A Study on Anomalous Turbulent Flows of Non-Newtonian Fluids : 2nd Report, Transitional Region from Laminar to Turbulent Flow

This book provides students and researchers in fluid engineering with an up-to-date overview of turbulent flow research in the areas of simulation and modeling. A key element of the book is the systematic, rational development of turbulence closure models and related aspects of modern turbulent flow theory and prediction. Starting with a review of the spectral dynamics of homogenous and inhomogeneous turbulent flows, succeeding chapters deal with numerical simulation techniques, renormalization group methods and turbulent closure modeling. Each chapter is authored by recognized leaders in their respective fields, and each provides a thorough and cohesive treatment of the subject.

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Large-eddy simulation of wall-bounded turbulent flow with high-order discrete unified gas-kinetic scheme

Advances in Aerodynamics ◽

10.1186/s42774-020-00051-w ◽

2020 ◽

Vol 2 (1) ◽

Author(s):

Rui Zhang ◽

Chengwen Zhong ◽

Sha Liu ◽

Congshan Zhuo

Keyword(s):

Turbulent Flow ◽

Turbulent Flows ◽

Parallel Implementation ◽

Kinetic Scheme ◽

Cavity Flow ◽

Equilibrium Distribution Function ◽

Third Order ◽

Two Stage ◽

Large Eddy ◽

Unified Gas Kinetic Scheme

AbstractIn this paper, we introduce the discrete Maxwellian equilibrium distribution function for incompressible flow and force term into the two-stage third-order Discrete Unified Gas-Kinetic Scheme (DUGKS) for simulating low-speed turbulent flows. The Wall-Adapting Local Eddy-viscosity (WALE) and Vreman sub-grid models for Large-Eddy Simulations (LES) of turbulent flows are coupled within the present framework. Meanwhile, the implicit LES are also presented to verify the effect of LES models. A parallel implementation strategy for the present framework is developed, and three canonical wall-bounded turbulent flow cases are investigated, including the fully developed turbulent channel flow at a friction Reynolds number (Re) about 180, the turbulent plane Couette flow at a friction Re number about 93 and lid-driven cubical cavity flow at a Re number of 12000. The turbulence statistics, including mean velocity, the r.m.s. fluctuations velocity, Reynolds stress, etc. are computed by the present approach. Their predictions match precisely with each other, and they are both in reasonable agreement with the benchmark data of DNS. Especially, the predicted flow physics of three-dimensional lid-driven cavity flow are consistent with the description from abundant literature. The present numerical results verify that the present two-stage third-order DUGKS-based LES method is capable for simulating inhomogeneous wall-bounded turbulent flows and getting reliable results with relatively coarse grids.

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Model for laminar and turbulent flows of viscous and nonlinear viscous non-Newtonian fluids

Journal of Mathematical Physics ◽

10.1063/1.3578752 ◽

2011 ◽

Vol 52 (5) ◽

pp. 053102 ◽

Cited By ~ 3

Author(s):

W. G. Litvinov

Keyword(s):

Turbulent Flows ◽

Newtonian Fluids ◽

Laminar And Turbulent Flows

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Parameter Extension Simulation of Turbulent Flows in a Compressor Cascade With a High Reynolds Number

Volume 2C: Turbomachinery ◽

10.1115/gt2020-14809 ◽

2020 ◽

Author(s):

Yan Jin

Keyword(s):

Reynolds Number ◽

Turbulent Flow ◽

Turbulent Flows ◽

Stokes Equations ◽

Simulation Method ◽

Potential Method ◽

Navier Stokes ◽

Reference Solution ◽

Compressor Cascade ◽

High Reynolds

Abstract The turbulent flow in a compressor cascade is calculated by using a new simulation method, i.e., parameter extension simulation (PES). It is defined as the calculation of a turbulent flow with the help of a reference solution. A special large-eddy simulation (LES) method is developed to calculate the reference solution for PES. Then, the reference solution is extended to approximate the exact solution for the Navier-Stokes equations. The Richardson extrapolation is used to estimate the model error. The compressor cascade is made of NACA0065-009 airfoils. The Reynolds number 3.82 × 105 and the attack angles −2° to 7° are accounted for in the study. The effects of the end-walls, attack angle, and tripping bands on the flow are analyzed. The PES results are compared with the experimental data as well as the LES results using the Smagorinsky, k-equation and WALE subgrid models. The numerical results show that the PES requires a lower mesh resolution than the other LES methods. The details of the flow field including the laminar-turbulence transition can be directly captured from the PES results without introducing any additional model. These characteristics make the PES a potential method for simulating flows in turbomachinery with high Reynolds numbers.

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Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

10.5194/egusphere-egu21-14221 ◽

2021 ◽

Author(s):

Christina Tsai ◽

Kuang-Ting Wu

Keyword(s):

Turbulent Flow ◽

Turbulent Flows ◽

Coherent Structures ◽

Large Scale ◽

Streamwise Velocity ◽

Turbulent Structures ◽

Temporal Properties ◽

Turbulent Statistics ◽

Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995)&#160;</span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions. &#160;<span>Subsequently,&#160;</span><span>de Silva et al. (2017)&#160;</span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div>&#160;</div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

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Unravelling turbulence near walls

Journal of Fluid Mechanics ◽

10.1017/s0022112009007708 ◽

2009 ◽

Vol 630 ◽

pp. 1-4 ◽

Cited By ~ 23

Author(s):

IVAN MARUSIC

Keyword(s):

Laminar Flow ◽

Turbulent Flow ◽

Numerical Simulations ◽

Turbulent Flows ◽

Direct Numerical Simulations ◽

Aircraft Wing ◽

Physical Mechanisms ◽

Drag And Lift

Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for example. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct numerical simulations have contributed significantly towards this understanding.

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Optimized Cooling System for PEM Fuel Cell Stack Based on Entropy Generation Minimization

Volume 1 ◽

10.1115/esda2004-58203 ◽

2004 ◽

Author(s):

M. H. Saidi ◽

A. A. Mozafari ◽

L. Sharifian

Keyword(s):

Fuel Cell ◽

Turbulent Flow ◽

Turbulent Flows ◽

Entropy Generation ◽

Design Methodology ◽

Cooling System ◽

Pem Fuel Cell ◽

Fuel Cell Stack ◽

Entropy Generation Minimization ◽

Lower Entropy

Cell temperature in fuel cells is an important parameter which highly affects fuel cell stack efficiency. A suitable cooling system should satisfy an acceptable temperature range. In this research a relevant cooling system for a specified PEM fuel cell stack has been proposed complying with the criteria and cooling requirements of the fuel cell. The effect of various parameters on the entropy generation and temperature distribution in the cooling plates are surveyed. The number of cooling plates, the number of channels in each cooling plate and the channel width is determined. Two flow regimes namely laminar and turbulent flows of the cooling fluid in channels are analyzed and a design methodology is proposed for each regime of flow. The proposed design methodology in turbulent flow will be optimized while the work destruction is minimized. However, the proposed design in laminar flow is not the optimum one but the most efficient between different configurations. The comparison between these two proposed designs show that the turbulent flow has a lower entropy generation. In addition to entropy generation minimization, to have a desirable optimum cooling system, other parameters such as the size of the cooling plates and temperature uniformity inside cooling system have been investigated in this analysis.

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Common features between the Newtonian laminar–turbulent transition and the viscoelastic drag-reducing turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.567 ◽

2019 ◽

Vol 877 ◽

pp. 405-428 ◽

Cited By ~ 8

Author(s):

Anselmo S. Pereira ◽

Roney L. Thompson ◽

Gilmar Mompean

Keyword(s):

Reynolds Number ◽

Turbulent Flow ◽

Drag Reduction ◽

Turbulent Flows ◽

Temporal Dynamics ◽

Homoclinic Orbits ◽

Theoretical Development ◽

Transitional Flows ◽

Turbulent Transition ◽

Laminar Turbulent Transition

The transition from laminar to turbulent flows has challenged the scientific community since the seminal work of Reynolds (Phil. Trans. R. Soc. Lond. A, vol. 174, 1883, pp. 935–982). Recently, experimental and numerical investigations on this matter have demonstrated that the spatio-temporal dynamics that are associated with transitional flows belong to the directed percolation class. In the present work, we explore the analysis of laminar–turbulent transition from the perspective of the recent theoretical development that concerns viscoelastic turbulence, i.e. the drag-reducing turbulent flow obtained from adding polymers to a Newtonian fluid. We found remarkable fingerprints of the variety of states that are present in both types of flows, as captured by a series of features that are known to be present in drag-reducing viscoelastic turbulence. In particular, when compared to a Newtonian fully turbulent flow, the universal nature of these flows includes: (i) the statistical dynamics of the alternation between active and hibernating turbulence; (ii) the weakening of elliptical and hyperbolic structures; (iii) the existence of high and low drag reduction regimes with the same boundary; (iv) the relative enhancement of the streamwise-normal stress; and (v) the slope of the energy spectrum decay with respect to the wavenumber. The maximum drag reduction profile was attained in a Newtonian flow with a Reynolds number near the boundary of the laminar regime and in a hibernating state. It is generally conjectured that, as the Reynolds number increases, the dynamics of the intermittency that characterises transitional flows migrate from a situation where heteroclinic connections between the upper and the lower branches of solutions are more frequent to another where homoclinic orbits around the upper solution become the general rule.

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