A cell-based smoothed finite element method for incompressible turbulent flows

Purpose The purpose of this paper is to investigate the feasibility of solving turbulent flows based on smoothed finite element method (S-FEM). Then, the differences between S-FEM and finite element method (FEM) in dealing with turbulent flows are compared. Design/methodology/approach The stabilization scheme, the streamline-upwind/Petrov-Galerkin stabilization is coupled with stabilized pressure gradient projection in the fractional step framework. The Reynolds-averaged Navier-Stokes equations with standard k-epsilon model are selected to solve turbulent flows based on S-FEM and FEM. Standard wall functions are applied to predict boundary layer profiles. Findings This paper explores a completely new application of S-FEM on turbulent flows. The adopted stabilization scheme presents a good performance on stabilizing the flows, especially for very high Reynolds numbers flows. An advantage of S-FEM is found in applying wall functions comparing with FEM. The differences between S-FEM and FEM have been investigated. Research limitations/implications The research in this work is limited to the two-dimensional incompressible turbulent flow. Practical implications The verification and validation of a new combination are conducted by several numerical examples. The new combination could be used to deal with more complicated turbulent flows. Social implications The applications of the new combination to study basic and complex turbulent flow are also presented, which demonstrates its potential to solve more turbulent flows in nature and engineering. Originality/value This work carries out a great extension of S-FEM in simulations of fluid dynamics. The new combination is verified to be very effective in handling turbulent flows. The performances of S-FEM and FEM on turbulent flows were analyzed by several numerical examples. Superior results were found compared with existing results and experiments. Meanwhile, S-FEM has an advantage of accuracy in predicting boundary layer profile.

Large Eddy Simulation with wall functions of Ahmed body

Large Eddy Simulation with Wall Function (WFLES) is known to be a cheap alternative to classical LES methods for simulation of flow where large and complex computational meshes are typically required. This makes it attractive for engineering applications. However experience of applying such methods to complex turbulent flows with flow separation and reattachment is still little-known in literature. In this work WFLES of flow around simplified car body with slant angle equal to 25 degrees and ReL = 2.8 · 106 is carried out on Octree mesh to demonstrate the capabilities and limitations of the method in such type of the flow. The results on a series of meshes show that even though the general flow topology is well captured, the critical part of the flow on the slant is hardly predicted even on 100 mln mesh. It is concluded that the prediction of separation above the slant requires significant mesh refinement even in the frame of WFLES.

On mesh requirements for Large Eddy Simulation with Wall Functions

The results of using Large Eddy Simulation with Wall Functions (WFLES) in application to basic wall-bounded flows, such as turbulent boundary layer and channel flow cases are presented. In particular, it is shown that WFLES is suitable for predicting wall bounded flows and provides reasonable accuracy when using appropriate grids. The grid for WFLES should have isotropic cells with size smaller than 10% of the boundary layer thickness. Using coarser grids or anisotropic cells leads to significant reduction of accuracy.

Simulation of turbulent flow over the hill

An airflow around a hilly area is simulated by numerically solving the Reynolds-averaged Navier-Stokes equations within the open OpenFOAM 2006 package. To simulate turbulence, standard turbulence models implemented in OpenFOAM 2006 were used together with wall functions. The results of numerical calculations were compared to the numerical data obtained using the CFL3D and FUN3D packages.

Physical–numerical parameters in laminar simulations of natural convection on three-dimensional square plates

Purpose The purpose of this study is to analyze the influence of the main physical–numerical parameters in the computational evaluation of natural convection heat transfer rates in isothermal flat square plates in the laminar regime. Moreover by experimentally validate the results of the numerical models and define the best parameter settings for the problem situation studied. Design/methodology/approach The present work is an extension of the study by Verderio Junior et al. (2021), differing in the modeling, results analysis and conclusions for the laminar flow regime with Rade=1×105. The analysis of the influence and precision of the physical–numerical parameters: boundary conditions, degree of mesh refinement, refinement layers and κ – ω SST and κ – ε turbulence models, occurred from the results from 48 numerical models, which were simulated using the OpenFOAM® software. Comparing the experimental mean Nusselt number with the numerical values obtained in the simulations and the analysis of the relative errors were used in the evaluation of the advantages, restrictions and selection of the most adequate parameters to the studied problem situation. Findings The numerical results of the simulations were validated, with excellent precision, from the experimental reference by Kitamura et al. (2015). The application of the κ – ω SST and κ – ε turbulence models and the boundary conditions (with and without wall functions) were also physically validated. The use of the κ – ω SST and κ – ε turbulence models, in terms of cost-benefit and precision, proved to be inefficient in the problem situation studied. Simulations without turbulence models proved to be the best option for the physical model for the studies developed. The use of refinement layers, especially in applications with wall functions and turbulence models, proved unfeasible. Practical implications Use of the physical–numerical parameters studied and validated, and application of the modeling and analysis methodology developed in projects and optimizations of natural convection thermal systems in a laminar flow regime. Just like, reduce costs and the dependence on the construction of experimental apparatus to obtain experimental results and in the numerical-experimental validation process. Social implications Exclusive use of free and open-source computational tools as an alternative to feasible research in the computational fluid dynamics area in conditions of budget constraints and lack of higher value-added infrastructure, with applicability in the academic and industrial areas. Originality/value The results and discussions presented are original and new for the applied study of laminar natural convection in isothermal flat plate, with analysis and validation of the main physical and numerical influence parameters.

Development of virtual fan flow and acoustic performance testers based on RANS solvers and acoustic analogy

As the potential of computational resources dramatically increases, the so-called computer-aided engineering readily replaces experiment-based engineering in related industrial fields. In this study, the virtual fan flow and acoustic performance testers are developed using the RANS solvers and the acoustic analogy. Two types of forward-curved centrifugal fans are selected for numerical and experimental investigations into its flow and acoustic performances. First, to experimentally evaluate the performances of the centrifugal fan units, their P-Q curves and sound power levels are measured using a fan flow performance tester and a semi-anechoic chamber, respectively. Second, the virtual fan flow and acoustic performance testers are constructed using the RANS solvers and the acoustic analogy based on the FW-H equation and CFD method. The validity of the current virtual methods is confirmed by comparing the prediction results with the measured ones. During the validation, the effects of the wall functions, y+ distribution, and turbulence models on predicted flow performance accuracy are closely examined. The effects of the integral surfaces used for the computation of the FW-H equations are also assessed on the predicted spectral levels of sound pressure.

Physical–numerical parameters in turbulent simulations of natural convection on three-dimensional square plates

Purpose This paper aims to study, experimentally validate and select the main physical and numerical parameters of influence in computational numerical simulations to evaluate mean heat flux by natural convection on square flat plates. Design/methodology/approach Several numerical models were built to study the influence of physical and numerical parameters about the predictions of the natural convection heat transfer rates on the surface of a flat plate with aspect ratio = 1, in isothermal conditions, turbulent regime and using the free and open-source software OpenFOAM®. The studied parameters were: boundary conditions (using or not using wall functions in properties ε, κ, νt and ω), degree of mesh refinement, refinement layers and turbulence models [κ – ε and κ – ω Shear Stress Transport (SST)]. From the comparison of the values of the mean Nusselt number, obtained from numerical simulations and literature experimental results, the authors evaluated the precision of the studied parameters, validating and selecting the most appropriate to the analyzed problem situation. Findings The validation and agreement of the numerical results could be proven with excellent precision from experimental references of the technical scientific literature. More refined meshes with refinement layers were not suitable for the studies developed. The κ – ε and κ – ω SST turbulence models, in meshes without refinement layers, proved to be equivalent. Whether or not to use wall functions in turbulent boundary conditions proved to be irrelevant as to the accuracy of results for the problem situation studied. Practical implications Use of the physical and numerical parameters is studied and validated for various applications in natural convection heat transfer of technology and industry areas. Social implications Use of free and open-source software as a research tool in the Computational Fluid Dynamics (CFD) area, especially in conditions without large financial resources or state-of-the-art infrastructure. Originality/value To the best of the authors’ knowledge, this work is yet not available in existing literature.

Experimental and Numerical Study of Free Convection in a Vertical Channel with Opposing Buoyancy Forces

Free convective heat transfer inside a vertical channel was studied both experimentally and numerically. An experimental model of an isothermally, asymmetrically heated vertical channel was constructed to study various cases of opposing buoyancy forces. Many studies in the literature have investigated buoyancy forces in a single direction. The study presented here investigated opposing buoyancy forces, where one wall is warmer than the ambient and the other wall is cooler than the ambient. Five different temperature ratios were studied using four different channel spacings between the two channel walls. A Mach-Zehnder interferometer provided temperature field visualization. In addition, local and average heat transfer measurements were made with the interferometer. Flow visualization was conducted to determine the flow pattern inside the channel. The measured local and average Nusselt number data were compared to numerical solutions obtained using ANSYS FLUENT. A steady laminar model and a steady k-ε turbulence model with two different wall functions were used. Numerical solutions were obtained for a Prandtl number of 0.71 and Rayleigh numbers ranging from the laminar fully developed flow regime to the turbulent isolated boundary layer regime.