Download or read book Rough Wall Turbulent Boundary Layers written by and published by . This book was released on 2004 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this project is to improve our fundamental knowledge of turbulent flows over rough surfaces. Specifically, we hope to investigate the manner in which roughness affects the near-wall drag-producing turbulent structures, and to what extent surface roughness affects the outer part of rough-wall boundary layers. Ultimately we hope to use this knowledge to propose control strategies to reduce momentum loss in rough-wall boundary layers.

Download or read book Rough Wall Turbulent Boundary Layers written by Anthony Edward Perry and published by . This book was released on 1968 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: The paper describes a detailed experimental study of turbulent boundary layer development over rough walls in both zero and adverse pressure gradients. Skin friction was determined by pressure tapping the roughness elements and measuring their form drag. Two wall roughness geometries were chosen each giving a different law of behaviour. However, it has been found that results for both types of roughness correlate with a Reynolds number based on wall shear velocity and on the distance below the crests of the elements from which the logarithmic distribution of velocity is measured. One important implication of this is that a zero pressure gradient boundary layer with a cavity type rough wall conforms to Rotta's condition of precise self preserving flow. (Author).

Download or read book Mean Force Structure and Scaling of Rough wall Turbulent Boundary Layers written by Faraz Mehdi and published by . This book was released on 2012 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Thermal and Hydrodynamic Behavior of Thick Rough wall Turbulent Boundary Layers written by P. M. Ligrani and published by . This book was released on 1979 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thick, fully rough, and transitionally rough turbulent boundary layers were studied in order to investigate the differences between fully rough and transitionally rough behavior and to observe how downstream development affects these flows as the boundary layers become very thick. Measurements included Stanton numbers, skin friction coefficients, mean temperature and velocity profiles, Reynolds stress tensor component profiles, and spectra of the longitudinal velocity fluctuations. Predictions of wall heat transfer, wall shear, and mean profiles were made using a mixing-length and turbulent Prandtl number closure scheme which accounted for the effects of wall roughness in the boundary layer equations. The turbulent layers were artificially thickened using an array of solid obstacles which produced a two-dimensional equilibrium flow field with properties representative of natural bounday layers, at least up to the level of the turbulent correlations on a smooth wall, and to the level of the spectra of longitudinal velocity fluctuations on a rough wall. A rough-wall boundary layer environment was provided in which all measurements of lower order than the turbulence correlations could be discussed regarding the influence of roughness, and considered to have properties representative of natural behavior. (Author).

Download or read book Numerical Simulations of Rough wall Turbulent Boundary Layers written by and published by . This book was released on 2015 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: At sufficiently high Reynolds number, all surfaces are rough, and roughness affects most flows in engineering and the natural sciences. Examples range from atmospheric boundary layers over buildings and canopies, to engineering surfaces with erosion, deposits, etc. To study the roughness effects, we take a high-resolution approach to capture the flow around individual roughness elements using direct and large-eddy simulations (DNS and LES); the goal is to elucidate phenomena which have been difficult to access using physical experiments, and to help develop engineering correlations and models. First, most experiments and turbulence models are based on a standardized type of roughness, sand-grain roughness, which can be described using a single length scale. The relationship between the geometry of an arbitrary surface and the canonical one must be known, to predict critical flow parameters such as the drag, using either experimental correlations or turbulence models. Using numerical experiments, we relate this length-scale to the roughness geometry, and propose a guideline for its prediction in the industrial setting. Next, to explain the dependence of drag on the topographical details, we examine the role of the wake of the roughness elements in the drag generation of a rough surface. The wake field is found to promote vertical momentum transfer and near-wall instability; it might provide a link between geometry details and the engineering modeling of roughness effects. Lastly, we focus on a more realistic flow scenario -- the one with freestream accelerations -- and study the combined effects of roughness and acceleration, a phenomenon widely present in engineering flows over airfoils or complex landscapes. It is first shown, by comparing equilibrium accelerating flows obtained in the present study with the non-equilibrium flows in the literature, that the roughness and acceleration effects are interdependent and depend on the flow equilibrity. Then, using DNS data of a spatially developing flat-plate boundary layer, it is found that the effect coupling develops as the roughness affects the turbulence time scale and thus the flow susceptibility of the acceleration stabilization, while acceleration changes the wake velocity and ultimately the roughness destabilization level.

Download or read book A Study of Rough wall Turbulent Boundary layer Flows Including Effect of Stagnation Heating written by Peeush K. Bishnoi and published by . This book was released on 1985 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Inner outer Interactions in a Rough wall Turbulent Boundary Layer written by Gokul Pathikonda and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Vorticity and Drag Measurements in Rough wall Turbulent Boundary Layers written by Alan Baker Folz and published by . This book was released on 1993 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Turbulent Boundary Layer Rough Wall Pressure Spectrum written by M. S. Howe and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Viscous Fluid Flow written by Frank M. White and published by . This book was released on 1991 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt: Designed for higher level courses in viscous fluid flow, this text presents a comprehensive treatment of the subject. This revision retains the approach and organization for which the first edition has been highly regarded, while bringing the material completely up-to-date. It contains new information on the latest technological advances and includes many more applications, thoroughly updated problems and exercises.

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 An Experimental Study of Turbulent Boundary Layer on Rough Walls written by C. K. Liu and published by . This book was released on 1966 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental data are presented on flow structure, mean, and fluctuating velocities in turbulent boundary layers over a family of flat surfaces with transverse roughness elements made of square bars of variable spacing. All flows were incompressible and had zero streamwise pressure gradient. The flow structures are described for surfaces extending from hydraulically smooth to fully rough. A distinct flow pattern is observed in the wall region for each of four cases: smooth, skimming, wake-interference and isolated-roughness flow. Maximum roughness was observed with a ratio of gap to bar width of approximately 11. The most obvious effect of an increase in surface roughness is the distinct increase of turbulence production and the concomittant increase in the value of eddy viscosity. It is shown that this increase in eddy viscosity increases the total thickness of the layer in the same way that an increase in molecular viscosity would do in a laminar layer. The normalization of eddy viscosity for the outer portion of the layer as suggested by Clauser is found to apply to the rough surfaces studied. (Author).

Download or read book Open Channel Turbulent Boundary Layers and Wall Jets on Rough Surfaces written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: For many industrial and environmental flows, the momentum and convective heat transfer rates at the surface are determined by the turbulence structure in the near-wall region. Although many flows of practical interest occur on rough surfaces, our understanding and ability to predict rough wall turbulent flows lags far behind the corresponding technology for smooth surfaces. This provides reasonable grounds for additional refined rough wall measurements with the expectation of improving our physical understanding of practically relevant turbulent flows. This thesis reports an experimental investigation of wall roughness effects on the characteristics of turbulent boundary layers and wall jets. The measurements are obtained for smooth wall and three different roughness elements using a laser-Doppler anemometer. An insightful presentation of the results requires that the correct scaling laws must be used. In the case of the turbulent boundary layer, the appropriateness of the log law proposed by Millikan (1938) to model the overlap region of the mean flow and the power laws proposed by Barenblatt (1993) and George and Castillo (1997) is compared. The boundary layer results show that the theory proposed by George and Castillo (1997) has important advantages over the log law in modeling the mean velocity profiles as well as predicting the wall shear stress. The results also show that wall roughness increases the turbulence fluctuations and transport terms, which suggests that rough wall turbulence models must explicitly account for roughness effects in order to predict the mixing characteristics accurately. This promises to provide significant challenges to rough wall turbulence models. The wall jet results show that wall roughness increases the inner layer thickness but the jet half-width does not show any important sensitivity to surface roughness. The spread rates for the jet half-width are higher than the values obtained in earlier measurements. This may be attribute.

Download or read book On the Generation of Wall Pressure Fluctuations for Turbulent Boundary Layers Over Rough Walls written by Thomas E. Burton and published by . This book was released on 1971 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of pressure-velocity correlation in turbulent flow was extended to turbulent boundary layer flow over a roughened wall in the absence of a longitudinal pressure gradient. The results obtained are qualitatively similar to those previously measured over smooth walls. A theory is presented to partially explain the behavior of the measured correlations in both the smooth-wall and rough-wall cases.

Download or read book Turbulent Boundary Layers on a Systematically Varied Rough Wall written by and published by . This book was released on 2009 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of an experimental investigation of the flow over a model roughness are presented. The series of roughness consists of close-packed pyramids in which both the height and the slope were systematically varied. The aim of this work was to document the mean flow and subsequently gain insight into the physical roughness scales which contribute to drag. The mean velocity profiles for all nine rough surfaces collapse with smooth-wall results when presented in velocity-defect form, supporting the use of similarity methods. The results for the six steepest surfaces indicate that the roughness function U+ scales almost entirely on the roughness height with little dependence on the slope of the pyramids. However, DeltaU+ for the three surfaces with the smallest slope does not scale satisfactorily on the roughness height, indicating that these surfaces might not be thought of as surface "roughness" in a traditional sense but instead surface "waviness."

Download or read book Turbulent Boundary Layer Wall Pressure Statistics on Smooth and Rough Walls written by William K. Blake and published by . This book was released on 1969 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mach Number Effects on Rough Wall Turbulent Boundary Layers written by Morad Alvarez and published by . This book was released on 2017 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of surface roughness on compressible turbulent flow have not been studied as closely as the effects of surface roughness on incompressible flow. To date, our knowledge of fully-rough high-speed turbulent flows comes from experiments, large eddy simulations, or direct numerical simulations of rough-wall channel flows. This dissertation seeks to extend our understanding of rough-wall boundary layers by examining the effect of the freestream Mach number. A previously-verified fifth-order hybrid weighted essentially non-oscillatory scheme with geometries imposed by a third-order cut-stencil method was modified to handle turbulent inflow boundary conditions and spanwise periodicity. The turbulence capabilities of the code were then validated against published results of a Mach 2.5 smooth-wall turbulent boundary layer. Two direct numerical simulations of different freestream Mach numbers, 2.5 and 5.0, were conducted. The results show that scaling the root mean square (RMS) of velocity and vorticity fluctuations with the local density accounts for the difference in magnitude. Scaling the RMS of non-dimensionalized temperature fluctuations by the ratio of wall temperature and freestream temperature, provides reasonable collapse between both simulations. Similarly, scaling by the ratio of wall density and freestream density offers reasonable collapse for the RMS of density fluctuations. Both of these scalings offer good collapse regardless of the surface topology. The Favre-averaged Reynolds shear stresses exhibit increased magnitude in regions with local compression. Conversely the Favre-averaged Reynolds shear stresses decreased in regions with increased expansion. A similar trend was observed for the wall-normal Favre-averaged Reynolds stress, but is not as pronounced. The location of the expansion and compression waves from the edges of the roughness is directly affected by the local Mach angle. For the \mf case, the Mach angles varied much more resulting in regions of decreased dilatation. The freestream Mach number plays an indirect role in setting the shift in the log-layer. The compressible results from both Mach numbers do not compare well to incompressible results. This could be due to the different topologies.