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Book Aerodynamic Analysis of Helicopter Rotors Using a Higher Order Free Wake Method

Download or read book Aerodynamic Analysis of Helicopter Rotors Using a Higher Order Free Wake Method written by Tenzin Choephel and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The wake has a strong influence on the aerodynamics of a helicopter rotor, andthe accurate prediction of its geometry and the resulting induced velocity fieldis extremely important for rotorcraft aerodynamic analysis. In this thesis, a newhigher-order, free-wake method for rotor aerodynamic analysis is presented. Themethod uses elements of distributed vorticity to model the lifting surfaces and theassociated wake. The use of such higher-order spanwise elements ensures higherresolution compared to traditional filament-based free-wake analysis and does notrequire explicit vortex core modeling with a user-specified core size. Since themethod uses a full-span, singularity-free, relaxed wake, it can resolve the effect ofon-blade, partial-span devices.The free-wake method is validated in both hover and forward flight againstmeasured data from well-documented experiments. In hover, the blade spanwiselift coefficients predicted by the free-wake analysis correlate well with the measureddata from the classic Caradonna-Tung model rotor experiment. The figure of merit,which is a measure of rotor efficiency, predicted by the present method is comparedto that from the experiments conducted by Knight and Hefner, and the correlationsare found to be quite good given the level of fidelity of this method, which is basedon potential flow theory. Rotor downwash, which is one of the most importantconsiderations in rotor aerodynamic analysis, is predicted very well by the free-wakemethod when compared to measured data from a full-scale rotor test performedby Boatwright. These correlation studies provide a lot of promise as to the abilityof the method in predicting the challenging aerodynamics of a helicopter rotor inhover.Validation studies are also performed to assess the accuracy of the free-wakeanalysis in predicting downwash distribution in forward flight. Comparison ofnumerical predictions with experimental data requires the rotor to be trimmed tothe conditions recorded in the experiment. To ensure this, the free-wake programis coupled with RCAS, a comprehensive helicopter analysis code developed by theiiiUS Army, in order to take advantage of its robust trim algorithm, among othercapabilities. The coupling is achieved through what is called a loose-couplingmethodology, whereby data is exchanged at the end of each coupling iteration orconverged rotor revolution. The downwash distributions predicted by the presentmethod are compared to measured data for a model rotor at various advancedratios and thrust levels taken at the U.S. Army/NASA Langley Research Center(LaRC) facility. The free-wake method not only captures the important phenomenaobserved in the experiments but the results also correlate well with the measureddata both in terms of magnitude and distribution. However, exceptions exist atthe highest advance ratio, where other methods also demonstrate poor correlations.The results from this free-wake analysis are also compared to predictions by otherexisting methods such as the University of Maryland free-wake method (UMDFW)and the vortex transport method (VTM). The present method yields resultscomparable to the ones obtained using VTM, both of which correlate better withmeasurements than does UMD-FW.Sensitivity studies show that the blade panel density and azimuthal time-stepsize do not have a significant influence on the solution fidelity. In addition, free-wakeanalyses with the azimuthal time-step size of = 3o demonstrate the robustnessof the method even with small time-steps, which is important for certain problemsincluding rotor acoustics.The thesis concludes with a discussion on the capability of the new free-wakemethod in resolving on-blade, partial-span devices. An analysis of a 2-bladed rotorwith a partial-span deflection is performed and the resulting changes in sectionalloadings, downwash distribution, wake geometry and aggregate performance parametersare highlighted to demonstrate its potential as a tool for future rotorcraftanalysis.

Book Free Wake Aerodynamic Analysis of Helicopter Rotors

Download or read book Free Wake Aerodynamic Analysis of Helicopter Rotors written by Luigi Morino and published by . This book was released on 1983 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: A formulation for the free wake analysis of helicopter rotors in incompressible potential flows is presented here. The formulation encompasses both the theory and its numerical implementation. For the case of a single-bladed rotor in hover, the formulation is validated by numerical results which are in good agreement with the generalized wake of Landdgrebe. Extension of the theory to compressible flows is also outlined. These results indicate that the formulation does not require any empirical assumption (such as the rate of contraction of the radius of the wake) in order to avoid numerical instabilities. To our knowledge, the results presented here are the first ones ever obtained not requiring any ad-hoc assumptions in order to avoid such problems. (Author).

Book Unsteady Free Wake Viscous Aerodynamic Analysis of Helicopter Rotors

Download or read book Unsteady Free Wake Viscous Aerodynamic Analysis of Helicopter Rotors written by Luigi Morino and published by . This book was released on 1989 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report contains the results for research on unsteady free-wake viscous aerodynamic analysis of helicopter rotors. The effort may be divided into three general areas. The first deals with further developments of the zeroth-order potential-flow analysis; the second with the first-order analysis; and the third with the Poincare decomposition for the analysis of viscous flows. Keywords: Aerodynamic analysis. (EDC).

Book Special Opportunities in Helicopter Aerodynamics

Download or read book Special Opportunities in Helicopter Aerodynamics written by W. J. McCroskey and published by . This book was released on 1983 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerodynamic research relating to modern helicopters includes the study of three-dimensional, unsteady, nonlinear flow fields. A selective review is made of some of the phenomenon that hamper the development of satisfactory engineering prediction techniques, but which provides a rich source of research opportunities: flow separations, compressibility effects, complex vortical wakes, and aerodynamic interference between components. Several examples of work in progress are given, including dynamic stall alleviation, the development of computational methods for transonic flow, rotor-wake predictions, and blade-vortex interactions. (Author).

Book Rotor Design Optimization Using a Free Wake Analysis

Download or read book Rotor Design Optimization Using a Free Wake Analysis written by and published by . This book was released on 1993 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Rotor body Aerodynamic Interactions

Download or read book Rotor body Aerodynamic Interactions written by Mark D. Betzina and published by . This book was released on 1983 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: A wind-tunnel investigation was conducted in which independent, steady-state aerodynamic forces and moments were measured on a 2.24-m-diam, two- bladed helicopter rotor and on several different bodies. The objective was to determine the mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry. the results of the investigation show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. This report presents the effects of various parameters on the interactions and discusses the difficulties encountered in determining the effect of the body on the rotor performance.

Book Principles of Helicopter Aerodynamics

Download or read book Principles of Helicopter Aerodynamics written by J. Gordon Leishman and published by Cambridge University Press. This book was released on 2002-12-23 with total page 544 pages. Available in PDF, EPUB and Kindle. Book excerpt: Helicopters are highly capable and useful rotating-wing aircraft with roles that encompass a variety of civilian and military applications. Their usefulness lies in their unique ability to take off and land vertically, to hover stationary relative to the ground, and to fly forward, backward, or sideways. These unique flying qualities, however, come at a high cost including complex aerodynamic problems, significant vibrations, high levels of noise, and relatively large power requirements compared to fixed-wing aircraft. This book, written by an internationally recognized expert, provides a thorough, modern treatment of the aerodynamic principles of helicopters and other rotating-wing vertical lift aircraft. Every chapter is extensively illustrated and concludes with a bibliography and homework problems. Advanced undergraduate and graduate students, practising engineers, and researchers will welcome this thorough and up-to-date text on rotating-wing aerodynamics.

Book Principles of Helicopter Aerodynamics with CD Extra

Download or read book Principles of Helicopter Aerodynamics with CD Extra written by Gordon J. Leishman and published by Cambridge University Press. This book was released on 2006-04-24 with total page 860 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by an internationally recognized teacher and researcher, this book provides a thorough, modern treatment of the aerodynamic principles of helicopters and other rotating-wing vertical lift aircraft such as tilt rotors and autogiros. The text begins with a unique technical history of helicopter flight, and then covers basic methods of rotor aerodynamic analysis, and related issues associated with the performance of the helicopter and its aerodynamic design. It goes on to cover more advanced topics in helicopter aerodynamics, including airfoil flows, unsteady aerodynamics, dynamic stall, and rotor wakes, and rotor-airframe aerodynamic interactions, with final chapters on autogiros and advanced methods of helicopter aerodynamic analysis. Extensively illustrated throughout, each chapter includes a set of homework problems. Advanced undergraduate and graduate students, practising engineers, and researchers will welcome this thoroughly revised and updated text on rotating-wing aerodynamics.

Book Computation of Rotor Aerodynamic Loads in Forward Flight Using a Full Span Free Wake Analysis

Download or read book Computation of Rotor Aerodynamic Loads in Forward Flight Using a Full Span Free Wake Analysis written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of an advanced computational analysis of unsteady aerodynamic loads on isolated helicopter rotors in forward flight is described. The primary technical focus of the development was the implementation of a freely distorting filamentary wake model composed of curved vortex elements laid out along contours of constant vortex sheet strength in the wake. This model captures the wake generated by the full span of each rotor blade and makes possible a unified treatment of the shed and trailed vorticity in the wake. This wake model was coupled to a modal analysis of the rotor blade dynamics and a vortex lattice treatment of the aerodynamic loads to produce a comprehensive model for rotor performance and air loads in forward flight dubbed RotorCRAFT (Computation of Rotor Aerodynamics in Forward Flight). The technical background on the major components of this analysis are discussed and the correlation of predictions of performance, trim, and unsteady air loads with experimental data from several representative rotor configurations is examined. The primary conclusions of this study are that the RotorCRAFT analysis correlates well with measured loads on a variety of configurations and that application of the full span free wake model is required to capture several important features of the vibratory loading on rotor blades in forward flight. Quackenbush, Todd R. and Bliss, Donald B. and Wachspress, Daniel A. and Boschitsch, Alexander H. and Chua, Kiat Unspecified Center AERODYNAMIC LOADS; COMPUTATIONAL FLUID DYNAMICS; HELICOPTERS; HORIZONTAL FLIGHT; ROTARY WINGS; ROTOR AERODYNAMICS; ROTOR DYNAMICS; WAKES; UNSTEADY AERODYNAMICS; VIBRATORY LOADS; VORTEX SHEETS; VORTICES...

Book Free Wake Analysis of Helicopter Rotor Flow Fields Using a Coupled Vorticity Embedding Fractional Step Method

Download or read book Free Wake Analysis of Helicopter Rotor Flow Fields Using a Coupled Vorticity Embedding Fractional Step Method written by and published by . This book was released on 2000 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: A hybrid CFD (Computational Fluid Dynamics) method combining a potential-based Vorticity Embedding method with an Euler solver is presented and validated for isolated rotor flows. First, a formulation of Vorticity Embedding is developed and validated for Cartesian grids. This formulation is utilized together with simple lifting lines to represent an isolated rotor in hover. The results for an isolated rotor are then compared with experiment. The method is then hybridized by coupling the Vorticity Embedding grid containing the rotor to a region containing a ground plane where a standard finite difference Euler solver is utilized. initial results from this hybrid scheme are presented including a demonstration of the code's potential to calculate the ground vortex roll-up generated by a rotor in ground effect in the presence of a cross-wind.

Book Basic Helicopter Aerodynamics

Download or read book Basic Helicopter Aerodynamics written by John M. Seddon and published by John Wiley & Sons. This book was released on 2011-08-22 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: Basic Helicopter Aerodynamics is widely appreciated as an easily accessible, rounded introduction to the first principles of the aerodynamics of helicopter flight. Simon Newman has brought this third edition completely up to date with a full new set of illustrations and imagery. An accompanying website www.wiley.com/go/seddon contains all the calculation files used in the book, problems, solutions, PPT slides and supporting MATLAB® code. Simon Newman addresses the unique considerations applicable to rotor UAVs and MAVs, and coverage of blade dynamics is expanded to include both flapping, lagging and ground resonance. New material is included on blade tip design, flow characteristics surrounding the rotor in forward flight, tail rotors, brown-out, blade sailing and shipborne operations. Concentrating on the well-known Sikorsky configuration of single main rotor with tail rotor, early chapters deal with the aerodynamics of the rotor in hover, vertical flight, forward flight and climb. Analysis of these motions is developed to the stage of obtaining the principal results for thrust, power and associated quantities. Later chapters turn to the characteristics of the overall helicopter, its performance, stability and control, and the important field of aerodynamic research is discussed, with some reference also to aerodynamic design practice. This introductory level treatment to the aerodynamics of helicopter flight will appeal to aircraft design engineers and undergraduate and graduate students in aircraft design, as well as practising engineers looking for an introduction to or refresher course on the subject.

Book Free Wake Analysis of Helicopter Rotor Blades in Hover Using a Finite Volume Technique

Download or read book Free Wake Analysis of Helicopter Rotor Blades in Hover Using a Finite Volume Technique written by Krishnamurthi Ramachandran and published by . This book was released on 1987 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the computation of helicopter rotor flow fields, wake effects can be very important since each blade passes close to the wake produced by the preceding ones, causing a large local effect. Also, the vortical flow from the wake of a number of blade passages causes a large global effect. Extensive work has been done on helicopter rotor flows using integral methods to follow the vortex wake. These generally cannot treat compressibility effects. Also, they have difficulty attaining stable solutions, particularly in hover, where a large number of interacting vortex sheets must be treated. A new method has been developed which like integral methods does not constrain or spread the wake. Also, like finite difference methods, it can treat compressibility effects. This method has been developed into a computer program for the computation of rotor flow fields in hover with free wakes. The method utilizes a finite volume potential flow technique. The basic approach involves modifying the potential flow wake treatment so that, within the numerical approximation, the momentum is conserved there as in the rest of the flow field. The internal structure of the vortex is not solved for, but is modeled and spread over several grid points. The wake position and vorticity strength are computed so that the momentum over the wake is balanced in an integral sense. Results computed by this approach for the circulation and wake geometry are compared with experimentally measured data. Cases treated include subsonic and transonic flows, high and low aspect ratios, and two and four-bladed rotor configurations. (SDW).