Numerical experiments have been performed with correlation to experimental databases that examine the ability of computational fluid dynamics to accurately model airfoil characteristics at these angles of attack. It is observed that the use of recently developed hybrid Reynolds-averaged Navier-Stokes and large-eddy simulation turbulence methods result in a significant improvement in the ability of computational fluid dynamics to predict the characteristics of airfoils in these angle-of-attack regimes. Modeling of the airfoil trailing edge is more sensitive when reverse-flow angles of attack are considered.

关键词： Airfoils Trailing edges Hydrodynamics rotor BLADE rotor disks flight velocity Advance ratio Aerodynamics ANGLE OF ATTACK airfoil aerodynamics

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Discrete-blade, Navier-Stokes computational fluid dynamics analysis of ducted-fan flow

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JOURNAL OF AIRCRAFT 2005年第5期42卷 1109-1117页

作者： Ruzicka, GC Strawn, RC Meadowcroft, ET Boeing Co Boeing US Arm Program & Mil Rotorcraft Ridley Pk PA 19142 USA USA NASA Ames Res Ctr Rotorcraft DivAeroflight Dynam Directorate Moffett Field CA 94035 USA

The application of overset grid methods to studying the flowfield of the FANTAIL (TM) antitorque system of the RAH-66 rotorcraft is described. The FANTAIL itself and the experimental program used to design it are described first. Then, OVERFLOW-D, an overset grid-based, Navier-Stokes computational fluid dynamics code is reviewed, and its adaptation to the ducted fan geometry of the FANTAIL is explained. The modeling of the FANTAIL using OVERFLOW-D, including grids and boundary conditions, is explained in detail. The results of numerical studies of the hovering FANTAIL are presented and are shown to compare well with experiment. Flowfield visualizations are presented and are used to explain how the blade tip vortices combine with the adverse pressure gradient beneath the rotor disk to impact flow along the duct wall beneath the disk.

关键词： Dynamic analysis ducted fans BLADE TIPS rotor disks Capsizing BACK PRESSURE pressure gradients Rotary wing aircraft

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Blade Wake Interaction noise for a main rotor

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JOURNAL OF THE AMERICAN HELICOPTER SOCIETY 2004年第1期49卷 11-27页

作者： Brooks, TF Burley, CL NASA Langley Res Ctr Hampton VA 23665 USA

Fundamental characteristics of Blade Wake Interaction (BWI) noise are determined, and a prediction method is developed, using acoustic and blade pressure data from a 4-bladed BO-105 model helicopter main rotor. BWI is a broadband noise source caused by the blade interactions with turbulence in the rotor wake, particularly about tip vortices. The data are from the rotor aeroacoustic test program called HART that was jointly conducted by European and American government agencies in the German-Dutch Wind Tunnel, DNW. The test data include simultaneous measurements of instantaneous blade pressures and acoustic time histories. The statistical character of the BWI is determined from the instantaneous surface pressures. A BWI noise metric is developed and BWI noise directivity contours (similar to those typically presented for BVI noise) are presented and shown to be a function of rotor tip-path-plane angle. Similarly, BWI blade pressure contours over the rotor disk are presented. Causality relations between the blade pressures and acoustic data are developed for the prediction of BWI noise. The predictions use blade response coherence functions obtained using cross-spectral methods. Comparison between predicted and measured noise shows good agreement over the large range of rotor flight tilt angles of the test. This success demonstrates that the causality of the BWI noise problem is established and the prediction code can form a basis of a comprehensive rotor broadband noise capability.

关键词： Prediction methods Acoustic data Broad band noise Acoustics Blades wake current interference Model helicopter rotor disks government agencies blade vortex interaction noise

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Miniature trailing-edge effectors for rotorcraft performance enhancement

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JOURNAL OF THE AMERICAN HELICOPTER SOCIETY 2007年第2期52卷 146-158页

作者： Kinzel, Michael P. Maughmer, Mark D. Lesieutre, George A. Penn State Univ Dept Aerosp Engn University Pk PA 16802 USA

The rotor performance effects of miniature trailing-edge effectors, or MiTEs, mounted at the trailing edge of a rotor blade have been explored using blade-element theory. MiTEs are best described as deployable Gurney flaps and can be used to actively control the loading on a helicopter rotor blade for enhanced performance, vibration control, and possibly even noise reduction. A method has been developed to model the unsteady aerodynamics of MiTE deployment, as well with the unsteady aerodynamics associated with airfoil oscillations through dynamic stall. Such modeling is necessary for exploring the usage of the devices for performance enhancement, as well as for any future work in evaluating their potential for vibration and noise control. The rotor performance studies presented here are based on optimal scheduling of the MiTEs, such that they typically deploy on the retreating side of the rotor disk to increase the maximum lift. The results display a significant increases in the flight envelope, including up to a 20% gain in the maximum flight speed, a 16% increase in the maximum lift-to-drag ratio, and up to 10% increases in the available thrust at all flight speeds.

关键词： rotor BLADE unsteady aerodynamics flight Noise reduction Effectors Trailing edges Agistemus FLIGHT ENVELOPE Miniature dynamic stall rotor disks Optimal scheduling enhancing performance Rotary wing aircraft

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rotor wake aerodynamics in large amplitude maneuvering flight

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JOURNAL OF THE AMERICAN HELICOPTER SOCIETY 2006年第3期51卷 225-243页

作者： Ananthan, Shreyas Leishman, J. Gordon Univ Maryland Dept Aerosp Engn Alfred Gessow Rotorcraft Ctr College Pk MD 20742 USA

The rotor wake dynamics of a helicopter undergoing large amplitude, high-rate maneuvering flight conditions, typical of those used in some types of military tactics, were simulated using a time-accurate free-vortex wake method with a viscous splitting scheme. The maneuver simulations showed that the wake dynamics were accompanied by considerable lags and reorganization of the wake structure, which also significantly influenced the time-history of the lift distribution over the rotor disk. In some maneuvers, it was found that the rotor operates well inside its own wake, giving rise to particularly large unsteady airloads fluctuations. Roll maneuvers were shown to be characterized by a more significant asymmetric wake structure between the advancing and retreating sides of the rotor disk. A roll reversal maneuver was noted to introduce large temporal lags in the wake developments, the results also depending on whether a port-starboard-port or a starboard-port-starboard roll maneuver was performed. During some maneuvers, especially those involving high rotor disk angles of attack, like a quickstop or pull-up, the tip vortices were shown to bundle into a vortical ring structure below the rotor. This ring then passes up through the rotor disk, creating locally high unsteady airloads. Overall, the predicted results demonstrate the large nonlinear wake dynamics that would be produced during certain combat flight maneuvers, and the necessity of simulating large amplitude or short time period maneuvers using a rotor wake model with sufficiently high spatial and temporal resolution if the important features of the wake dynamics are to be properly captured.

关键词： lift distribution wake flow model tip vortex rotor disks maneuver flight Wake Island

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A review of progress and challenges in flapping foil power generation (vol 67, pg 2, 2014)

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PROGRESS IN AEROSPACE SCIENCES 2014年第May期67卷 1-28页

作者： Young, John Lai, Joseph C. S. Platzer, Max F. Univ New S Wales Sch Engn & Informat Technol Canberra ACT 2600 Australia AeroHydro Res & Technol Associates Pebble Beach CA 93953 USA

Power may be extracted from a flowing fluid in a variety of ways. Turbines using one or more oscillating foils are under increasingly active investigation, as an alternative to rotary wind turbines and river, oceanic and tidal current water turbines, although industrial development is at a very nascent stage. Such flapping foil turbines promise some key potential advantages, including lower foil velocities (and hence lower noise and wildlife impact), and more effective small-scale and shallow water operation. The role of a number of parameters is investigated, including foil kinematics (modes, frequencies, amplitudes and time histories of motion), foil and system geometry (shape, configuration and structural flexibility), and flow physics effects (Reynolds number and turbulence, shear flows and ground effect). Details of the kinematics are shown to have the single largest influence on power output and efficiency (measured as the ratio of power output to that available and accessible in the fluid stream). The highest levels of power and efficiency are associated with very large foil pitch angles (upwards of 70°) and angles of attack (30–40°), such that the flow is massively separated for much of the flapping cycle, in contrast to rotary turbines which rely on attached flow over as much of the rotor disk as possible. This leads to leading edge vortices comparable in size to the foil chord, and the evolution and interaction of these vortices with the foil as it moves play a central role in determining performance. The other parameters also influence the vortex behaviour, but in general to a lesser degree. Numerous gaps in the research literature and outstanding issues are highlighted.

关键词： Power generation Energy harvesting Flapping foil Fluid structure interaction (FSI) Leading edge vortex (LEV) Ground effect hydraulic turbines turbines foils Power output fluid flow flapping energy harvesting rotor disks Power production

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