Parallel Simulation of Turbulent Flow in a Backward-Facing Step (original) (raw)
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Direct numerical simulation of turbulent flow over a backward-facing step
Journal of Fluid Mechanics, 1997
Turbulent flow in a channel with a sudden expansion is simulated using the incompressible Navier-Stokes equations. The objective is to provide statistical data on the dynamical properties of flow over a backward-facing step that could be used to improve turbulence modeling. The expansion ratio is E R = 2.0 and the Reynolds number, based on the step height and mean inlet velocity, is Re h = 9000. The discretisation is performed using a spanwise periodic spectral/hp element method. The inlet flow has turbulent velocity and pressure fields that are formed by a regenerating channel segment upstream of the inlet. Time and spanwise averages show secondary and tertiary corner eddies in addition to the primary recirculation bubble, while streamlines show a small eddy forming at the downstream tip of the secondary corner eddy. This eddy has the same circulation direction as the secondary vortex. Analysis of three-dimensional time-averages shows a wavy spanwise structure that leads to spanwise variations of the mean reattachment location. The visualisation of spanwise averaged pressure fluctuations and streamwise velocity shows that the interaction of vortices with the recirculation bubble is responsible for the flapping of the reattachment position, which has a characteristic frequency of St = 0.078.
Large Eddy Simulation of Backward Facing Step Flow
The paper describes the implementation and applicability of the Large eddy simulation (LES) technique for simulating turbulent flows. The LES approach is implemented in the in-house RANS research code Spider-3D. The Spider-LES code is validated by studying the unsteady flow over a backward-facing step (BFS). The LES simulation over the BFS is carried out at a Reynolds number of 5100 based on the inlet free-stream velocity. Finite-volume discretization schemes for the non-linear convective terms and sub-grid stress (SGS) models used for LES approach are discussed in the present study. To investigate mesh dependency, two types of grid resolution are studied. The results computed from Spider-LES are validated against DNS reference data by Le et al. The mean longitudinal, vertical velocity profile and the turbulence intensities compare satisfactory with the DNS data at the normalized coordinates X * = (x − X r ) /X r . The reattachment length X r in the longitudinal direction, varies from 7.2h to 7.4h with different SGS models used as compared to the DNS value of 6.28h.
Numerical Simulation of Fluid Flow over a Modified Backward-Facing Step using CFD
2020
1B.E student, Mechanical Engineering, Shri Sant Gajanan Maharaj College of Engineering, Maharashtra, India 2Assistant Prof., Mechanical Engineering, Shri Sant Gajanan Maharaj College of Engineering, Maharashtra, India ---------------------------------------------------------------------***---------------------------------------------------------------------Abstract In this paper, numerical analysis is carried out on backward-facing step geometry in the Driver and Seegmiller experiment and then by modifying the backwardfacing step geometry. Modified geometry will alter the size and characteristics of the recirculation vortex and turbulent kinetic energy profile downstream of the step. The application of sudden expansion geometry can be found in the combustor where the distribution of turbulent kinetic energy within the recirculation region determines the burning velocity of fresh reactants. Based on the CFD package ANSYS Fluent, we carried out the non-reactive numerical simulation. N...
CFD Analysis of a Backward Facing Step Flows
International Journal of Automotive Science and Technology, 2018
This paper introduces a lot of situations about the Computational Fluid Dynamics (CFD) analysis of backward facing step flows. The main point of this paper is incompressible flow in a backward step, measured by drivers and Seegmiller experiments. The researchers concluded that validation parameters chosen for the study are the locations of the surface hydrostatic pressure and the reattachment compression impact downstream of the step. The surface static pressures predicted by WIND using a two-equation SST turbulence model are shown below. This figure includes a comparison of earlier versions of NPARC and WIND with experimental data. The WIND code slightly overestimates the surface pressure drop from the free flow value to about 5% of the corner value of the separation area (base pressure). This may be due to the fact that the transition point is experimentally unknown and not accurately predicted by the natural transition of the turbulence model. However, this over-forecasting predi...
IRJET- Numerical Simulation of Fluid Flow over a Modified Backward-Facing Step using CFD
IRJET, 2020
In this paper, numerical analysis is carried out on backward-facing step geometry in the Driver and Seegmiller experiment and then by modifying the backward-facing step geometry. Modified geometry will alter the size and characteristics of the recirculation vortex and turbulent kinetic energy profile downstream of the step. The application of sudden expansion geometry can be found in the combustor where the distribution of turbulent kinetic energy within the recirculation region determines the burning velocity of fresh reactants. Based on the CFD package ANSYS Fluent, we carried out the non-reactive numerical simulation. Numerical simulation was performed on 2-D geometry using the Reynolds Averaged Navier-Stokes (RANS) approach in the framework of the SST k turbulence model. The experimental reference by Driver and Seegmiller was used for validation purposes. For the modified geometry, results show an increase in turbulent kinetic energy in the recirculation region and a slight decrease in reattachment length as compared to the original/traditional backward-facing step geometry.
Advances in Engineering Software, 2007
In this paper, we present parallel simulations of three-dimensional complex flows obtained on an ORIGIN 3800 computer and on homogeneous and heterogeneous (processors of different speeds and RAM) computational grids. The solver under consideration, which is representative of modern numerics used in industrial computational fluid dynamics (CFD) software, is based on a mixed element-volume method on unstructured tedrahedrisations. The parallelisation strategy combines mesh partitioning techniques, a message-passing programming model and an additive Schwarz algorithm. The parallelisation performances are analysed on a two-phase compressible flow and a turbulent flow past a square cylinder.
A highly-resolved numerical study of turbulent separated flow past a backward-facing step
International Journal of Engineering Science, 1991
aurner~c~ study of fairy-deve~o~d turbtdent flow past a ba~ward-fauns step is performed to analyze the e&et of mesh ~~~nerne~t on the computed results. The time averaged equations of conse~a~ou of mass and momentum are solved by a fi~te-volume method using two versions of the K-E model af turbulence. The computations are performed with both the standard and the non&ear K-E turbulence models for 166 x 73 and 332 x 145 mesh points. The comparkon of the results with available ex~~me~ta~ findings indicate that no&near terms must be ittcorporated into the K-s model to account far normal stress differences, and that even with very fine ~so~ution, the standard K-E model fails to provide accurate predictions elf the flow field. me
Comptes Rendus Mécanique, 2006
We use Large Eddy Simulation to investigate the influence of upstream boundary conditions on the development of a backward facing step flow. The first inlet condition consists of a mean turbulent boundary layer velocity profile perturbed by a white noise. The second relies upon a precursor calculation where the development of a quasi-temporal turbulent boundary layer is simulated. In this case, the quasi-longitudinal vortices in the upstream turbulent boundary-layer trigger the destabilization of the shear layer just behind the step, resulting in a shortening of the recirculation length and an increase of the characteristic frequency associated to the Kelvin-Helmholtz vortices. The mean flow and the characteristic frequencies of pressure fluctuations are strongly dependent of the upstream flow. It demonstrates the importance of realistic boundary conditions for the simulation of complex 3D flows or for flow control simulations. To cite this article: J.-L. Aider, A. Danet, C. R. Mecanique 334 (2006).
Comparison of Turbulence Models in the Flow over a Backward-Facing Step
—This work presents the numerical simulation and analysis of the turbulent flow over a two-dimensional channel with a backward-facing step. The computational simulation performed in this study is based on the Reynolds equations using a technique denominated Reynolds Average Navier-Stokes (RANS). The main objective of the present work is the comparison of different models of turbulence applied to the turbulent flow over a backward-facing step. The performance of each RANS model used will be discussed and compared with the results obtained through a direct numerical simulation present in the literature. The RANS turbulence models used are k-ω, k-ε, Shear Stress Transport k-ω (SST k-ω) and the second-order closure model called Reynolds Stress Model (RSM). The Reynolds number used in all the numerical simulations constructed in this study is equal to 9000, based on the height of the step h and the inlet velocity U b. The results are the reattachment length, the mean velocity profiles and the turbulence intensities profiles. The k-ε model obtained poor results in most of the analyzed variables in this study. Among the RANS turbulence models, the SST k-ω model presented the best results of reattachment length, mean velocity profile and contour when compared to results obtained in the literature. The RSM model found the best results of turbulence intensity profile, when compared to the models of two partial differential equations that use the Boussines hypothesis.
Computers & Fluids, 2008
Numerical calculations of the 2-D steady incompressible driven cavity flow are presented. The Navier-Stokes equations in streamfunction and vorticity formulation are solved numerically using a fine uniform grid mesh of 601 × 601. The steady driven cavity solutions are computed for Re ≤ 21,000 with a maximum absolute residuals of the governing equations that were less than 10 −10. A new quaternary vortex at the bottom left corner and a new tertiary vortex at the top left corner of the cavity are observed in the flow field as the Reynolds number increases. Detailed results are presented and comparisons are made with benchmark solutions found in the literature.