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Topical Collection "Advances in Turbulence"

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Keywords
Published Papers

A topical collection in Fluids (ISSN 2311-5521). This collection belongs to the section "Turbulence".

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Editor

Prof. Dr. Ramesh Agarwal

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Collection Editor

Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, 1 Brookings Drive, Campus Box 1099, St. Louis, MO 63130, USA
Interests: computational fluid dynamics (CFD); computational magnetohydrodynamics (MHD); electromagnetics; computational aeroacoustics; multidisciplinary design and optimization; rarefied gas dynamics and hypersonic flows, bio-fluid dynamics; flow and flight control
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Topical Collection Information

Dear Colleagues,

The aim of this Topic Collection is to invite research and review papers from the scientific community engaged in foundational, modeling, computational, and experimental research in turbulence. Turbulent flow investigations in all physical, biological, and engineering sciences are welcome. Foundational papers in turbulence may include statistical methods and theories, chaos theory and reduced order models, and other novel formulations and approaches. Modeling and computational methods may include Reynolds-averaged Navier–Stokes (RANS) models, large eddy simulation (LES), wall-modeled (WM)-LES, wall-resolved (WR)-LES, DES/DDES/IDDES, machine learning and data-driven modeling, transition modeling, intermittancy, uncertainty quantification of turbulence models, and direct numerical simulation DNS. Experimental methods may include hot-wire-anemometry (HWA), laser-Doppler-velocimetry (LDV), particle-image-velocimetry (PIV), and flow visualization techniques. Applications may include atmospheric, oceanic, and other nature-occuring flows, bioological/biomimitic flows, and flows related to industries such as aircraft, turbomachinery, automotive, agriculture, energy, and the environment, etc.

Prof. Dr. Ramesh Agarwal
Collection Editor

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Keywords

statistical theories of turbulence
chaos theory of turbulence and reduced order models
Reynolds-averaged Navier–Stokes (RANS) turbulence models of all types and categories
large eddy simulation (LES) including wall-modeled (WM) LES and wall-resolved (WR) LES
hybrid RANS/LES (DES, DDES, IDDES, SBES)*
data-driven modeling including improvement of turbulence models using uncertainty quantification (UQ) and machine learning
intermittency and transition modeling including methods based on non-linear stability theory
direct numerical simulation (DNS)
hot-wire-anemometry (HWA), laser-Doppler-velocimetry (LDV), particle-image-velocimetry (PIV)
flow visualization
applications to atmospheric, oceanic, and other nature-occurring flows
applications to external and internal biological/biomimetic flows
applications to aircraft, turbomachinery, automobiles, and other industrial products
applications to problems in energy, the environment, and agriculture etc.
any topic or application related to turbulence

*DES= Detached Eddy Simulation, DDES = Delayed Detached Eddy Simulation

IDDES= Improved Detached Eddy Simulation, SBES= Stress Blended Eddy Simulation

Published Papers (8 papers)

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2023

Jump to: 2022, 2021

Open AccessArticle

Theoretical Estimates of the Critical Reynolds Number in the Flow around the Sphere on the Basis of Theory of Stochastic Equations and Equivalence of Measures

Artur V. Dmitrenko

and

Vladislav M. Ovsyannikov

Fluids 2023, 8(3), 81; https://doi.org/10.3390/fluids8030081 - 23 Feb 2023

Viewed by 373

Abstract

The aim of this investigation is to show the solution for the critical Reynolds number in the flow around the sphere on the basis of theory of stochastic equations and equivalence of measures between turbulent and laminar motions. Solutions obtained by numerical methods (DNS, LES, RANS) require verification and in this case the theoretical results have special value. For today in the scientific literature, there is J. Talor’s implicit formula connecting the critical Reynolds number with the parameters of the initial fluctuations in the flow around the sphere. Here the derivation of the explicit formula is presented. The results show a satisfactory correspondence of the obtained theoretical dependence for the critical Reynolds number to the experiments in the flow around the sphere. Full article

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Open AccessArticle

Numerical Study of Flow Downstream a Step with a Cylinder Part 2: Effect of a Cylinder on the Flow over the Step

and

Fluids 2023, 8(2), 60; https://doi.org/10.3390/fluids8020060 - 10 Feb 2023

Viewed by 494

Abstract

In this study, divided into two parts, the effect on a two-dimensional backward-facing step flow (BFSF) of a cylinder placed downstream of the step was numerically investigated. While in Part 1, the numerical simulations carried out without the cylinder were validated using the available literature data, in Part 2 the effect of the cylinder was investigated. In the laminar regime, different Reynolds numbers were considered. In the turbulent regime, the effects on the flow structure of a cylinder placed at different horizontal and vertical locations downstream of the step were comparatively studied. When the cylinder was positioned below the step edge mid-plane, flow over the step was not altered by a cylinder. However, in other locations of a cylinder, the added cylinder modified the structure of flow, increasing the skin friction coefficient in the recirculation zone. Furthermore, the pressure coefficient of the bottom wall increased immediately downstream of the cylinder and farther downstream of the reattachment point and remained stable in the flow recovery process. Moreover, the presence of the step significantly influenced the dynamics of the vortex generation and shedding leading to an asymmetric wake distribution. Full article

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Open AccessArticle

Numerical Study of Flow Downstream a Step with a Cylinder Part 1: Validation of the Numerical Simulations

and

Fluids 2023, 8(2), 55; https://doi.org/10.3390/fluids8020055 - 03 Feb 2023

Cited by 1 | Viewed by 441

Abstract

The backward-facing step flow (BFSF) is a classical problem in fluid mechanics, hydraulic engineering, and environmental hydraulics. The nature of this flow, consisting of separation and reattachment, makes it a problem worthy of investigation. In this study, divided into two parts, the effect of a cylinder placed downstream of the step on the 2D flow structure was investigated. In Part 1, the classical 2D BFSF was validated by using OpenFOAM. The BFSF characteristics (reattachment, recirculation zone, velocity profile, skin friction coefficient, and pressure coefficient) were validated for a step-height Reynolds number in the range from 75 to 9000, covering both laminar and turbulent flow. The numerical results at different Reynolds numbers of laminar flow and four RANS turbulence models (standard k-ε, RNG k-ε, standard k-ω, and SST k-ω) were found to be in good agreement with the literature data. In laminar flow, the average error between the numerical results and experimental data for velocity profiles and reattachment lengths and the skin friction coefficient were lower than 8.1, 18, and 20%, respectively. In turbulent flow, the standard k-ε was the most accurate model in predicting pressure coefficients, skin friction coefficient, and reattachment length with an average error lower than 20.5, 17.5, and 6%, respectively. In Part 2, the effect on the 2D flow structure of a cylinder placed at different horizontal and vertical locations downstream of the step was investigated. Full article

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2022

Jump to: 2023, 2021

Open AccessCommunication

Sonic Eddy Model of the Turbulent Boundary Layer

Paul Dintilhac

and

Robert Breidenthal

Fluids 2022, 7(1), 37; https://doi.org/10.3390/fluids7010037 - 15 Jan 2022

Cited by 1 | Viewed by 1517

Abstract

The effects of Mach number on the skin friction and velocity fluctuations of the turbulent boundary layer are considered through a sonic eddy model. Originally proposed for free shear flows, the model assumes that the eddies responsible for momentum transfer have a rotation Mach number of unity, with the entrainment rate limited by acoustic signaling. Under this assumption, the model predicts that the skin friction coefficient should go as the inverse Mach number in a regime where the Mach number is larger than unity but smaller than the square root of the Reynolds number. The velocity fluctuations normalized by the friction velocity should be the inverse square root of the Mach number in the same regime. Turbulent transport is controlled by acoustic signaling. The density field adjusts itself such that the Reynolds stresses correspond to the momentum transport. In contrast, the conventional van Driest–Morkovin view is that the Mach number effects are due to density variations directly. A new experiment or simulation is proposed to test this model using different gases in an incompressible boundary layer, following the example of Brown and Roshko in the free shear layer. Full article

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Graphical abstract

Open AccessArticle

Instability and Transition of a Boundary Layer over a Backward-Facing Step

Ming Teng

and

Ugo Piomelli

Fluids 2022, 7(1), 35; https://doi.org/10.3390/fluids7010035 - 14 Jan 2022

Viewed by 2232

Abstract

The development of secondary instabilities in a boundary layer over a backward-facing step is investigated numerically. Two step heights are considered,

h / δ_{o}^{*} = 0.5

and

1.0

(where

δ_{o}^{*}

is the displacement thickness at the step location), in [...] Read more.

The development of secondary instabilities in a boundary layer over a backward-facing step is investigated numerically. Two step heights are considered,

h / δ_{o}^{*} = 0.5

and

1.0

(where

δ_{o}^{*}

is the displacement thickness at the step location), in addition to a reference flat-plate case. A case with a realistic freestream-velocity distribution is also examined. A controlled K-type transition is initiated using a narrow ribbon upstream of the step, which generates small and monochromatic perturbations by periodic blowing and suction. A well-resolved direct numerical simulation is performed. The step height and the imposed freestream-velocity distribution exert a significant influence on the transition process. The results for the

h / δ_{o}^{*} = 1.0

case exhibit a rapid transition primarily due to the Kelvin–Helmholtz instability downstream of step; non-linear interactions already occur within the recirculation region, and the initial symmetry and periodicity of the flow are lost by the middle stage of transition. In contrast, case

h / δ_{o}^{*} = 0.5

presents a transition road map in which transition occurs far downstream of the step, and the flow remains spatially symmetric and temporally periodic until the late stage of transition. A realistic freestream-velocity distribution (which induces an adverse pressure gradient) advances the onset of transition to turbulence, but does not fundamentally modify the flow features observed in the zero-pressure gradient case. Considering the budgets of the perturbation kinetic energy, both the step and the induced pressure-gradient increase, rather than modify, the energy transfer. Full article

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Graphical abstract

2021

Jump to: 2023, 2022

Open AccessArticle

A New Anisotropic Four-Parameter Turbulence Model for Low Prandtl Number Fluids

Giacomo Barbi

Valentina Giovacchini

and

Sandro Manservisi

Fluids 2022, 7(1), 6; https://doi.org/10.3390/fluids7010006 - 22 Dec 2021

Cited by 1 | Viewed by 1654

Abstract

Due to their interesting thermal properties, liquid metals are widely studied for heat transfer applications where large heat fluxes occur. In the framework of the Reynolds-Averaged Navier–Stokes (RANS) approach, the Simple Gradient Diffusion Hypothesis (SGDH) and the Reynolds Analogy are almost universally invoked for the closure of the turbulent heat flux. Even though these assumptions can represent a reasonable compromise in a wide range of applications, they are not reliable when considering low Prandtl number fluids and/or buoyant flows. More advanced closure models for the turbulent heat flux are required to improve the accuracy of the RANS models dealing with low Prandtl number fluids. In this work, we propose an anisotropic four-parameter turbulence model. The closure of the Reynolds stress tensor and turbulent heat flux is gained through nonlinear models. Particular attention is given to the modeling of dynamical and thermal time scales. Numerical simulations of low Prandtl number fluids have been performed over the plane channel and backward-facing step configurations. Full article

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Open AccessFeature PaperArticle

Predictions of Vortex Flow in a Diesel Multi-Hole Injector Using the RANS Modelling Approach

Aishvarya Kumar

Jamshid Nouri

and

Ali Ghobadian

Fluids 2021, 6(12), 421; https://doi.org/10.3390/fluids6120421 - 23 Nov 2021

Viewed by 1818

Abstract

The occurrence of vortices in the sac volume of automotive multi-hole fuel injectors plays an important role in the development of vortex cavitation, which directly influences the flow structure and emerging sprays that, in turn, influence the engine performance and emissions. In this study, the RANS-based turbulence modelling approach was used to predict the internal flow in a vertical axis-symmetrical multi-hole (6) diesel fuel injector under non-cavitating conditions. The project aimed to predict the aforementioned vortical structures accurately at two different needle lifts in order to form a correct opinion about their occurrence. The accuracy of the simulations was assessed by comparing the predicted mean axial velocity and RMS velocity of LDV measurements, which showed good agreement. The flow field analysis predicted a complex, 3D, vortical flow structure with the presence of different types of vortices in the sac volume and the nozzle hole. Two main types of vortex were detected: the “hole-to-hole” connecting vortex, and double “counter-rotating” vortices emerging from the needle wall and entering the injector hole facing it. Different flow patterns in the rotational direction of the “hole-to-hole” vortices have been observed at the low needle lift (anticlockwise) and full needle lift (clockwise), due to their different flow passages in the sac, causing a much higher momentum inflow at the lower lift with its much narrower flow passage. Full article

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Open AccessArticle

A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations

Dustin Steven Weaver

and

Sanja Mišković

Fluids 2021, 6(8), 271; https://doi.org/10.3390/fluids6080271 - 31 Jul 2021

Cited by 6 | Viewed by 1750

Abstract

This paper presents an analysis of linear viscous stress Favre averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier–Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 13,000 and 51,000 using two different tube diameters. It is found that a modified k-

ε

turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k-

ω

SST/BSL also provided suitable results. Full article

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Published Papers (8 papers)

2023

Jump to: 2022, 2021

2022

Jump to: 2023, 2021

2021

Jump to: 2023, 2022

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