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R. A. Antonia - One of the best experts on this subject based on the ideXlab platform.
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estimation of mean Turbulent Kinetic Energy and temperature variance dissipation rates using a spectral chart method
Physics of Fluids, 2020Co-Authors: Jean Lemay, L. Djenidi, R. A. AntoniaAbstract:A method aimed at estimating ek and eθ, respectively, the mean dissipation rates of Turbulent Kinetic Energy k and half the temperature variance θ2/2, is developed for slightly heated Turbulent flows of air. It is limited to a Prandtl number near unity and applicable to flows where temperature can be treated as a passive scalar. A significant advantage of the method is that ek and eθ can both be estimated from the measurement of a temperature frequency spectrum, Gθθ(f). The method relies on the collapse in the dissipative range of one-dimensional temperature spectra, ϕθ(k1η), when normalized with eθ, ek, and ν. This collapse ensues from a similarity analysis of scale-by-scale budgets of the second-order structure function for the temperature. A generic spectrum ϕθG(k1η), defined in the wavenumber range 0.07 ≤ k1η ≤ 0.7, is used to construct a spectral chart. The method has been tested in several flows and found to be reliable. In particular, it is tested on the axis of a slightly heated round jet, where ek and eθ can be estimated accurately via the budgets of k and θ2/2, and the agreement between these estimates and the spectral chart results is almost perfect.
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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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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.
João Paulo Teixeira - One of the best experts on this subject based on the ideXlab platform.
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scaling behavior of a Turbulent Kinetic Energy closure scheme for the stably stratified atmosphere a steady state analysis
arXiv: Atmospheric and Oceanic Physics, 2020Co-Authors: M Macdonald, João Paulo TeixeiraAbstract:We present a Turbulent Kinetic Energy (TKE) closure scheme for the stably stratified atmosphere in which the mixing lengths for momentum and heat are not parameterized in the same manner. The key difference is that, while the mixing length for heat tends towards the stability independent mixing length for momentum in neutrally stratified conditions, it tends towards one based on the Brunt-Vaisala time scale and square root of the TKE in the limit of large stability. This enables a unique steady-state solution for TKE to be obtained, which we demonstrate would otherwise be impossible if the mixing lengths were the same. Despite the model's relative simplicity, it is shown to perform reasonably well with observational data from the 1999 Cooperative Atmosphere-Surface Exchange Study (CASES-99) using commonly employed model constants. Analyzing the scaling behavior of the non-dimensional velocity and potential temperature gradients, or of the stability (correction) functions, reveals that for large stability the present model scales in the same manner as the first-order operational scheme of Viterbo et al. (Quart. J. Roy. Meteor. Soc. 125, 2401-2426, 1999). Alternatively, it appears as a blend of two cases of the TKE closure scheme of Baas et al. (Bound.-Layer Meteor. 127, 17-36, 2008). Critically, because a unique steady-state TKE can be obtained, the present model avoids the non-physical behavior identified in one of the cases of Baas et al. (2008).
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a scale adaptive Turbulent Kinetic Energy closure for the dry convective boundary layer
Journal of the Atmospheric Sciences, 2017Co-Authors: Marcin J Kurowski, João Paulo TeixeiraAbstract:AbstractA pragmatic scale-adaptive Turbulent Kinetic Energy (TKE) closure is proposed to simulate the dry convective boundary layer for a variety of horizontal grid resolutions: from 50 m, typical of large-eddy simulation models that use three-dimensional turbulence parameterizations/closures, up to 100 km, typical of climate models that use one-dimensional turbulence and convection parameterizations/closures. Since parameterizations/closures using the TKE approach have been frequently used in these two asymptotic limits, a simple method is proposed to merge them with a mixing-length-scale formulation for intermediate resolutions. This new scale-adaptive mixing length naturally increases with increasing grid length until it saturates as the grid length reaches mesoscale-model resolution. The results obtained using this new approach for dry convective boundary layers are promising. The mean vertical profiles of potential temperature and heat flux remain in good agreement for different resolutions. A contin...
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an eddy diffusivity mass flux approach to the vertical transport of Turbulent Kinetic Energy in convective boundary layers
Journal of the Atmospheric Sciences, 2011Co-Authors: Marcin L Witek, João Paulo Teixeira, Georgios MatheouAbstract:AbstractIn this study a new approach to the vertical transport of the Turbulent Kinetic Energy (TKE) is proposed. The principal idea behind the new parameterization is that organized updrafts or convective plumes play an important role in transferring TKE vertically within convectively driven boundary layers. The parameterization is derived by applying an updraft environment decomposition to the vertical velocity triple correlation term in the TKE prognostic equation. The additional mass flux (MF) term that results from this decomposition closely resembles the features of the TKE transport diagnosed from the large-eddy simulation (LES) and accounts for 97% of the LES-diagnosed transport when the updraft fraction is set to 0.13. Another advantage of the MF term is that it is a function of the updraft vertical velocity and can be readily calculated using already existing parameterization. The new MF approach, combined with several eddy diffusivity (ED) formulations, is implemented into a simplified 1D TKE p...
David Saloner - One of the best experts on this subject based on the ideXlab platform.
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magnetic resonance measurement of Turbulent Kinetic Energy for the estimation of irreversible pressure loss in aortic stenosis
Jacc-cardiovascular Imaging, 2013Co-Authors: Petter Dyverfeldt, Michael D Hope, Elaine E Tseng, David SalonerAbstract:ObjectivesThe authors sought to measure the Turbulent Kinetic Energy (TKE) in the ascending aorta of patients with aortic stenosis and to assess its relationship to irreversible pressure loss.Backg ...
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magnetic resonance measurement of Turbulent Kinetic Energy for the estimation of irreversible pressure loss in aortic stenosis
Jacc-cardiovascular Imaging, 2013Co-Authors: Petter Dyverfeldt, Michael D Hope, Elaine E Tseng, David SalonerAbstract:ObjectivesThe authors sought to measure the Turbulent Kinetic Energy (TKE) in the ascending aorta of patients with aortic stenosis and to assess its relationship to irreversible pressure loss.Backg ...
L. Djenidi - One of the best experts on this subject based on the ideXlab platform.
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estimation of mean Turbulent Kinetic Energy and temperature variance dissipation rates using a spectral chart method
Physics of Fluids, 2020Co-Authors: Jean Lemay, L. Djenidi, R. A. AntoniaAbstract:A method aimed at estimating ek and eθ, respectively, the mean dissipation rates of Turbulent Kinetic Energy k and half the temperature variance θ2/2, is developed for slightly heated Turbulent flows of air. It is limited to a Prandtl number near unity and applicable to flows where temperature can be treated as a passive scalar. A significant advantage of the method is that ek and eθ can both be estimated from the measurement of a temperature frequency spectrum, Gθθ(f). The method relies on the collapse in the dissipative range of one-dimensional temperature spectra, ϕθ(k1η), when normalized with eθ, ek, and ν. This collapse ensues from a similarity analysis of scale-by-scale budgets of the second-order structure function for the temperature. A generic spectrum ϕθG(k1η), defined in the wavenumber range 0.07 ≤ k1η ≤ 0.7, is used to construct a spectral chart. The method has been tested in several flows and found to be reliable. In particular, it is tested on the axis of a slightly heated round jet, where ek and eθ can be estimated accurately via the budgets of k and θ2/2, and the agreement between these estimates and the spectral chart results is almost perfect.
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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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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.
Michael Manhart - One of the best experts on this subject based on the ideXlab platform.
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dissipation of Turbulent Kinetic Energy in a cylinder wall junction flow
Flow Turbulence and Combustion, 2018Co-Authors: W Schanderl, Michael ManhartAbstract:The subject of this study is the discussion of the dissipation of Turbulent Kinetic Energy and its Reynolds number scaling in front of a wall-mounted cylinder. We employed highly resolved Large-Eddy Simulation and ensured that the computational grid was fine enough to resolve most of the scales. A perceptible fraction of the total dissipation is modeled. However, this fraction - about one third - is small enough so that the total dissipation suffers only marginally from some potential shortcomings of the turbulence model. Individual terms of the pseudo dissipation tensor and their Reynolds number scaling are discussed and compared. This tensor and thus the Turbulent small scale structures are not isotropic at the Reynolds numbers investigated. Furthermore, the near-wall anisotropy under the horseshoe vortex is likely to persist to larger Reynolds numbers as it can be linked to a flapping of the near-wall layer. The Turbulent length scale shows a strong spatial variability. In the region of the vortex system in the cylinder front, the distribution reveals a similar shape as the one of the Turbulent Kinetic Energy and its amplitude is in the order of magnitude of the cylinder diameter. In contrast to the region dominated by the approach flow, the Turbulent length scale is independent of the Reynolds number in the region dominated by the vortex system. Even though the flow investigated is in non-equilibrium, common a priori estimations and scalings of the Kolmogorov length scale based on macro scales give satisfying results.
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the structure and budget of Turbulent Kinetic Energy in front of a wall mounted cylinder
Journal of Fluid Mechanics, 2017Co-Authors: W Schanderl, Ulrich Jenssen, C Strobl, Michael ManhartAbstract:We investigate the flow and turbulence structure in front of a cylinder mounted on a flat plate by a combined study using highly resolved large-eddy simulation and particle image velocimetry. The Reynolds number based on the bulk velocity and cylinder diameter is $Re_{D}=39\,000$ . As the cylinder is placed in an open channel, we take special care to simulate open-channel flow as the inflow condition, including secondary flows that match the inflow in the experiment. Due to the high numerical resolution, subgrid contributions to the Reynolds stresses are negligible and the modelled dissipation plays a minor role in major parts of the flow field. The accordance of the experimental and numerical results is good. The shear in the approach flow creates a vertical pressure gradient, inducing a downflow in the cylinder front. This downflow, when deflected in the upstream direction at the bottom plate, gives rise to a so-called horseshoe vortex system. The most upstream point of flow reversal at the wall is found to be a stagnation point which appears as a sink instead of a separation point in the symmetry plane in front of the cylinder. The wall shear stress is largest between the main (horseshoe) vortex and the cylinder, and seems to be mainly governed by the strong downflow in front of the cylinder as Turbulent stresses are small in this region. Due to a strong acceleration along the streamlines, a region of relatively small Turbulent Kinetic Energy is found between the horseshoe vortex and the cylinder. When passing under the horseshoe vortex, the upstream-directed jet formed by the deflected downflow undergoes a deceleration which gives rise to a strong production of Turbulent Kinetic Energy. We find that pressure transport of Turbulent Kinetic Energy is important for the initiation of the large production rates by increasing the turbulence level in the upstream jet near the wall. The distribution of the dissipation of Turbulent Kinetic Energy is similar to that of the Turbulent Kinetic Energy. Large values of dissipation occur around the centre of the horseshoe vortex and near the wall in the region where the jet decelerates. While the small scales are nearly isotropic in the horseshoe vortex centre, they are anistotropic near the wall. This can be explained by a vertical flapping of the upstream-directed jet. The distribution and level of dissipation, Turbulent and pressure transport of Turbulent Kinetic Energy are of crucial interest to turbulence modelling in the Reynolds-averaged context. To the best of our knowledge, this is the first time that these terms have been documented in this kind of flow.
