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An Analytical Study Of The Effect Of Surface Roughness On Boundary Layer Stability
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Book Synopsis An Analytical Study of the Effect of Surface Roughness on Boundary-Layer Stability by : Charles L. Merkle
Download or read book An Analytical Study of the Effect of Surface Roughness on Boundary-Layer Stability written by Charles L. Merkle and published by . This book was released on 1977 with total page 69 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of surface roughness on the transition of a laminar boundary layer are basically two-fold: (1) it can distort the mean velocity and temperature profiles thus altering the stability characteristics of the layer and (2) it can induce additional disturbances to the boundary layer which may lead to an earlier transition. Only the first of these effects is considered in this report. Three different types of surface roughness are investigated here; distributed roughness, surface waviness, and a single two-dimensional bump. An analytical model which describes the effect of distributed roughness on the mean flow and its stability is described. This model is further validated by comparison with Achenbach's experimental results and is then applied to the flow about an underwater body in order to illustrate the effects of surface roughness in a more realistic situation. Surface irregularities can play a dominant role in determining the practical limit for the application of boundary-layer control techniques. The present distributed roughness model as incorporated into the TAPS code can provide a reasonable prediction of its effect in the presence of boundary-layer control techniques (shaping, heating, suction) on the transition location for an underwater vehicle.
Book Synopsis An Analytical Study of the Effect of Surface Roughness on the Stability of a Heated Water Boundary Layer by : Michael A. Kosecoff
Download or read book An Analytical Study of the Effect of Surface Roughness on the Stability of a Heated Water Boundary Layer written by Michael A. Kosecoff and published by . This book was released on 1976 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: The onset of transition from laminar to turbulent flow in a high Reynolds number, water boundary layer was investigated with emphasis on predicting the global effects of distributed surface roughness on transition. The authors used the results of linear stability theory as an indicator of transition, but, this paper presents only comparisons of the stability results (not actual transition predictions). The effects of surface roughness on transition were induced by means of an existing phenomenological model for the effects of distributed roughness on the mean flow profiles. This model, originally developed for high Mach number, compressible boundary layers, was applied without change to the present incompressible, water boundary-layer environment, and identical values of the required empirical constants were used in both cases. One conclusion obtained from the numerical results is that the presence of favorable pressure gradients and/or surface heating make the boundary layer more susceptible to roughness, not only when compared in terms of the actual roughness height, but also when compared in terms of the roughness height to momentum thickness ratio. When the roughness is sufficiently large, its presence can change the effect of surface heat addition from a strongly stabilizing factor to a strongly destabilizing phenomena.
Book Synopsis An Analytical Study of the Effects of Surface Roughness on Boundary-Layer Transition by :
Download or read book An Analytical Study of the Effects of Surface Roughness on Boundary-Layer Transition written by and published by . This book was released on 1974 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical model has been developed to describe the manner in which distributed surface roughness affects transition. The model pictures the roughness as having two distinct effects: one, it introduces higher disturbance levels in the boundary layer; and two, it alters the mean velocity profile and, hence, the growth rate of the disturbances. The alteration of the mean velocity profile is described by means of a 'turbulent sublayer', which visualizes an enhanced momentum transfer in a narrow layer next to the surface. The corresponding change in the amplification of disturbances is then determined by means of linear stability theory, and is related to transition by an empirical transition criterion.
Download or read book משחקידע written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Analytical Study of the Effects of Surface Roughness on a Compressible Turbulent Boundary Layer by :
Download or read book An Analytical Study of the Effects of Surface Roughness on a Compressible Turbulent Boundary Layer written by and published by . This book was released on 1983 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: A previous study on the effect of surface roughness on the turbulent boundary layer, using a Fortran code, ITRACT, solved for the characteristics of a laminar, transitional and turbulent boundary layer on smooth surfaces. The present study investigates the influence of surface roughness on a compressible turbulent boundary layer and then extends the usefulness of ITRACT by including in it the optional capability of rough-surface boundary-layer calculations. Surface roughness was represented by distributed sources and sinks in the appropriate governing equations. The most important term is a sink term in the mean momentum equation, representing the form drag due to the roughness element. Governing boundary-layer equations for continuity, momentum, and energy were derived in a form to account for blockage effects due to roughness elements. The modified governing equations were then transformed using Probstein-Elliott and Levy-Lees transformations. The resulting equations, with appropriate boundary conditions, were solved by finite-difference techniques to determine the nondimensional velocity components and temperature at a finite number of nodes in the boundary-layer flow field.
Book Synopsis An Analytical Study of the Effects of Surface Roughness on a Compressible Turbulent Boundary Layer by : Zakir H. Khan (SQDN LDR, Pakistani AF.)
Download or read book An Analytical Study of the Effects of Surface Roughness on a Compressible Turbulent Boundary Layer written by Zakir H. Khan (SQDN LDR, Pakistani AF.) and published by . This book was released on 1983 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Technical Paper written by and published by . This book was released on 1980 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Study of the Effect of Free-stream Turbulence Upon Disturbances in the Pre-transitional Laminar Boundary Layer by : James M. Kendall
Download or read book Study of the Effect of Free-stream Turbulence Upon Disturbances in the Pre-transitional Laminar Boundary Layer written by James M. Kendall and published by . This book was released on 1982 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: Part I: Hot wire anemometry has been employed to determine certain characteristics of the turbulence in the free-stream of a low-speed, low-turbulence wind tunnel and to study the influence on such turbulence upon the fluctuations within a flat-plate boundary layer. A technique was employed which provided information concerning the propagation speed of the disturbances and this was used as a means of classification as to type or cause. It was found that Tollmien-Schlichting waves did not possess significant energy until a Reynolds number considerably higher than that of the theoretical neutral point was attained and that the subsequent growth exceeded the prediction of linear analysis. Part II: Distributed roughness present upon an aerodynamic surface alters the laminar boundary layer mean velocity profile such as to increase the instability presented here of the profile distortion for the case of small roughness in a Blasius boundary layer. The roughnesses tested include a single protuberance at Reynolds numbers below 50, the interaction between two such elements, the interaction between one element and a multitude of others, and the distortion due to distributed roughness. (Author).
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 1994 with total page 1028 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book NASA Reference Publication written by and published by . This book was released on 1977 with total page 984 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers by : Kahei Danny Fong
Download or read book A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers written by Kahei Danny Fong and published by . This book was released on 2017 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current understanding and research efforts on surface roughness effects in hypersonic boundary-layer flows focus, almost exclusively, on how roughness elements trip a hypersonic boundary layer to turbulence. However, there were a few reports in the literature suggesting that roughness elements in hypersonic boundary-layer flows could sometimes suppress the transition process and delay the formation of turbulent flow. These reports were not common and had not attracted much attention from the research community. Furthermore, the mechanisms of how the delay and stabilization happened were unknown. A recent study by Duan et al. showed that when 2-D roughness elements were placed downstream of the so-called synchronization point, the unstable second-mode wave in a hypersonic boundary layer was damped. Since the second-mode wave is typically the most dangerous and dominant unstable mode in a hypersonic boundary layer for sharp geometries at a zero angle of attack, this result has pointed to an explanation on how roughness elements delay transition in a hypersonic boundary layer. Such an understanding can potentially have significant practical applications for the development of passive flow control techniques to suppress hypersonic boundary-layer transition, for the purpose of aero-heating reduction. Nevertheless, the previous study was preliminary because only one particular flow condition with one fixed roughness parameter was considered. The study also lacked an examination on the mechanism of the damping effect of the second mode by roughness. Hence, the objective of the current research is to conduct an extensive investigation of the effects of 2-D roughness elements on the growth of instability waves in a hypersonic boundary layer. The goal is to provide a full physical picture of how and when 2-D roughness elements stabilize a hypersonic boundary layer. Rigorous parametric studies using numerical simulation, linear stability theory (LST), and parabolized stability equation (PSE) are performed to ensure the fidelity of the data and to study the relevant flow physics. All results unanimously confirm the conclusion that the relative location of the synchronization point with respect to the roughness element determines the roughness effect on the second mode. Namely, a roughness placed upstream of the synchronization point amplifies the unstable waves while placing a roughness downstream of the synchronization point damps the second-mode waves. The parametric study also shows that a tall roughness element within the local boundary-layer thickness results in a stronger damping effect, while the effect of the roughness width is relatively insignificant compared with the other roughness parameters. On the other hand, the fact that both LST and PSE successfully predict the damping effect only by analyzing the meanflow suggests the mechanism of the damping is by the meanflow alteration due to the existence of roughness elements, rather than new mode generation. In addition to studying the unstable waves, the drag force and heating with and without roughness have been investigated by comparing the numerical simulation data with experimental correlations. It is shown that the increase in drag force generated by the Mach wave around a roughness element in a hypersonic boundary layer is insignificant compared to the reduction of drag force by suppressing turbulent flow. The study also shows that, for a cold wall flow which is the case for practical flight applications, the Stanton number decreases as roughness elements smooth out the temperature gradient in the wall-normal direction. Based on the knowledge of roughness elements damping the second mode gained from the current study, a novel passive transition control method using judiciously placed roughness elements has been developed, and patented, during the course of this research. The main idea of the control method is that, with a given geometry and flow condition, it is possible to find the most unstable second-mode frequency that can lead to transition. And by doing a theoretical analysis such as LST, the synchronization location for the most unstable frequency can be found. Roughness elements are then strategically placed downstream of the synchronization point to damp out this dangerous second-mode wave, thus stabilizing the boundary layer and suppressing the transition process. This method is later experimentally validated in Purdue's Mach 6 quiet wind tunnel. Overall, this research has not only provided details of when and how 2-D roughness stabilizes a hypersonic boundary layer, it also has led to a successful application of numerical simulation data to the development of a new roughness-based transition delay method, which could potentially have significant contributions to the design of future generation hypersonic vehicles.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1964 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Monthly Catalog of United States Government Publications by :
Download or read book Monthly Catalog of United States Government Publications written by and published by . This book was released on 1959 with total page 1698 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Symposium on Naval Hydrodynamics by :
Download or read book Symposium on Naval Hydrodynamics written by and published by . This book was released on 1978 with total page 660 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Influence of Surface Roughness on Supersonic High Reynolds Number Turbulent Boundary Layer Flow by : Robert M. Latin
Download or read book The Influence of Surface Roughness on Supersonic High Reynolds Number Turbulent Boundary Layer Flow written by Robert M. Latin and published by . This book was released on 1998-03-01 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive study of rough-wall high speed (M=2.9) high Reynolds number (Re/m = 1.9. 10 to the 7th power) turbulent boundary layer flow was performed consisting of experimental, analytical, and numerical methods. Six wall topologies consisting of a smooth and five rough surfaces (two and three dimensional machined roughness plates; and 80, 36, and 20 grit sand-grain roughened plates) were studied. A confocal laser scan microscope was used to measure the topography of the sand grain roughnesses. The experimental measurement techniques included a convention Pitot pressure probe, laser Doppler velocimetry, hot wire anemometry; color schlieren and laser sheet Mie scattering images. Mean measurements included velocity, Mach number, density, and mass flux. Turbulent measurements included velocity and mass flux turbulence intensities, kinematic Reynolds shear stress, compressible Reynolds shear stress in two planes, and the traverse apparent mass flux. Kinematic turbulent flow statistical properties were found to scale by local mean quantities and displayed a weak dependence on surface roughness. Turbulent flow statistical properties with the explicit appearance of density did not scale by local mean quantities, and had a strong linear dependence on roughness. Surface roughness also had a significant effect on the flow structure size, angles, and energy spectra. A theoretical analysis was performed and a new integral method for the estimation of skin friction was developed. The skin friction estimates were within 4% of compressible semi-empirical relations. A numerical study was performed which used a parabolized Navier Stokes solver with two algebraic turbulence models and the Rotta model for surface roughness. A new method for the estimation of momentum loss improved the numerical flow predictability.
Book Synopsis Review of the Effect of Distributed Surface Roughness on Boundary-layer Transition by : A. L. Braslow
Download or read book Review of the Effect of Distributed Surface Roughness on Boundary-layer Transition written by A. L. Braslow and published by . This book was released on 1960 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: A discussion is presented on the transition phenomena associated with distributed roughness, a correlation of three-dimensional roughness effects at both subsonic and supersonic speeds, and the effect of laminar boundary-layer stability as influenced by heat transfer, pressure gradients, and boundary-layer control on the sensitivity of laminar flow to distributed roughness. Results indicate that the transition-triggering mechanism of three-dimensionaltype surface roughness appears to be the same at supersonic and subsonic speeds. In either case, a Reynolds number based on the height of the roughness and the local flow conditions at the top of the roughness can be used to predict with reasonable accuracy the height of threedimensional roughness required to cause premature transition. Neither the three-dimensional roughness Reynolds number nor the lateral spread of turbulence behind the roughness is changed to any important extent by increasing the laminar boundary-layer stability to theoretically small disturbances. Therefore, for a given stream Mach number and Reynolds number, surface cooling, boundary-layer suction, or a favorable pressure gradient will, in the presence of three-dimensional roughness, promote rather than delay transition. (Author).
Author :National Aeronautics and Space Administration (NASA) Publisher :Createspace Independent Publishing Platform ISBN 13 :9781723038815 Total Pages :104 pages Book Rating :4.0/5 (388 download)
Book Synopsis Effect of Sound on Boundary Layer Stability by : National Aeronautics and Space Administration (NASA)
Download or read book Effect of Sound on Boundary Layer Stability written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed. Saric, William S. and Spencer, Shelly Anne Unspecified Center ASYMPTOTIC SERIES; BOUNDARY LAYER STABILITY; BOUNDARY LAYERS; LEADING EDGES; MATHEMATICAL MODELS; NEAR FIELDS; SOUND WAVES; SURFACE ROUGHNESS; WIND TUNNEL TESTS; NORMAL DENSITY FUNCTIONS; PREDICTION ANALYSIS TECHNIQUES; VIBRATION...
