How can the appropriate near-wall grid size for gas cyclone CFD simulation be estimated?

2021 ◽  
Author(s):  
Eakarach Bumrungthaichaichan
Keyword(s):  
Cfd Simulation ◽  
Grid Size ◽  
Near Wall

scholarly journals CFD simulation of a turbulent fiber suspension flow – a modified near-wall treatment

2015 ◽  
Vol 9 (1) ◽  
pp. 233-246 ◽  
Author(s):  
Carla Cotas ◽  
Dariusz Asendrych ◽  
Fernando Garcia ◽  
Pedro Faia ◽  
Maria Graça Rasteiro
Keyword(s):  
Cfd Simulation ◽  
Fiber Suspension ◽  
Suspension Flow ◽  
Fiber Suspension Flow ◽  
Turbulent Fiber Suspension ◽  
Near Wall

A CFD Simulation of Near Wall Turbulent Flow in Concentric Annulus

2013 ◽  
Author(s):  
Aziz Rahman ◽  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Experimental Data ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Water Flow ◽  
Simulation Study ◽  
Cfd Simulation ◽  
Concentric Annulus ◽  
Sst Model ◽  
Cfd Analyses ◽  
Near Wall

A CFD simulation study was conducted to analyse the near wall turbulence characteristics of water flow through concentric annulus. The continuity and momentum equations were solved by using a commercial CFD package (CFX 14) with the Shear-Stress-Transport (SST) model option. The simulation results were compared to the experimental data obtained by using high resolution Particle Image Velocimetry (PIV) analyses of water flow in a horizontal concentric annulus. A fully developed turbulent flow of water through a horizontal flow loop (ID = 9.5 cm) with concentric annular geometry (inner to outer pipe radius ratio = 0.4) was used for comparison purpose. Reynolds number ranged from 17,500 to 68,500. Annular velocity profile obtained from simulation study showed good agreement with the experimental data. Near wall velocity profile obtained from CFD simulation followed the universal wall law (u+ = y+) up to y+ = 11. CFD analyses using the SST model resulted a good number of velocity data up to y+ = 11, which is normally a very difficult task to achieve experimentally. The CFD analyses using SST model is computationally inexpensive and therefore, can be conveniently used for investigating the near wall turbulent characteristics of flow in concentric annulus.

Wind Tunnel Experiment and Numerical Simulation of the Pressure Distribution on a Sedan Exterior Surface

2013 ◽  
Vol 300-301 ◽  
pp. 1027-1031
Author(s):  
Bo Yang ◽  
Li Na Huang ◽  
De Jiu Wu ◽  
Xing Jun Hu
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Pressure Distribution ◽  
Cfd Simulation ◽  
Wind Tunnel Experiment ◽  
Aerodynamic Noise ◽  
Computational Domain ◽  
Side View ◽  
Side Window ◽  
Near Wall

The wind tunnel measurement and numerical simulation of a 50% scaled sedan model surface pressure distribution were made in order to provide fundamental data for improving the Computational Fluid Dynamics (CFD) simulation accuracy of the aerodynamic noise related flow field around automobiles. The pressure measurement positions of the wind tunnel experiment were on the side window and the door. The wind tunnel test section speed was 30m/s at 0° yawing angle. As for the CFD simulation, the wind tunnel shape computational domain and four settings of the near wall computational mesh were made. Both the k-ω SST and the Realizable k-ε turbulence models were chosen. And three value ranges of the near wall computational mesh’s dimensionless wall distance (y+) were realized. Compared with the experimental data, the pressure coefficient (CP) simulation results showed good agreement with the measurement at the re-attaching region on the side window and the attaching region on the door. But the large CPprediction errors happened in the region of the front pillar vortex, the side view mirror wake. It was also shown that the predicted CPvalues were almost independent of the y+value, except the comparatively larger CPpredicted errors on the side window obtained by using the k-ω SST turbulent model when the y+value ranged from 4 to 7. Further unsteady CFD simulation and the exterior aerodynamic noise measurement need be carried out due to the unsteady features of the separated flows, including the front pillar vortex and the side view mirror wake.

Bubble Size and Group Influence for CFD Simulation in Vertical Tube Upward Flow

2010 ◽  
Author(s):  
Songwei Li ◽  
Hong Zhang
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Void Fraction ◽  
Wall Temperature ◽  
Cfd Simulation ◽  
Vertical Tube ◽  
Size Group ◽  
Upward Flow ◽  
Wall Area ◽  
Near Wall

The near-wall bubble congregating in vertical tube upward flow exerts an influence on fluid heat transfer. A 0.5m test section is simulated using CFX10.0 to research the bubble influence on the heat transfer. The vapor-water two-phase CFD calculation is done. The bubbles are added at near wall area, taking no account of the mass transfer between water and vapor. The different bubble max diameter and the different MUSIG model size group get different calculation results, these results are compared, include the distribution of vapor void fraction, the wall temperature distribution and near-wall water temperature distribution, the bubble mean diameter. A guide setting is advised. The calculation result shows that the max bubble diameter and the MUSIG size group on the vapor void fraction distribution is large. The near-wall void fraction gets down to the least (nearly zero, while at the inlet, near wall vapor fraction is 0.95) at 0.1m∼0.14m axis height, then rises. The wall temperature gets highest at the same height, and then appears a flat, keeping this temperature about 0.1m long, after that the temperature gets down, then rises along the axis.

A One-Dimensional Subgrid Near Wall Treatment forTurbulent Flow CFD Simulation

2005 ◽  
Author(s):  
Seth H. Myers ◽  
D. Keith Walters
Keyword(s):  
Cfd Simulation ◽  
Computational Cost ◽  
Gradient Flow ◽  
Grid Cell ◽  
Significant Loss ◽  
Wall Region ◽  
Wall Function ◽  
Wall Functions ◽  
One Dimensional ◽  
Near Wall

Prediction of the near wall region is crucial to the accuracy of turbulent flow computational fluid dynamics (CFD) simulation. However, sufficient near-wall resolution is often prohibitive for high Reynolds number flows with complex geometries, due to high memory and processing requirements. A common approach in these cases is to use wall functions to bridge the region from the first grid node to the wall. This paper presents an alternative method that relaxes the near wall resolution requirement by solving one dimensional transport equations for velocity and turbulent kinetic energy across a locally defined subgrid contained within wall adjacent grid cells. The addition of the subgrid allows for wall adjacent primary grid sizes to vary arbitrarily from low-Re model sizing (y+≈1) to wall function sizing without significant loss of accuracy or increase in computational cost. The method is applied to zero pressure gradient flow over a flat plate and yields solutions comparable to low-Re modeling with high near-wall resolution. Unlike low-Re or wall function modeling, the new method is shown to be insensitive to size variations of the first primary grid cell.

scholarly journals The Effect of the Computational Grid Size on the Prediction of a Flammable Cloud Dispersion

2014 ◽  
Author(s):  
Adriana Miralles Schleder ◽  
Marcelo Ramos Martins ◽  
Elsa Pastor Ferrer ◽  
Eulàlia Planas Cuchi
Keyword(s):  
Cfd Simulation ◽  
Complex Geometry ◽  
Computational Cost ◽  
Computational Grid ◽  
Grid Size ◽  
Hazardous Substances ◽  
Gas Dispersion ◽  
Vapor Cloud ◽  
Predicted Values ◽  
Simulation Parameters

The consequence analysis is used to define the extent and nature of effects caused by undesired events being of great help when quantifying the damage caused by such events. For the case of leaking of flammable and/or toxic materials, effects are analyzed for explosions, fires and toxicity. Specific models are used to analyze the spills or jets of gas or liquids, gas dispersions, explosions and fires. The central step in the analysis of consequences in such cases is to determine the concentration of the vapor cloud of hazardous substances released into the atmosphere, in space and time. With the computational advances, CFD tools are being used to simulate short and medium scale gas dispersion events, especially in scenarios where there is a complex geometry. However, the accuracy of the simulation strongly depends on diverse simulation parameters, being of particular importance the grid resolution. This study investigates the effects of the computational grid size on the prediction of a cloud dispersion considering both the accuracy and the computational cost. Experimental data is compared with the predicted values obtained by means of CFD simulation, exploring and discussing the influence of the grid size on cloud concentration the predicted values. This study contributes to optimize CFD simulation settings concerning grid definition when applied to analyses of consequences in environments with complex geometry.

scholarly journals Assessment of RANS turbulence closure models for predicting airflow in neutral ABL over hilly terrain

2021 ◽  
Author(s):  
Amahjour Narjisse ◽  
Khamlichi Abdellatif
Keyword(s):  
Experimental Data ◽  
Wind Speed ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Computational Time ◽  
Recirculation Region ◽  
Leeward Side ◽  
Hilly Terrain ◽  
Steep Hill ◽  
Near Wall

AbstractImplementing wind farms in heights of a hilly terrain where wind speed is expected to be large may be viewed as a means to increase wind energy production without occupying fertile lands. Micro sitting of a wind farm in these conditions can gain dramatically from CFD simulation of fluid flow in the ABL above complex topography. However, this issue still poses tough challenges regarding the turbulence model to be used and the way to operate the near wall treatment in the presence eventually of separation. In this work, prediction capacity of RANS turbulence models was studied for a typical hill under the assumption of steady state and incompressible airflow regime in neutral ABL. Two models were analyzed by using COMSOL Multiphysics software packages. These included standard , and shear-stress transport . The most up-to-date procedures dedicated to near wall treatment were applied along with refined closer coefficients adjusted for the particular case of ABL. Considering wind tunnel test data, performance of the previous models was discussed in terms of converging mesh, computational time, reattachment point position and propensity of the model to retrieve the right level of turbulence flow in conditions of neutral stratifications. Then, a numerical simulation of the turbulent airflow over two slopes shapes of the symmetry hill by the validation of the experimental data has been then carried out. Both turbulence models agree well with air-velocity tested windward of the hills H3 and H5. Therefore, it was found that the standard model performs very well at the different positions of the low slope hill, and at the summit of a steep hill, but it over-predicts wind speed close to the wall, which requires an improvement of the near-wall treatment. However, the model in neutral case of the ABL was given consistent simulation results with experimental data for prediction of the flow separation and recirculation region at the leeward side of a steep hill, whereas standard model under the neutral condition and the model by using standard coefficients were failed to predict accurately detailed characteristics of recirculation region process.

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