scholarly journals Optimal Strategy to Tackle a 2D Numerical Analysis of Non-Uniform Flow over Artificial Dune Regions: A Comparison with Bibliography Experimental Results

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2331
Author(s):  
Jungkyu Ahn ◽  
Jaelyong Lee ◽  
Sung Won Park
Keyword(s):  
Open Channel ◽  
Roughness Length ◽  
Separation Zone ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Sst Model ◽  
Bed Roughness ◽  
Channel Bottom

Flow simulation over a dune requires the proper input of roughness coefficients. This study analyzed a numerical simulation of open-channel turbulent flow over two-dimensional fixed dunes to reveal the effect of roughness on the dune bottom, and to determine the optimized combination of the turbulence scheme and the roughness height formula. The most appropriate roughness values and turbulence models were applied using Reynolds-averaged Navier–Stokes models. Seven methods were chosen to estimate the bed roughness properties at the inlet boundary section. The results of all cases calculated with the OpenFOAM toolbox were compared with laboratory experimental data for model validation. The performances of all bed roughness variations were evaluated according to the stream-wise and depth-wise directions with nondimensional values. Consequently, it was revealed that the combination of bottom roughness length scale at the inlet boundary and the k-ω shear-stress transport (SST) model was the most suitable for the flow separation zone and turbulent properties near the channel bottom.

scholarly journals Viscous Flow Calculations in Turbomachinery Channels

1989 ◽  
Author(s):  
Francesco Martelli ◽  
Vittorio Michelassi
Keyword(s):  
Stokes Equations ◽  
Turbulent Viscosity ◽  
Axisymmetric Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Algebraic Expression ◽  
Two Dimensional ◽  
Approximate Factorization ◽  
Navier Stokes Equations ◽  
Flow Configurations

An implicit procedure based on the artificial compressibility formulation is presented for the numerical solution of the two-dimensional incompressible steady Navier-Stokes equations in the presence of large separated regions. Turbulence effects are accounted for by the Chien low Reynolds number form of the K-ε turbulence model and the Baldwin-Lomax algebraic expression for turbulent viscosity. The governing equations are written in conservative form and implicitly solved in fully coupled form using the approximate factorization technique. Preliminary tests were carried out in a laminar flow regime to check the accuracy and stability of the method in two-dimensional and cylindrical axisymmetric flow configurations. After testing in laminar and turbulent flow regimes and comparing the two turbulence models, the code was successfully applied to an actual gas turbine diffuser at low Mach numbers.

Measurements and Predictions of Surface Roughness Effects on the Turbine Vane Aerodynamics

2003 ◽  
Author(s):  
R. J. Boyle ◽  
R. G. Senyitko
Keyword(s):  
Surface Roughness ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Linear Cascade ◽  
Wide Range ◽  
Turbine Vane

The aerodynamic performance of a turbine vane was measured in a linear cascade. These measurements were conducted for exit-true chord Reynolds numbers between 150,000 and 1,800,000. The vane surface rms roughness-to-true chord ratio was approximately 2 × 10−4. Measurements were made for exit Mach numbers between 0.3 and 0.9 to achieve different loading distributions. Measurements were made at three different inlet turbulence levels. High and intermediate turbulence levels were generated using two different blown grids. The turbulence was low when no grid was present. The wide range of Reynolds numbers was chosen so that, at the lower Reynolds numbers the rough surfaces would be hydraulically smooth. The primary purpose of the tests was to provide data to verify CFD predictions of surface roughness effects on aerodynamic performance. Data comparisons are made using a two-dimensional Navier-Stokes analysis. Both two-equation and algebraic roughness turbulence models were used. A model is proposed to account for the increase in loss due to roughness as the Reynolds number increases.

A Methodology for Simulating Compressible Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 405-412 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Bluff Body ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Fine Grid ◽  
Local Flow

A flow simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modeling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for Reynolds averaged Navier-Stokes (RANS)) and scaling of the model terms with a “contribution function.” The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that it approaches direct numerical simulations (DNS) in the fine-grid limit and such that it provides modeling of all scales in the coarse-grid limit and thus approaches a RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in large eddy simulation (LES). However, FSM is distinctly different from LES in that it allows for a consistent transition between RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step and a plane wake behind a bluff body, both at low Mach number, and supersonic axisymmetric wakes. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for simulations of turbulent compressible flows for complex geometries.

scholarly journals Two-Dimensional Computational Model for Wave Rotor Flow Dynamics

1997 ◽  
Vol 119 (4) ◽  
pp. 978-985 ◽  
Author(s):  
G. E. Welch
Keyword(s):  
Stokes Equations ◽  
Flow Simulation ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Wave Rotor ◽  
Navier Stokes Equations ◽  
Flow Features ◽  
Rotor Experiment ◽  
Two Dimensional Flow ◽  
Rotor Flow

A two-dimensional (θ, z) Navier–Stokes solver for multiport wave rotor flow simulation is described. The finite-volume forms of the unsteady thin-layer Navier–Stokes equations are integrated in time on multiblock grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified.

Simulation of Open Channel Turbulent Flow Over Bridge Decks and Formation of Scour Hole Beneath the Bridge Under Flooding Conditions

2009 ◽  
Author(s):  
Bishwadipa Adhikary ◽  
Pradip Majumdar ◽  
Milivoje Kostic ◽  
Steven A. Lottes
Keyword(s):  
Shear Stress ◽  
Turbulent Flow ◽  
Open Channel ◽  
Moving Boundary ◽  
Bridge Decks ◽  
Critical Shear Stress ◽  
Navier Stokes ◽  
Scour Hole ◽  
Scour Holes ◽  
Bed Roughness

This study is focused on the simulation of open channel turbulent flow over flooded laboratory scale bridge decks and formation of scour holes under various flooding conditions. Solutions for turbulent flow field are based on Reynolds Averaged Navier-Stokes (RANS) equations and turbulence closure models using the STAR-CD commercial computational fluid dynamics (CFD) software. An iterative computational methodology is developed for predicting equilibrium scour profiles using the single-phase flow model with a moving boundary formulation. The methodology relies on an empirical correlation for critical bed shear stress that is used to characterize the condition for onset of sediment motion and an effective bed roughness that is a function of sediment particle size. The computational model and iterative methodology were stable and converged to an equilibrium scour hole shape and size that compares reasonably well with experiment using a constant critical shear stress value.

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.

Prediction of Unsteady Flow around a Square Cylinder Using RANS

2011 ◽  
Vol 52-54 ◽  
pp. 1165-1170
Author(s):  
Fu You Xu ◽  
Xu Yong Ying ◽  
Zhe Zhang
Keyword(s):  
Standard Model ◽  
Unsteady Flow ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Surface Flow ◽  
Two Dimensional ◽  
Square Cylinder ◽  
Complex Flow ◽  
Near Surface ◽  
Sst Model

The results of unsteady Reynolds averaged Navier-Stokes (URANS) simulations of flow around a square cylinder using two-dimensional hybrid meshes were presented in this paper. The first part examined the accuracy of various RANS turbulence models, i.e. the standard model, RNG model, realizable model, standard model, SST model, and RSM, by comparing their results with available experimental data. Despite the limits imposed by the RANS approach and the relatively inexpensive two-dimensional computations, the main features of this complex flow can be predicted reasonably well. Among the computations using various RANS models compared here, the SST model shows the best agreement with the experiment. The second part investigated the effects of corner cutoffs on unsteady flow characteristics around a square cylinder by using the SST model. Especially the detailed near-surface flow structure around the cylinder was focused on, aiming at giving an explanation for the drastic modification of the aerodynamic characteristics as the corner shape is slightly changed.

scholarly journals Two-Equation Turbulence Models for Prediction of Heat Transfer on a Transonic Turbine Blade

2001 ◽  
Author(s):  
Vijay K. Garg ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Suction Side ◽  
Navier Stokes ◽  
Production Term ◽  
Passage Vortex ◽  
Sst Model ◽  
Transonic Turbine

Two versions of the two-equation k-ω model and a shear stress transport (SST) model are used in a three-dimensional, multi-block, Navier-Stokes code to compare the detailed heat transfer measurements on a transonic turbine blade. It is found that the SST model resolves the passage vortex better on the suction side of the blade, thus yielding a better comparison with the experimental data than either of the k-ω models. However, the comparison is still deficient on the suction side of the blade. Use of the SST model does require the computation of distance from a wall, which for a multi-block grid, such as in the present case, can be complicated. However, a relatively easy fix for this problem was devised. Also addressed are issues such as (1) computation of the production term in the turbulence equations for aerodynamic applications, and (2) the relation between the computational and experimental values for the turbulence length scale, and its influence on the passage vortex on the suction side of the turbine blade.

Two-dimensional nonsteady viscous flow simulation on the Navier-Stokes Computer miniNode

1986 ◽  
Vol 1 (1) ◽  
pp. 53-73 ◽  
Author(s):  
Daniel M. Nosenchuck ◽  
Michael G. Littman ◽  
William Flannery
Keyword(s):  
Viscous Flow ◽  
Flow Simulation ◽  
Navier Stokes ◽  
Two Dimensional

scholarly journals Unsteady RANS Modeling of Flow around Two-Dimensional Rectangular Cylinders with Different Side Ratios at Reynolds Number 6.85 × 105

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shubiao Wang ◽  
Wenming Cheng ◽  
Run Du ◽  
Yupu Wang
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Practical Engineering ◽  
Unsteady Rans ◽  
Rectangular Cylinders

In practical engineering, the Reynolds number (Re) of box girder structure is usually very high (Re ≥ 105), while most investigations of the flow around bluff bodies are concentrated on relatively lower Reynolds numbers (i.e., Re = 103–104). This paper presented a numerical study of the unsteady flow around two-dimensional rectangular cylinders under a Reynolds number of 6.85 × 105 with different side ratios (R = b/h, width to height) ranging from 0.1 to 4.0. Three unsteady Reynolds-averaged Navier-Stokes (RANS) two-equation k-ε turbulence models (standard, RNG, and realizable) were adopted in the study. The realizable k-ε model was chosen because it was found to perform the best among three models in the main aerodynamic integral parameters. According to the distinctions of aerodynamic characteristics with different side ratios, three regimes were divided and discussed in detail. The distribution of surface pressure over cylinders, the wake parameters, and vorticity contours of the rectangular cylinders with different side ratios were discussed.

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