The Turbulence Structure Of Trailing Vortice Wakes

Grandezza: 49,50 MB
Formato: PDF, Kindle
Vista: 8348
Scaricare Leggi Online

The present investigation is a two-part study of the mean flow and turbulence structure of isolated vortices and counter-rotating vortex pairs. In the first part, the turbulence structure of an isolated vortex was studied using three-component velocity measurements. Vortices were generated using two symmetrical airfoils. Measurements were made in cross-sectional grids and profiles over a range of Reynolds numbers and downstream distances. Contours of axial normal stress were high-pass filtered to remove the contributions of wandering to the velocity fluctuations. This process reveals a vortex core which is laminar and is surrounded by a region of high turbulence. Core velocity profiles reveal that maximum tangential velocity increases with Reynolds number and decreases with distance downstream. Core radius increases with distance downstream and decreases with Reynolds number. In the second part, flow visualizations of the wake behind a delta wing model were made for a range of Reynolds numbers and lift coefficients. These visualizations reveal the near-instantaneous turbulence structure of the wing wake which is dominated by a vortex pair and a connecting 'braid' wake. The braid spacing decreases with increasing Reynolds number and is independent of lift coefficient. The extent of the braid downstream of the wing increases with lift coefficient and decreases with increasing Reynolds number. The large turbulence scales in the wing wake were found to increase in discrete jumps indicating some sort of reorganization of turbulence such as pairing. This reorganization of turbulence was found to occur more quickly as Reynolds number is increased.

Advances In Turbulence Vi

Autore: S. Gavrilakis
Editore: Springer Science & Business Media
ISBN: 9400902972
Grandezza: 25,56 MB
Formato: PDF, Kindle
Vista: 9984
Scaricare Leggi Online

Advances in Turbulence VI presents an update on the state of turbulence research with some bias towards research in Europe, since it represents an almost complete collection of the paper presentations at the Sixth European Turbulence Conference, sponsored by EUROMECH, ERCOFTAC and COST, and held at the Swiss Federal Institute of Technology in Lausanne, July 2-5, 1996. The problem of transition, together with the structural description of turbulence, and the scaling laws of fully developed turbulence have continued to receive most attention by the research community and much progress has been made since the last European Turbulence Conference in 1994. The volume is thus geared towards specialists in the area of flow turbulence who could not attend the conference, as well as anybody who wishes quickly to assess the most active current research areas and the groups associated with them.

Turbulence Structure And Vortex Dynamics

Autore: J. C. Vassilicos
Editore: Cambridge University Press
ISBN: 9780521781312
Grandezza: 67,91 MB
Formato: PDF
Vista: 3039
Scaricare Leggi Online

Edited volume on turbulence, first published in 2000.

Aircraft Wake Turbulence And Its Detection

Autore: John Olsen
Editore: Springer Science & Business Media
ISBN: 1468483463
Grandezza: 53,24 MB
Formato: PDF, ePub
Vista: 8925
Scaricare Leggi Online

The combination of increasing airport congestion and the ad vent of large transports has caused increased interest in aircraft wake turbulence. A quantitative understanding of the interaction between an aircraft and the vortex wake of a preceding aircraft is necessary for planning future high density air traffic patterns and control systems. The nature of the interaction depends on both the characteristics of the following aircraft and the characteristics of the wake. Some of the questions to be answered are: What deter mines the full characteristics of the vortex wake? What properties of the following aircraft are important? What is the role of pilot response? How are the wake characteristics related to the genera ting aircraft parameters? How does the wake disintegrate and where? Many of these questions were addressed at this first Aircraft Wake Turbulence Symposium sponsored by the Air Force Office of Sci entific Research and The Boeing Company. Workers engaged in aero dynamic research, airport operations, and instrument development came from several count ries to present their results and exchange information. The new results from the meeting provide a current picture of the state of the knowledge on vortex wakes and their interactions with other aircraft. Phenomena previously regarded as mere curiosities have emerged as important tools for understanding or controlling vortex wakes. The new types of instability occurring within the wake may one day be used for promoting early dis integration of the hazardous twin vortex structure.

Naca 0015 Wing Pressure And Trailing Vortex Measurements

Editore: DIANE Publishing
ISBN: 142891546X
Grandezza: 14,41 MB
Formato: PDF
Vista: 2207
Scaricare Leggi Online

Vortex Wakes Of Aircrafts

Autore: A.S. Ginevsky
Editore: Springer Science & Business Media
ISBN: 3642017606
Grandezza: 71,17 MB
Formato: PDF, Mobi
Vista: 3187
Scaricare Leggi Online

Investigation of vortex wakes behind various aircraft, especially behind wide bodied and heavy cargo ones, is of both scientific and practical in terest. The vortex wakes shed from the wing’s trailing edge are long lived and attenuate only atdistances of10–12kmbehindthe wake generating aircraft. The encounter of other aircraft with the vortex wake of a heavy aircraft is open to catastrophic hazards. For example, air refueling is adangerous operationpartly due to thepossibility of the receiver aircraft’s encountering the trailing wake of the tanker aircraft. It is very important to know the behavior of vortex wakes of aircraft during theirtakeoff andlanding operations whenthe wakes canpropagate over the airport’s ground surface and be a serious hazard to other depart ing or arriving aircraft. This knowledge can help in enhancing safety of aircraft’s movements in the terminal areas of congested airports where the threat of vortex encounters limits passenger throughput. Theoreticalinvestigations of aircraft vortex wakes arebeingintensively performedinthe major aviationnations.Usedforthispurpose are various methods for mathematical modeling of turbulent flows: direct numerical simulation based on the Navier–Stokes equations, large eddy simulation using the Navier–Stokes equations in combination with subrigid scale modeling, simulation based on the Reynolds equations closed with a differential turbulence model. These approaches are widely used in works of Russian and other countries’ scientists. It should be emphasized that the experiments in wind tunnels and studies of natural vortex wakes behind heavy and light aircraft in flight experiments are equally important.

Advances In Les Of Complex Flows

Autore: Rainer Friedrich
Editore: Springer Science & Business Media
ISBN: 0306483831
Grandezza: 42,99 MB
Formato: PDF
Vista: 293
Scaricare Leggi Online

The articles focus on new developments in the field of large-eddy simulation of complex flows and are related to the topics: modelling and analysis of subgrid scales, numerical issues in LES cartesian grids for complex geometries, curvilinear and non-structured grids for complex geometries. DES and RANS-LES coupling, aircraft wake vortices, combustion and magnetohydrodynamics. Progress has been made not only in understanding and modelling the dynamics of unresolved scales, but also in designing means that prevent the contamination of LES predictions by discretization errors. Progress is reported as well on the use of cartesian and curvilinear coordinates to compute flow in and around complex geometries and in the field of LES with unstructured grids. A chapter is dedicated to the detached-eddy simulation technique and its recent achievements and to the promising technique of coupling RANS and LES solutions in order to push the resolution-based Reynolds number limit of wall-resolving LES to higher values. Complexity due to physical mechanisms links the last two chapters. It is shown that LES constitutes the tool to analyse the physics of aircraft wake vortices during landing and takeoff. Its thorough understanding is a prerequisite for reliable predictions of the distance between consecutive landing airplanes. Subgrid combustion modelling for LES of single and two-phase reacting flows is demonstrated to have the potential to deal with finite-rate kinetics in high Reynolds number flows of full-scale gas turbine engines. Fluctuating magnetic fields are more reliably predicted by LES when tensor-diffusivity rather than gradient-diffusion models are used. An encouraging result in the context of turbulence control by magnetic fields.

Turbulence And Coherent Structures

Autore: O. Métais
Editore: Springer Science & Business Media
ISBN: 9401579040
Grandezza: 46,55 MB
Formato: PDF, Docs
Vista: 6226
Scaricare Leggi Online

In the last 25 years, one of the most striking advances in Fluid Mecha nics was certainly the discovery of coherent structures in turbulence: lab oratory experiments and numerical simulations have shown that most turbulent flows exhibit both spatially-organized large-scale structures and disorganized motions, generally at smaller scales. The develop ment of new measurement and visualization techniques have allowed a more precise characterization and investigation of these structures in the laboratory. Thanks to the unprecedented increase of computer power and to the development of efficient interactive three-dimensional colour graphics, computational fluid dynamicists can explore the still myste rious world of turbulence. However, many problems remain unsolved concerning the origin of these structures, their dynamics, and their in teraction with the disorganized motions. In this book will be found the latest results of experimentalists, theoreticians and numerical modellers interested in these topics. These coherent structures may appear on airplane wings or slender bodies, mixing layers, jets, wakes or boundary-layers. In free-shear flows and in boundary layers, the results presented here highlight the intense three-dimensional character of the vortices. The two-dimensional large scale eddies are very sensitive to three-dimensional perturbations, whose amplification leads to the formation of three-dimensional coherent vorti cal structures, such as streamwise, hairpin or horseshoe vortex filaments. This book focuses on modern aspects of turbulence study. Relations between turbulence theory and optimal control theory in mathematics are discussed. This may have important applications with regard to, e. g. , numerical weather forecasting.

Summary Of Flow Modulation And Fluid Structure Interaction Findings

Autore: Wolfgang Schröder
Editore: Springer Science & Business Media
ISBN: 3642040888
Grandezza: 57,26 MB
Formato: PDF, ePub, Docs
Vista: 5955
Scaricare Leggi Online

Perspectives In Turbulence Studies

Autore: Hans U. Meier
Editore: Springer Science & Business Media
ISBN: 3642829945
Grandezza: 41,94 MB
Formato: PDF, Docs
Vista: 1576
Scaricare Leggi Online

The present volume entitled "Perspectives in Turbulence Stud ies" is dedicated to Dr. Ing. E. h. Julius C. Rotta in honour of his 75th birthday. J. C. Rotta, born on January 1, 1912, started his outstanding career in an unusual way, namely in a drawing office (1928 - 1931). At the same time he - as a purely self taught perso- took a correspondence course in airplane construction. From 1934 to 1945 he worked in the aircraft industry on different subjects in the fields of flight mechanics, structures, air craft design, and aerodynamics. In 1945 he moved to Gottingen and worked from that time at the Aerodynamische Versuchsanstalt (AVA, now DFVLR) and the Max-Planck-Institut fur Stromungsforschung (1947-1958), interrupted only by a stay in the U. S. at the Glenn L. Martin Company (1954 - 1955) and a visiting professorship at the Laval University in Quebec, Canada (1956). Already during his activities in industry, Dr. Rotta discovered his special liking for aerodynamics. In Gottingen, he was attracted by Ludwig Prandtl's discussions about problems associated with turbulence and in particular his new contribution to fully developed turbulence, published in 1945. At that time, W. Heisenberg and C. F. v. Weizacker pub lished their results on the energy spectra of isotropic turbu lence at large wave numbers. Since that time his main research interest in reasearch has been in turbulence problems.