Mean Force Structure and Scaling of Rough-wall Turbulent Boundary Layers PDF Download

Author: Faraz Mehdi
Publisher:
ISBN:
Category :
Languages : en
Pages : 260

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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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.

Author: William K. Blake
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 105

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Turbulent boundary layer wall pressure measurements were made with 'pinhole' microphones three times smaller (relative to boundary layer thickness) than microphones used in earlier work. The improved high frequency resolution permitted examination of the influence of high frequency eddies on smooth wall pressure statistics. It was found that the space-time decay rate is considerably higher than previously reported. Measurements of cross-spectral density made with 5 Hz band width filters disclosed low phase speeds at low frequency and small separation. Measurements were repeated on rough walls and parallels were drawn from knowledge of a smooth wall boundary layer structure to propose a structure for a rough wall boundary layer. The effect of independently varying roughness height and separation on the large and small scale turbulence structure was deduced from the measurements. It was found that roughness separation affected the very large scale structure, whereas the roughness height influenced the medium and very small scale turbulence. (Author).

Author: A. A. R. Townsend
Publisher: Cambridge University Press
ISBN: 9780521298193
Category : Mathematics
Languages : en
Pages : 450

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Develops a physical theory from the mass of experimental results, with revisions to reflect advances of recent years.

Author: Hermann Schlichting (Deceased)
Publisher: Springer
ISBN: 366252919X
Category : Technology & Engineering
Languages : en
Pages : 814

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This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject.

Author: R. Goldstein
Publisher: Routledge
ISBN: 1351447823
Category : Technology & Engineering
Languages : en
Pages : 740

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This revised edition provides updated fluid mechanics measurement techniques as well as a comprehensive review of flow properties required for research, development, and application. Fluid-mechanics measurements in wind tunnel studies, aeroacoustics, and turbulent mixing layers, the theory of fluid mechanics, the application of the laws of fluid mechanics to measurement techniques, techniques of thermal anemometry, laser velocimetry, volume flow measurement techniques, and fluid mechanics measurement in non-Newtonian fluids, and various other techniques are discussed.

Author: C. K. Liu
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 171

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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).

Author: Bruno Eckhardt
Publisher: Springer
ISBN: 9783662519325
Category : Science
Languages : en
Pages : 0

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Lagrangian aspects.- Lagrangian modeling and properties of particles with inertia.- Effect of Faxén forces on acceleration statistics of material particles in turbulent flow.- Lagrangian analysis of turbulent convection.- Linear and angular dynamics of an inertial particle in turbulence.- Collision rate between heavy particles in a model turbulent flow.- From cloud condensation nuclei to cloud droplets: a turbulent model.- Lagrangian statistics of inertial particles in turbulent flow.- Lagrangian statistics of two–dimensional turbulence in a square container.- Measurement of Lagrangian Particle Trajectories by Digital in-line Holography.- 3-D Particle Tracking Velocimetry (PTV) in gas flows using coloured tracer particles.- Two-particle dispersion in 2D inverse cascade turbulence and its telegraph equation model.- Numerical simulations of particle dispersion in stratified flows.- Instability and Transition.- Experimental study of the von Kármán flow from = 10 to 10: spontaneous symmetry breaking and turbulent bifurcations.- Flow reversals in a vertical channel.- Linear Instability of Streamwise Corner Flow.- DNS of turbulent plane Couette flow with emphasis on turbulent stripe.- Geometry of state space in plane Couette flow.- Linear and nonlinear instabilities of sliding Couette flow.- Localization in plane Couette edge dynamics.- Nonlinear optimal perturbations in plane Couette flow.- Order parameter in laminar-turbulent patterns.- Pattern formation in low Reynolds number plane Couette flow.- Quasi-stationary and chaotic convection in low rotating spherical shells.- Linear stability of 2D rough channels.- Transient turbulent bursting in enclosed flows.- On New Localized Vortex Solutions in the Couette-Ekman Layer.- Shear instabilities in Taylor-Couette flow.- Particle Tracking Velocimetry in Transitional Plane Couette Flow.- Experimental study of coherent structures in turbulent pipe flow.- Forced localized turbulence in pipe flows.- From localized to expanding turbulence.- Influence of test-rigs on the laminar-to-turbulent transition of pipe flows.- Interaction of turbulent spots in pipe flow.- Large-scale transitional dynamics in pipe flow.- Nonlinear coherent structures in a square duct.- Quantitative measurement of the life time of turbulence in pipe flow.- Experimental investigation of turbulent patch evolution in spatially steady boundary layers.- Interaction of noise disturbances and streamwise streaks.- Linear generation of multiple time scales by 3D unstable perturbations.- Convection at very high Rayleigh number: signature of transition from a micro-thermometer inside the flow.- Estimating local instabilities for irregular flows in the differentially heated rotating annulus.- Search for the “ultimate state” in turbulent Rayleigh-Bénard convection.- Rayleigh–Taylor instability in two dimensions and phase-field method.- Split energy cascade in quasi-2D turbulence.- Stabililty and laminarisation of turbulent rotating channel flow.- The vortical flow pattern exhibited by the channel flow on a rotating system just past transition under the influence of the Coriolis force.- Transient evolution and high stratification scaling in horizontal mixing layers.- Control of turbulent flows.- Toward cost-effective Control of Wall Turbulence for Skin Friction Drag Reduction.- Active control of turbulent boundary layer using an array of piezo-ceramic actuators.- Flat plate turbulent boundary-layer control using vertical LEBUs.- Estimation of the spanwise wall shear stress based on upstream information for wall turbulence control.- Interactions between vortex generators and a flat plate boundary layer. Application to the control of separated flows..- Modulated global mode of a controlled wake.- Swirl effects in turbulent pipe flow.- Control of an axisymmetric turbulent wake by a pulsed jet.- Direct Numerical Simulations of turbulent mixed convection in enclosures with heated obstacles.-

Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 252

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 302

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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.