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Computational Fluid Dynamics and Conjugate Heat Transfer

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A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Thermodynamics".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 31424

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Special Issue Editors

Dr. Florent Duchaine

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Guest Editor

Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique, 01 31057 Toulouse Cedex, France
Interests: computational fluid dynamics; large eddy simulations; Multiphysics; conjugate heat transfer; combustion; turbomachinery; high-performance computing

Dr. Daniel Mira

E-Mail Website
Guest Editor

Barcelona Supercomputing Centre, 08034 Barcelona, Spain
Interests: computational fluid dynamics; combustion; high-performance computing; Multiphysics; conjugate heat transfer; large eddy simulations; propulsion; numerical methods; machine learning

Special Issue Information

Dear Colleagues,

Multiphysics, multi-scale and multi-component simulations will play an increasing role in gathering a better understanding of turbulent non-reacting and reacting flows, as well as in the design of new technologies. This is particularly true of the thermal field, which is present in a very large number of applications: knowing the thermal environment is of prime importance for design purposes (the melting of combustion chamber walls), as well as to well for understanding physical mechanisms (liquid evaporation, flame stabilization). Although complex fluid motions are of prime importance for first order flow predictions, higher quality numerical predictions will require advanced computational fluid dynamics (CFD) coupled to more physics. In many fields (combustion, rotating machines, aerodynamic, acoustic) unsteady flow methods such as large eddy simulation (LES) or direct numerical simulation (DNS) already give very accurate results. The step forward is, hence, to couple these solutions with other physics, to compose Multiphysics: muti-component frameworks addressing coupled real flows. The special issue of Entropy on "Computational Fluid Dynamics and Conjugate Heat Transfer" aims to provide state of the art methodologies in the field of conjugate heat transfer, where CFD solvers are coupled to heat transfer (including conduction and radiation). Specific topics could include, but are not limited to, physical modeling, numerics, high performance computing, methodologies and framework, with particular interest in academic research and industrial applications.

Dr. Florent Duchaine
Dr. Daniel Mira
Guest Editors

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Keywords

computational fluid dynamics
conjugate heat transfer
code coupling
high fidelity simulations
high performance computing
turbulent flows
convection
conduction
radiation
combustion

Published Papers (11 papers)

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Research

24 pages, 7590 KiB

Open AccessFeature PaperArticle

Implicit Subgrid-Scale Modeling of a Mach 2.5 Spatially Developing Turbulent Boundary Layer

by Guillermo Araya and Christian Lagares

Entropy 2022, 24(4), 555; https://doi.org/10.3390/e24040555 - 15 Apr 2022

Cited by 3 | Viewed by 1963

Abstract

We employ numerically implicit subgrid-scale modeling provided by the well-known streamlined upwind/Petrov–Galerkin stabilization for the finite element discretization of advection–diffusion problems in a Large Eddy Simulation (LES) approach. Whereas its original purpose was to provide sufficient algorithmic dissipation for a stable and convergent numerical method, more recently, it has been utilized as a subgrid-scale (SGS) model to account for the effect of small scales, unresolvable by the discretization. The freestream Mach number is 2.5, and direct comparison with a DNS database from our research group, as well as with experiments from the literature of adiabatic supersonic spatially turbulent boundary layers, is performed. Turbulent inflow conditions are generated via our dynamic rescaling–recycling approach, recently extended to high-speed flows. Focus is given to the assessment of the resolved Reynolds stresses. In addition, flow visualization is performed to obtain a much better insight into the physics of the flow. A weak compressibility effect is observed on thermal turbulent structures based on two-point correlations (IC vs. supersonic). The Reynolds analogy (

u^{'}

vs.

t^{'}

) approximately holds for the supersonic regime, but to a lesser extent than previously observed in incompressible (IC) turbulent boundary layers, where temperature was assumed as a passive scalar. A much longer power law behavior of the mean streamwise velocity is computed in the outer region when compared to the log law at Mach 2.5. Implicit LES has shown very good performance in Mach 2.5 adiabatic flat plates in terms of the mean flow (i.e.,

C_{f}

and

U_{V D}^{+}

). iLES significantly overpredicts the peak values of

u'

, and consequently Reynolds shear stress peaks, in the buffer layer. However, excellent agreement between the turbulence intensities and Reynolds shear stresses is accomplished in the outer region by the present iLES with respect to the external DNS database at similar Reynolds numbers. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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20 pages, 7640 KiB

Open AccessArticle

Numerical and Experimental Investigation of the Conjugate Heat Transfer for a High-Pressure Pneumatic Control Valve Assembly

by Mboulé Ngwa, Longlong Gao and Baoren Li

Entropy 2022, 24(4), 451; https://doi.org/10.3390/e24040451 - 24 Mar 2022

Cited by 3 | Viewed by 2545

Abstract

This paper uses heat transfer experiments and computational fluid dynamics (CFD) simulations to investigate the conjugate heat transfer (CHT) in a high-pressure pneumatic control valve assembly. A heat transfer test rig was constructed, and time–temperature histories of five test points placed on the valve assembly’s outer surface were recorded for study validation. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) CFD methods with the standard k-ε turbulence closure equations were adopted in the numerical computations. Polyhedral grids were used; time step and mesh convergence studies were conducted. Simulated and measured temperatures profile comparisons revealed a good agreement. The CHT results obtained from CFD showed huge velocity fields downstream of the valve throat and the vent hole. The airflow through the valve was icy, mainly in the supersonic flow areas. Low temperatures below 273.15 K were recorded on the internal and external walls of the valve assembly. The consistency of the measured data with the numerical results demonstrates the effectiveness of polyhedral grids in exploring the CHT using CFD methods. The local entropy production rate analysis revealed that irreversibility is mainly due to viscous dissipation. The current CHT investigation provides a potential basis for thermostress analysis and optimization. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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20 pages, 4713 KiB

Open AccessArticle

Prediction of Wall Heat Fluxes in a Rocket Engine with Conjugate Heat Transfer Based on Large-Eddy Simulation

by Luc Potier, Florent Duchaine, Bénédicte Cuenot, Didier Saucereau and Julien Pichillou

Entropy 2022, 24(2), 256; https://doi.org/10.3390/e24020256 - 9 Feb 2022

Cited by 4 | Viewed by 2035

Abstract

Although a lot of research and development has been done to understand and master the major physics involved in cryogenic rocket engines (combustion, feeding systems, heat transfer, stability, efficiency, etc.), the injection system and wall heat transfer remain critical issues due to complex physics, leading to atomization in the subcritical regime and the interactions of hot gases with walls. In such regimes, the fuel is usually injected through a coaxial annulus and triggers the atomization of the central liquid oxidizer jet. This type of injector is often referred to as air-assisted, or coaxial shear, injector, and has been extensively studied experimentally. Including such injection in numerical simulations requires specific models as simulating the atomization process is still out of reach in practical industrial systems. The effect of the injection model on the flame stabilization process and thus on wall heat fluxes is of critical importance when it comes to the design of wall-cooling systems. Indeed, maximizing the heat flux extracted from the chamber can lead to serious gain for the cooling and feeding systems for expander-type feeding cycles where the thermal energy absorbed by the coolant is converted into kinetic energy to drive the turbo-pumps of the feeding system. The methodology proposed in this work to numerically predict the flame topology and associated heat fluxes is based on state-of-the-art methods for turbulent reactive flow field predictions for rocket engines, including liquid injection, combustion model, and wall treatment. For this purpose, high-fidelity Large Eddy Simulation Conjugate Heat Transfer, along with a reduced kinetic mechanism for the prediction of

H_{2} / O_{2}

chemistry, liquid injection model LOx sprays, and the use of a specific wall modeling to correctly predict heat flux for large temperature ratio between the bulk flow and the chamber walls, is used. A smooth and a longitudinally ribbed combustor configuration from JAXA are simulated. The coupling strategy ensures a rapid convergence for a limited additional cost compared to a fluid-only simulation, and the wall heat fluxes display a healthy trend compared to the experimental measurements. An increase of heat transfer coherent with the literature is observed when walls are equipped with ribs, compared to smooth walls. The heat transfer enhancement of the ribbed configuration with respect to the smooth walls is coherent with results from the literature, with an increase of around

+ 80 %

of wall heat flux extracted for the same chamber diameter. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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19 pages, 4452 KiB

Open AccessArticle

Numerical Investigation of Heat Transfer Characteristics of scCO₂ Flowing in a Vertically-Upward Tube with High Mass Flux

by Kaigang Gong, Bingguo Zhu, Bin Peng and Jixiang He

Entropy 2022, 24(1), 79; https://doi.org/10.3390/e24010079 - 1 Jan 2022

Cited by 4 | Viewed by 1616

Abstract

In this work, the heat transfer characteristics of supercritical pressure CO₂ in vertical heating tube with 10 mm inner diameter under high mass flux were investigated by using an SST k-ω turbulent model. The influences of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the heat transfer of supercritical pressure CO₂ were discussed. Our results show that the buoyancy and flow acceleration effect based on single phase fluid assumption fail to explain the current simulation results. Here, supercritical pseudo-boiling theory is introduced to deal with heat transfer of scCO₂. scCO₂ is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. A physical model of scCO₂ heat transfer in vertical heating tube was established containing a gas-like layer near the wall and a liquid-like fluid layer. Detailed distribution of thermophysical properties and turbulence in radial direction show that scCO₂ heat transfer is greatly affected by the thickness of gas-like film, thermal properties of gas-like film and turbulent kinetic energy in the near-wall region. Buoyancy parameters Bu < 10⁻⁵, Bu* < 5.6 × 10⁻⁷ and flow acceleration parameter K_v < 3 × 10⁻⁶ in this paper, which indicate that buoyancy effect and flow acceleration effect has no influence on heat transfer of scCO₂ under high mass fluxes. This work successfully explains the heat transfer mechanism of supercritical fluid under high mass flux. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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17 pages, 6051 KiB

Open AccessArticle

Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins

by Yuting Jia, Jianwei Huang, Jingtao Wang and Hongwei Li

Entropy 2021, 23(11), 1482; https://doi.org/10.3390/e23111482 - 9 Nov 2021

Cited by 19 | Viewed by 2303

Abstract

A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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46 pages, 2168 KiB

Open AccessArticle

Application of Euler Neural Networks with Soft Computing Paradigm to Solve Nonlinear Problems Arising in Heat Transfer

by Naveed Ahmad Khan, Osamah Ibrahim Khalaf, Carlos Andrés Tavera Romero, Muhammad Sulaiman and Maharani A. Bakar

Entropy 2021, 23(8), 1053; https://doi.org/10.3390/e23081053 - 16 Aug 2021

Cited by 48 | Viewed by 4378

Abstract

In this study, a novel application of neurocomputing technique is presented for solving nonlinear heat transfer and natural convection porous fin problems arising in almost all areas of engineering and technology, especially in mechanical engineering. The mathematical models of the problems are exploited by the intelligent strength of Euler polynomials based Euler neural networks (ENN’s), optimized with a generalized normal distribution optimization (GNDO) algorithm and Interior point algorithm (IPA). In this scheme, ENN’s based differential equation models are constructed in an unsupervised manner, in which the neurons are trained by GNDO as an effective global search technique and IPA, which enhances the local search convergence. Moreover, a temperature distribution of heat transfer and natural convection porous fin are investigated by using an ENN-GNDO-IPA algorithm under the influence of variations in specific heat, thermal conductivity, internal heat generation, and heat transfer rate, respectively. A large number of executions are performed on the proposed technique for different cases to determine the reliability and effectiveness through various performance indicators including Nash–Sutcliffe efficiency (NSE), error in Nash–Sutcliffe efficiency (ENSE), mean absolute error (MAE), and Thiel’s inequality coefficient (TIC). Extensive graphical and statistical analysis shows the dominance of the proposed algorithm with state-of-the-art algorithms and numerical solver RK-4. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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28 pages, 6086 KiB

Open AccessArticle

Prediction of Liner Metal Temperature of an Aeroengine Combustor with Multi-Physics Scale-Resolving CFD

by Davide Bertini, Lorenzo Mazzei and Antonio Andreini

Entropy 2021, 23(7), 901; https://doi.org/10.3390/e23070901 - 15 Jul 2021

Cited by 2 | Viewed by 2507

Abstract

Computational Fluid Dynamics is a fundamental tool to simulate the flow field and the multi-physics nature of the phenomena involved in gas turbine combustors, supporting their design since the very preliminary phases. Standard steady state RANS turbulence models provide a reasonable prediction, despite some well-known limitations in reproducing the turbulent mixing in highly unsteady flows. Their affordable cost is ideal in the preliminary design steps, whereas, in the detailed phase of the design process, turbulence scale-resolving methods (such as LES or similar approaches) can be preferred to significantly improve the accuracy. Despite that, in dealing with multi-physics and multi-scale problems, as for Conjugate Heat Transfer (CHT) in presence of radiation, transient approaches are not always affordable and appropriate numerical treatments are necessary to properly account for the huge range of characteristics scales in space and time that occur when turbulence is resolved and heat conduction is simulated contextually. The present work describes an innovative methodology to perform CHT simulations accounting for multi-physics and multi-scale problems. Such methodology, named U-THERM3D, is applied for the metal temperature prediction of an annular aeroengine lean burn combustor. The theoretical formulations of the tool are described, together with its numerical implementation in the commercial CFD code ANSYS Fluent. The proposed approach is based on a time de-synchronization of the involved time dependent physics permitting to significantly speed up the calculation with respect to fully coupled strategy, preserving at the same time the effect of unsteady heat transfer on the final time averaged predicted metal temperature. The results of some preliminary assessment tests of its consistency and accuracy are reported before showing its exploitation on the real combustor. The results are compared against steady-state calculations and experimental data obtained by full annular tests at real scale conditions. The work confirms the importance of high-fidelity CFD approaches for the aerothermal prediction of liner metal temperature. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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30 pages, 3468 KiB

Open AccessArticle

A Coupling Framework for Multi-Domain Modelling and Multi-Physics Simulations

by Dario Amirante, Vlad Ganine, Nicholas J. Hills and Paolo Adami

Entropy 2021, 23(6), 758; https://doi.org/10.3390/e23060758 - 16 Jun 2021

Cited by 3 | Viewed by 2426

Abstract

This paper describes a coupling framework for parallel execution of different solvers for multi-physics and multi-domain simulations with an arbitrary number of adjacent zones connected by different physical or overlapping interfaces. The coupling architecture is based on the execution of several instances of the same coupling code and relies on the use of smart edges (i.e., separate processes) dedicated to managing the exchange of information between two adjacent regions. The collection of solvers and coupling sessions forms a flexible and modular system, where the data exchange is handled by independent servers that are dedicated to a single interface connecting two solvers’ sessions. Accuracy and performance of the strategy is considered for turbomachinery applications involving Conjugate Heat Transfer (CHT) analysis and Sliding Plane (SP) interfaces. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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20 pages, 6892 KiB

Open AccessArticle

Predictions of Conjugate Heat Transfer in Turbulent Channel Flow Using Advanced Wall-Modeled Large Eddy Simulation Techniques

by Yongxiang Li, Florian Ries, Kaushal Nishad and Amsini Sadiki

Entropy 2021, 23(6), 725; https://doi.org/10.3390/e23060725 - 7 Jun 2021

Cited by 5 | Viewed by 2462

Abstract

In this paper, advanced wall-modeled large eddy simulation (LES) techniques are used to predict conjugate heat transfer processes in turbulent channel flow. Thereby, the thermal energy transfer process involves an interaction of conduction within a solid body and convection from the solid surface by fluid motion. The approaches comprise a two-layer RANS–LES approach (zonal LES), a hybrid RANS–LES representative, the so-called improved delayed detached eddy simulation method (IDDES) and a non-equilibrium wall function model (WFLES), respectively. The results obtained are evaluated in comparison with direct numerical simulation (DNS) data and wall-resolved LES including thermal cases of large Reynolds numbers where DNS data are not available in the literature. It turns out that zonal LES, IDDES and WFLES are able to predict heat and fluid flow statistics along with wall shear stresses and Nusselt numbers accurately and that are physically consistent. Furthermore, it is found that IDDES, WFLES and zonal LES exhibit significantly lower computational costs than wall-resolved LES. Since IDDES and especially zonal LES require considerable extra work to generate numerical grids, this study indicates in particular that WFLES offers a promising near-wall modeling strategy for LES of conjugated heat transfer problems. Finally, an entropy generation analysis using the various models showed that the viscous entropy production is zero inside the solid region, peaks at the solid–fluid interface and decreases rapidly with increasing wall distance within the fluid region. Except inside the solid region, where steep temperature gradients lead to high (thermal) entropy generation rates, a similar behavior is monitored for the entropy generation by heat transfer process. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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28 pages, 12777 KiB

Open AccessArticle

Computational Modeling of Boundary Layer Flashback in a Swirling Stratified Flame Using a LES-Based Non-Adiabatic Tabulated Chemistry Approach

by Xudong Jiang, Yihao Tang, Zhaohui Liu and Venkat Raman

Entropy 2021, 23(5), 567; https://doi.org/10.3390/e23050567 - 2 May 2021

Cited by 8 | Viewed by 2749

Abstract

When operating under lean fuel–air conditions, flame flashback is an operational safety issue in stationary gas turbines. In particular, with the increased use of hydrogen, the propagation of the flame through the boundary layers into the mixing section becomes feasible. Typically, these mixing regions are not designed to hold a high-temperature flame and can lead to catastrophic failure of the gas turbine. Flame flashback along the boundary layers is a competition between chemical reactions in a turbulent flow, where fuel and air are incompletely mixed, and heat loss to the wall that promotes flame quenching. The focus of this work is to develop a comprehensive simulation approach to model boundary layer flashback, accounting for fuel–air stratification and wall heat loss. A large eddy simulation (LES) based framework is used, along with a tabulation-based combustion model. Different approaches to tabulation and the effect of wall heat loss are studied. An experimental flashback configuration is used to understand the predictive accuracy of the models. It is shown that diffusion-flame-based tabulation methods are better suited due to the flashback occurring in relatively low-strain and lean fuel–air mixtures. Further, the flashback is promoted by the formation of features such as flame tongues, which induce negative velocity separated boundary layer flow that promotes upstream flame motion. The wall heat loss alters the strength of these separated flows, which in turn affects the flashback propensity. Comparisons with experimental data for both non-reacting cases that quantify fuel–air mixing and reacting flashback cases are used to demonstrate predictive accuracy. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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16 pages, 768 KiB

Open AccessArticle

Lattice Boltzmann Solver for Multiphase Flows: Application to High Weber and Reynolds Numbers

by Seyed Ali Hosseini, Hesameddin Safari and Dominique Thevenin

Entropy 2021, 23(2), 166; https://doi.org/10.3390/e23020166 - 29 Jan 2021

Cited by 11 | Viewed by 2617

Abstract

The lattice Boltzmann method, now widely used for a variety of applications, has also been extended to model multiphase flows through different formulations. While already applied to many different configurations in low Weber and Reynolds number regimes, applications to higher Weber/Reynolds numbers or larger density/viscosity ratios are still the topic of active research. In this study, through a combination of a decoupled phase-field formulation—the conservative Allen–Cahn equation—and a cumulant-based collision operator for a low-Mach pressure-based flow solver, we present an algorithm that can be used for higher Reynolds/Weber numbers. The algorithm was validated through a variety of test cases, starting with the Rayleigh–Taylor instability in both 2D and 3D, followed by the impact of a droplet on a liquid sheet. In all simulations, the solver correctly captured the flow dynamics andmatched reference results very well. As the final test case, the solver was used to model droplet splashing on a thin liquid sheet in 3D with a density ratio of 1000 and kinematic viscosity ratio of 15, matching the water/air system at We = 8000 and Re = 1000. Results showed that the solver correctly captured the fingering instabilities at the crown rim and their subsequent breakup, in agreement with experimental and numerical observations reported in the literature. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics and Conjugate Heat Transfer)

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