Download or read book Analysis and Control of Three dimensional Turbulent Wakes written by Mathieu Grandemange and published by . This book was released on 2013 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study of the turbulent wake past different geometries is performed by increasing the complexity from axisymmetric bodies to road vehicles. Whatever the geometry is, two kinds of coherent wake motions are likely to be observed. First, at timescales of the order of 5D/U, D and U being the characteristic size and velocity of the flow respectively, the wake may generate periodic oscillations. These coherent motions are usually associated with the interaction of two facing shear layers of opposite vorticity. As the corresponding frequencies rely at first order on the distance between the shear layers, two distinct frequencies are reported when the afterbody has a cross-flow aspect ratio different than 1. These unsteady global modes seem to weaken when the Reynolds number and the complexity of the geometry increase. The second type of coherent motions corresponds to the development of stationary cross-flow instabilities. They are linked to the symmetry breaking modes observed in laminar regimes and their domains of appearance are defined from geometry considerations in the cases of parallelepiped bodies in ground proximity. These instabilities are responsible for strong asymmetries in the instantaneous flow and may generate bistable dynamics with a characteristic time scale of the order of 1000D/U. The study of these phenomena, combined with sensitivity analyses to small perturbations, places the diminution of the cross-flow asymmetries of the instantaneous wake as a relevant strategy for drag reduction. In particular, it is found that both local and global pressure gradients on the sides of the body are source of streamwise vortices increasing the drag. Parabolic dependences between the drag and the cross-flow forces are reported suggesting similarities with the mechanisms of induced drag that are well-known in aeronautics. Consequently, as they often generate significant wake asymmetries, the development of the cross-flow instabilities is identified as a drag contributor. On the contrary, the part of the drag related to the periodic global modes seems to be negligible especially for complex geometries at high Reynolds number.
Download or read book Analysis of Three dimensional Turbulent Wakes by Momentum Integral Technique written by B. Lakshminarayana and published by . This book was released on 1987 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Three dimensional Turbulent Wake written by Yung-Huang Kuo and published by . This book was released on 1965 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Phase averaged Large scale Structures in Three dimensional Turbulent Wakes written by Jonathon Hugh Watmuff and published by . This book was released on 1979 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigation of a Three dimensional Wake written by G. Pailhas and published by . This book was released on 1989 with total page 51 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Spatial Instability of Compressible Wakes with Three dimensional Disturbances written by Y. Y. Chan and published by 1974.. This book was released on 1974 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: The linear spatial stability of a compressible thin turbulent wake bound by two side walls is analyzed by the stability theory of an inviscid shear flow. The disturbance propagating in the wake is assumed to be three-dimensional. For free stream Mach numbers up to 2 the analysis shows that in the high frequency region the most unstable mode of the wake is induced by two-dimensional disturbances. However, at the low frequency region the wake is more unstable to three-dimensional disturbances than to two-dimensional ones.
Download or read book Three dimensional Structure in Laminar and Turbulent Wakes written by Anil Prasad and published by . This book was released on 1996 with total page 584 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Calculation of Three Dimensional Turbulent Wake boundary Layer Mixing Flows written by M. Nasrullah and published by . This book was released on 1991 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Progress in Vehicle Aerodynamics and Thermal Management written by Jochen Wiedemann and published by Springer. This book was released on 2017-12-04 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: The books presents latest information about new car developments, new or improved testing techniques and new or improved calculation procedures. Presenters are from industry and academia.
Download or read book Two Dimensional Turbulent Wakes written by Canada. Defence Research Board. Reprints and published by . This book was released on 1966 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: The equations of mean motion indicate that two-dimensional turbulent wakes, when subjected to appropriately tailored adverse pressure gradients, can be self-preserving. An experimental examination of two nearly self-preserving wakes is reported. Mean velocity, longitudinal and lateral turbulence intensity, intermittency and shear stress distributions were measured and compared with Townsend's data from the small-deficit undistorted wake. In comparison with the undistorted case, the present wakes have slightly lower turbulent intensities and significantly lower shear stresses, all quantities being nondimensionalized by a local velocity scale taken as the maximum mean velocity deficit. A consideration of the reasons for the shear stress reduction leads to an expression from which the shear stresses in any symmetrical free equilibrium shear flow can be found. This relationship is used to calculate the rate of growth in the measured wakes, with reasonable success. (Author).
Download or read book Transition and Turbulence Control written by Mohamed Gad-el-Hak and published by World Scientific. This book was released on 2006 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains articles based on lectures given at the Workshop on Transition and Turbulence Control, hosted by the Institute for Mathematical Sciences, National University of Singapore, 8OCo10 December 2004. The lecturers included 13 of the worldOCOs foremost experts in the control of transitioning and turbulent flows. The chapters cover a wide range of subjects in the broad area of flow control, and will be useful to researchers working in this area in academia, government laboratories and industry. The coverage includes control theory, passive, active and reactive methods for controlling transitional and turbulent wall-bounded flows, noise suppression and mixing enhancement of supersonic turbulent jets, compliant coatings, modern flow diagnostic systems, and swept wing instabilities."
Download or read book On Three dimensional Swirling Wakes written by Martin H. Steiger and published by . This book was released on 1962 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: The velocity fields of three-dimensional viscous wakes with small swirl and streamwise pressure gradients are examined with the use of the boundary layer approximations, Ossen's linearization of the convective terms, and the assumption of constant fluid properties. Transform methods yield mathematically exact solutions with general types of initial conditions. The theory, while applicable to many practical problems (such as describing the phenomena in a tip vortex), is not applied here an its application is left for future investigation.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Particle Image Velocimetry written by Ronald J. Adrian and published by Cambridge University Press. This book was released on 2011 with total page 585 pages. Available in PDF, EPUB and Kindle. Book excerpt: Particle image velocimetry, or PIV, refers to a class of methods used in experimental fluid mechanics to determine instantaneous fields of the vector velocity by measuring the displacements of numerous fine particles that accurately follow the motion of the fluid. Although the concept of measuring particle displacements is simple in essence, the factors that need to be addressed to design and implement PIV systems that achieve reliable, accurate, and fast measurements and to interpret the results are surprisingly numerous. The aim of this book is to analyze and explain them comprehensively.
Download or read book Three dimensional Momentumless Wakes in Density stratified Liquids written by Philip Joseph Stockhausen and published by . This book was released on 1966 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments were performed to investigate the configuration and surface effects of the turbulent wake generated by a self-propelled body moving in a linearly density-stratified liquid. The experiments were performed in a 50-foot long tank filled to a depth of 2 1/2 ft. For all experiments, the Reynolds number, based on the diameter of the circular disc mounted on the model's bow, was 89,000. It was found that the mixed region generated by the turbulent wak5 rapidly attained a maximum vertical extent, and then collapsed vertically while continuing to expand laterally. The vertical collapse of the wake was accompanied by the convergence toward the model of the fluid at the free surface. The convergence did not occur with homogeneous liquids. It was concluded that this surface convergence is possible only if the turbulent wake extends to the free surface. A new method was developed for generating linear density profiles in large tanks. (Author).
Download or read book Three dimensional Effects in Viscous Wakes written by Martin H. Steiger and published by . This book was released on 1962 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: The velocity, energy and concentration fields of three-dimensional viscous wakes are examined with the boundary layer approximations and Oseens' linearization of the acceleration terms. Solutions are derived for both incompressible and compressible wakes, without and with axial pressure gradients. In the incompressible cases the governing equations are linear and transform methods yield exact solutions for general types of initial conditions. In the compressible case the energy equation admits a Crocco integral when the Prandtl and Lewis numbers are equal to unity, and a similar integral of the concentration equation is derived for Le/Pr=1 and Wi tends toward 0. However, due to the nonlinearities associated with compressible flows, solutions for the velocity components can only be achieved by approximate methods. Two methods are presented; the first involves an iteration scheme, while the second assumes that the density and viscosity are only a function of the axial coordinate. In both methods transform theory is used and solutions are presented for general types of initial conditions. As an illustration, it is demonstrated that the axial velocity distribution in isobaric wakes whose initial isovels (lines of constant velocity) are of elliptic shape decay to axial symmetry. (Author).
Download or read book Handbook of Wind Energy Aerodynamics written by Bernhard Stoevesandt and published by Springer Nature. This book was released on 2022-08-04 with total page 1495 pages. Available in PDF, EPUB and Kindle. Book excerpt: This handbook provides both a comprehensive overview and deep insights on the state-of-the-art methods used in wind turbine aerodynamics, as well as their advantages and limits. The focus of this work is specifically on wind turbines, where the aerodynamics are different from that of other fields due to the turbulent wind fields they face and the resultant differences in structural requirements. It gives a complete picture of research in the field, taking into account the different approaches which are applied. This book would be useful to professionals, academics, researchers and students working in the field.
