Eddy Viscosity and Reynolds Stress Models of Entropy Generation in Turbulent Channel Flows

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
J. Sun ◽  
D. Kuhn ◽  
G. Naterer
Keyword(s):  
Shear Stress ◽  
Entropy Production ◽  
Eddy Viscosity ◽  
Reynolds Shear Stress ◽  
Channel Flows ◽  
Alternative Formulation ◽  
Mean Flow ◽  
Turbulent Channel Flows ◽  
Entropy Transport ◽  
New Models

This paper presents new models of entropy production for incompressible turbulent channel flows. A turbulence model is formulated and analyzed with direct numerical simulation (DNS) data. A Reynolds-averaged Navier–Stokes (RANS) approach is used and applied to the turbulence closure of mean and fluctuating variables and entropy production. The expression of the mean entropy production in terms of other mean flow quantities is developed. This paper presents new models of entropy production by incorporating the eddy viscosity into the total shear stress. Also, the Reynolds shear stress is used as an alternative formulation. Solutions of the entropy transport equations are presented and discussed for both laminar and turbulent channel flows.

scholarly journals On the structure of streamwise wall-shear stress fluctuations in turbulent channel flows

2020 ◽  
Vol 1522 ◽  
pp. 012010
Author(s):  
Cheng Cheng ◽  
Weipeng Li ◽  
Adrián Lozano-Durán ◽  
Yitong Fan ◽  
Hong Liu
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Channel Flows ◽  
Turbulent Channel Flows ◽  
Wall Shear

Modeling of Entropy Production in Turbulent Flows

2004 ◽  
Vol 126 (6) ◽  
pp. 893-899 ◽  
Author(s):  
O. B. Adeyinka ◽  
G. F. Naterer
Keyword(s):  
Entropy Production ◽  
Turbulent Flows ◽  
Incompressible Flows ◽  
Momentum Equation ◽  
Ideal Gas ◽  
Equation Modeling ◽  
Mean Flow ◽  
Ideal Gas Law ◽  
Empirical Relations ◽  
Entropy Transport

This article presents new modeling of turbulence correlations in the entropy transport equation for viscous, incompressible flows. An explicit entropy equation of state is developed for gases with the ideal gas law, while entropy transport equations are derived for both gases and liquids. The formulation specifically considers incompressible forced convection problems without a buoyancy term in the y-momentum equation, as density variations are neglected. Reynolds averaging techniques are applied to the turbulence closure of fluctuating temperature and entropy fields. The problem of rigorously expressing the mean entropy production in terms of other mean flow quantities is addressed. The validity of the newly developed formulation is assessed using direct numerical simulation data and empirical relations for the friction factor. Also, the dissipation (ε) of turbulent kinetic energy is formulated in terms of the Second Law. In contrast to the conventional ε equation modeling, this article proposes an alternative method by utilizing both transport and positive definite forms of the entropy production equation.

Numerical and theoretical investigation of pulsatile turbulent channel flows

2016 ◽  
Vol 792 ◽  
pp. 98-133 ◽  
Author(s):  
Chenyang Weng ◽  
Susann Boij ◽  
Ardeshir Hanifi
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Nonlinear Effects ◽  
Turbulent Channel Flow ◽  
Theoretical Models ◽  
Phase Lag ◽  
Reynolds Stresses ◽  
Turbulent Eddies ◽  
Turbulent Channel Flows ◽  
Physical Features

A turbulent channel flow subjected to imposed harmonic oscillations is studied by direct numerical simulation (DNS) and theoretical models. Simulations have been performed for different pulsation frequencies. The time- and phase-averaged data have been used to analyse the flow. The onset of nonlinear effects during the production of the perturbation Reynolds stresses is discussed based on the DNS data, and new physical features observed in the DNS are reported. A linear model proposed earlier by the present authors for the coherent perturbation Reynolds shear stress is reviewed and discussed in depth. The model includes the non-equilibrium effects during the response of the Reynolds stress to the imposed periodic shear straining, where a phase lag exists between the stress and the strain. To validate the model, the perturbation velocity and Reynolds shear stress from the model are compared with the DNS data. The performance of the model is found to be good in the frequency range where quasi-static assumptions are invalid. The viscoelastic characteristics of the turbulent eddies implied by the model are supported by the DNS data. Attempts to improve the model are also made by incorporating the DNS data in the model.

The response of sheared turbulence to additional distortion

1980 ◽  
Vol 98 (1) ◽  
pp. 171-191 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Shear Stress ◽  
Energy Transfer ◽  
Water Waves ◽  
Reynolds Shear Stress ◽  
Equations Of Motion ◽  
Mixing Layer ◽  
Wall Turbulence ◽  
Mean Flow ◽  
History Of ◽  
Stress Ratios

In unidirectional flows, the ratios of Reynolds shear stress to total intensity (except near positions of zero stress) remain remarkably constant from one flow to another, but curvature or strong divergence of the mean flow causes very considerable changes in the stress ratios. A scheme for calculating the changes is described, based on the rapid-distortion approximation of the equations of motion. The results depend to some extent on the effective history of distortion of the turbulence and on the magnitude of an eddy viscosity that models the effect of nonlinear transfer of energy to smaller eddies of the dissipation sequence, but the correspondence with measured values in a distorted wake and in a curved mixing layer is fairly good. In particular, the curious behaviour of stress ratios in the curved mixing-layer can be reproduced qualitatively without any difficulty. Small perturbations of wall turbulence provide a simple application, and earlier calculations of the energy transfer between wind and water waves have been repeated including the changes in the stress ratios predicted by the scheme. In the latter case, very large changes in the distributions of pressure and shear stress are found, and the rates of energy transfer are much larger and in better agreement with observations.

DNS of Drag-Reducing Turbulent Channel Flow With Coexisting Newtonian and Non-Newtonian Fluid

2005 ◽  
Vol 127 (5) ◽  
pp. 929-935 ◽  
Author(s):  
Bo Yu ◽  
Yasuo Kawaguchi
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Flow Region ◽  
Turbulent Channel Flow ◽  
Turbulent Convection ◽  
Turbulent Channel Flows ◽  
Entire Flow ◽  
Shear Induced Structure ◽  
Induced Structure ◽  
And Diffusion

In the present study, we numerically investigated drag-reducing turbulent channel flows by surfactant additives. Surfactant additives were assumed to be uniformly distributed in the entire flow region by turbulent convection and diffusion, etc., but it was assumed that the shear-induced structure (SIS) (network of rod-like micelles) could form either in the region next to the walls or in the center region of the channel, making the fluid viscoelastic. In other regions surfactant additives were assumed to be incapable of building a network structure, and to exist in the form of molecules or micelles that do not affect the Newtonian properties of the fluid. With these assumptions, we studied the drag-reducing phenomenon with coexisting Newtonian and non-Newtonian fluids. From the study we identified the effectiveness of the network structures at different flow regions, and showed that the phenomenon of drag-reduction (DR) by surfactant additives is not only closely associated with the reduction of Reynolds shear stress but also related to the induced viscoelastic shear stress.

scholarly journals The Role of Forcing and Eddy Viscosity Variation on the Log-Layer Mismatch Observed in Wall-Modeled Large-Eddy Simulations

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Rey DeLeon ◽  
Inanc Senocak
Keyword(s):  
Flow Rate ◽  
Eddy Viscosity ◽  
Degree Of Freedom ◽  
Channel Flows ◽  
Momentum Balance ◽  
Mean Velocity ◽  
Turbulent Channel Flows ◽  
The Mean ◽  
Viscosity Variation

We investigate the role of eddy viscosity variation and the effect of zonal enforcement of the mass flow rate on the log-layer mismatch problem observed in turbulent channel flows. An analysis of the mean momentum balance shows that it lacks a degree-of-freedom (DOF) when eddy viscosity is large, and the mean velocity conforms to an incorrect profile. Zonal enforcement of the target flow rate introduces an additional degree-of-freedom to the mean momentum balance, similar to an external stochastic forcing term, leading to a significant reduction in the log-layer mismatch. We simulate turbulent channel flows at friction Reynolds numbers of 2000 and 5200 on coarse meshes that do not resolve the viscous sublayer. The second-order turbulence statistics agree well with the direct numerical simulation benchmark data when results are normalized by the velocity scale extracted from the filtered velocity field. Zonal enforcement of the flow rate also led to significant improvements in skin friction coefficients.

A Note on a Generalized Eddy-Viscosity Hypothesis

1992 ◽  
Vol 114 (3) ◽  
pp. 463-466 ◽  
Author(s):  
P. Andreasson ◽  
U. Svensson
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Velocity Gradient ◽  
Eddy Viscosity ◽  
Channel Flows ◽  
Length Scale ◽  
Asymmetric Channel ◽  
Boundary Layer Flows ◽  
Turbulent Length Scale ◽  
Model Predictions

The standard eddy-viscosity concept postulates that zero velocity gradient is accompanied by zero shear stress. This is not true for many boundary layer flows: wall jets, asymmetric channel flows, countercurrent flows, for example. The generalized eddy-viscosity hypothesis presented in this paper, relaxes this limitation by recognizing the influence of gradients in the turbulent length scale and the shear. With this new eddy-viscosity concept, implemented into the standard k–ε model, predictions of some boundary layer flows are made. The modelling results agree well with measurements, where predictions with the standard eddy-viscosity concept are known to fail.

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