scholarly journals Evaluating the Impact of Turbulence Closure Models on Solute Transport Simulations in Meandering Open Channels

2020 ◽  
Vol 10 (8) ◽  
pp. 2769 ◽  
Author(s):  
Jun Song Kim ◽  
Donghae Baek ◽  
Inhwan Park
Keyword(s):  
Solute Transport ◽  
Flow Separation ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Breakthrough Curves ◽  
Secondary Flows ◽  
Mean Velocity ◽  
Form Complex ◽  
Tracking Model ◽  
The Impact

River meanders form complex 3D flow patterns, including secondary flows and flow separation. In particular, the flow separation traps solutes and delays their transport via storage effects associated with recirculating flows. The simulation of the separated flows highly relies in the performance of turbulence models. Thus, these closure schemes can control dispersion behaviors simulated in rivers. This study performs 3D simulations to quantify the impact of the turbulence models on solute transport simulations in channels under different sinuosity conditions. The 3D Reynolds-averaged Navier-Stokes equations coupled with the k − ε , k − ω and SST k − ω models are adopted for flow simulations. The 3D Lagrangian particle-tracking model simulates solute transport. An increase in sinuosity causes strong transverse gradients of mean velocity, thereby driving the onset of the separated flow recirculation along the outer bank. Here, the onset and extent of the flow separation are strongly influenced by the turbulence models. The k − ε model fails to reproduce the flow separation or underestimates its size. As a result, the k − ε model yields residence times shorter than those of other models. In contrast, the SST k − ω model exhibits a strong tailing of breakthrough curves by generating more pronounced flow separation.

scholarly journals Steady flow separation patterns in a 45 degree junction

2000 ◽  
Vol 411 ◽  
pp. 1-38 ◽  
Author(s):  
C. ROSS ETHIER ◽  
SUJATA PRAKASH ◽  
DAVID A. STEINMAN ◽  
RICHARD L. LEASK ◽  
GREGORY G. COUCH ◽  
...  
Keyword(s):  
Flow Separation ◽  
Stokes Equations ◽  
Bypass Graft ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Measured Velocity ◽  
Curved Tube

Numerical and experimental techniques were used to study the physics of flow separation for steady internal flow in a 45° junction geometry, such as that observed between two pipes or between the downstream end of a bypass graft and an artery. The three-dimensional Navier–Stokes equations were solved using a validated finite element code, and complementary experiments were performed using the photochromic dye tracer technique. Inlet Reynolds numbers in the range 250 to 1650 were considered. An adaptive mesh refinement approach was adopted to ensure grid-independent solutions. Good agreement was observed between the numerical results and the experimentally measured velocity fields; however, the wall shear stress agreement was less satisfactory. Just distal to the ‘toe’ of the junction, axial flow separation was observed for all Reynolds numbers greater than 250. Further downstream (approximately 1.3 diameters from the toe), the axial flow again separated for Re [ges ] 450. The location and structure of axial flow separation in this geometry is controlled by secondary flows, which at sufficiently high Re create free stagnation points on the model symmetry plane. In fact, separation in this flow is best explained by a secondary flow boundary layer collision model, analogous to that proposed for flow in the entry region of a curved tube. Novel features of this flow include axial flow separation at modest Re (as compared to flow in a curved tube, where separation occurs only at much higher Re), and the existence and interaction of two distinct three-dimensional separation zones.

Influence of Inlet Velocity Condition on Unsteady Flow Characteristics in Piping With a Short-Elbow at High Reynolds Number Condition

2014 ◽  
Author(s):  
Ayako Ono ◽  
Masaaki Tanaka ◽  
Jun Kobayashi ◽  
Hideki Kamide
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Velocity Fluctuation ◽  
Complex Geometry ◽  
Perforated Plate ◽  
Secondary Flows ◽  
Curvature Radius ◽  
Mean Velocity ◽  
Inlet Velocity ◽  
Velocity Condition

In design of the Japan Sodium-cooled Fast Reactor (JSFR), mean velocity of the coolant is approximately 9 m/s in the primary hot leg (H/L) piping which diameter is 1.27 m. The Reynolds number in the H/L piping reaches 4.2×107. Moreover, a short-elbow which has Rc/D = 1.0 (Rc: Curvature radius, D: Pipe diameter) is used in the hot leg piping in order to achieve compact plant layout and reduce plant construction cost. In the H/L piping, flow-induced vibration (FIV) is concerned due to excitation force which is caused by pressure fluctuation on the wall closely related with the velocity fluctuation in the short-elbow. In the previous study, relation between the flow separation and the pressure fluctuations in the short-elbow was revealed under the specific inlet condition with flat distribution of time-averaged axial velocity and relatively weak velocity fluctuation intensity in the pipe. However, the inlet velocity condition of the H/L in a reactor may have ununiformed profile with highly turbulent due to the complex geometry in reactor vessel (R/V). In this study, the influence of the inlet velocity condition on unsteady characteristics of velocity in the short-elbow was studied. Although the flow around the inlet of the H/L in R/V could not simulate completely, inlet velocity conditions were controlled by installing the perforated plate with plugging the flow-holes appropriately. Then expected flow patterns were made at 2D upstream position from the elbow inlet in the experiments. It was revealed that the inlet velocity profiles affected circumferential secondary flow and the secondary flows affected an area of flow separation at the elbow, by local velocity measurement by the PIV (particle image velocimetry). And it was found that the low frequent turbulence in the upstream piping remained downstream of the elbow though their intensity was attenuated.

Numerical Investigation of Gas-Solid Suspension Flow in 180° Curved Duct

2007 ◽  
Author(s):  
K. A. Ibrahim ◽  
M. A. El-Kadi ◽  
Mofreh H. Hamed ◽  
Samy M. El-Behery
Keyword(s):  
Stokes Equations ◽  
Turbulence Models ◽  
Flow Behaviour ◽  
Published Data ◽  
Phase Flow ◽  
Particle Rotation ◽  
Two Phase ◽  
Curved Duct ◽  
Tracking Model ◽  
Particles Trajectories

In this paper, a two-way coupling Eulerian-Lagrangian approach is presented for the simulation of gas-solid two-phase flow in 180° curved duct. In the present study, Reynolds averaged Navier-Stokes equations (RANS) and two turbulence models namely; standard k-ε model and RNG (Renormalization Group) based k-ε model are adopted. The effects of particle rotation and lift forces are included in the particle tracking model while the effect of inter-particle collisions is neglected. The present predictions are compared with published experimental data for single-phase flow and published particles trajectories. The comparisons show that the RNG based k-ε model predicts the flow behaviour better than the standard k-ε model. Furthermore, the particles trajectories are compared very well with published data. The effects of inlet gas velocity, bend geometry, loading ratio and solid properties on the flow behaviour are also discussed. The results show that the flow behaviour is greatly affected by the above parameters.

scholarly journals Investigating the impact of exit effects on solute transport in macroporous media

2021 ◽  
Vol 25 (2) ◽  
pp. 671-683
Author(s):  
Jérôme Raimbault ◽  
Pierre-Emmanuel Peyneau ◽  
Denis Courtier-Murias ◽  
Thomas Bigot ◽  
Jaime Gil Roca ◽  
...  
Keyword(s):  
Solute Transport ◽  
Finite Size ◽  
Breakthrough Curves ◽  
Macropore Flow ◽  
Reactive Solute Transport ◽  
The Matrix ◽  
Magnetic Resonance Imaging Mri ◽  
Breakthrough Experiments ◽  
Water Saturated ◽  
The Impact

Abstract. The effect of macropore flow on solute transport has spurred much research over the last forty years. In this study, non-reactive solute transport in water-saturated columns filled with porous media crossed by a macropore was experimentally and numerically investigated. The emphasis was put on the study of exit effects, whose very existence is inherent to the finite size of any experimental column. We specifically investigated the impact of a filter at the column outlet on water flow and solute transport in macroporous systems. Experiments involving breakthrough measurements and magnetic resonance imaging (MRI) showed that solute transport displayed some significant non-unidirectional features, with a strong mass exchange at the interface between the macropore and the matrix. Fluid dynamics and transport simulations indicated that this was due to the non-unidirectional nature of the flow field close to the outlet filter. The flow near the exit of the column was shown to be strongly impacted by the presence of the outlet filter, which acts as a barrier and redistributes water from the macropore to the matrix. This impact was apparent on the breakthrough curves and the MRI images. It was also confirmed by computer simulations and could, if not properly taken into account, impede the accurate inference of the transport properties of macroporous media from breakthrough experiments.

Experimental and Numerical Investigation of Two-Dimensional Parallel Jets

2001 ◽  
Vol 123 (2) ◽  
pp. 401-406 ◽  
Author(s):  
Elgin A. Anderson ◽  
Robert E. Spall
Keyword(s):  
Good Accuracy ◽  
Stokes Equations ◽  
Numerical Models ◽  
Symmetry Plane ◽  
Turbulence Models ◽  
Turbulent Jets ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Navier Stokes Equations ◽  
The Mean

The flowfield of dual, parallel planar turbulent jets is investigated experimentally using an x-type hot-wire probe and numerically by solving the Reynolds-averaged Navier-Stokes equations. The performance of both differential Reynolds stress (RSM) and standard k-ε turbulence models is evaluated. Results show that the numerical models predict the merge and combined point characteristics to good accuracy. However, both turbulence models show a narrower width of the jet envelope than measured by experiment. The predicted profiles of the mean velocity along the symmetry plane agree well with the experimental results.

scholarly journals Numerical Investigation of Jet Angle Effect on Airfoil Stall Control

2019 ◽  
Vol 9 (15) ◽  
pp. 2960 ◽  
Author(s):  
Junkyu Kim ◽  
Young Min Park ◽  
Junseong Lee ◽  
Taesoon Kim ◽  
Minwoo Kim ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow Separation Control ◽  
Angle Effect ◽  
Stall Control ◽  
The Impact

Numerical study on flow separation control is conducted for a stalled airfoil with steady-blowing jet. Stall conditions relevant to a rotorcraft are of interest here. Both static and dynamic stalls are simulated with solving compressible Reynolds-averaged Navier-Stokes equations. It is expected that a jet flow, if it is applied properly, provides additional momentum in the boundary layer which is susceptible to flow separation at high angles of attack. The jet angle can influence on the augmentation of the flow momentum in the boundary layer which helps to delay or suppress the stall. Two distinct jet angles are selected to investigate the impact of the jet angle on the control authority. A tangential jet with a shallow jet angle to the surface is able to provide the additional momentum to the flow, whereas a chord-normal jet with a large jet angle simply averts the external flow. The tangential jet reduces the shape factor of the boundary layer, lowering the susceptibility to the flow separation and delaying both the static and dynamic stalls.

scholarly journals Viscous Analysis of Steam Turbine Rotor Blade Aerodynamics

1997 ◽  
Author(s):  
R. S. Amano ◽  
B. Lin ◽  
B. Song
Keyword(s):  
Steam Turbine ◽  
Rotor Blade ◽  
Stokes Equations ◽  
Energy Levels ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Forced Response ◽  
Turbulence Energy ◽  
Mean Velocity

Unsteady load predictions on steam turbine blades are needed for a better understanding of high cycle fatigue blade failures. The forced response due to rotor-stator interaction and the unsteady loads due to blade oscillatory motion are major factors for the cause of stresses. In addition, turbulence, which is generated through the stator nozzle passages of a turbine, significantly affects the flow characteristics and heat transfer of the rotor blades. This paper presents a numerical modeling of turbulence effects of a flow around a rotor blade which was extended to demonstrate unsteady calculations due to blade oscillations. The grids were generated by employing the boundary-fitted algebraic grid generation technique. In the computations, the unsteady compressible Navier-Stokes equations were solved for the simulation of the flows in the above mentioned regions to determine mean velocity components, the turbulence energy levels, pressures, and thermodynamic properties such as temperatures and densities. The computed pressure distributions along a blade were compared with the published experimental data and the code was validated by showing reasonable agreement with the results. Some numerical examples are presented by using different turbulence models to investigate the nature of the turbulence occurring in the flow around a blade. Furthermore, the computational model was tested for its applicability to blade flutter in three vibrational modes — tangential, axial, and twist modes.

Application of the k-ε Turbulence Model to Buoyant Adiabatic Wall Plumes

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Michael A. Delichatsios ◽  
C. P. Brescianini ◽  
D. Paterson ◽  
H. Y. Wang ◽  
J. M. Most
Keyword(s):  
Stokes Equations ◽  
Reynolds Shear Stress ◽  
Mixture Fraction ◽  
Turbulence Models ◽  
Lateral Spread ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Wall Boundary Conditions ◽  
The Mean ◽  
Wall Plume

Computational fluid dynamics based on Reynolds averaged Navier–Stokes equations is used to model a turbulent planar buoyant adiabatic wall plume. The plume is generated by directing a helium/air source upwards at the base of the wall. Far from the source, the resulting plume becomes self-similar to a good approximation. Several turbulence models based predominantly on the k-ε modeling technique, including algebraic stress modeling, are examined and evaluated against experimental data for the mean mixture fraction, the mixture fraction fluctuations, the mean velocity, and the Reynolds shear stress. Several versions of the k-ε model are identified that can predict important flow quantities with reasonable accuracy. Some new results are presented for the variation in a mixing function for the mixture normal to the wall. Finally, the predicted (velocity) lateral spread is as expected smaller for wall flows in comparison to the free flows, but quite importantly, it depends on the wall boundary conditions in agreement with experiments, i.e., it is larger for adiabatic than for hot wall plumes.

scholarly journals Investigating the impact of exit effects on solute transport in macropored porous media

2020 ◽  
Author(s):  
Jérôme Raimbault ◽  
Pierre-Emmanuel Peyneau ◽  
Denis Courtier-Murias ◽  
Thomas Bigot ◽  
Jaime Gil Roca ◽  
...  
Keyword(s):  
Porous Media ◽  
Solute Transport ◽  
Finite Size ◽  
Breakthrough Curves ◽  
Macropore Flow ◽  
Reactive Solute Transport ◽  
The Matrix ◽  
Magnetic Resonance Imaging Mri ◽  
Breakthrough Experiments ◽  
The Impact

Abstract. The effect of macropore flow on solute transport has spurred much research over the last forty years. In this study, non-reactive solute transport in columns filled by macropored porous media was experimentally and numerically investigated, and the emphasis was put on the study of exit effects, whose very existence is inherent to the finite size of any experimental column. We specifically investigated the impact of the presence of a filter at the column outlet on water flow and solute transport in macropored systems. Experiments involving breakthrough measurements and magnetic resonance imaging (MRI) showed that solute transport displayed some significant non-unidirectional features, with a strong mass exchange at the interface between the macropore and the matrix. Fluid dynamics and transport simulations indicated that this was due to the non-unidirectional nature of the flow field close to the outlet filter. The flow near the exit of the column was shown to be strongly impacted by the presence of the outlet filter, which acts as a barrier and redistributes water from the macropore to the matrix. This impact was apparent on the breakthrough curves and the MRI images. It was also confirmed by computer simulations and could, if not properly taken into account, impede the accurate inference of the transport properties of macropored porous media from breakthrough experiments.

The Impact of Turbulence Model and Numerical Scheme on the Performance of a Linear Compressor Cascade

2014 ◽  
Author(s):  
J. Sans ◽  
M. Resmini ◽  
J. F. Brouckaert ◽  
S. Hiernaux
Keyword(s):  
Turbulence Model ◽  
Numerical Scheme ◽  
Model Comparison ◽  
Substantial Reduction ◽  
Turbulence Models ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Upwind Scheme ◽  
Compressor Cascade ◽  
The Impact

In the use of RANS models, it is well known that the selection of the turbulence model and the numerical scheme may have a critical impact not only in terms of convergence, but also on the reliability to simulate separated or secondary flows in general. The aim of the investigation, performed using the commercial software FINE/Turbo, is the understanding and the quantification of the effects of these two numerical parameters on the performance and the stability of a state-of-the-art controlled diffusion airfoil compressor cascade. A mesh sensitivity analysis has been carried out at both design and off-design conditions. The behaviour of the main flow parameters have been investigated over the whole incidence working range, considering a variation of the inlet Mach number between 0.35 and 0.65. Five different turbulence models have been tested: Baldwin-Lomax, Spalart-Allmaras, k–ε Yang-Shih, k–ε Launder-Sharma and k–ω SST. In a specific combination of incidences and Mach numbers, the impact of turbulence model settings has been assessed imposing boundary conditions according to different criteria. Two different numerical schemes have been tested: a Jameson central scheme and a second order upwind scheme. The results between the different simulations are discussed in terms of loss coefficient distribution and incidence range; considering the turbulence model comparison, the differences are significant in the whole incidence range, specially approaching the stall limit. Baldwin-Lomax and Spalart-Allmaras simulations present the same value of last stable incidence, while Yang-Shih and SST are characterized by a reduced stall margin. In many operating conditions, simulations computed with centered scheme present negative losses in a wide area of the outlet sections. This problem is reduced if an upwind scheme is used, but causes a substantial reduction of the incidence range.

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