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 Receptivity and Transition to Turbulene of Supersonic Boundary Layers with Surface Roughness written by Nicola De Tullio and published by . This book was released on 2013 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laminar Turbulent Transition written by H.F. Fasel and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 703 pages. Available in PDF, EPUB and Kindle. Book excerpt: The origins of turbulent flow and the transition from laminar to turbulent flow are among the most important unsolved problems of fluid mechanics and aerodynamics. Besides being a fundamental question of fluid mechanics, there are any number of applications for information regarding transition location and the details of the subsequent turbulent flow. The JUT AM Symposium on Laminar-Turbulent Transition, co-hosted by Arizona State University and the University of Arizona, was held in Sedona, Arizona. Although four previous JUT AM Symposia bear the same appellation (Stuttgart 1979, Novosibirsk 1984, Toulouse 1989, and Sendai 1994) the topics that were emphasized at each were different and reflect the evolving nature of our understanding of the transition process. The major contributions of Stuttgart 1979 centered on nonlinear behavior and later stages of transition in two-dimensional boundary layers. Stability of closed systems was also included with Taylor vortices in different geometries. The topics of Novosibirsk 1984 shifted to resonant wave interactions and secondary instabilities in boundary layers. Pipe- and channel-flow transition were discussed as model problems for the boundary layer. Investigations of free shear layers were presented and a heavy dose of supersonic papers appeared for the first time. The character of Toulouse 1989 was also different in that 3-D boundary layers, numerical simulations, streamwise vortices, and foundation papers on receptivity were presented. Sendai 1994 saw a number of papers on swept wings and 3-D boundary layers. Numerical simulations attacked a broader range of problems.
Download or read book Interacting Supersonic Turbulent Boundary Layers Over a Two dimensional Protuberance written by Arnold Polak and published by . This book was released on 1974 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report presents a numerical study of attached interacting supersonic turbulent boundary layers over a two-dimensional protuberance. Results are presented in terms of surface pressure, heat transfer and skin-friction distributions. These results indicate a strong effect of the size of the protuberance, Mach number, but a weak effect of Reynolds number and the ratio of wall-to-recovery temperature. The peak heating rates from a set of test cases compare well to a semi-empirical prediction method. In contradistinction to the laminar case, the turbulent recovery zone downstream of the protuberance is very short. (Author).
Download or read book Boundary Layer Transition at Supersonic Speeds written by E. R. Van Driest and published by . This book was released on 1961 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments carried out in the 12-inch supersonic wind tunnel to investigate the effect of three dimensional roughness elements (spheres) on boundary-layer transition on a 10-degree (apex angle) cone without heat transfer are described. The local Mach number for these tests was 2.71. The data show clearly that the minimum (effective) size of trip required to bring transition to its lowest Reynolds number varies power of the distance from the apex of the cone to the trip. Use of available data at other Mach numbers indicates that the Mach number influence for effective tripping is taken into account by a simple expression. Some remarks concerning the roughness variation for transition on a blunt body are made. Finally, a general criterion is introduced which gives insight to the transition phenomenon and anticipates effects of external and internal disturbances, Mach number transfer.
Download or read book Effect of Distributed Three dimensional Roughness and Surface Cooling on Boundary layer Transition and Lateral Spread of Turbulence at Supersonic Speeds written by Albert L. Braslow and published by . This book was released on 1959 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Small Steps on the Receptivity and Transition in High Speed Boundary Layer written by Sofia Yassir and published by . This book was released on 2016 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: The research on transition in supersonic and hypersonic boundary layers has been reinvigorated in the last decades because of the increased interest in high-speed flight. The receptivity to environmental disturbances of high-speed boundary layers developing over flat plates or curved surfaces is a very important problem because the transition process is directly impacted by it. The main objective of the research is to determine the effect of small steps on laminar high-speed boundary-layers that are excited by freestream disturbances in the form of vorticity and acoustic waves. Both supersonic and hypersonic regimes are analyzed using a high-order compressible Navier-Stokes numerical algorithm. It is found that both the backward and the forward steps are capable of stabilizing the disturbances that propagate inside the boundary layer. This will potentially delay the formation of three-dimensional disturbances that are precursors to transition into turbulence.
Download or read book Boundary layer Transition Study of Several Pointed Bodies of Revolution at Supersonic Speeds written by William A. Cassels and published by . This book was released on 1970 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boundary-layer transition by the sublimation and impact-pressure techniques and force tests have been performed on three Haack-Adams bodies of revolution of fineness ratios 7, 10, and 13 at zero angle of attack for free-stream Mach numbers of 2.00, 2.75, and 4.63 and a range of Reynolds numbers based on model length of 6 to 15 X 10(to the 6 power) with and without a roughness strip. The grit method of inducing turbulence was found to provide for a nearly complete turbulent flow over the models at the lower Mach numbers and higher Reynolds numbers considered in this study while the amount of trip drag was less than 8 percent of the model drag with transition fixed. A method of interpreting sublimation data was discussed and used and the results compared well with the impact-pressure results.
Download or read book Factors Affecting Transition at Supersonic Speeds written by K. R. Czarnecki and published by . This book was released on 1953 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper surveys the available material and summarizes what is known to date about boundary-layer transition at supersonic speeds. Variables studied include Mach number, Reynolds number, pressure gradients, heat transfer, surface roughness, and angle of attack. The discussion is limited to bodies of revolution because similar reliable data for wings is lacking.
Download or read book Seventh IUTAM Symposium on Laminar Turbulent Transition written by Philipp Schlatter and published by Springer Science & Business Media. This book was released on 2010-03-11 with total page 628 pages. Available in PDF, EPUB and Kindle. Book excerpt: The origins of turbulent ?ow and the transition from laminar to turbulent ?ow are the most important unsolved problems of ?uid mechanics and aerodynamics. - sides being a fundamental question of ?uid mechanics, there are numerous app- cations relying on information regarding transition location and the details of the subsequent turbulent ?ow. For example, the control of transition to turbulence is - pecially important in (1) skin-friction reduction of energy ef?cient aircraft, (2) the performance of heat exchangers and diffusers, (3) propulsion requirements for - personic aircraft, and (4) separation control. While considerable progress has been made in the science of laminar to turbulent transition over the last 30 years, the c- tinuing increase in computer power as well as new theoretical developments are now revolutionizing the area. It is now starting to be possible to move from simple 1D eigenvalue problems in canonical ?ows to global modes in complex ?ows, all - companied by accurate large-scale direct numerical simulations (DNS). Here, novel experimental techniques such as modern particle image velocimetry (PIV) also have an important role. Theoretically the in?uence of non-normality on the stability and transition is gaining importance, in particular for complex ?ows. At the same time the enigma of transition in the oldest ?ow investigated, Reynolds pipe ?ow tran- tion experiment, is regaining attention. Ideas from dynamical systems together with DNS and experiments are here giving us new insights.
Download or read book Instability and Transition written by M.Y. Hussaini and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt: These two volumes contain the proceedings of the workshop on the Institute for Computer Instability and Transition, sponsored by Applications in Science and Engineering (ICASE) and the Langley Research Center (LaRC), during May 15 to June 9, 1989. The work shop coincided with the initiation of a new, focused research pro gram on instability and transition at LaRC. The objectives of the workshop were to (i) expose the academic community to current technologically important issues of instability and transition in shear flows over the entire speed range, (ii) acquaint the academic com munity with the unique combination of theoretical, computational and experimental capabilities at LaRC and foster interaction with these facilities, (iii) review current state-of-the-art and propose fu ture directions for instability and transition research, (iv) accelerate progress in elucidating basic understanding of transition phenomena and in transferring this knowledge into improved design methodolo gies through improved transition modeling, and (v) establish mech anisms for continued interaction. The objectives (i) to (iii) were of course immediately met. It is still premature to assess whether ob jectives (iv) and (v) are achieved. The workshop program consisted of tutorials, research presenta tions, panel discussions, experimental and computational demonstra tions, and collaborative projects.
Download or read book Laminar Turbulent Transition in a Hypersonic Boundary Layer Receptivity and Instability Pre History written by and published by . This book was released on 1997 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report results from a contract tasking Moscow Inst. of Physics and Technology as follows: The contractor will perform research in accordance with contractor's proposal entitled, 'Laminar-Turbulent Transition in an Hypersonic Boundary Layer.' This report addresses the initial phase of hypersonic boundary-layer transition comprising excitation of unstable normal modes and their downstream evolution from receptivity regions to the instability growth onset (instability pre-history problem). It is shown that this phase is more complicated than in subsonic and moderate supersonic cases due to the following features of the disturbance field: (1) the first and second modes are synchronized with acoustic waves near the body nose region; (2) further downstream the first mode is synchronized with entropy/vorticity waves; (3) near the instability growth onset the first mode is synchronized with the second mode. Disturbance behavior in the synchronism regions (2) and (3) are studied using the multiple-mode method, which accounts for interaction between modes of discrete and continuous spectrum due to nonparallel effects of the mean flow. It is shown that vorticity/entropy waves are partially swallowed by the boundary layer and effectively generate the first mode due to Synchronism (2). This mechanism can compete with the leading edge receptivity to the freestream acoustic waves in cases of 'quiet' freestream conditions and conical body configurations. The inter-mode exchange rule coupling input and output characteristics of the first and second modes crossing the branch point vicinity was established. Combination of the receptivity estimates related to Synchronism (2) and the inter-mode exchange rule related to Synchronism; (3) allows the evaluation of instability initial amplitudes required for the PSE calculations of the transition onset point.
Download or read book Experimental Investigation of Induced Supersonic Boundary Layer Transition written by Henny Bottini and published by . This book was released on 2014 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence onset within an initially laminar flow is one of the most common phenomenon in Fluid Mechanics, yet is an open field of research. This is due to the many and diverse causes that can trigger turbulence, which often add to each other, change their effect upon the flow velocity, and are difficult to single out in real-world situations. This is why laminar-toturbulent transition experiments have been and still are a fundamental tool for the researcher. This thesis work has addressed the study of turbulence onset in supersonic flows from an experimental point of view. Two test campaigns have been carried out each in a dedicated supersonic wind tunnel. The first aimed at tracking turbulence onset triggered by a single tetrahedral roughness element. It has been carried out in a multiple-Mach-number supersonic wind tunnel whose qualification campaign has been completed within this thesis work. Two roughness heights were tested, both for two Mach numbers, 1.6 and 2.3. The second test campaign has investigated the effects of an oblique shock wave impinging onto a Mach-2 transitional boundary layer. The transitional state of a boundary layer is that state during which the boundary layer passes from fully laminar to fully turbulent. This passage can be either induced or natural, and it was represented in this thesis work by the trigger wake and by the boundary layer flow downstream of the release point of an electric spark, respectively. Surface sensors, as thin-films and piezoelectric pressure transducers, were used to measure steady and unsteady highfrequency flow evolutions. Different wall temperatures were set for the thin-films insert as to allow the experimental estimation of the recovery temperature. Convective heat-flux trends have been extracted from the steady measurements, which, together with the recovery temperature trends, allowed the calculation of the Stanton number trends. All these quantities let to conclude on the general state of the boundary layer investigated in the first test campaign. The post-processing of the unsteady measurements yielded temperature and pressure fluctuations spectra and RMS streamwise evolutions, along with spectral time evolution at a given position. For the first test campaign, they allowed the characterization of the unsteadiness produced by the roughness within the supersonic boundary layer at different downstream locations. In so doing, they helped conclude on the state of the boundary layer, thus on the effectiveness of the roughness in triggering transition to turbulence. For the second test campaign, they allowed to single out the unsteady effects of the shock impinging downstream of the single roughness and downstream of the electric spark release point. In this way, differences in the shock effect between the roughness configuration and the clean-plate configuration have been highlighted, and the effects of different spark release frequencies compared.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1991 with total page 1102 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Surface Roughness on the Mean and Turbulence Flow Properties of a Supersonic Boundary Layer written by Robert M. Latin 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 Observations of Turbulent burst Geometry and Growth in Supersonic Flow written by Carlton S. James and published by . This book was released on 1958 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three-dimensional burst geometry was determined for two typical turbulent bursts. From a comparison of burst plan forms and thickness profiles observed under different flow conditions, burst geometry was found to be insensitive to variation of Mach number, unit Reynolds number, and surface roughness. These variables, together with body shape, were fouud to have signlflcant effects 013. the rate at which a burst is swept along the surface, its growth rate (relative to distance traveled), and the rate of burst formation.
Download or read book Controlled Experiments on Instabilities and Transition to Turbulence in Supersonic Boundary Layers written by T. C. Corke and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
