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R. A. Antonia - One of the best experts on this subject based on the ideXlab platform.
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Characteristics of the turbulent Energy Dissipation Rate in a cylinder wake
Journal of Fluid Mechanics, 2017Co-Authors: J. G. Chen, R. A. Antonia, Yu Zhou, Tongming ZhouAbstract:This work aims to improve our understanding of the turbulent Energy Dissipation Rate in the wake of a circular cylinder. Ten of the twelve velocity derivative terms which make up the Energy Dissipation Rate are simultaneously obtained with a probe composed of four X-wires. Measurements are made in the plane of mean shear at $x/d=10$ , 20 and 40, where $x$ is the streamwise distance from the cylinder axis and $d$ is the cylinder diameter, at a Reynolds number of $2.5\times 10^{3}$ based on $d$ and free-stream velocity. Both statistical and topological features of the velocity derivatives as well as the Energy Dissipation Rate, approximated by a surrogate based on the assumption of homogeneity in the transverse plane, are examined. The spectra of the velocity derivatives indicate that local axisymmetry is first satisfied at higher wavenumbers while the departure at lower wavenumbers is caused by the Karman vortex street. The spectral method proposed by Djenidi & Antonia ( Exp. Fluids , vol. 53, 2012, pp. 1005–1013) based on the universality of the Dissipation range of the longitudinal velocity spectrum normalized by the Kolmogorov scales also applies in the present flow despite the strong perturbation from the Karman vortex street and violation of local isotropy at small $x/d$ . The appropriateness of the spectral chart method is consistent with Antonia et al. ’s ( Phys. Fluids , vol. 26, 2014, 45105) observation that the two major assumptions in Kolmogorov’s first similarity hypothesis, i.e. very large Taylor microscale Reynolds number and local isotropy, can be significantly relaxed. The data also indicate that vorticity spectra are more sensitive, when testing the first similarity hypothesis, than velocity spectra. They also reveal that the velocity derivatives $\unicode[STIX]{x2202}u/\unicode[STIX]{x2202}y$ and $\unicode[STIX]{x2202}v/\unicode[STIX]{x2202}x$ play an important role in the interaction between large and small scales in the present flow. The phase-averaged data indicate that the Energy Dissipation is concentRated mostly within the coherent spanwise vortex rollers, in contrast with the model of Hussain ( J. Fluid Mech. , vol. 173, 1986, pp. 303–356) and Hussain & Hayakawa ( J. Fluid Mech. , vol. 180, 1987, p. 193), who conjectured that it resides mainly in regions of strong turbulent mixing.
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Transport equation for the mean turbulent Energy Dissipation Rate on the centreline of a fully developed channel flow
Journal of Fluid Mechanics, 2015Co-Authors: S. L. Tang, R. A. Antonia, T Zhou, L. Danaila, L. Djenidi, H. Abé, Y ZhouAbstract:The transport equation for the mean turbulent Energy Dissipation Rate (epsilon) over bar along the centreline of a fully developed channel flow is derived by applying the limit at small separations to the two-point budget equation. Since the ratio of the isotropic Energy Dissipation Rate to the mean turbulent Energy Dissipation Rate (epsilon) over bar (iso)/(epsilon) over bar is sufficiently close to 1 on the centreline, our main focus is on the isotropic form of the transport equation. It is found that the imbalance between the production of (epsilon) over bar due to vortex stretching and the destruction of (epsilon) over bar caused by the action of viscosity is governed by the diffusion of (epsilon) over bar by the wall-normal velocity fluctuation. This imbalance is intrinsically different from the advection-driven imbalance in decaying-type flows, such as grid turbulence, jets and wakes. In effect, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative S-1,S-1 and the destruction coefficient G of enstrophy in different flows, thus resulting in non-universal approaches of S-1,S-1 towards a constant value as the Taylor microscale Reynolds number, R-lambda, increases. For example, the approach is slower for the measured values of S-1,S-1 along either the channel or pipe centreline than along the axis in the self-preserving region of a round jet. The data for S-1,S-1 collected in different flows strongly suggest that, in each flow, the magnitude of S-1,S-1 is bounded, the value being slightly larger than 0.5.
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transport equation for the mean turbulent Energy Dissipation Rate on the centreline of a fully developed channel flow
Journal of Fluid Mechanics, 2015Co-Authors: S. L. Tang, R. A. Antonia, Tongming Zhou, L. Djenidi, Luminita Danaila, Y ZhouAbstract:The transport equation for the mean turbulent Energy Dissipation Rate $\overline{{\it\epsilon}}$ along the centreline of a fully developed channel flow is derived by applying the limit at small separations to the two-point budget equation. Since the ratio of the isotropic Energy Dissipation Rate to the mean turbulent Energy Dissipation Rate $\overline{{\it\epsilon}}_{iso}/\overline{{\it\epsilon}}$ is sufficiently close to 1 on the centreline, our main focus is on the isotropic form of the transport equation. It is found that the imbalance between the production of $\overline{{\it\epsilon}}$ due to vortex stretching and the destruction of $\overline{{\it\epsilon}}$ caused by the action of viscosity is governed by the diffusion of $\overline{{\it\epsilon}}$ by the wall-normal velocity fluctuation. This imbalance is intrinsically different from the advection-driven imbalance in decaying-type flows, such as grid turbulence, jets and wakes. In effect, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative $S_{1,1}$ and the destruction coefficient $G$ of enstrophy in different flows, thus resulting in non-universal approaches of $S_{1,1}$ towards a constant value as the Taylor microscale Reynolds number, $R_{{\it\lambda}}$ , increases. For example, the approach is slower for the measured values of $S_{1,1}$ along either the channel or pipe centreline than along the axis in the self-preserving region of a round jet. The data for $S_{1,1}$ collected in different flows strongly suggest that, in each flow, the magnitude of $S_{1,1}$ is bounded, the value being slightly larger than 0.5.
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statistics of the turbulent kinetic Energy Dissipation Rate and its surrogates in a square cylinder wake flow
Physics of Fluids, 2014Co-Authors: N. Lefeuvre, L. Djenidi, F. Thiesset, R. A. AntoniaAbstract:A numerical simulation based on the lattice Boltzmann method is carried out in the wake of a square cylinder with the view to investigating possible surrogates for the instantaneous turbulent kinetic Energy Dissipation Rate, e, as well as its mean value, e¯. Various surrogate approximations of e, based on local isotropy (eiso), local axisymmetry along the streamwise direction x (ea, x) and the transverse direction y (ea, y), local homogeneity (ehom), and homogeneity in the transverse plane, (e4x), are assessed. All the approximations are in agreement with e¯ when the distance downstream of the obstacle is larger than about 40 diameters. Closer to the obstacle, the agreement remains reasonable only for e¯a,x, e¯hom and e¯4x. The probability density functions (PDF) and joint PDFs of e and its surrogates show that e4x correlates best with e while eiso and ehom present the smallest correlation. The results indicate that e4x is a very good surrogate for e and can be used for correctly determining the behaviour...
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Statistics of the turbulent kinetic Energy Dissipation Rate and its surrogates in a square cylinder wake flow
Physics of Fluids, 2014Co-Authors: N. Lefeuvre, L. Djenidi, F. Thiesset, R. A. AntoniaAbstract:A numerical simulation based on the lattice Boltzmann method is carried out in the wake of a square cylinder with the view to investigating possible surrogates for the instantaneous turbulent kinetic Energy Dissipation Rate, ε, as well as its mean value, ε Various surrogate approximations of ε, based on local isotropy (εiso), local axisymmetry along the streamwise direction x (εa, x) and the transverse direction y (εa, y), local homogeneity (εhom), and homogeneity in the transverse plane, (ε4x), are assessed. All the approximations are in agreement with ε when the distance downstream of the obstacle is larger than about 40 diameters. Closer to the obstacle, the agreement remains reasonable only for εa,x, εhom and ε4x. The probability density functions (PDF) and joint PDFs of ε and its surrogates show that ε4x correlates best with ε while εiso and εhom present the smallest correlation. The results indicate that ε4x is a very good surrogate for ε and can be used for correctly determining the behaviour of ε.
Stephen M. De Bruyn Kops - One of the best experts on this subject based on the ideXlab platform.
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Energy Dissipation Rate surrogates in incompressible Navier–Stokes turbulence
Journal of Fluid Mechanics, 2012Co-Authors: Saba Almalkie, Stephen M. De Bruyn KopsAbstract:AbstractHigh-resolution direct numerical simulations of isotropic homogeneous turbulence are used to understand the differences between the effects of spatial intermittency on the Energy Dissipation Rate and on surrogates for the Dissipation Rate that are based on measurements of a subset of the strain Rate tensor. In particular, the one-dimensional longitudinal and transverse surrogates, as well as a surrogate based on the asymmetric part of the strain Rate tensor, are considered. The instantaneous surrogates are studied locally, locally averaged in space and conditionally averaged to see what statistics of the Dissipation Rate might accuRately be inferred given measurements of the surrogates. The simulations with the Reynolds numbers based on the Taylor microscale of 102–235 are highly resolved for accuRate evaluation of higher-order statistics. The probability densities of the local and locally averaged surrogates are significantly different from the corresponding statistics for the Dissipation Rate itself. All of the surrogates are more intermittent than the Dissipation Rate, the transverse surrogate is more intermittent than the longitudinal and these trends are still prominent even when the fields are spatially averaged at length scales close to the integral length scale. As a consequence, the intermittency exponent computed from the moments of the locally averaged longitudinal and transverse surrogates is approximately 1.5 and 2.2 times higher, respectively, than that computed by the same method from the Dissipation Rate field. In addition, while different methods of computing intermittency exponent from the Dissipation Rate field yield the same result, different methods applied to a surrogate are inconsistent.
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relationship between vertical shear Rate and kinetic Energy Dissipation Rate in stably stratified flows
Geophysical Research Letters, 2006Co-Authors: David Hebert, Stephen M. De Bruyn KopsAbstract:[1] High resolution direct numerical simulations of strongly stratified turbulence are analyzed in order to investigate the relationship between vertical shearing of horizontal motions and the Dissipation Rate of kinetic Energy. The relative magnitude of each component of the Dissipation Rate is examined as a function of the Reynolds number and of the buoyancy Reynolds number. From the simulation results, in conjunction with published laboratory results, it is concluded that (1) the simulation results are consistent with the laboratory data but span a much larger range of buoyancy Reynolds number, (2) the ratio of the square of the vertical shear Rate to the Dissipation Rate is a strong function of buoyancy Reynolds number, and (3) the approximation that vertical shear Rate is the dominant cause of Energy Dissipation Rate is only good when the buoyancy Reynolds number is less than order one.
L. Djenidi - One of the best experts on this subject based on the ideXlab platform.
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Transport equation for the mean turbulent Energy Dissipation Rate on the centreline of a fully developed channel flow
Journal of Fluid Mechanics, 2015Co-Authors: S. L. Tang, R. A. Antonia, T Zhou, L. Danaila, L. Djenidi, H. Abé, Y ZhouAbstract:The transport equation for the mean turbulent Energy Dissipation Rate (epsilon) over bar along the centreline of a fully developed channel flow is derived by applying the limit at small separations to the two-point budget equation. Since the ratio of the isotropic Energy Dissipation Rate to the mean turbulent Energy Dissipation Rate (epsilon) over bar (iso)/(epsilon) over bar is sufficiently close to 1 on the centreline, our main focus is on the isotropic form of the transport equation. It is found that the imbalance between the production of (epsilon) over bar due to vortex stretching and the destruction of (epsilon) over bar caused by the action of viscosity is governed by the diffusion of (epsilon) over bar by the wall-normal velocity fluctuation. This imbalance is intrinsically different from the advection-driven imbalance in decaying-type flows, such as grid turbulence, jets and wakes. In effect, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative S-1,S-1 and the destruction coefficient G of enstrophy in different flows, thus resulting in non-universal approaches of S-1,S-1 towards a constant value as the Taylor microscale Reynolds number, R-lambda, increases. For example, the approach is slower for the measured values of S-1,S-1 along either the channel or pipe centreline than along the axis in the self-preserving region of a round jet. The data for S-1,S-1 collected in different flows strongly suggest that, in each flow, the magnitude of S-1,S-1 is bounded, the value being slightly larger than 0.5.
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transport equation for the mean turbulent Energy Dissipation Rate on the centreline of a fully developed channel flow
Journal of Fluid Mechanics, 2015Co-Authors: S. L. Tang, R. A. Antonia, Tongming Zhou, L. Djenidi, Luminita Danaila, Y ZhouAbstract:The transport equation for the mean turbulent Energy Dissipation Rate $\overline{{\it\epsilon}}$ along the centreline of a fully developed channel flow is derived by applying the limit at small separations to the two-point budget equation. Since the ratio of the isotropic Energy Dissipation Rate to the mean turbulent Energy Dissipation Rate $\overline{{\it\epsilon}}_{iso}/\overline{{\it\epsilon}}$ is sufficiently close to 1 on the centreline, our main focus is on the isotropic form of the transport equation. It is found that the imbalance between the production of $\overline{{\it\epsilon}}$ due to vortex stretching and the destruction of $\overline{{\it\epsilon}}$ caused by the action of viscosity is governed by the diffusion of $\overline{{\it\epsilon}}$ by the wall-normal velocity fluctuation. This imbalance is intrinsically different from the advection-driven imbalance in decaying-type flows, such as grid turbulence, jets and wakes. In effect, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative $S_{1,1}$ and the destruction coefficient $G$ of enstrophy in different flows, thus resulting in non-universal approaches of $S_{1,1}$ towards a constant value as the Taylor microscale Reynolds number, $R_{{\it\lambda}}$ , increases. For example, the approach is slower for the measured values of $S_{1,1}$ along either the channel or pipe centreline than along the axis in the self-preserving region of a round jet. The data for $S_{1,1}$ collected in different flows strongly suggest that, in each flow, the magnitude of $S_{1,1}$ is bounded, the value being slightly larger than 0.5.
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statistics of the turbulent kinetic Energy Dissipation Rate and its surrogates in a square cylinder wake flow
Physics of Fluids, 2014Co-Authors: N. Lefeuvre, L. Djenidi, F. Thiesset, R. A. AntoniaAbstract:A numerical simulation based on the lattice Boltzmann method is carried out in the wake of a square cylinder with the view to investigating possible surrogates for the instantaneous turbulent kinetic Energy Dissipation Rate, e, as well as its mean value, e¯. Various surrogate approximations of e, based on local isotropy (eiso), local axisymmetry along the streamwise direction x (ea, x) and the transverse direction y (ea, y), local homogeneity (ehom), and homogeneity in the transverse plane, (e4x), are assessed. All the approximations are in agreement with e¯ when the distance downstream of the obstacle is larger than about 40 diameters. Closer to the obstacle, the agreement remains reasonable only for e¯a,x, e¯hom and e¯4x. The probability density functions (PDF) and joint PDFs of e and its surrogates show that e4x correlates best with e while eiso and ehom present the smallest correlation. The results indicate that e4x is a very good surrogate for e and can be used for correctly determining the behaviour...
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Statistics of the turbulent kinetic Energy Dissipation Rate and its surrogates in a square cylinder wake flow
Physics of Fluids, 2014Co-Authors: N. Lefeuvre, L. Djenidi, F. Thiesset, R. A. AntoniaAbstract:A numerical simulation based on the lattice Boltzmann method is carried out in the wake of a square cylinder with the view to investigating possible surrogates for the instantaneous turbulent kinetic Energy Dissipation Rate, ε, as well as its mean value, ε Various surrogate approximations of ε, based on local isotropy (εiso), local axisymmetry along the streamwise direction x (εa, x) and the transverse direction y (εa, y), local homogeneity (εhom), and homogeneity in the transverse plane, (ε4x), are assessed. All the approximations are in agreement with ε when the distance downstream of the obstacle is larger than about 40 diameters. Closer to the obstacle, the agreement remains reasonable only for εa,x, εhom and ε4x. The probability density functions (PDF) and joint PDFs of ε and its surrogates show that ε4x correlates best with ε while εiso and εhom present the smallest correlation. The results indicate that ε4x is a very good surrogate for ε and can be used for correctly determining the behaviour of ε.
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a spectral chart method for estimating the mean turbulent kinetic Energy Dissipation Rate
Experiments in Fluids, 2012Co-Authors: L. Djenidi, R. A. AntoniaAbstract:We present an empirical but simple and practical spectral chart method for determining the mean turbulent kinetic Energy Dissipation Rate \( \left\langle \varepsilon \right\rangle \) in a variety of turbulent flows. The method relies on the validity of the first similarity hypothesis of Kolmogorov (C R (Doklady) Acad Sci R R SS, NS 30:301–305, 1941) (or K41) which implies that spectra of velocity fluctuations scale on the kinematic viscosity ν and \( \left\langle \varepsilon \right\rangle \) at large Reynolds numbers. However, the evidence, based on the DNS spectra, points to this scaling being also valid at small Reynolds numbers, provided effects due to inhomogeneities in the flow are negligible. The methods avoid the difficulty associated with estimating time or spatial derivatives of the velocity fluctuations. It also avoids using the second hypothesis of K41, which implies the existence of a −5/3 inertial subrange only when the Taylor microscale Reynods number Rλ is sufficiently large. The method is in fact applied to the lower wavenumber end of the dissipative range thus avoiding most of the problems due to inadequate spatial resolution of the velocity sensors and noise associated with the higher wavenumber end of this range.The use of spectral data (30 ≤ Rλ ≤ 400) in both passive and active grid turbulence, a turbulent mixing layer and the turbulent wake of a circular cylinder indicates that the method is robust and should lead to reliable estimates of \( \left\langle \varepsilon \right\rangle \) in flows or flow regions where the first similarity hypothesis should hold; this would exclude, for example, the region near a wall.
Adam W. Demarco - One of the best experts on this subject based on the ideXlab platform.
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Parametrizing the Energy Dissipation Rate in Stably Stratified Flows
Boundary-Layer Meteorology, 2020Co-Authors: Sukanta Basu, Adam W. DemarcoAbstract:We use a database of direct numerical simulations to evaluate parametrizations for Energy Dissipation Rate in stably stratified flows. We show that shear-based formulations are more appropriate for stable boundary layers than commonly used buoyancy-based formulations. As part of the derivations, we explore several length scales of turbulence and investigate their dependence on local stability.
Adrian H. Callaghan - One of the best experts on this subject based on the ideXlab platform.
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Estimates of Wave Breaking Energy Dissipation Rate from Measurements of Whitecap Coverage
Recent Advances in the Study of Oceanic Whitecaps, 2020Co-Authors: Adrian H. CallaghanAbstract:The easiest way to identify the occurrence, or recent occurrence of oceanic air-entraining breaking waves (whitecaps) from above the water surface is through photographic remote sensing of the sea surface. In this paper I estimate the Energy Dissipation Rate due to breaking wave whitecaps using measurements of whitecap coverage of the sea surface. Several datasets are used that employed different methodologies for determining the whitecap coverage spanning almost 4 decades of research. The results show that, on average, the ratio of the Energy Dissipation Rate due to whitecaps to the wind Energy input Rate to the upper ocean and wave field is close to unity above wind speeds of about 10 m s−1. Below 10 m s−1, this Energy flux ratio decreases steadily from unity as wind speed decreases, in agreement with several recent studies. The implication is that other dissipative processes play an important role in dissipating the wind Energy input to the upper ocean and wave field at low wind speeds. These results suggest that variability in this Energy flux ratio may be responsible for differences in measurements and parameterisations of whitecap coverage at low wind speeds.
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on the relationship between the Energy Dissipation Rate of surface breaking waves and oceanic whitecap coverage
Journal of Physical Oceanography, 2018Co-Authors: Adrian H. CallaghanAbstract:AbstractWave breaking is the most important mechanism that leads to the Dissipation of oceanic surface wave Energy. A relationship between the Energy Dissipation Rate associated with breaking wave ...