Advances in Turbulence

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

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Collection Editor
Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, 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 (15 papers)

2024

Jump to: 2023, 2022, 2021

14 pages, 5562 KiB  
Article
Grid Turbulence Measurements with an Acoustic Doppler Current Profiler
by Trygve K. Løken, David Lande-Sudall, Atle Jensen and Jean Rabault
Fluids 2024, 9(3), 60; https://doi.org/10.3390/fluids9030060 - 01 Mar 2024
Viewed by 832
Abstract
The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and [...] Read more.
The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and it is desirable to exploit this property in laboratory and field applications. The ADCP was tested in a towing tank, where turbulence was generated from a grid towed under controlled conditions. Grid-induced turbulence is a well-studied phenomenon and a good approximation for isotropic turbulence. Several previous experiments are available for comparison and there are developed theories within the topic. In the present experiments, a Nortek Vectrino acoustic Doppler velocimeter (ADV), which is an established instrument for turbulence measurements, was applied to validate the ADCP. It was found that the mean flow measured with the ADCP was accurate within 4% of the ADV. The turbulent variance was reasonably well resolved by the ADCP when large grid bars were towed at a high speed, but largely overestimated for lower towing speed and smaller grid bars. The effective cutoff frequency and turbulent eddy size were characterized experimentally, which provides detailed guidelines for when the ADCP data can be trusted and will allow future experimentalists to decide a priori if the Nortek Signature can be used in their setup. We conclude that the ADCP is not suitable for resolving turbulent spectra in a small-scale grid-induced flow due to the intrinsic Doppler noise and the low spatial and temporal sample resolution relative to the turbulent scales. Full article
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2023

Jump to: 2024, 2022, 2021

17 pages, 5299 KiB  
Article
Numerical Simulation of Taylor—Couette—Poiseuille Flow at Re = 10,000
by Andrey Gavrilov and Yaroslav Ignatenko
Fluids 2023, 8(10), 280; https://doi.org/10.3390/fluids8100280 - 19 Oct 2023
Viewed by 1300
Abstract
A fully developed turbulent flow in a concentric annulus, Re =10,000, ri/ro=0.5, with an inner rotating cylinder in the velocity range N=Uω/Ub=0÷4, is [...] Read more.
A fully developed turbulent flow in a concentric annulus, Re =10,000, ri/ro=0.5, with an inner rotating cylinder in the velocity range N=Uω/Ub=0÷4, is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k-ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N>0.51. With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS. Full article
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29 pages, 12576 KiB  
Article
The Effects of Flexible Cylinder Structural Dynamics to the near Wake Turbulence
by Sharul Sham Dol, Siaw Khur Wee, Tshun Howe Yong and Shaharin Anwar Sulaiman
Fluids 2023, 8(10), 270; https://doi.org/10.3390/fluids8100270 - 01 Oct 2023
Viewed by 1128
Abstract
The utilization of a rigid and projecting surface, coupled with an agitator and vortex generator, frequently results in the dissipation of more energy than the production of turbulence that meets the required criteria. By contrast, a passively oscillating flexible protruding surface can generate [...] Read more.
The utilization of a rigid and projecting surface, coupled with an agitator and vortex generator, frequently results in the dissipation of more energy than the production of turbulence that meets the required criteria. By contrast, a passively oscillating flexible protruding surface can generate a greater turbulence level. In the current study, a circular finite cylinder (cantilever) was used as the geometry of the rigid and protruding surface. Both the material and the aspect ratio were varied. Also, a local Reynolds number within the subcritical flow range (102 < ReD < 105) was considered. The results from the rigid protruding surface (finite cylinder) serve as a validation of the published results and a benchmark for the improvement of the turbulence generated by the flexible protruding surface. The results obtained via an ultrasonic velocity profiler have further demonstrated that the flexible cylinder is capable of generating greater turbulence by examining the turbulence intensity, the turbulence production term and the Reynolds stress. All the flexible cylinders that oscillate show an increase in turbulence production but at different percentages. The cylinders studied in this work ranged from the least structural stiffness (EVA) to moderate (aluminum) and the highest structural stiffness (carbon steel). Through studying the normalized amplitude responses graph for the flexible cylinders, it is found that the oscillating motion does indeed contribute to the increment. A further examination of the results shows that the increase is due to the structural velocity instead of just the oscillating motion. Full article
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25 pages, 14817 KiB  
Article
Effect of Schmidt Number on Forced Isotropic Turbulence with Passive Scalars
by Paolo Orlandi and Sergio Pirozzoli
Fluids 2023, 8(9), 248; https://doi.org/10.3390/fluids8090248 - 12 Sep 2023
Viewed by 918
Abstract
Traditionally, Fourier spectra have been employed to gain a deeper understanding of turbulence flow structures. The investigation of isotropic forced turbulence with passive scalars offers a straightforward means to examine the disparities between velocity and passive scalar spectra. This flow configuration has been [...] Read more.
Traditionally, Fourier spectra have been employed to gain a deeper understanding of turbulence flow structures. The investigation of isotropic forced turbulence with passive scalars offers a straightforward means to examine the disparities between velocity and passive scalar spectra. This flow configuration has been extensively studied in the past, encompassing a range of Reynolds and Schmidt numbers. In this present study, direct numerical simulations (DNS) of this flow are conducted at sufficiently high Reynolds numbers, enabling the formation of a wide inertial range. The primary focus of this investigation is to quantitatively assess the variations in scalar spectra with the Schmidt number (Sc). The spectra exhibit a transition from a k−5/3 scaling for low Sc to a k−4/3 scaling for high Sc. The emergence of the latter power law becomes evident at Sc = 2, with its width expanding as Sc increases. To gain further insights into the underlying flow structures, a statistical analysis is performed by evaluating quantities aligned with the principal axes of the strain field. The study reveals that enstrophy is primarily influenced by the vorticity aligned with the intermediate principal strain axis, while the scalar gradient variance is predominantly controlled by the compressive strain. To provide a clearer understanding of the differences between enstrophy and scalar gradient variance, joint probability density functions (PDFs) and visualizations of the budget terms for both quantities are presented. These visualizations serve to elucidate the distinctions between the two and offer insights into their respective behaviors. Full article
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21 pages, 8944 KiB  
Article
Numerical Study of Flow around Two Circular Cylinders in Tandem, Side-By-Side and Staggered Arrangements
by Gracjan M. Skonecki and James M. Buick
Fluids 2023, 8(5), 148; https://doi.org/10.3390/fluids8050148 - 07 May 2023
Viewed by 2021
Abstract
Simulations are presented for flow around pairs of circular cylinders at a Reynolds number of 3900. The flow is assumed to be two-dimensional and incompressible in nature and the simulations are performed using a RANS (Reynolds Averaged Navier Stokes) approach with a k [...] Read more.
Simulations are presented for flow around pairs of circular cylinders at a Reynolds number of 3900. The flow is assumed to be two-dimensional and incompressible in nature and the simulations are performed using a RANS (Reynolds Averaged Navier Stokes) approach with a k-ε model. Simulations are performed for three different configurations of the cylinders: A tandem configuration where the line joining the centre of the cylinders is parallel to the mean flow direction; side-by-side, where the centre line is perpendicular to the mean flow direction; and staggered where the centre line is an angle α to the flow direction. Simulation results are presented for cylinder separations ranging from 1.125 to 4 diameters and for values of α between 10° and 60°. The results are presented and discussed in terms of the lift and drag coefficients, the Strouhal number, the vorticity field and the flow regimes observed. The results and flow regimes are also compared to previous observations at lower Reynolds numbers to investigate the Reynolds number dependence of the phenomena. Full article
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18 pages, 6104 KiB  
Article
On the Development of an Implicit Discontinuous Galerkin Solver for Turbulent Real Gas Flows
by Edoardo Mantecca, Alessandro Colombo, Antonio Ghidoni, Gianmaria Noventa, David Pasquale and Stefano Rebay
Fluids 2023, 8(4), 117; https://doi.org/10.3390/fluids8040117 - 31 Mar 2023
Cited by 2 | Viewed by 1354
Abstract
The aim of this work is to describe an efficient implementation of cubic and multiparameter real gas models in an existing discontinuous Galerkin solver to extend its capabilities to the simulation of turbulent real gas flows. The adopted thermodynamic models are van der [...] Read more.
The aim of this work is to describe an efficient implementation of cubic and multiparameter real gas models in an existing discontinuous Galerkin solver to extend its capabilities to the simulation of turbulent real gas flows. The adopted thermodynamic models are van der Waals, Peng–Robinson, and Span–Wagner, which differ from each other in terms of accuracy and computational cost. Convective numerical fluxes across elements interfaces are calculated with a thermodynamic consistent linearized Riemann solver, whereas for boundary conditions, a linearized expression of the generalized Riemann invariants is employed. Transport properties are treated as temperature- and density-dependent quantities through multiparameter correlations. An implicit time integration is adopted; Jacobian matrix and thermodynamic derivatives are obtained with the automatic differentiation tool Tapenade. The solver accuracy is assessed by computing both steady and unsteady real gas test cases available in the literature, and the effect of the mesh size and polynomial degree of approximation on the solution accuracy is investigated. A good agreement with experimental and numerical reference data is observed and specific non-classical phenomena are well reproduced by the solver. Full article
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35 pages, 5362 KiB  
Article
Laboratory Models of Planetary Core-Style Convective Turbulence
by Emily K. Hawkins, Jonathan S. Cheng, Jewel A. Abbate, Timothy Pilegard, Stephan Stellmach, Keith Julien and Jonathan M. Aurnou
Fluids 2023, 8(4), 106; https://doi.org/10.3390/fluids8040106 - 23 Mar 2023
Cited by 5 | Viewed by 1681
Abstract
The connection between the heat transfer and characteristic flow velocities of planetary core-style convection remains poorly understood. To address this, we present novel laboratory models of rotating Rayleigh–Bénard convection in which heat and momentum transfer are simultaneously measured. Using water (Prandtl number, [...] Read more.
The connection between the heat transfer and characteristic flow velocities of planetary core-style convection remains poorly understood. To address this, we present novel laboratory models of rotating Rayleigh–Bénard convection in which heat and momentum transfer are simultaneously measured. Using water (Prandtl number, Pr6) and cylindrical containers of diameter-to-height aspect ratios of Γ3,1.5,0.75, the non-dimensional rotation period (Ekman number, E) is varied between 107E3×105 and the non-dimensional convective forcing (Rayleigh number, Ra) ranges from 107Ra1012. Our heat transfer data agree with those of previous studies and are largely controlled by boundary layer dynamics. We utilize laser Doppler velocimetry (LDV) to obtain experimental point measurements of bulk axial velocities, resulting in estimates of the non-dimensional momentum transfer (Reynolds number, Re) with values between 4×102Re5×104. Behavioral transitions in the velocity data do not exist where transitions in heat transfer behaviors occur, indicating that bulk dynamics are not controlled by the boundary layers of the system. Instead, the LDV data agree well with the diffusion-free Coriolis–Inertia–Archimedian (CIA) scaling over the range of Ra explored. Furthermore, the CIA scaling approximately co-scales with the Viscous–Archimedian–Coriolis (VAC) scaling over the parameter space studied. We explain this observation by demonstrating that the VAC and CIA relations will co-scale when the local Reynolds number in the fluid bulk is of order unity. We conclude that in our experiments and similar laboratory and numerical investigations with E107, Ra1012, Pr7, heat transfer is controlled by boundary layer physics while quasi-geostrophically turbulent dynamics relevant to core flows robustly exist in the fluid bulk. Full article
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12 pages, 414 KiB  
Article
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
by Artur V. Dmitrenko and Vladislav M. Ovsyannikov
Fluids 2023, 8(3), 81; https://doi.org/10.3390/fluids8030081 - 23 Feb 2023
Viewed by 1215
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 [...] Read more.
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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22 pages, 7697 KiB  
Article
Numerical Study of Flow Downstream a Step with a Cylinder Part 2: Effect of a Cylinder on the Flow over the Step
by Milad Abdollahpour, Paola Gualtieri, David F. Vetsch and Carlo Gualtieri
Fluids 2023, 8(2), 60; https://doi.org/10.3390/fluids8020060 - 10 Feb 2023
Cited by 1 | Viewed by 1670
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 [...] Read more.
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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20 pages, 3182 KiB  
Article
Numerical Study of Flow Downstream a Step with a Cylinder Part 1: Validation of the Numerical Simulations
by Milad Abdollahpour, Paola Gualtieri, David F. Vetsch and Carlo Gualtieri
Fluids 2023, 8(2), 55; https://doi.org/10.3390/fluids8020055 - 03 Feb 2023
Cited by 3 | Viewed by 1596
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 [...] Read more.
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: 2024, 2023, 2021

7 pages, 1017 KiB  
Communication
Sonic Eddy Model of the Turbulent Boundary Layer
by Paul Dintilhac and Robert Breidenthal
Fluids 2022, 7(1), 37; https://doi.org/10.3390/fluids7010037 - 15 Jan 2022
Cited by 1 | Viewed by 2105
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 [...] Read more.
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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18 pages, 3841 KiB  
Article
Instability and Transition of a Boundary Layer over a Backward-Facing Step
by Ming Teng and Ugo Piomelli
Fluids 2022, 7(1), 35; https://doi.org/10.3390/fluids7010035 - 14 Jan 2022
Cited by 2 | Viewed by 3412
Abstract
The development of secondary instabilities in a boundary layer over a backward-facing step is investigated numerically. Two step heights are considered, h/δo*=0.5 and 1.0 (where δo* 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/δo*=0.5 and 1.0 (where δo* 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/δo*=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/δo*=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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2021

Jump to: 2024, 2023, 2022

19 pages, 1971 KiB  
Article
A New Anisotropic Four-Parameter Turbulence Model for Low Prandtl Number Fluids
by 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 2323
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 [...] Read more.
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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19 pages, 6765 KiB  
Article
Predictions of Vortex Flow in a Diesel Multi-Hole Injector Using the RANS Modelling Approach
by Aishvarya Kumar, Jamshid Nouri and Ali Ghobadian
Fluids 2021, 6(12), 421; https://doi.org/10.3390/fluids6120421 - 23 Nov 2021
Viewed by 2518
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 [...] Read more.
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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19 pages, 1256 KiB  
Article
A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations
by Dustin Steven Weaver and Sanja Mišković
Fluids 2021, 6(8), 271; https://doi.org/10.3390/fluids6080271 - 31 Jul 2021
Cited by 18 | Viewed by 4027
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 [...] Read more.
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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