Download or read book Alteration of the Tip Vortex Structure of a Hovering Rotor by Blowing written by Zhijian Liu and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Alteration of the Tip Vortex Structure of a Hovering Rotor Using Oscillatory Jet Excitation written by Zhijian Liu and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Helicopter Blade Tip Vortex Modifications in Hover Using Piezoelectrically Modulated Blowing written by Roxana Vasilescu and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Aeroacoustic investigations regarding different types of helicopter noise have indicated that the most annoying noise is caused by impulsive blade surface pressure changes in descent or forward flight conditions. Blade Vortex Interaction (BVI) is one of the main phenomena producing significant impulsive noise by the unsteady fluctuation in blade loading due to the rapid change of induced velocity field during interaction with vortices shed from previous blades. The tip vortex core structure and the blade vortex miss distance were identified as having a primary influence on BVI. In this thesis, piezoelectrically modulated and/or vectored blowing at the rotor blade tip is theoretically investigated as an active technique for modifying the structure of the tip vortex core as well as for increasing blade vortex miss distance. The mechanisms of formation and convection of rotor blade tip vortices up to and beyond 360 degrees wake age are described based on the CFD results for the baseline cases of a hovering rotor with rounded and square tips. A methodology combining electromechanical and CFD modeling is developed and applied to the study of a piezoelectrically modulated and vectored blowing two-dimensional wing section. The thesis is focused on the CFD analysis of rotor flow with modulated tangential blowing over a rounded blade tip, and with steady mid-plane blade tip blowing, respectively. Computational results characterizing the far-wake flow indicate that for steady tangential blowing the miss distance can be doubled compared to the baseline case, which may lead to a significant reduction in BVI noise level if this trend shown in hover can be replicated in low speed forward flight. Moreover, near-wake flow analysis show that through modulated blowing a higher dissipation of vorticity can be obtained.
Download or read book Devices that Alter the Tip Vortex of a Rotor written by and published by . This book was released on 2001 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: Small devices were attached near the tip of a hovering rotor blade in order to alter the structure and trajectory of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. A procedure for analyzing the 3D-velocity field is presented that includes a method for accounting for vortex wander. The results show that a vortex generator can alter the trajectory of the trailing vortex and that a major change in the size and intensity of the trailing vortex can be achieved by introducing a high level of turbulence into the core of the vortex.
Download or read book Exploratory Investigation of the Structure of the Tip Vortex of a Semispan Wing for Several Wing tip Modifications written by James Scheiman and published by . This book was released on 1970 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Devices That Alter the Tip Vortex of a Rotor written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-27 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: Small devices were attached near the tip of a hovering rotor blade 'in order to alter the structure and trajectory of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. A procedure for analyzing the 3D-velocity field is presented that includes a method for accounting for vortex wander. The results show that a vortex generator can alter the trajectory of the trailing vortex and that a major change in the size and intensity of the trailing vortex can be achieved by introducing a high level of turbulence into the core of the vortex. McAlister, Kenneth W. and Tung, Chee and Heineck, James T. Ames Research Center RTOP 712-10-12
Download or read book 37th AIAA Aerospace Sciences Meeting and Exhibit written by and published by . This book was released on 1999 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tip Vortex Development and Structure at BVI for a Hovering Rotor with Swept Back Tip Shapes Using the Flow Visualization Gun Technique written by R. H. G. Muller and published by . This book was released on 1994 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Large Eddy Simulation of the Tip Flow of a Rotor in Hover written by and published by . This book was released on 2005 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The blade-tip vortex is one of the most important aerodynamic feature of a helicopter rotor wake, The strength, size, location and orientation of the tip vortices affect the blade loads and rotor performance. The overall goal of the current project was to develop a large-eddy simulation (LES) capability to simulate the rotor-tip vortex and use these simulations to perform a detailed analysis of the dynamics of this flow, The specific objectives of this research project are (1) Develop a LES based computational approach for simulating the tip flow of a rotor in hover. (2) Validate the computational approach against PIV measurements of a hovering rotor (3) Use the solver to gain insight into the formation, structure and downstream evolution of the tip-vortex and the dynamics of the turbulence associated with the tip vortex.
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1016 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings of the ASME Fluids Engineering Division Summer Conference 2006 written by American Society of Mechanical Engineers. Fluids Engineering Division and published by . This book was released on 2006 with total page 992 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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:
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
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of Tip Vortex Aperiodicity in Hover written by Anand Karpatne and published by . This book was released on 2012 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous research has indicated aperiodicity in the positions of tip vortices emitted from a helicopter rotor blade in hover. The objective of the current study is to develop an analysis of the tip vortex aperiodicity in hover and to validate it with measurements on a reduced-scale, 1m diameter, four-bladed rotor. A "vortex ring emitter model" (VREM) was developed to study the statistics of the tip vortices emitted from a rotor blade during hover. In order to better model the rotor wake, a number of independent vortex blobs were used to describe a vortex ring. An empirical model for viscosity was also considered which helped model the core radius growth of the vortex ring with vortex age. A parametric analysis was then performed to obtain a comprehensive qualitative and quantitative convergence study of the time step, viscosity parameter, initial core size, number of rings shed, number of blobs and overlap factor. It was observed that the solution converged rapidly for all the parameters used. The locations of tip vortex cores for vortex ages ranging from 0° to 260° were measured on the reduced-scale rotor using a stereo PIV system. The blade loading for the reduced scaled rotor was C[subscript t]/[sigma] = 0.044 and the blade rotational speed was 1520 RPM, which corresponds to a tip Reynolds number of 248,000. The 95% confidence region for the position of tip vortex cores exhibited an anisotropic, aperiodic pattern, approximating an ellipse. It was seen that the principal axis of this ellipse appeared to be aligned perpendicular to the slipstream boundary. The analytical model showed good correlation with experimental data in terms of the orientation and extent of the anisotropy. Moreover, an estimate of the total thrust produced and spanwise loading along the rotor blade was also obtained and compared with Blade Element Momentum Theory (BEMT). It was seen that by using more blobs to represent a vortex ring, the solution converged to the BEMT estimate.
Download or read book Velocity Measurements Near the Blade Tip and in the Tip Vortex Core of a Hovering Model Rotor written by Thomas Lee Thompson and published by . This book was released on 1986 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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:
