Tensor geometry in the turbulent cascade

2017 ◽  
Vol 835 ◽  
pp. 1048-1064 ◽  
Author(s):  
Joseph G. Ballouz ◽  
Nicholas T. Ouellette
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Energy Cascade ◽  
Three Dimensions ◽  
Inner Product ◽  
Transfer Energy ◽  
Average Value ◽  
Energy Cascades ◽  
Using Data ◽  
Highly Turbulent Flows

The defining characteristic of highly turbulent flows is the net directed transport of energy from the injection scales to the dissipation scales. This cascade is typically described in Fourier space, obscuring its connection to the mechanics of the flow. Here, we recast the energy cascade in mechanical terms, noting that for some scales to transfer energy to others, they must do mechanical work on them. This work can be expressed as the inner product of a turbulent stress and a rate of strain. But, as with all inner products, the relative alignment of these two tensors matters, and determines how strong the energy transfer will be. We show that this tensor alignment behaves very differently in two and three dimensions; in particular, the tensor eigenvalues affect the inner product in very different ways. By comparing the observed energy flux to the maximum possible if the tensors were in perfect alignment, we define an efficiency for the energy cascade. Using data from a direct numerical simulation of isotropic turbulence, we show that this efficiency is perhaps surprisingly low, with an average value of approximately 25 % in the inertial range, although it is spatially heterogeneous. Our results have implications for how the stress and strain-rate magnitudes influence the flux of energy between scales, and may help to explain why the energy cascades in two and three dimensions are different.

Effect of Selective Modification of Turbulence on Two-Equation Models for Particle-Laden Turbulent Flows

1994 ◽  
Vol 116 (4) ◽  
pp. 778-784 ◽  
Author(s):  
K. D. Squires ◽  
J. K. Eaton
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Large Mass ◽  
Momentum Exchange ◽  
Two Phase ◽  
Heavy Particles ◽  
Turbulent Vortex ◽  
Simulation Results ◽  
Grid Points ◽  
Using Data

The effect of selective modification of turbulence by particles on K–ε models for dilute two-phase flows has been evaluated using data from direct numerical simulation of particle-laden isotropic turbulence. Simulation results were obtained using as many as 643 grid points and up to 106 particles. The ratio of the particle time constant to large-eddy turbulence time scale varied from 0.14 to 1.50 and particle mass loadings of 0.0, 0.1, 0.5, and 1.0 were used in the simulations. Simulation results demonstrate that the balance between enstrophy production by turbulent vortex stretching and viscous destruction is disrupted by momentum exchange with the particle cloud. Selective modification of the turbulence by lighter particles results in a significant attenuation of enstrophy production by turbulent vortex stretching. The decrease in enstrophy production causes the model constant Cε2 to increase for large mass loading. Heavy particles are found to act as a sink of enstrophy for all mass loadings used in the simulations. Preferential concentration of lighter particles by turbulence, however, can generate vorticity fluctuations, especially at higher mass loadings. For these cases conventional modeling of the destruction of dissipation by particles term in the ε equation requires that Cε3 be negative.

scholarly journals Beyond Kolmogorov cascades

2019 ◽  
Vol 867 ◽  
Author(s):  
Bérengère Dubrulle
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Scale Space ◽  
Energy Cascade ◽  
Cloud Formation ◽  
Small Scale ◽  
Weak Formulation ◽  
Anisotropic Flow ◽  
Energy Cascades ◽  
Homogeneity Hypothesis

The large-scale structure of many turbulent flows encountered in practical situations such as aeronautics, industry, meteorology is nowadays successfully computed using the Kolmogorov–Kármán–Howarth energy cascade picture. This theory appears increasingly inaccurate when going down the energy cascade that terminates through intermittent spots of energy dissipation, at variance with the assumed homogeneity. This is problematic for the modelling of all processes that depend on small scales of turbulence, such as combustion instabilities or droplet atomization in industrial burners or cloud formation. This paper explores a paradigm shift where the homogeneity hypothesis is replaced by the assumption that turbulence contains singularities, as suggested by Onsager. This paradigm leads to a weak formulation of the Kolmogorov–Kármán–Howarth–Monin equation (WKHE) that allows taking into account explicitly the presence of singularities and their impact on the energy transfer and dissipation. It provides a local in scale, space and time description of energy transfers and dissipation, valid for any inhomogeneous, anisotropic flow, under any type of boundary conditions. The goal of this article is to discuss WKHE as a tool to get a new description of energy cascades and dissipation that goes beyond Kolmogorov and allows the description of small-scale intermittency. It puts the problem of intermittency and dissipation in turbulence into a modern framework, compatible with recent mathematical advances on the proof of Onsager’s conjecture.

Lattice Boltzmann for Turbulence Modeling

2018 ◽  
Author(s):  
Sauro Succi
Keyword(s):  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Turbulence Modeling ◽  
Real Life ◽  
Practical Interest ◽  
Reynolds Numbers ◽  
Full Resolution ◽  
To Come ◽  
Highly Turbulent Flows ◽  
Main Ideas

This chapter introduces the main ideas behind the application of LBE methods to the problem of turbulence modeling, namely the simulation of flows which contain scales of motion too small to be resolved on present-day and foreseeable future computers. Many real-life flows of practical interest exhibit Reynolds numbers far too high to be directly simulated in full resolution on present-day computers and arguably for many years to come. This raises the challenge of predicting the behavior of highly turbulent flows without directly simulating all scales of motion which take part to turbulence dynamics, but only those that fall within the computer resolution at hand.

Small-scale energy cascade in homogeneous isotropic turbulence

2019 ◽  
Vol 4 (10) ◽  
Author(s):  
Mohamad Ibrahim Cheikh ◽  
James Chen ◽  
Mingjun Wei
Keyword(s):  
Isotropic Turbulence ◽  
Energy Cascade ◽  
Small Scale ◽  
Homogeneous Isotropic Turbulence

scholarly journals On the different contributions of coherent structures to the spectra of a turbulent round jet and a turbulent boundary layer

2001 ◽  
Vol 448 ◽  
pp. 367-385 ◽  
Author(s):  
T. B. NICKELS ◽  
IVAN MARUSIC
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Isotropic Turbulence ◽  
Structural Models ◽  
Spectral Measurements ◽  
Round Jet ◽  
Good Account ◽  
Single Size

This paper examines and compares spectral measurements from a turbulent round jet and a turbulent boundary layer. The conjecture that is examined is that both flows consist of coherent structures immersed in a background of isotropic turbulence. In the case of the jet, a single size of coherent structure is considered, whereas in the boundary layer there are a range of sizes of geometrically similar structures. The conjecture is examined by comparing experimental measurements of spectra for the two flows with the spectra calculated using models based on simple vortex structures. The universality of the small scales is considered by comparing high-wavenumber experimental spectra. It is shown that these simple structural models give a good account of the turbulent flows.

The Effects of Turbulence Length Scale on the Performance of Piezoelectric Harvesters

2015 ◽  
Author(s):  
Yiannis Andreopoulos ◽  
Amir H. Danesh-Yazdi ◽  
Oleg Goushcha ◽  
Niell Elvin
Keyword(s):  
Turbulent Flows ◽  
Power Output ◽  
Isotropic Turbulence ◽  
Spatial Scales ◽  
Mechanical Energy ◽  
Relative Size ◽  
Analytical Description ◽  
Length Scale ◽  
Linear Effect ◽  
Turbulence Length

Turbulent flows carry mechanical energy distributed over a range of temporal and spatial scales and their interaction with a thin immersed piezoelectric beam results in a strain field which generates electrical charge. This energy harvesting method can be used for developing self-powered electronic devices such as flow sensors. In the present experimental work, various energy harvesters were placed in a turbulent boundary layer or inside a decaying flow field of homogeneous and isotropic turbulence. The role of large instantaneous turbulent structures in this rather complex fluid-structure interaction is discussed in interpreting the electrical output results. The forces acting on the vibrating beams have been measured dynamically and a theory has been developed which incorporates the effects of mean local velocity, turbulence intensity, the relative size of the beam’s length to the integral length scale of turbulence, the structural properties of the beam and the electrical properties of the active piezoelectric layer to provide reasonable estimates of the mean electrical power output. Experiments have been carried out in which these fluidic harvesters are immersed first in inhomogeneous turbulence like that encountered in boundary layers developing over solid walls and homogeneous and isotopic turbulence for which a simplified analytical description exists. It was found that there is a non-linear effect of turbulence length scales on the power output of the fluidic harvesters.

scholarly journals PENERAPAN MODEL PEMBELAJARAN KOOPERATIF JIGSAW UNTUK MENINGKATKAN MOTIVASI PADA SISWA KELAS V SEKOLAH DASAR

2020 ◽  
Vol 7 (2) ◽  
pp. 56-63
Author(s):  
Bandi Usman ◽  
Khairil Akbar ◽  
Kurnia Dyah Anggorowati
Keyword(s):  
Physical Education ◽  
Student Learning ◽  
Learning Model ◽  
Point Of View ◽  
Learning Motivation ◽  
Fifth Grade ◽  
Motivation To Learn ◽  
Average Value ◽  
Fifth Grade Students ◽  
Using Data

Abstrak: This study aims to increase student learning motivation in the field of physical education, sports and health. The learning model used is the application of the learning model through cooperative jigsaw to increase learning motivation in the field of physical education, sports and healthfor fifth grade students. Classroom action research (PTK) is carriedout using data collection techniques, namely motivation tests and questionnaires. The results of this study showed that in cycle 1, the average value of student learning motivation was 73% in the motivated category but not yet complete. Then in cycle II obtained a percentage of learning motivation of 90% categorized as motivated according to the success criteria and seen from the point of view of the maximum completeness criteria (KKM) students are said to be complete. The percentage of increasing learning motivation from cycle I to cycle II was 17%. The jigsaw cooperative learning model can increase student motivation, especially in sports and health physical education subjects.Keywords: learning Model, motivation to learn physical education sports and health.Abstrak: Penelitian ini bertujuan untuk meningkatkan motivasi belajar siswa pada bidang studi Pendidikan Jasmani Olahraga dan Kesehatan. Model pembelajaran yang digunakan adalah penerapan model pembelajaran melalui kooperatif Jigsaw untuk meningkatkan motivasi belajar pada bidang studi Pendidikan Jasmani Olahraga dan Kesehatan pada siswa kelas V, dilakukan penelitian tindakan kelas (PTK) dengan teknik pengumpulan data yakni tes dan angket motivasi. Hasil penelitian ini diperoleh siklus I nilai rata-rata motivasi belajar siswa presentase sebesar 73% kategori termotivasi tetapi belum tuntas. Kemudian pada siklus II diperoleh presentase motivasi belajar sebesar 90% dikategorikan termotivasi sesuai kriteria keberhasilan dan dilihat dari sudut pandang kriteria ketuntasan maksimal (KKM) siswa sudah dikatakan tuntas. Presentase peningkatan motivasi belajar siklus I ke siklus II yaitu 17%. Model pembelajaran kooperatif jigsaw dapat meningkatkan motivasi belajar siswa, terutama pada mata pelajaran Pendidikan Jasmani Olahraga dan Kesehatan.Kata Kunci: Model Pembelajaran, Motivasi Belajar Pendidikan Jasmani Olahraga dan Kesehatan

scholarly journals Persepsi Pengunjung Domestik Terhadap Wisata Entertainment di Daya Tarik Wisata Kawasan Luar Pura Uluwatu

2020 ◽  
Vol 8 (2) ◽  
pp. 376
Author(s):  
Kesya Marcella Tjampan ◽  
Saptono Nugroho
Keyword(s):  
Qualitative Method ◽  
Three Dimensions ◽  
Local Culture ◽  
Tourist Attraction ◽  
Literature Study ◽  
Average Value ◽  
Analysis Technique ◽  
Learning Enjoyment ◽  
Outer Area ◽  
Descriptive Statistical Analysis

The strategy forming tourist attraction to attract repeating guest is by developing entertainment tourism which offers sense of pleasure, satisfaction, and valuable experience. Uluwatu Kecak Fire Dance in Outer Area Uluwatu Temple was recognized as the most famous entertainment forms by domestic visitors. This aim of study is to identifying characteristics and measuring perception of domestic visitors to Uluwatu Kecak Fire Dance based on seven operational dimensions of entertainment tourism (Learning, Enjoyment, Escape, Refreshment, Novelty, Involvement, and Local Culture). The research used qualitative method with data collection techniques are questionnaire (number of samples were 65 respondents) and literature study. The data analysis technique used descriptive statistical analysis with continuum lines. The results showed that the perception of 65 domestic visitors for entertainment tourism in Uluwatu Temple were strongly agreed on Learning (277.5) and Enjoyment (285). While perception that were agreed are Escape (227), Refreshment (248.5), Novelty (259.25), Involvement (266), and Local Culture (272.33). In determining the dominant indicators of each dimension of entertainment tourism, the author uses the highest frequency capacity value. The three dimensions with highest average value are Enjoyment (285), Learning (277.5), and Local Culture (272.33). The administrator Outer Area Uluwatu Temple emphasize strategies that can maintain the three dimensions of entertainment tourism that have a dominant value, which is the Enjoyment dimension, Learning dimension, and the Local Culture dimension.   Keyword: Visitor Perception, Socio-demographic Characteristics, Entertainment Tourism, Domestic Visitors

Spatial attenuation of intensities for central U.S. earthquakes

1976 ◽  
Vol 66 (3) ◽  
pp. 743-751
Author(s):  
Indra N. Gupta ◽  
Otto W. Nuttli
Keyword(s):  
United States ◽  
Ground Motion ◽  
Epicentral Distance ◽  
Near Field ◽  
Mississippi Valley ◽  
Average Value ◽  
Anelastic Attenuation ◽  
Central United States ◽  
Using Data ◽  
Spatial Attenuation

abstract Attenuation of ground motion in the central United States has to be determined principally using the Modified Mercalli (MM) intensity observations because of the absence of instrumental strong ground-motion data. Nuttli's previous studies of Mississippi Valley earthquakes indicate that higher-mode surface waves produce the largest ground motion except possibly in the near-field region. Particle velocity rather than acceleration correlates directly with intensity and the coefficient of anelastic attenuation has an average value of 0.10 per degree. Using data from isoseismals of the November 9, 1968, southern Illinois and the December 16, 1811, New Madrid, Missouri earthquakes and assuming a linear relationship between log(A/T) and MM intensity, attenuation is expressed by the equation, valid for I(R) ≧IV (MM), I ( R ) = I 0 + 3.7 − 0.0011 R − 2.7 log ⁡ R ; for R ≧ 20 k m where R is the epicentral distance in kilometers. This relationship shows fairly good agreement with isoseismals of many large earthquakes in the central United States and may therefore be useful in providing realistic estimates of spatial attenuation and hence of design earthquakes for a given site. It can also be sometimes useful in estimating the epicentral intensity of an earthquake whose maximum intensity is not reliably known.

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