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An Experimental Investigation Of The Vortex Wakes Of Hovering And Descending Rotors
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Book Synopsis An Experimental Investigation of the Vortex Wakes of Hovering and Descending Rotors by : James Anthony Stack
Download or read book An Experimental Investigation of the Vortex Wakes of Hovering and Descending Rotors written by James Anthony Stack and published by . This book was released on 2006 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Experimental Investigation of Vortex Stability, Tip Shapes, Compressibility, and Noise for Hovering Model Rotors by : James L. Tangler
Download or read book An Experimental Investigation of Vortex Stability, Tip Shapes, Compressibility, and Noise for Hovering Model Rotors written by James L. Tangler and published by . This book was released on 1973 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Experimental Investigation of the Far-field Rotorcraft Wake Structure by : James Harold Stephenson
Download or read book Experimental Investigation of the Far-field Rotorcraft Wake Structure written by James Harold Stephenson and published by . This book was released on 2012 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: The tumbling tip vortex effect of a reduced-scale, 1 m diameter, four-bladed rotor during hover is studied using vortex methods, combined with a center of mass analysis approach. Measurements of all three components of the velocity field are acquired using a stereo PIV system synchronized to capture up to 500 degrees of vortex age, with 10 degree wake age offsets, during hover conditions. The nominal operating condition of the rotor is at a rotational rate of 1520RPM, corresponding to ReC = 248,000 with a chord length of 58.5mm. The rotor is operated with a pitch of 7.2± 0.5 degrees and a CT/sigma of 0.045. The far wake vortex tumbling phenomenon is captured and described. It is shown that tip vortices from two blades tumble through approximately 90 degrees of rotation before they coalesce. It is also seen that the constituent parent vortices do not combine to create a stronger daughter vortex as was previously thought to happen. Instead, the merged vortex has a lower large-radius circulation than either of its parent vortices. An accurate characterization and prediction of the trajectory of the far wake vortex tumbling can enhance the ability to predict and alleviate the resuspension of particles during brownout as well as provide a database for far wake validation of CFD codes.
Book Synopsis Vortex-wake Analysis of a Single-bladed Hovering Rotor and a Comparison with Experimental Data by : Robin B. Gray
Download or read book Vortex-wake Analysis of a Single-bladed Hovering Rotor and a Comparison with Experimental Data written by Robin B. Gray and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Evaluation of Linearized Vortex Theory as Applied to Single and Multiple Rotors Hovering in and Out of Ground Effect by : Harry H. Heyson
Download or read book An Evaluation of Linearized Vortex Theory as Applied to Single and Multiple Rotors Hovering in and Out of Ground Effect written by Harry H. Heyson and published by . This book was released on 1959 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dissertation Abstracts International by :
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2007 with total page 960 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Analytical and Experimental Study of Farfield Rotor Wake Geometry and Velocity by : Thomas Alan Egolf
Download or read book An Analytical and Experimental Study of Farfield Rotor Wake Geometry and Velocity written by Thomas Alan Egolf and published by . This book was released on 1973 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: All fixed wing aircraft generate trailing vortex wakes whose circulatory strength is dependent on flight conditions and aircraft geometry. A rotor also generates a vortex wake. A vortex sheet is shed from each blade. Each sheet rolls up rapidly outboard to form a tip vortex. The purpose of the study reported here is to estimate the rotor wake geometry and velocity field downstream of the rotor for the particular case where the rotor wake exhibits strong similarities to the fixed wing wake. A method is developed by which the helicopter far field wake can be readily compared to the far field wake generated by an equivalent wing. (Author).
Book Synopsis Vortex Wake of Coaxial Rotors in Hover by : Mehmet Fatih Konus
Download or read book Vortex Wake of Coaxial Rotors in Hover written by Mehmet Fatih Konus and published by . This book was released on 2017 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt: An extensive sets of experiments are carried out regarding the stability characteristics of helical vortex filaments o a coaxial rotor model. A coaxial rotor model consisting of two 26-cm (10.25-in) diameter counter-rotating rotors with a root cut-out of 3.2 cm (25%) is employed in these experiments in one- and two-bladed configurations. Axial rotor separation varied from 25% of the rotor radius to one rotor radius. Rotor speed ranged from 2 to 8 rps at each rotor spacing. Dye flow visualization, particle flow visualization and particle image velocimetry are employed in order to take measurements of the flow field. For one-bladed tests, helical tip vortex filament trailed from the lower rotor blade is observed to develop strong deformations soon after its formation at the rotor spacing of a quarter rotor radius as opposed to that of upper rotor. This deformation is less pronounced at the rotor spacing of 0:8R. Upper and lower rotor vortices are seen to develop long-wave vortex pairing instabilities where they orbit around each other as they travel downstream, particularly at smaller rotor spacing, which is also confirmed in PIV results. Successive turns of the upper rotor helices appear to be stable as opposed to unstable nature of lower rotor helix in both rotor separations. At H=R = 0:8, the upper rotor wake contraction is markedly higher than that of the lower rotor. Vortex filaments develop short-wave instabilities at 2 & 4 rps just immediately after their inceptions in both rotor separations. In two-bladed configurations, in all cases tip vortices trailed from the lower rotor experience extreme distortions, resulting in the loss of their orderly helical shapes, which is a clear manifestation of the effect of the upper rotor on the lower one. At smaller rotor spacings up to 50% radius, lower rotor filaments develop long-wave vortex pairing instabilities in similar ways to what is found in single rotor wakes although they differ to the extent lower vortex filaments undergo deformations. At this rotor spacing range, upper rotor filaments does not have sufficient space between the rotors to develop mutual interactions before they reach the plane of the lower rotor and interact with lower rotor blades, i.e. interrotor blade-vortex interactions (BVIs). As the rotor spacing is further increased up to a rotor radius, upper rotor filaments are seen to develop long-wave pairing instabilities similar to what is observed in the wakes of single rotor runs. As in the one-bladed configurations, upper rotor filaments possess a more stable nature whereas those from lower rotor becomes unstable within first rotor revolution beneath the lower rotor. At rotor spacing of 50% radius, hairpin vortices are observed to form beneath the lower rotor during the long-wave instability mode developed by the lower rotor filaments where streamwise elongation of the vortex filament from a particular blade of the lower rotor in each rotor revolution is observed. At other rotor spacings, similar deformation of the vortex filaments in the streamwise direction is seen to occur however distinct hairpin vortex structures are only seen at the rotor spacing of 0:5R. Upper rotor wakes contract to more inward than those of the lower rotor wakes for all the rotor separation distances tested, which is also confirmed from the PIV measurements and particle visualization results. Increasing rotor spacing changes the wake contraction of the upper rotor at the plane of the lower rotor where it reaches a more fully-developed state towards the rotor spacing of one radius. This is further confirmed from the streamline patterns from the PIV results. Regardless of the rotor spacing, short-wave instabilities formed along the helical filaments at 2 & 4 rps cases from their generation whereas at 6 & 8 rps filaments are only observed to develop these types of instabilities long after their formation and not in an explicit manner since they become superimposed with long-wave instability mode where filaments develop strong distortions beneath the lower rotor.
Book Synopsis Flow Visualizations and Extended Thrust Time Histories of Rotor Vortex Wakes in Descent by :
Download or read book Flow Visualizations and Extended Thrust Time Histories of Rotor Vortex Wakes in Descent written by and published by . This book was released on 2004 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study is performed on a three-bladed rotor model in two water tanks. The blade pitch, rotational velocity, descent angle, and descent speed are all varied in order to simulate a wide range of rotorcraft operating states, focusing on descent cases where the rotor is operating in or near vortex ring state--an area in which there is currently very little available data. Flow visualization is done by injecting air bubbles and fluorescent dye tangentially from the blade tips to mark the vortex core, showing the development of both short-wave ("sinuous") and long-wave ("leapfrogging") instabilities on the helical vortices in the wake. Strain gages are used to record transient loads, allowing a correlation between the rotor thrust performance and the development of the vortex wake. Reynolds numbers are of order 105 and test runs are performed for extended periods--up to 500 rotor revolutions-- demonstrating the repeatability of the patterns of thrust variation. The data indicate that as the instabilities develop, adjacent vortices merge and form thick vortex rings, particularly during descent. Periodic shedding of these rings from the wake associated with vortex ring state is observed, resulting in peak-to-peak thrust fluctuations of up to 95% of the mean and occurring at regular intervals of 20-50 rotor revolutions, depending on flow parameters.
Book Synopsis Free-Wake Analysis of a Rotor in Hover by : C. S. Chen
Download or read book Free-Wake Analysis of a Rotor in Hover written by C. S. Chen and published by . This book was released on 1987 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: A numerical method based on the axisymmetric, incompressible Navier-Stokes equations is combined with a lifting surface code to predict the vortex wake of hovering rotors. The lifting surface code, AMI Hover, is used to obtain the circulation distribution on the blade. This circulation distribution is fed into the Navier-Stokes code to compute the vortex wake under this specified circulation distribution. An iteration approach is used between these two codes to converge the circulation distribution and the shape of the vortex wake. A relaxation scheme is developed to resolve the instability encountered among the tip vortices. A reconcentration scheme is used to solve the diffusion problem due to the strong artificial viscosity. The results from the present method are compared with experimental data obtained by smoke-flow visualization and hot-wire measurements for several rotor blade configurations. The comparisons show that the present method is able to predict the complex wake system shed by a hovering rotor.
Book Synopsis Experimental Investigation of Model Variable-geometry and Ogee Tip Rotors by : Anton J. Landgrebe
Download or read book Experimental Investigation of Model Variable-geometry and Ogee Tip Rotors written by Anton J. Landgrebe and published by . This book was released on 1974 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation was conducted to systematically explore the effects of inter-blade spatial relationships and pitch variations on rotor performance and wake geometry. Variable-geometry rotors consisting of various combinations of blade length, axial spacing, azimuth spacing, and collective pitch were tested at model scale in hover and forward flight. In addition, a hover test of a model rotor with an ogee blade tip design was conducted to determine its performance and wake characteristics. The results of this investigation indicate that properly selected variable geometry rotor configurations can offer substantial improvements in hover performance without adversely affecting forward flight performance. Axial spacing of alternate blades was found to provide the greatest performance benefit, and further improvements were achieved by combining azimuth spacing with axial spacing. The performance benefit appears to be related to the relief of local adverse aerodynamic phenomena produced by vortex interference. The ogee tip design was found to substantially reduce the concentrated core intensity of the tip vortex, and could thus prove beneficial for the relief of blade-vortex interaction problems. However, the ogee tip was found to reduce hover performance at model scale.
Book Synopsis The Experimental Investigation of Vortex Wakes from Oscillating Airfoils by : Mathew Bussière
Download or read book The Experimental Investigation of Vortex Wakes from Oscillating Airfoils written by Mathew Bussière and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1988 with total page 972 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Experimental Investigation of Flutter in Lifting Rotors for Hovering Flight by : Stanley Irwin Weiss
Download or read book An Experimental Investigation of Flutter in Lifting Rotors for Hovering Flight written by Stanley Irwin Weiss and published by . This book was released on 1945 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :National Aeronautics and Space Administration (NASA) Publisher :Createspace Independent Publishing Platform ISBN 13 :9781721038596 Total Pages :32 pages Book Rating :4.0/5 (385 download)
Book Synopsis Vortex Core Size in the Rotor Near-Wake by : National Aeronautics and Space Administration (NASA)
Download or read book Vortex Core Size in the Rotor Near-Wake written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-12 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a kinetic energy conservation approach, a number of simple analytic expressions are derived for estimating the core size of tip vortices in the near-wake of rotors in hover and axial-flow flight. The influence of thrust, induced power losses, advance ratio, and vortex structure on rotor vortex core size is assessed. Experimental data from the literature is compared to the analytical results derived in this paper. In general, three conclusions can be drawn from the work in this paper. First, the greater the rotor thrust, t h e larger the vortex core size in the rotor near-wake. Second, the more efficient a rotor is with respect to induced power losses, the smaller the resulting vortex core size. Third, and lastly, vortex core size initially decreases for low axial-flow advance ratios, but for large advance ratios core size asymptotically increases to a nominal upper limit. Insights gained from this work should enable improved modeling of rotary-wing aerodynamics, as well as provide a framework for improved experimental investigations of rotor a n d advanced propeller wakes.Young, Larry A.Ames Research CenterVORTICES; ROTORS; AERODYNAMICS; AXIAL FLOW; BOUNDARY LAYERS; HOVERING; PROPELLERS; WAKES; ROTARY WINGS
Book Synopsis An Experimental Determination of the Motion of a Vortex Sheet in the Wake of an Isolated Two-bladed Hovering Model Helicopter Rotor by : James Irvin Scott
Download or read book An Experimental Determination of the Motion of a Vortex Sheet in the Wake of an Isolated Two-bladed Hovering Model Helicopter Rotor written by James Irvin Scott and published by . This book was released on 1958 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Principles of Helicopter Aerodynamics with CD Extra by : Gordon J. Leishman
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.
