Download or read book On the Secondary Instability of the Most Dangerous Goertler Vortex written by Institute for Computer Applications in Science and Engineering and published by . This book was released on 1993 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Control of G rtler Vortices in High speed Boundary Layers written by Radwa Alaziz and published by . This book was released on 2017 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Görtler vortices develop in boundary layer flows over concave surfaces due to the imbalance between centrifugal forces and the wall-normal pressure gradient. These vortices can be efficient precursors to transition in boundary layers exposed to freestream disturbance or surface non-uniformities, because they can alter the mean flow causing the laminar flow to breakdown into turbulence. In this thesis, a control technique aimed at reducing the energy associated with Görtler vortices that develop in supersonic boundary layers is introduced and tested. The control algorithm is based on distributed blowing and suction, with sensors placed either in the flow or at the wall. The result show that there is a dependence between the efficiency of the control algorithm and the spanwise separation of the vortices, that is the energy reduction is more significant for larger spanwise separations. The efficiency of the control algorithm seems to be insensitive to the variation of the Mach number.
Download or read book Secondary Instabilities in Compressible Boundary Layers written by Institute for Computer Applications in Science and Engineering and published by . This book was released on 1990 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper examines secondary instabilities in compressible boundary layers at Mach numbers M at = 0, 0.8, 1.6, and 4.5. We find that there is a broad-dand of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M
Download or read book The Nonlinear Evolution of Secondary Instabilities in Boundary Layers written by Jeffrey Dale Crouch and published by . This book was released on 1988 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Growth of Goertler Vortices in Compressible Boundary Layers written by and published by . This book was released on 1987 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Receptivity and Transition to Turbulence of Supersonic Boundary Layers with Surface Roughness written by Nicola De Tullio and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A deeper understanding of the different factors that influence the laminar-turbulent transition in supersonic boundary layers will help the design of efficient high-speed vehicles. In this work we study the effects of surface roughness on the stability and transition to turbulence of supersonic boundary layers. The investigation is carried out by direct numerical simulations (DNS) of the compressible Navier-Stokes equations and focuses on the modifications introduced in the transition process by localised roughness elements, for Mach numbers M∞ = 6.0 and M∞ = 2.5, and distributed slender pores at M∞ = 6.0. The first part of the investigation into the effects of localised roughness deals with the receptivity and initial exponential amplification of disturbances in boundary layers subjected to small external perturbations. Different transition scenarios are investigated by considering different free-stream disturbances and roughness elements with different heights. The results show that, for roughness heights approaching the local displacement thickness, transition is dominated by the growth of a number of instability modes in the roughness wake. These modes are damped by wall cooling and their receptivity is found to be more efficient in the case of free-stream disturbances dominated by sound. At M∞ = 6 the growth of Mack modes in the boundary layer is found to play a crucial role in the excitation of the most unstable wake modes. An investigation into the nonlinear stages of transition shows that the breakdown to turbulence starts with nonlinear interactions of the wake instability modes. This leads to the formation of a turbulent wedge behind the roughness element, which spreads laterally following mechanisms similar to those observed for the evolution of compressible turbulent spots. An oblique shock impinging on the transitional boundary layer significantly accelerates the breakdown process and leads to a wider turbulent wedge. The study ends with an analysis of porous walls as a passive method for transition control, which is carried out using a temporal DNS approach. The results show damping of both the primary, of second or Mack mode type, and secondary instabilities and indicate that, despite the high Mack number, first mode waves regain importance in this modified transition scenario.
Download or read book Boundary layer induced Vortex Instability written by Masood Parang and published by . This book was released on 1972 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Goetler Vortex Instabilities of Incompressible and Compressible Boundary Layers written by Philip David Wadey and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book G rtler vortex instabilities of imcompressible and compressible boundary layers written by Philip David Wadey and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research on Instabilities and Transition in Three Dimensional Boundary Layers with Emphasis on Gas Turbine Blade Flows written by and published by . This book was released on 2000 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Absolute instability of (Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third-year work under this grant. For the most part, the Gortler vortices have been investigated in an incompressible boundary layer over thin-wing sections or artificial inserts on an otherwise flat plate. The cascade of modern aircraft engines operate in the high subsonic Mach number regime with velocity fields strongly affected by centrifugal forces maintained by the large curvature of profiles. Unsteady spiral-type vortices developing in these environments provoke the absolute instability in the streamwise direction of the boundary layer leading to earlier transition. An effort undertaken after the meeting in Shalimar (May 29-31, 2002) show that the heat transfer coefficient is even more susceptible to enhancing oscillations in the upstream moving wave packets than the pressure.
Download or read book Instabilities and Transition in Three Dimensional Boundary Layers with Emphasis on Gas Turbine Blade Flows written by and published by . This book was released on 2000 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Absolute instability of (Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third-year work under this grant. For the most part, the Gortler vortices have been investigated in an incompressible boundary layer over thin-wing sections or artificial inserts on an otherwise flat plate. The cascade of modem aircraft engines operate in the high subsonic Mach number regime with velocity fields strongly affected by centrifugal forces maintained by the large curvature of profiles. Unsteady spiral-type vortices developing in these environments provoke the absolute instability in the streamwise direction of the boundary layer leading to earlier transition. An effort undertaken after the meeting in Shalimar (May 29-31, 2002) show that the heat transfer coefficient is even more susceptible to enhancing oscillations in the upstream moving wave packets than the pressure.
Download or read book Vortex Shedding Characteristics of the Wake of a Thin Flat Plate with a Circular Trailing Edge written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2019-01-14 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: The near and very near wake of a thin flat plate with a circular trailing edge are investigated with direct numerical simulations (DNS). Data obtained for two different Reynolds numbers (based on plate thickness, D) are the main focus of this study. The separating boundary layers are turbulent in both cases. An earlier investigation of one of the cases (Case F) showed shed vortices in the wake that were about 1.0 D to 4.0 D in spanwise length. Considerable variation in both the strength and frequency of these shed vortices was observed. One objective of the present investigation is to determine the important contributors to this variability in strength and frequency of shed vortices and their finite spanwise extent. Analysis of the data shows that streamwise vortices in the separating boundary layer play an important role in strengthening/weakening of the shed vortices and that high/low-speed streaks in the boundary layer are important contributors to variability in shedding frequency. Both these features of the boundary layer contribute to the finite extent of the vortices in the spanwise direction. The second plate DNS (Case G, with 40 percent of the plate thickness of Case F) shows that while shedding intensity is weaker than obtained in Case F, many of the wake features are similar to that of Case F. This is important in understanding the path to the wake of the thin plate with a sharp trailing edge where shedding is absent. Here we also test the efficacy of a functional relationship between the shedding frequency and the Reynolds numbers based on the boundary layer momentum thickness (Re (sub theta) and D (Re (sub D)); data for developing this behavioral model is from Cases F & G and five earlier DNSs of the flat plate wake. Rai, Man Mohan Ames Research Center NASA/TM-2018-219752, ARC-E-DAA-TN52073
Download or read book In Flight Simulators and Fly by Wire Light Demonstrators written by Peter G. Hamel and published by Springer. This book was released on 2017-03-15 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book offers the first complete account of more than sixty years of international research on In-Flight Simulation and related development of electronic and electro-optic flight control system technologies (“Fly-by-Wire” and “Fly-by-Light”). They have provided a versatile and experimental procedure that is of particular importance for verification, optimization, and evaluation of flying qualities and flight safety of manned or unmanned aircraft systems. Extensive coverage is given in the book to both fundamental information related to flight testing and state-of-the-art advances in the design and implementation of electronic and electro-optic flight control systems, which have made In-Flight Simulation possible. Written by experts, the respective chapters clearly show the interdependence between various aeronautical disciplines and in-flight simulation methods. Taken together, they form a truly multidisciplinary book that addresses the needs of not just flight test engi neers, but also other aeronautical scientists, engineers and project managers and historians as well. Students with a general interest in aeronautics as well as researchers in countries with growing aeronautical ambitions will also find the book useful. The omission of mathematical equations and in-depth theoretical discussions in favor of fresh discussions on innovative experiments, together with the inclusion of anecdotes and fascinating photos, make this book not only an enjoyable read, but also an important incentive to future research. The book, translated from the German by Ravindra Jategaonkar, is an extended and revised English edition of the book Fliegende Simulatoren und Technologieträger , edited by Peter Hamel and published by Appelhans in 2014.
Download or read book Nonlinear Spatial Evolution of Inviscid Instabilities on Hypersonic Boundary Layers written by and published by . This book was released on 1996 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Linear and Nonlinear Instabilities of Blasius Boundary Layer Perturbed by Streamwise Vortices Part II Intermittent Instability Induced by Long wavelength Klebanoff Modes written by and published by . This book was released on 2001 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents theoretical results on the stability properties of a Blasius boundary layer perturbed by Klebanoff distortions with a relatively long spanwise scale. Even relatively weak Klebanoff modes can alter the near-wall curvature of the underlying flow by O(1) and, hence, introduce linear instabilities with larger characteristic growth rates and frequencies than those of the Tollmien-Schlichting waves in an unperturbed Blasius flow. A localised distortion supports both sinuous and varicose modes of instability, with the growth rates of the sinuous modes being likely to be larger, in general. Overall, the instability is intermittent in time and localised in space, being confined to a finite part of the Klebanoff mode cycle and to a specific window(s) along the streamwise direction. A spanwise periodic distortion supports spatially quasi-periodic modes (via the parametric resonance mechanism), which may be viewed as modified T-S waves with excess growth rates when the Klebanoff modes are weak. In spite of the simplifications involved in this theory, its predictions appear qualitatively consistent with some of the unusual characteristics of the high-frequency wavepackets observed during previous experiments. The nonlinear development of a localised sinuous mode is followed across a sequence of asymptotic regimes using the non-equilibrium critical-layer theory.
Download or read book Boundary Layer Instability Induced by Distributed Surface Suction microform written by Philip James Douglas Roberts and published by National Library of Canada = Bibliothèque nationale du Canada. This book was released on 2001 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: The linear instability of accelerated, decelerated and flat plate boundary layers modified by uniform surface suction blowing and/or periodic (distributed) wall suction is investigated. All boundary layer flows considered in this work are assumed to be incompressible and parallel. Small but finite suction non-uniformities are found to induce an instability in the form of stationary streamwise vortices for each of the boundary layer configurations studied; this instability is shown to be (i) strongly influenced by the suction non-uniformity amplitude and flow Reynolds number but only (ii) moderately influenced by the application of uniform suction or uniform blowing. It is found that the classical TS (Tollmien-Schlichting) wave instability changes in a complex manner when the suction non-uniformity amplitude is varied. Oblique TS waves are shown in several instances to be more unstable than two-dimensional TS waves depending on the suction non-uniformity magnitude and the type of boundary layer under consideration. A resonance mechanism that causes a strong flow response is demonstrated to occur when infinitesimally small surface suction non-uniformities travel with the phase speed and wave number nearby either the neutral or most weakly attenuated Tollmien-Schlichting waves.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1988 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:
