Statistical approach to wall turbulence tardu sedat
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Sedat Tardu is Associate Professor at Grenoble University in France where he teaches turbulent shear flows, heat transfer, fluid dynamics, and chaos. Isotropic homogeneous turbulence 20 1. Support for axisymmetry is demonstrated by anisotropy invariant maps of the dissipation and vorticity tensors. The structure of the wall turbulence is intimately related to the coherent structures that play a fundamental role in the transport process. In the log region, roughly one-half of the large scale motions sampled had zone-averaged streamwise velocity defects. In this paper, selected findings of a detailed experimental investigation are reported concerning the effects of forced free-stream unsteadiness on a turbulent boundary layer.

A new type of hot wire anemometer was developed by using surface micro machining techniques. Inner and Outer Scales: Spectral Behavior 105 3. The higher of these frequencies was of the order of the turbulent bursting frequency in the flow, and the other can be regarded as an intermediate frequency at which the flow still departed significantly from quasi-steady behaviour. The time mean flow is insensitive to the forcing. The specific thrust of the theoretical studies has been focussed on three areas: how two and three dimensional vortex structures interact with wall boundary layers, the development of a new type of prediction method for two dimensional turbulent boundary-layer flows, and improvement in numerical techniques for solving parabolic, boundary-layer equations.

General characteristics of vorticity 259 5. The von Karman constant and the renormalization group 140 4. Basic theoretical research and laboratory experiments alone are incomplete without a feedback from field observations and measurements. Ensemble averages of the Reynolds stress show that the large structure accounts for very large contributions to the Reynolds stress. The E-mail message field is required. Several books exist on fluid turbulence, but Statistical Approach to Wall Turbulence is original in the sense that it focuses solely on the turbulent flows bounded by solid boundaries. Reynolds Number-Based Effects 137 4.

Large variations of the spread in the fully turbulent region are also observed. Eddy viscosity closures 56 2. The forced unsteadiness was sinusoidal and was superimposed locally on an otherwise-steady mainstream, beyond a turbulent boundary layer which had developed under constant-pressure conditions. This best-selling handbook is now more convenient than ever, and its coverage is unparalleled. Flow visualization studies of the zero-pressure-gradient turbulent boundary layer over the Reynolds-number range 500 to 17,500 have shown large Reynolds-number effects on boundary-layer structure. In particular, the bursting frequency varies with an amplitude of 56 percent during the cycle and in phase with the turbulent intensity even if the detection threshold is modulated with this intensity. It is shown that for large scale motions the path of the maximum space-time correlation will, in general, deviate from the local mean streamline because of the distorting effect of the mean shear on the turbulent vorticity field.

Instead, it is quite accurately described by a local length scale that models the momentary value of the total shear distortion of large eddies of the flow. The modulation characteristics of the convection velocity coincide reasonably well with those of the local velocity showing that the Taylor hypothesis may still be used in unsteady flows. Fine structure 249 Chapter 5. While a few similar experiments have been reported in the recent literature, the present study stands out from the others in respect of the flow regimes investigated, the magnitude of flow modulation, the detailed nature of the measurements and most importantly the identification of a relevant parameter to characterize unsteady shear flows. Apart from geoscientists it is also of special interest to people involved in fluid mechanics who want to understand near wall turbulence and the effects of coherent structures on the mechanisms of sediment transport.

Extensions of spanwise forcing 131 4. Description Wall turbulence is encountered in many technological applications as well as in the atmosphere, and a detailed understanding leading to its management would have considerable beneficial consequences in many areas. Alteration of the inner structure by outer layer devices 67 3. This decay of the turbulence response is faster for the wall shear stress. The modulation of the ejection frequency depends strongly upon the imposed frequency and it is not related in a simple manner to the modulation of the inner nor the outer time scales.

The modulation of ejections and bursts in the near-wall region in pulsatile channel flow is inves. The von Karman constant and the renormalization group 140 4. A lot of inspired work by experimenters,theoreticians, engineers and mathematicians has been accomplishedover recent decades on this important topic and StatisticalApproach to Wall Turbulence provides an updated and integrated viewon the progress made in this area. This indicates that only part of the regeneration mechanism of the near wall coherent structures is driven by the inner layer. It is shown that none of these phenomena occur in the jet generated from laminar tube flow. A model relating Eulerian spatial and temporal autocorrelations is also used for this purpose.

New experimental data on the wall and Reynolds shear stresses are reported. The data obtained include turbulent intensities, Reynolds shear stress, energy spectra and autocorrelations. The field has changed so much that this Second Edition is now available in three volumes. Exact equations for fully developed channel flow 61 2. This book provides an up-to-date overview on the progress made in this specific area in recent years. Calculations are presented to show that this effect can account for the shapes of the curves of maximum correlation in a boundary layer as reported by Favre some years ago.

Effect of the riblets on the fine structure of wall turbulence 76 3. The comprehension of their regeneration mechanism is indispensable for the development of efficient strategies in terms of drag control and near wall turbulence management. General characteristics of vorticity 259 5. Townsend s attached eddies 185 4. Estimating the importance of non-linearity close to the wall 284 5. This proceedings are a good source for those interested in the state of the art. Optimal active control 143 4.

Measurements are presented of the time variation of the wall shear stress caused by the imposition of a sinusoidal oscillation on a turbulent pipe flow. It is shown that the latter develop when Re exceeds a critical value and become stronger with increasing Re. Estimating the importance of non-linearity close to the wall 284 5. The wall shear stress was measured while the Reynolds number, amplitude and frequency were varied systematically. Preface vii Notations ix Chapter 1. Active and passive Townsend eddies 239 4. These magnitudes are not consistent with the assumption of local isotropy except perhaps near the duct center-line.