INVESTIGATION OF INLET EFFECTS ON BACKWARD-FACING STEP FLOW PREDICTION

2016 ◽  
Vol 40 (3) ◽  
pp. 317-329 ◽  
Author(s):  
Mustafa Kemal Isman
Keyword(s):  
Experimental Data ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Backward Facing Step ◽  
Step Flow ◽  
Uniform Velocity ◽  
Flow Prediction ◽  
Rans Turbulence Models ◽  
Negative Effect ◽  
Inlet Boundary Condition

The turbulent flow over backward-facing step (BFS) is numerically investigated by using FLUENT® code. Both uniform and non-uniform velocity profiles are used as inlet boundary condition. Five different Reynolds averaged Navier–Stokes (RANS) turbulence models are employed. The Std. k–ω model shows the best agreement with the experimental data among the models used under the conditions considered in this study. The results show that using a uniform velocity profile has a negative effect on predictions if the domain is not sufficiently extended upstream from the inlet. To eliminate this effect, the domain should be extended upstream by about 10Dh from the inlet. However, results show that this extension causes absorption effects of inlet parameters such as inlet turbulence intensity.

Verification and Validation of the Caelus Library: Incompressible Turbulence Models

2017 ◽  
Author(s):  
Darrin W. Stephens ◽  
Aleksandar Jemcov ◽  
Chris Sideroff
Keyword(s):  
Incompressible Flows ◽  
Turbulence Models ◽  
Verification And Validation ◽  
Navier Stokes ◽  
Backward Facing Step ◽  
External Data ◽  
Rans Turbulence Models ◽  
Predictor Corrector ◽  
Naca 0012 ◽  
Incompressible Turbulence

In this work verification and validation of Reynolds Averaged Navier-Stokes (RANS) turbulence models for incompressible flows was performed on the numerical library, Caelus [1]. Caelus is free and open source licensed under the GNU Public License (GPL). The focus of this study is on the verification and validation of the k-ω SST [2, 3], Spalart-Allmaras [4], and realizable k-ε models [5]. The cases used in this work include the zero pressure gradient flat plate, two-dimensional bump in a channel flow, NACA 0012 airfoil, and backward facing step. All cases except the backward facing step include mesh dependency studies. A comprehensive description of the test cases and computed results are provided. The results were, in general, found to be in excellent agreement with external data suggesting that the turbulence model implementations in Caelus are correct. A companion study on verification and validation of a predictor corrector steady-state solver algorithm [6] had similar goals and results as this work.

scholarly journals Assessment of Numerical Methods for Plunging Breaking Wave Predictions

2021 ◽  
Vol 9 (3) ◽  
pp. 264
Author(s):  
Shanti Bhushan ◽  
Oumnia El Fajri ◽  
Graham Hubbard ◽  
Bradley Chambers ◽  
Christopher Kees
Keyword(s):  
Solitary Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Wave Crest ◽  
Breaking Wave ◽  
Rans Turbulence Models ◽  
Run Up ◽  
Better Than

This study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking, including assessment of the effect of grid resolution, turbulence model, and VoF, CLSVoF interface models on predictions. For this purpose, 2D simulations are performed for four test cases: dam break, solitary wave run up on a slope, flow over a submerged bump, and solitary wave over a submerged rectangular obstacle. Plunging wave breaking involves high wave crest, plunger formation, and splash up, followed by second plunger, and chaotic water motions. Coarser grids reasonably predict the wave breaking features, but finer grids are required for accurate prediction of the splash up events. However, instabilities are triggered at the air–water interface (primarily for the air flow) on very fine grids, which induces surface peel-off or kinks and roll-up of the plunger tips. Reynolds averaged Navier–Stokes (RANS) turbulence models result in high eddy-viscosity in the air–water region which decays the fluid momentum and adversely affects the predictions. Both VoF and CLSVoF methods predict the large-scale plunging breaking characteristics well; however, they vary in the prediction of the finer details. The CLSVoF solver predicts the splash-up event and secondary plunger better than the VoF solver; however, the latter predicts the plunger shape better than the former for the solitary wave run-up on a slope case.

Investigation of the Flow Structures in Supersonic Free and Impinging Jet Flows

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
C. Chin ◽  
M. Li ◽  
C. Harkin ◽  
T. Rochwerger ◽  
L. Chan ◽  
...  
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Optical Methods ◽  
Navier Stokes ◽  
Jet Flows ◽  
Shock Cell ◽  
Rans Turbulence Models

A numerical study of compressible jet flows is carried out using Reynolds averaged Navier–Stokes (RANS) turbulence models such as k-ɛ and k-ω-SST. An experimental investigation is performed concurrently using high-speed optical methods such as Schlieren photography and shadowgraphy. Numerical and experimental studies are carried out for the compressible impinging at various impinging angles and nozzle-to-wall distances. The results from both investigations converge remarkably well and agree with experimental data from the open literature. From the flow visualizations of the velocity fields, the RANS simulations accurately model the shock structures within the core jet region. The first shock cell is found to be constraint due to the interaction with the bow-shock structure for nozzle-to-wall distance less than 1.5 nozzle diameter. The results from the current study show that the RANS models utilized are suitable to simulate compressible free jets and impinging jet flows with varying impinging angles.

Heat Transfer and Hydraulic Resistance in Turbulent Flow in Vertical Round Tubes At Supercritical Pressures. Part 1. Results From Numerical Simulations Using Algebraic Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulent Flow ◽  
Hydraulic Resistance ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Heating And Cooling ◽  
Prediction Techniques ◽  
Vertical Tubes

Abstract The review of numerical studies on supercritical pressure (SCP) coolants heat transfer and hydraulic resistance in turbulent flow in vertical round tubes based on Reynolds-averaged Navier-Stokes (RANS) equations and different models for turbulent viscosity is presented. The paper is the first part of the general analysis, the works based on using algebraic turbulence models of different complexity are considered in it. The main attention is paid to Petukhov-Medvetskaya and Popov et al. models. They were developed especially for simulating heat transfer in tubes of the coolants with significantly variable properties (droplet liquids, gases, SCP fluids) under heating and cooling conditions. These predictions were verified on the entire reliable experimental data base. It is shown that in the case of turbulent flow in vertical round tubes these models make it possible predicting heat transfer and hydraulic resistance characteristics of SCP flows that agree well with the existed reliable experimental data on normal and certain modes of deteriorated heat transfer, if significant influence of buoyancy and radical flow restructuring are absent. For the more complicated cases than a flow in round vertical tubes, as well as for the case of rather strong buoyancy effect, more sophisticated prediction techniques must be applied. The state-of-the-art of these methods and the problems of their application are considered in the Part II of the analysis.

scholarly journals Prediction of Airfoil Stall Based on a Modified k−v2¯−ω Turbulence Model

Mathematics ◽  
2022 ◽  
Vol 10 (2) ◽  
pp. 272
Author(s):  
Chenyu Wu ◽  
Haoran Li ◽  
Yufei Zhang ◽  
Haixin Chen
Keyword(s):  
Experimental Data ◽  
Shear Layer ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Trailing Edge ◽  
Naca0012 Airfoil ◽  
Separated Shear Layer ◽  
Non Equilibrium

The accuracy of an airfoil stall prediction heavily depends on the computation of the separated shear layer. Capturing the strong non-equilibrium turbulence in the shear layer is crucial for the accuracy of a stall prediction. In this paper, different Reynolds-averaged Navier–Stokes turbulence models are adopted and compared for airfoil stall prediction. The results show that the separated shear layer fixed k−v2¯−ω (abbreviated as SPF k−v2¯−ω) turbulence model captures the non-equilibrium turbulence in the separated shear layer well and gives satisfactory predictions of both thin-airfoil stall and trailing-edge stall. At small Reynolds numbers (Re~105), the relative error between the predicted CL,max of NACA64A010 by the SPF k−v2¯−ω model and the experimental data is less than 3.5%. At high Reynolds numbers (Re~106), the CL,max of NACA64A010 and NACA64A006 predicted by the SPF k−v2¯−ω model also has an error of less than 5.5% relative to the experimental data. The stall of the NACA0012 airfoil, which features trailing-edge stall, is also computed by the SPF k−v2¯−ω model. The SPF k−v2¯−ω model is also applied to a NACA0012 airfoil, which features trailing-edge stall and an error of CL relative to the experiment at CL>1.0 is smaller than 3.5%. The SPF k−v2¯−ω model shows higher accuracy than other turbulence models.

Accuracy Verification of a 2D Adaptive Mesh Refinement Method Using Backward-Facing Step Flow of Low Reynolds Numbers

2020 ◽  
pp. 2041012
Author(s):  
Zhenquan Li ◽  
Miao Li
Keyword(s):  
Adaptive Mesh Refinement ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Mesh Refinement ◽  
Computational Cost ◽  
Adaptive Mesh ◽  
Navier Stokes ◽  
Vortex Center ◽  
Backward Facing Step ◽  
Step Flow

Identifying centers of vortices of fluid flow accurately is one of the accuracy measures for computational methods. After verifying the accuracy of the 2D adaptive mesh refinement (AMR) method in the benchmarks of 2D lid-driven cavity flow, this paper shows the accuracy verification by the benchmarks of 2D backward-facing step flow. The AMR method refines a mesh using the numerical solution of the Navier–Stokes equations computed on the mesh by an open source software Navier2D which implemented a vertex centered finite volume method (FVM) using the median dual mesh to form control volumes about each vertex. The accuracy is shown by the comparison between vortex center locations calculated from the linearly interpolated numerical solutions and those obtained in the benchmark. The AMR method is proposed based on the qualitative theory of differential equations, and it can be applied to refine a mesh as many times as required and used to seek accurate numerical solutions of the mathematical models including the continuity equation for incompressible fluid or steady-state compressible flow with low computational cost.

Minimum Wall Distance Computations With Time-Dependent Geometry for CFD

2021 ◽  
Author(s):  
Liwu Wang ◽  
Jian Feng ◽  
Yu Liu ◽  
Sijun Zhang
Keyword(s):  
Present Method ◽  
Turbulence Models ◽  
Time Dependent ◽  
Navier Stokes ◽  
Field Function ◽  
Convection Diffusion ◽  
Convection Diffusion Equation ◽  
Wall Distance ◽  
Rans Turbulence Models ◽  
Computational Fluid Dynamics Cfd

Abstract This paper presents an efficient and scalable method to calculate the minimum wall distance (MWD), which is necessary for the Reynolds-Averaged Navier-Stokes (RANS) turbulence models. The MWD is described by the distance field function which is essentially a partial differential equation (PDE). The PDE is a type of convection-diffusion equation and can be solved by existing computational fluid dynamics (CFD) codes with minor modifications. Parallel computations for the PDE are conducted to study its efficiency and scalability. Encouraging results are obtained and demonstrate the present method is more efficient than all the alternate methods.

Direct Numerical Simulation and RANS Comparison of Turbulent Convective Heat Transfer in a Staggered Ribbed Channel With High Blockage

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Luca Marocco ◽  
Andrea Franco
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Convective Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Reference Solution ◽  
Ribbed Channel ◽  
Sst Model ◽  
Rans Turbulence Models ◽  
Better Than

A turbulent convective flow of an incompressible fluid inside a staggered ribbed channel with high blockage at ReH ≈ 4200 is simulated with direct numerical simulation (DNS) and Reynolds-averaged Navier–Stokes (RANS) techniques. The DNS results provide the reference solution for comparison of the RANS turbulence models. The k–ε realizable, k–ω SST, and v2¯–f model are accurately analyzed for their strengths and weaknesses in predicting the flow and temperature field for this geometry. These three models have been extensively used in literature to simulate this configuration and boundary conditions but with discordant conclusions upon their performance. The v2¯–f model performs much better than the k–ε realizable while the k–ω SST model results to be inadequate.

Numerical study of the flow field characteristics over a backward facing step using k-kl-ω turbulence model: comparison with different models

2018 ◽  
Vol 15 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Yasser M. Ahmed ◽  
A.H. Elbatran
Keyword(s):  
Experimental Data ◽  
Fluid Mechanics ◽  
Turbulence Model ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Numerical Results ◽  
Backward Facing Step ◽  
Content Type ◽  
Case Comparison

Purpose This paper aims to investigate numerically the turbulent flow characteristics over a backward facing step. Different turbulence models with hybrid computational grid have been used to study the detached flow structure in this case. Comparison between the numerical results and the available experiment data is carried out in the present study. The results of the different turbulence models were in a good agreement with the experimental results. The numerical results also concluded that the k-kl-ω turbulence model gave favorable results compared with the experiment. Design/methodology/approach It is very important to study the flow characteristics of detached flows. Therefore, the current study investigates numerically the flow characteristics in backward facing step by using two-, three- and seven-equation turbulence models in the finite volume code ANSYS Fluent. In addition, hybrid grid has been used to improve the capability of the unstructured mesh elements for predicting the flow separation in this case. Comparison between the different turbulence models and the available experimental data was done to find the most suitable turbulence model for simulating such cases of detached flows. Findings The present numerical simulations with the different turbulence models predicted efficiently the flow characteristics over the backward facing step. The transition k-kl-ω gave the best acceptable results compared with experimental data. This is a good concluded remark in the fields of fluid mechanics and hydrodynamics because the phenomenon of flow separation is not easy to be predicted numerically and can affect greatly on the predicted drag of moving bodies in many engineering applications. Originality/value The CFD results of using different turbulence models have been validated with the experimental work, and the results of k-kl-ω proven acceptable with flow characteristics. The results of the current study conclude that the use of k-kl-ω turbulence model will contribute towards a more efficient utilization in the fields of fluid mechanics and hydrodynamics.

Evaluation of Performance and Code-to-Code Variation of a Dynamic Hybrid RANS/LES Model for Simulation of Backward-Facing Step Flow

2018 ◽  
Author(s):  
Olalekan O. Shobayo ◽  
D. Keith Walters
Keyword(s):  
Cfd Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Mean Flow ◽  
Backward Facing Step ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Dynamic Hybrid ◽  
Les Model

Computational fluid dynamics (CFD) simulation results are presented for the canonical test case of flow over a backward facing step (BFS). The BFS case exhibits complex physics including turbulent separation, reattachment, and boundary layer restart. Results are obtained using two different turbulence models as representative examples of two classes of modeling: Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS-LES (large-eddy simulation). The specific models used are k-ω SST and dynamic hybrid RANS-LES (DHRL). The objective of the study is to compare the performance of both turbulence models as implemented in three different flow solvers (Flow Psi, Loci-CHEM, and Ansys FLUENT) and using three different methods for numerical discretization of the convective terms in the governing equations. Results are compared to experimental data for validation purposes. Results show that both k-ω SST and DHRL models are capable of reproducing the mean flow physics with reasonable accuracy. The differences due to solver algorithm and convective discretization scheme are apparent for both models, but the DHRL model shows more sensitivity, as expected. Overall the results highlight the importance of considering all integrated aspects of a turbulent CFD simulation to ensure that an optimum combination of model and numerical method are employed.

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