1,721,357 research outputs found
Fractal-Generated Turbulent Scaling Laws from a New Scaling Group of the Multi-Point Correlation Equation
No full textInvestigating the multi-point correlation (MPC) equations for the velocity and pressure fluctuations in the limit of homogeneous turbulence a new scaling symmetry has been discovered. Interesting enought this property is not shared with the Euler or Navier-Stokes equations from which the MPC equations have orginally emerged. This was first observed for parallel wall-bounded shear flows (see [2]) though there this property only holds true for the two-point equation. Hence, in a strict sense there it is broken for higher order correlation equations. Presently using this extended set of symmetry groups a much wider class of invariant solutions or turbulent scaling laws is derived for homogeneous and homogeneous-isotropic turbulence which is in stark contrast to the classical power law decay arising from Birkhoff’s or Loitsiansky’s integrals. In particular, we show that the experimentally observed specific scaling properties of fractal-generated turbulence (see [1, 4]) fall into this new class of solutions. Due to this specific grid a breaking of the classical scaling symmetries due to a wide range of scales acting on the flow is accomplished. This in particular leads to a constant integral and Taylor length scale downstream of the fractal grid and the exponential decay of the turbulent kinetic energy along the same axis. These particular properties can only be conceived from MPC equations using the new scaling symmetry. The latter new scaling law may have been the first clear indication towards the existence of the extended statistical scaling group. Though the latter is not obvious from the instantaneous Euler or Navier-Stokes equations it is directly implied
Modeling of the pressure-strain and diffusion-term in rotatiang flows
No full textWe reconsider the problem of shear free turbulent diffusion in a rotating frame, rotating about x1. Therefore turbulence is generated at a vibrating grid in the x2 − x3 plane and diffuses away from the grid in x1-direction. The flow
geometry is given in figure 1. An important property of this flow is that there is no mean flow-velocity. With the help of Lie-group methods Reynoldsstress transport models can be analyzed for this kind of flow in a rotating
frame. From the analysis it can be found that the turbulent diffusion only influences a finite domain. Insertion of this solution in the model equations shows that even fully nonlinear Reynolds-stress transport models (nonlinear in
the Reynolds-stresses for the pressure-strain model) are insensitive to rotation for this type of flow. To improve this serious shortcoming of these models, a new model equation which is fully nonlinear in the mean-velocity gradient
is needed. There appears to be one one-point model which may account for system rotation for this type of flow. It is the second-moment closure model by Sj¨ogren and Johansson [3] which is nonlinear in the mean-velocity gradient.
Therefore new model equations for the pressure-strain-correlation and the diffusion term have been developed along the lines of this model
Symmetry theory and turbulent jet scaling laws of a spatially evolving turbulent round jet
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Turbulence and Uncertainty for Future Renewable Energy Reliability
No full textCurrent climate change concerns accelerate interest in developing reliable renewable energy sources. Two of the most significant, in the wind and sea, are subject to turbulence, where its mathematics are at the forefront and the topic of this Conference.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Wind Energ
6th iTi Conference
No full textThis volume collects the edited and reviewed contributions presented in the 6th iTi Conference in Bertinoro, covering fundamental and applied aspects in turbulence. In the spirit of the iTi conference, the volume has been produced after the conference so that the authors had the possibility to incorporate comments and discussions raised during the meeting. In the present book the contributions have been structured according to the topics : I Theory II Wall bounded flows III Particles in flows IV Free flows V Complex flows The volume is dedicated to the memory of Prof. Konrad Bajer who prematurely passed away in Warsaw on August 29, 2014.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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