Download or read book Effects of Small Isolated Roughness Elements on Turbulent Boundary Layers written by H. H. M. Nigim and published by . This book was released on 1981 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Height and Density of Roughness Elements on Turbulent Boundary Layers written by G.-K. Kerevanian and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Flexible Roughness Elements on Diffusion in a Turbulent Boundary Layer written by Ali Akhtar Quraishi and published by . This book was released on 1963 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Spacing and Geometry of Distributed Roughness Elements on a Two Dimensional Turbulent Boundary Layer written by and published by . This book was released on 2005 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is a study of the effects of distributed roughness elements on a two-dimensional turbulent boundary layer. Measurements were taken on a total of ten rough wall configurations: four involving Gaussian spikes, and six with circular cylindrical posts. Rough wall flows are particularly suited to study with Laser Doppler Velocimetry (LDV) due to the fact that measurements are required near a solid surface, as well has in highly turbulent fluid. The LDV system used in this study is a fine resolution (50pm), three-component, fiber-optic system. All mean velocities, Reynolds stresses, and triple products are measured. This study is unique in the range and variety of roughness cases for which data was taken. The data show that flow over a rough wall is characterized by high levels of turbulence near the roughness element peaks at the interface between low-speed, near-wall fluid and the higher speed fluid above. Behind an element, high-momentum fluid sweeps toward the wall, and there is a small region of ejection of low-momentum fluid. Cylindrical elements typically have larger magnitudes of turbulent stresses at their peaks compared to Gaussian elements. Trends in mean velocity profile parameters such as displacement height, roughness effect, and wake parameter are examined with respect to roughness element geometry and spacing.
Download or read book Boundary Layer and Flow Control written by G. V. Lachmann and published by Elsevier. This book was released on 2014-05-12 with total page 768 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boundary Layer and Flow Control: Its Principles and Application, Volume 2 focuses on the layer of fluid in the immediate area of a bounding surface where the effects of viscosity are substantial. This book is organized into two main topics—boundary layer control for low drag, and shock-induced separation and its prevention by design and boundary layer control. It specifically discusses the nature of transition, effect of two-dimensional and isolated roughness on laminar flow, and progress in the design of low drag aerofoils. The onset of separation effects for aerofoils and wings, shock-induced separation for laminar boundary layers, and shock-induced separation for laminar boundary layers are also deliberated. This volume is recommended to physicists and specialists interested in boundary layer and flow control.
Download or read book The Effect of the Gap Size Between Roughness Elements on a Turbulent Boundary Layer written by David Scott Barber and published by . This book was released on 1979 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Study of Turbulent Boundary Layers Over Rough Surfaces with Emphasis on the Effects of Roughness Character and Mach Number written by M. L. Finson and published by . This book was released on 1982 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Reynolds stress model for turbulent boundary layers on rough walls is used to investigate the effects of roughness character and compressibility. The flow around roughness elements is treated as form drag. A method is presented for deriving the required roughness shape and spacing from profilometer surface measurements. Calculations based on the model compare satisfactorily with low speed data on roughness character and hypersonic measurements with grit roughness. The computer model is exercised systematically over a wide range of parameters to derive a practical scaling law for the equivalent roughness. In contrast to previous correlations, for most roughness element shapes the effective roughness is not predicted to show a pronounced maximum as the element spacing decreases. The effect of roughness tends to be reduced with increasing edge mach number, primarily due to decreasing density in the vicinity of the roughness elements. It is further shown that the required roughness Reynolds number for fully rough behavior increases with increasing Mach number, explaining the small roughness effects observed in some hypersonic tests. (Author).
Download or read book Effects of Various Shaped Roughness Elements in Two dimensional High Reynolds Number Turbulent Boundary Layers written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Modeling the effects of surface roughness is an area of concern in many practical engineering applications. Many current roughness models to this point have involved the use of empirical 'constants' and equivalent sand grain roughness. These underdeveloped concepts have little direct relationship to realistic roughness and cannot predict accurately and consistently the flow characteristics for different roughness shapes. In order to aid in the development of turbulence models, the present research is centered around the experimental investigation of seven various shaped single roughness elements and their effects on turbulence quantities in a two-dimensional turbulent boundary layer. The elements under scrutiny are as follows: cone, cone with spatial variations equal to the smallest sublayer structure length scale, cone with spatial variations equal to 2.5 times the smallest sublayer structure length scale, Gaussian-shaped element, hemisphere, cube aligned perpendicular to the flow (cube at 90)̊, and a cube rotated 45 ̊relative to the flow. The roughness element heights, k+, non-dimensionalized by the friction velocity (Utau) of the approaching turbulent boundary layer, are 145, 145, 145, 145, 80, 98, and 98 respectively. Analysis of a three-dimensional fetch of the same Gaussian-shaped elements described previously was also undertaken. In order to analyze the complex flow fields, detailed measurements were obtained using a fine-measurement-volume (50 micron diameter) three-velocity component laser-Doppler velocimetry (LDV) system.
Download or read book Generalized Roughness Effects on Turbulent Boundary Layer Heat Transfer A Discrete Element Predictive Approach for Turbulent Flow Over Rough Surfaces written by H. W. Coleman and published by . This book was released on 1983 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: A discrete element model for turbulent flow over rough surfaces has been rigorously derived from basic principles. This model includes surface roughness effects as a constituent part of the partial differential equations which describe momentum and energy transport in turbulent flows. The model includes the necessary empirical information on the interaction between the roughness elements and the flow around and between the elements in a general way which does not require experimental data on each specific surface. This empirical information is input via algebraic models for the local element drag coefficient and Nusselt number. These models have been calibrated by comparison with base data sets from surfaces with three-dimensional (distributed) roughness elements. Calculations using the present discrete element model are compared with experimental data from 118 separate experimental runs. The results of these comparisons range from good to excellent. The calculations are shown to compare equally well with both transitionally rough turbulent flow and fully rough turbulent flow without modification of the roughness model. In the course of the present work it was discovered that the definitive data set of Schlichting is flawed. Corrected values are presented for this data set.
Download or read book Some Effects of Sparsely Distributed Three dimensional Roughness Elements on Two dimensional Turbulent Boundary Layers written by Jacob George 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 Effects of Roughness on Turbulent Boundary Layers written by Steven Wayne Raggard and published by . This book was released on 1980 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Boundary Layers on Rough Walls written by A. F. Mills and published by . This book was released on 1976 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: The influence of wall roughness on the alteration of the characteristics of the turbulent boundary layer to produce increased heat transfer and skin friction during re-entry is examined. Attention is restricted to roughness heights which are small compared with the boundary layer thickness. It is shown that rough wall transfer rates can be calculated almost as reliably as for smooth walls provided that the geometry of the roughness is known. In this regard it is pointed out that models of roughness effects for use in finite-difference boundary layer calculation procedures should be in the form of drag coefficients and sub-layer Stanton numbers to be applied as 'slip' values at a characteristic roughness height; use of mixing length models of turbulent transport with nonzero wall values is shown to have serious shortcomings. The effect of heat conduction through roughness elements is demonstrated and the implications with respect to the validity of existing sub-layer Stanton number correlations are discussed. A thorough review of the pertinent literature is included with the view towards making this report a self contained treatment of the subject.
Download or read book Structure of 2 D and 3 D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The present study deals with the effects of sparsely distributed three-dimensional elements on two-dimensional (2-D) and three-dimensional (3-D) turbulent boundary layers (TBL) such as those that occur on submarines, ship hulls, etc. This study was achieved in three parts: Part 1 dealt with the cylinders when placed individually in the turbulent boundary layers, thereby considering the effect of a single perturbation on the TBL; Part 2 considered the effects when the same individual elements were placed in a sparse and regular distribution, thus studying the response of the flow to a sequence of perturbations; and in Part 3, the distributions were subjected to 3-D turbulent boundary layers, thus examining the effects of streamwise and spanwise pressure gradients on the same perturbed flows as considered in Part 2. The 3-D turbulent boundary layers were generated by an idealized wing-body junction flow. Detailed 3-velocity-component Laser-Doppler Velocimetry (LDV) and other measurements were carried out to understand and describe the rough-wall flow structure. The measurements include mean velocities, turbulence quantities (Reynolds stresses and triple products), skin friction, surface pressure and oil flow visualizations in 2-D and 3-D rough-wall flows for Reynolds numbers, based on momentum thickness, greater than 7000. Very uniform circular cylindrical roughness elements of 0.38mm, 0.76mm and 1.52mm height (k) were used in square and diagonal patterns, yielding six different roughness geometries of rough-wall surface. For the 2-D rough-wall flows, the roughness Reynolds numbers, based on the element height (k) and the friction velocity, range from 26 to 131. Results for the 2-D rough-wall flows reveal that the velocity-defect law is similar for both smooth and rough surfaces, and the semi-logarithmic velocity-distribution curve is shifted by an amount depending on the height of the roughness element, showing that this amount is a function of roughness Reynolds number and the wall geometry.
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 An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds written by Felix W. Fenter and published by . This book was released on 1953 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: A theory is described which can be used to predict accurately the skin friction drag of surfaces with uniform grain-type roughness. The roughness does not necessarily have to extend to the leading edge of the surface for an accurate calculation to be made. Uniform surface roughness composed of spherical beads does not affect the boundary layer in a manner significantly different from grain-type roughness, provided that the grains and the spheres are bonded to the surface in a similar manner. Consequently, the theory accurately predicts the effects of spherical roughness elements on skin friction under these conditions. The effect of a given type of roughness on turbulent boundary layer characteristics is strongly dependent upon the density of distribution of the roughness elements. The effect of maximum density V-grooves on turbulent boundary layer characteristics is dependent upon the sweepback angle. The effect of increasing sweepback is to reduce the skin friction drag. (Author).
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.
Download or read book Turbulent Boundary Layers written by Helmut E. Weber and published by . This book was released on 1979 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt:
