Numerical Simulation of Turbid-Density Current Using v2 – f Turbulence Model

2005 ◽  
Author(s):  
A. Mehdizadeh ◽  
B. Firoozabadi ◽  
B. Farhanieh
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Isotropic Turbulence ◽  
Turbidity Current ◽  
Solid Particles ◽  
Density Currents ◽  
Complex Flow ◽  
Fall Velocity ◽  
High Reynolds ◽  
Near Wall

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2 – f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2 – f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2 – f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current, (its critical Reynolds no. is about 1000), the κ - ε model, which was standardized for high Reynolds number and isotropic turbulence flow, cannot simulate the anisotropy and non-homogenous behavior near wall. In this study, turbidity current with uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with experimental data sets. Moreover, results have been compared with the standard κ - ε turbulent model. Results show that the κ - ε model has the poor result on this current. In addition, results show that the coarse particles settle down rapidly and make the higher deposition rate. The deposition of particles and the effects of their fall velocity on concentration distribution, height of body, and entrainment coefficient are also investigated.

scholarly journals Turbulence model performance for ventilation components pressure losses

2021 ◽  
Author(s):  
Karsten Tawackolian ◽  
Martin Kriegel
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Pressure Loss ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Test Case ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Near Wall

AbstractThis study looks to find a suitable turbulence model for calculating pressure losses of ventilation components. In building ventilation, the most relevant Reynolds number range is between 3×104 and 6×105, depending on the duct dimensions and airflow rates. Pressure loss coefficients can increase considerably for some components at Reynolds numbers below 2×105. An initial survey of popular turbulence models was conducted for a selected test case of a bend with such a strong Reynolds number dependence. Most of the turbulence models failed in reproducing this dependence and predicted curve progressions that were too flat and only applicable for higher Reynolds numbers. Viscous effects near walls played an important role in the present simulations. In turbulence modelling, near-wall damping functions are used to account for this influence. A model that implements near-wall modelling is the lag elliptic blending k-ε model. This model gave reasonable predictions for pressure loss coefficients at lower Reynolds numbers. Another example is the low Reynolds number k-ε turbulence model of Wilcox (LRN). The modification uses damping functions and was initially developed for simulating profiles such as aircraft wings. It has not been widely used for internal flows such as air duct flows. Based on selected reference cases, the three closure coefficients of the LRN model were adapted in this work to simulate ventilation components. Improved predictions were obtained with new coefficients (LRNM model). This underlined that low Reynolds number effects are relevant in ventilation ductworks and give first insights for suitable turbulence models for this application. Both the lag elliptic blending model and the modified LRNM model predicted the pressure losses relatively well for the test case where the other tested models failed.

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

2009 ◽  
Vol 367 (1899) ◽  
pp. 2885-2903 ◽  
Author(s):  
Michael Leschziner ◽  
Ning Li ◽  
Fabrizio Tessicini
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Major Elements ◽  
Wall Layer ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Models ◽  
High Reynolds ◽  
Near Wall

This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier–Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.

An Analysis Methodology for Internal Swirling Flow Systems With a Rotating Wall

1991 ◽  
Vol 113 (1) ◽  
pp. 83-90 ◽  
Author(s):  
M. Williams ◽  
W. C. Chen ◽  
G. Bache´ ◽  
A. Eastland
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Gas Turbines ◽  
High Reynolds Number ◽  
Rotating Disk ◽  
Rotating Wall ◽  
Analysis Methodology ◽  
Flow Systems ◽  
Flow Through ◽  
High Reynolds

This paper presents an analysis methodology for the calculation of the flow through internal flow components with a rotating wall such as annular seals, impeller cavities, and enclosed rotating disks. These flow systems are standard components in gas turbines and cryogenic engines and are characterized by subsonic viscous flow and elliptic pressure effects. The Reynolds-averaged Navier-Stokes equations for turbulent flow are used to model swirling axisymmetric flow. Bulk-flow or velocity profile assumptions aren’t required. Turbulence transport is assumed to be governed by the standard two-equation high Reynolds number turbulence model. A low Reynolds number turbulence model is also used for comparison purposes. The high Reynolds number turbulence model is found to be more practical. A novel treatment of the radial/swirl equation source terms is developed and used to provide enhanced convergence. Homogeneous wall roughness effects are accounted for. To verify the analysis methodology, the flow through Yamada seals, an enclosed rotating disk, and a rotating disk in a housing with throughflow are calculated. The calculation results are compared to experimental data. The calculated results show good agreement with the experimental results.

A Dynamic Procedure for Wall-Modeled Large-Eddy Simulation of High Reynolds Number Flows

2011 ◽  
Author(s):  
Soshi Kawai
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
High Reynolds Number ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Shear ◽  
High Reynolds ◽  
Near Wall

This paper addresses the error in large-eddy simulation with wall-modeling (i.e., when the wall shear stress is modeled and the viscous near-wall layer is not resolved): the error in estimating the wall shear stress from a given outer-layer velocity field using auxiliary near-wall RANS equations where convection is not neglected. By considering the behavior of turbulence length scales near a wall, the cause of the errors is diagnosed and solutions that remove the errors are proposed based solidly on physical reasoning. The resulting method is shown to accurately predict equilibrium boundary layers at very high Reynolds number, with both realistic instantaneous fields (without overly elongated unphysical near-wall structures) and accurate statistics (both skin friction and turbulence quantities).

scholarly journals Enhanced wall turbulence model for flow over cylinder at high Reynolds number

AIP Advances ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 095012 ◽  
Author(s):  
A. Aravind Raghavan Sreenivasan ◽  
B. Kannan Iyer
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
High Reynolds Number ◽  
Wall Turbulence ◽  
Flow Over Cylinder ◽  
High Reynolds

scholarly journals Circulation in High Reynolds Number Isotropic Turbulence is a Bifractal

2019 ◽  
Vol 9 (4) ◽  
Author(s):  
Kartik P. Iyer ◽  
Katepalli R. Sreenivasan ◽  
P. K. Yeung
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Isotropic Turbulence ◽  
High Reynolds
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