Download or read book Modelling of Airfoil vortex Interaction and Application to a Helicopter Rotor written by Gilles Rahier and published by . This book was released on 1998 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Full Potential Modeling of Blade Vortex Interactions written by Henry E. Jones and published by . This book was released on 1997 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study of the full-potential modeling of a blade-vortex interaction was made. A primary goal of this study was to investigate the effectiveness of the various methods of modeling the vortex. The model problem restricts the interaction to that of an infinite wing with an infinite line vortex moving parallel to its leading edge. This problem provides a convenient testing ground for the various methods of modeling the vortex while retaining the essential physics of the full three-dimensional interaction. A full-potential algorithm specifically tailored to solve the blade-vortex interaction (BVI) was developed to solve this problem. The basic algorithm was modified to include the effect of a vortex passing near the airfoil. Four different methods of modeling the vortex were used: (1) the angle-of-attack methods, (2) the lifting-surface method, (3) the branch-cut method, and (4) the split-potential method. A side-by-side comparison of the four models was conducted. these comparisons included comparing generated velocity fields, a subcritical interaction, and a critical interaction. The subcritical and critical interactions are compared with experimentally generate results. The split-potential model was used to make a survey of some of the more critical parameters which affect the BVI.

Download or read book Modelling of Airfoil vortex Interaction and Aplication to a Helicopter Rotor written by Gilles Rahier and published by . This book was released on 1998 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Some Recent Advances in Computational Aerodynamics for Helicopter Applications written by W. J. McCroskey and published by . This book was released on 1985 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Some Rotorcraft Applications of Computational Fluid Dynamics written by and published by . This book was released on 1988 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growing application of computational aerodynamics to nonlinear rotorcraft problems is outlined, with particular emphasis on the development of new methods based on Euler and thin-layer Navier-Stokes equations. Rotor airfoil characteristics can now be calculated accurately over a wide range of transonic flow conditions. However, unsteady three-dimensional viscous codes remain in the research stage, and a numerical simulation of the complete flow field about a helicopter in forward flight is not currently feasbile. Nevertheless, impressive progress is being made in preparation for future supercomputers that will enable meaningful calculations to be made for arbitrary rotorcraft configurations. (fr).

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).

Download or read book Experimental Simulation of Transonic Vortex Airfoil Interactions written by Donald R. Wilson and published by . This book was released on 1988 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from an experimental investigation of helicopter rotor blade-vortex interaction (BVI) phenomena at transonic Mach numbers and at Reynolds numbers representative of actual helicopter flight operations are presented. The study examined both perpendicular (vortex core perpendicular to the blade leading edge) and parallel (vortex core parallel to blade leading edge) interaction geometries. The significant results are: 1. Perpendicular Interaction: The effect of the vortex causes a large reduction in upper surface pressure distribution (lift increase). This lift increase correlates with strength of the vortex and closeness of the vortex encounter. The interaction is most pronounced near the leading edge of the airfoil. A large spanwise deflection of the vortex is observed as it passes over the airfoil. 2. Parallel Interaction: A similar reduction in upper surface pressure distribution is also observed during the transient passage of the parallel vortex over the airfoil. Like the perpendicular interaction, this effect is also most pronounced near the leading edge, which is in contrast to the general results of numerous CFD simulations. For certain combinations of vortex strength and encounter distance, a class-C shock motion (forward propagation of the airfoil shock wave) was observed. Keywords: Blade vortex interaction; Transonic aerodynamics. (jhd).

Download or read book Calculation of Helicopter Rotor Blade vortex Interaction by Navier Stokes Procedures written by and published by . This book was released on 1987 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book LES for Wing Tip Vortex Around an Airfoil written by Jiangang Cai and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The wing tip vortex is very important because of its effects on the noise generation, blade/vortex interactions on helicopter blades, propeller cavitations on ships, and other fields. The objective of this work is to use the numerical simulation with high order accuracy and high resolution to investigate the formation and the near field evolution of a wing tip vortex at high Reynolds number. The computational domain includes a rectangular half-wing with a NACA 0012 airfoil section, a rounded wing tip and the surrounding boundaries. The wing has an aspect ratio of 0.75. The angle of attack is 10 degrees. The Reynolds number based on iv free-stream velocity and the chord length is 4.6x10 6. In the simulations, the free-stream Mach number is set to 0.2. The flow field is solved by a fully-implicit time-marching N-S solver with 6th order compact scheme and 8th order filter. Non-reflecting boundary conditions with buffer are also utilized in the code to avoid non-physical reflection. The code uses MPI parallel computation whose performance scales almost linearly over a large number of processors. The numerical simulation showed that the turbulent shear layer and the interaction between the primary and the secondary vortices are the major sources of turbulent activity in the vortex core. The information about the phenomena provided by the simulation can be used in various engineering applications at high Reynolds numbers.

Download or read book Helicopter Impulsive Noise Theoretical and Experimental Status written by F. H. Schmitz and published by . This book was released on 1983 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade-vortex interaction impulsive noise. A thorough physical explanation of both generating mechanisms is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanisms of high speed impulsive noise are fairly well understood - theory and experiment compare nicely over Mach number ranges typical of today's helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory-experiment are suggested.

Download or read book Helicopter Rotor Wake Geometry and Its Influence in Forward Flight Volume 1 Generalized Wake Geometry and Wake Effect on Rotor Airloads and Performance written by T. A. Egolf and published by . This book was released on 1983 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

Download or read book Helicopter Blade vortex Interaction Locations written by Danny R. Hoad and published by . This book was released on 1987 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rotating Hot wire Investigation of the Vortex Responsible for Blade vortex Interaction Noise written by and published by . This book was released on 1988 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Airfoil Self Noise and Prediction 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 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given. Brooks, Thomas F. and Pope, D. Stuart and Marcolini, Michael A. Langley Research Center AEROACOUSTICS; AERODYNAMIC NOISE; AIRFOIL PROFILES; AIRFOILS; BLADE-VORTEX INTERACTION; BOUNDARY LAYER SEPARATION; BOUNDARY LAYERS; NOISE PREDICTION (AIRCRAFT); VORTEX SHEDDING; AERODYNAMIC STALLING; APPLICATIONS PROGRAMS (COMPUTERS); NOISE MEASUREMENT; NOISE SPECTRA; ROTARY WINGS; STROUHAL NUMBER; TRAILING EDGES; VORTICES; WIND TUNNEL TESTS...

Download or read book Analysis and Indicial Modelling of Helicopter Tail Rotor Orthogonal Blade Vortex Interaction written by David R. Suttie and published by . This book was released on 2006 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Vortex Lattice Method for the Rotor vortex Interaction Problem written by Raghuveera Padakannaya and published by . This book was released on 1974 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: The rotor blade-vortex interaction problem and the resulting impulsive airloads which generate undesirable noise levels are discussed. A numerical lifting surface method to predict unsteady aerodynamic forces induced on a finite aspect ratio rectangular wing by a straight, free vortex placed at an arbitrary angle in a subsonic incompressible free stream is developed first. Using a rigid wake assumption, the wake vortices are assumed to move downsteam with the free steam velocity. Unsteady load distributions are obtained which compare favorably with the results of planar lifting surface theory. The vortex lattice method has been extended to a single bladed rotor operating at high advance ratios and encountering a free vortex from a fixed wing upstream of the rotor. The predicted unsteady load distributions on the model rotor blade are generally in agreement with the experimental results. This method has also been extended to full scale rotor flight cases in which vortex induced loads near the tip of a rotor blade were indicated. In both the model and the full scale rotor blade airload calculations a flat planar wake was assumed which is a good approximation at large advance ratios because the downwash is small in comparison to the free stream at large advance ratios. The large fluctuations in the measured airloads near the tip of the rotor blade on the advance side is predicted closely by the vortex lattice method.

Download or read book Wind Tunnel Evaluation of a Model Helicopter Main Rotor Blade With Slotted Airfoils at the Tip written by and published by . This book was released on 2001 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: Data for rotors using unconventional airfoils are of interest to permit an evaluation of this technology's capability to meet the U.S. Army's need for increased helicopter mission effectiveness and improved safety and survivability. Thus, an experimental investigation was conducted in the Langley Transonic Dynamics Tunnel (TDT) to evaluate the effect of using slotted airfoils in the rotor blade tip region (85 to 100 percent radius) on rotor aerodynamic performance and loads. Four rotor configurations were tested in forward flight at advance ratios from 0.15 to 0.45 and in hover in-ground effect. The hover tip Mach number was 0.627, which is representative of a design point of 4000-ft geometric altitude and a temperature of 95 degrees F. The baseline rotor configuration had a conventional single element airfoil in the tip region. A second rotor configuration had a forward-slotted airfoil with a -6 degrees slat, a third configuration had a forward-slotted airfoil with a -10 degrees slat, and a fourth configuration had an aft-slotted airfoil with a 3 degrees flap (trailing edge down). The results of this investigation indicate that the -6 degrees slat configuration offers some performance and loads benefits over the other three configurations.