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(New page: ='''Cyclone separator'''= '''Application Challenge 3-03''' © copyright ERCOFTAC 2004 =='''Overview of CFD Simulations'''== This section of the document describes the CFD...)
 
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{{AC|front=AC 3-03|description=Description_AC3-03|testdata=Test Data_AC3-03|cfdsimulations=CFD Simulations_AC3-03|evaluation=Evaluation_AC3-03|qualityreview=Quality Review_AC3-03|bestpractice=Best Practice Advice_AC3-03|relatedUFRs=Related UFRs_AC3-03}}
='''Cyclone separator'''=
='''Cyclone separator'''=


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=='''Overview of CFD Simulations'''==
=='''Overview of CFD Simulations'''==


This section of the document describes the CFD analysis carried out to simulate the flow pattern in the cyclone shown in Figure 2 with the operating conditions presented in section 2.2.
This section of the document describes the CFD analysis carried out to simulate the flow pattern in the cyclone shown in [[Description_AC3-03#|Figure 2]] with the operating conditions presented in section 2.2.




{|border="1" cell padding="20" cell spacing="3"
{|border="1" cell padding="20" cell spacing="3" width="600" align="center"
!'''''Name'''''!!'''''GNDPs'''''!!colspan="2"| '''''PDPs (problem definition parameters)'''''!!colspan="2"| '''''SPs (simulated parameters)'''''
|+ align="bottom" | Table 3 CFD-A Summary Description of All Test Cases
!'''''Name'''''!!'''''GNDPs'''''!!colspan="2"| '''''[[DOAPs#PDPs:_Problem_Definition_Parameters|PDPs]]'''''!!colspan="2"| '''''[[DOAPs#SPs:_Simulated_Parameters|SPs]]'''''
|-
|-
! || Inlet re || Air inflow rate <math>\[{(m^3/s)}\]</math> || Release density <math>\[{(kg/m^3)}\]</math> || Detailed data || [[DOAPs]]
! || Inlet re || Air inflow rate (m<sup>3</sup>/s) || Release density (kg/m<sup>3</sup>) || Detailed data || [[DOAPs#DOAPs:_Design_or_Assessment_Parameters|DOAPs]]
|-
|-
!'''CFD 1''' (velocity predictions)
!'''CFD 1''' (velocity predictions)
Line 19: Line 22:
|}
|}


=='''Simulation Case CFD1'''==




'''Solution strategy'''


The [http://www.fluent.com/ Fluent software version 5.0] was used for the purpose of the CFD simulations. The segregated solution algorithm was selected. The Reynolds stress (RSM) turbulence model was used and in this model due to the anisotropic nature of the turbulence in cyclones. In the RSM the individual Reynolds stresses are calculated using differential transport equations. The individual Reynolds stresses are then used to obtain closure of the Reynolds averaged momentum equation. The discretisation schemes are summarised below.


 
<span id="Table 4">
 
{|border="1" cell padding="20" cell spacing="3" align="center"
 
|+ align="bottom" | Table 4 Discretisation Schemes
Table 3 CFD-A Summary description of all test cases
!  !! '''Discretisation Scheme'''
© ERCOFTAC 2004
|-
Simulation Case CFD1
|Pressure || PRESTO
© ERCOFTAC 2004
|-
Solution strategy
|Momentum || QUICK
 
|-
The Fluent software version 5.0 was used for the purpose of the CFD simulations. The segregated solution algorithm was selected. The Reynolds stress (RSM) turbulence model was used and in this model due to the anisotropic nature of the turbulence in cyclones. In the RSM the individual Reynolds stresses are calculated using differential transport equations. The individual Reynolds stresses are then used to obtain closure of the Reynolds averaged momentum equation. The discretisation schemes are summarised below.
|Turbulent kinetic energy || QUICK
 
|-
|Turbulent dissipation rate || QUICK
|-
|Reynold's stresses || QUICK
|}
</span>
   
   


   
   


Discretisation Scheme
Further details on the RSM and the discretisation schemes presented in [[#Table 4|Table 4]] can be found in the Fluent User Guide [[Evaluation_AC3-03#9|9]] and other literature sources [[Evaluation_AC3-03#10|10]]. Using the segregated solution algorithm the governing equations are solved sequentially and because the governing equations are non linear (and coupled) several iterations of the solution loop must be performed. PRESTO (or PRESsure Staggered Option) is a pressure interpolation scheme that is similar to staggered grid schemes used with structured meshes [[Evaluation_AC3-03#11|11]] and uses the discrete continuity balance for a staggered control volume about the face to compute the face pressure.


Pressure
 
PRESTO
 
Momentum
 
QUICK


Turbulent kinetic energy
'''Computational Domain'''


QUICK
The cyclone chamber shown in [[Description_AC3-03#|Figure 2]] was represented using a relatively coarse unstructured hexahedral mesh that consisted of approximately 41000 cells. [[#Figure 4|Figure 4]] shows the mesh used.
 
Turbulent dissipation rate
 
QUICK
 
Reynold’s stresses
 
QUICK
 
Table 4 Discretisation schemes


   
   
<span id="Figure 4">
Figure 4 The computational mesh


Further details on the RSM and the discretisation schemes presented in Table 4 can be found in the Fluent User Guide [9] and other literature sources [10]. Using the segregated solution algorithm the governing equations are solved sequentially and because the governing equations are non linear (and coupled) several iterations of the solution loop must be performed. PRESTO (or PRESsure Staggered Option) is a pressure interpolation scheme that is similar to staggered grid schemes used with structured meshes [11] and uses the discrete continuity balance for a staggered control volume about the face to compute the face pressure.
[[Image:Image007.jpg]]


   
   
© ERCOFTAC 2004
Computational Domain


The cyclone chamber shown in Figure 2 was represented using a relatively coarse unstructured hexahedral mesh that consisted of approximately 41000 cells. Figure 4 shows the mesh used.
</span>
'''Boundary Conditions'''


A velocity inlet boundary was used to specify an air inflow rate of 0.08m<sup>3</sup>/s. The average inlet velocity (U<sub>avg</sub>) was 20m/s based on an inlet duct area of 0.004m<sup>2</sup>. The turbulence intensity (I) was set at 10% or 0.1. No sensitivity analysis has been carried out on this parameter. The turbulent length scale <math>l</math> was set at 0.0028m and this was calculated based on an approximate relationship between the length scale and the physical size of the inlet duct. The length scale being set as 0.07 times a cross sectional duct dimension. In this case the duct dimension used was 0.04m. No sensitivity study was carried on this parameter. From these parameters the values of the Reynolds stresses and the turbulence dissipation rate, ε, specified at the inlet were derived. The turbulent kinetic energy, k, was derived based on equation 1.


Figure 4 The computational mesh
<math>k = \frac{3}{2}{(U_{avg}I)}^2 \qquad\qquad\qquad\qquad
\qquad\qquad\qquad\qquad(1)</math>


The derived Reynolds stresses were then calculated as shown by equation 2 and the derived turbulence dissipation rate was derived according to equation 3.


<math>
\overline{u^{\prime 2}_i} = \frac{2}{3}k\quad{(i=1,2,3)}\qquad
\text{and }\overline{u^\prime_{i}u^\prime_{j}}=0.0\quad\text{when } i\ne j\qquad(2)
</math>


© ERCOFTAC 2004
Boundary Conditions


A velocity inlet boundary was used to specify an air inflow rate of 0.08m3/s. The average inlet velocity (Uavg) was 20m/s based on an inlet duct area of 0.004m2. The turbulence intensity (I) was set at 10% or 0.1. No sensitivity analysis has been carried out on this parameter. The turbulent length scale () was set at 0.0028m and this was calculated based on an approximate relationship between the length scale and the physical size of the inlet duct. The length scale being set as 0.07 times a cross sectional duct dimension. In this case the duct dimension used was 0.04m. No sensitivity study was carried on this parameter. From these parameters the values of the Reynolds stresses and the turbulence dissipation rate, ε, specified at the inlet were derived. The turbulent kinetic energy, k, was derived based on equation 1.
<math>\varepsilon = C^{3/4}_\mu\frac{k^{3/2}}{{l}}</math>  where <math>C_\mu = 0.09
\qquad\qquad\qquad\qquad\quad\ \ (3)</math>


(1)


The derived Reynolds stresses were then calculated as shown by equation 2 and the derived turbulence dissipation rate was derived according to equation 3.
The simulations were carried out with a zero underflow component. The underflow was therefore represented using a wall boundary. An outflow boundary condition was used to represent the cyclone overflow.


(2)


where Cm = 0.09 (3)
'''Application of Physical Models'''


The RSM with standard Fluent wall functions, after Launder and Spalding [[Evaluation_AC3-03#12|12]] was applied in this case. Using the standard wall function approach, the viscosity affected inner region near the wall is not resolved. Instead, semi-empirical formulas are used to bridge the viscosity affected region between the wall and the fully turbulent region and this obviates the need to modify the turbulence models to account for the presence of the wall. Further details of this approach can be found in the Fluent User Guide [[Evaluation_AC3-03#9|9]]. The simulations were isothermal, steady state and incompressible. The flow and turbulence within a cyclone are determined principally by the main flow and are less sensitive to boundary layer effects. This was recently demonstrated by Slack et al. [[Evaluation_AC3-03#13|13]] who compared the axial and tangential velocity predictions obtained by the CFD model described here with those of an LES turbulence model of the same cyclone with a computational mesh that consisted of 640,000 cells. The LES and fine mesh simulation results were only marginally more accurate than the coarse mesh simulation when compared with experimental data.


The simulations were carried out with a zero underflow component. The underflow was therefore represented using a wall boundary. An outflow boundary condition was used to represent the cyclone overflow.
© ERCOFTAC 2004
Application of Physical Models


The RSM with standard Fluent wall functions, after Launder and Spalding [12] was applied in this case. Using the standard wall function approach, the viscosity affected inner region near the wall is not resolved. Instead, semi-empirical formulas are used to bridge the viscosity affected region between the wall and the fully turbulent region and this obviates the need to modify the turbulence models to account for the presence of the wall. Further details of this approach can be found in the Fluent User Guide [9]. The simulations were isothermal, steady state and incompressible. The flow and turbulence within a cyclone are determined principally by the main flow and are less sensitive to boundary layer effects. This was recently demonstrated by Slack et al. [13] who compared the axial and tangential velocity predictions obtained by the CFD model described here with those of an LES turbulence model of the same cyclone with a computational mesh that consisted of 640,000 cells. The LES and fine mesh simulation results were only marginally more accurate than the coarse mesh simulation when compared with experimental data.
'''Numerical Accuracy'''
© ERCOFTAC 2004
Numerical Accuracy


In the AC, the flow profile in the radial direction was monitored using the x-y plotting function along a series of line surfaces distributed evenly throughout the chamber domain. The x-y plot generated was written to a file such that the change in the profile was monitored with the increase in the number of solution iterations.
In the AC, the flow profile in the radial direction was monitored using the x-y plotting function along a series of line surfaces distributed evenly throughout the chamber domain. The x-y plot generated was written to a file such that the change in the profile was monitored with the increase in the number of solution iterations.
Line 116: Line 103:


A mesh sensitivity study was not undertaken at this stage.
A mesh sensitivity study was not undertaken at this stage.
© ERCOFTAC 2004
 
CFD Results
 
'''CFD Results'''


The results of the CFD analysis are presented in direct comparison with the experimental data in the following section.
The results of the CFD analysis are presented in direct comparison with the experimental data in the following section.
[[Image:Image017.jpg]]


   
   
 
[[Image:Image019.jpg]]
   
   


[[Image:Image021.jpg]]
   
   




© copyright ERCOFTAC 2004
© copyright ERCOFTAC 2004
----


Contributors: Chris Carey - Fluent Europe Ltd
Contributors: Chris Carey - Fluent Europe Ltd


Site Design and Implementation: Atkins and UniS
Site Design and Implementation: [[Atkins]] and [[UniS]]
 
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{{AC|front=AC 3-03|description=Description_AC3-03|testdata=Test Data_AC3-03|cfdsimulations=CFD Simulations_AC3-03|evaluation=Evaluation_AC3-03|qualityreview=Quality Review_AC3-03|bestpractice=Best Practice Advice_AC3-03|relatedUFRs=Related UFRs_AC3-03}}

Latest revision as of 16:05, 11 February 2017

Front Page

Description

Test Data

CFD Simulations

Evaluation

Best Practice Advice

Cyclone separator

Application Challenge 3-03 © copyright ERCOFTAC 2004


Overview of CFD Simulations

This section of the document describes the CFD analysis carried out to simulate the flow pattern in the cyclone shown in Figure 2 with the operating conditions presented in section 2.2.


Table 3 CFD-A Summary Description of All Test Cases
Name GNDPs PDPs SPs
Inlet re Air inflow rate (m3/s) Release density (kg/m3) Detailed data DOAPs
CFD 1 (velocity predictions) 0.08 1.225 Axial and tangential velocity components Axial and tangential velocity profiles

Simulation Case CFD1

Solution strategy

The Fluent software version 5.0 was used for the purpose of the CFD simulations. The segregated solution algorithm was selected. The Reynolds stress (RSM) turbulence model was used and in this model due to the anisotropic nature of the turbulence in cyclones. In the RSM the individual Reynolds stresses are calculated using differential transport equations. The individual Reynolds stresses are then used to obtain closure of the Reynolds averaged momentum equation. The discretisation schemes are summarised below.

Table 4 Discretisation Schemes
Discretisation Scheme
Pressure PRESTO
Momentum QUICK
Turbulent kinetic energy QUICK
Turbulent dissipation rate QUICK
Reynold's stresses QUICK



Further details on the RSM and the discretisation schemes presented in Table 4 can be found in the Fluent User Guide 9 and other literature sources 10. Using the segregated solution algorithm the governing equations are solved sequentially and because the governing equations are non linear (and coupled) several iterations of the solution loop must be performed. PRESTO (or PRESsure Staggered Option) is a pressure interpolation scheme that is similar to staggered grid schemes used with structured meshes 11 and uses the discrete continuity balance for a staggered control volume about the face to compute the face pressure.


Computational Domain

The cyclone chamber shown in Figure 2 was represented using a relatively coarse unstructured hexahedral mesh that consisted of approximately 41000 cells. Figure 4 shows the mesh used.


Figure 4 The computational mesh

Image007.jpg


Boundary Conditions

A velocity inlet boundary was used to specify an air inflow rate of 0.08m3/s. The average inlet velocity (Uavg) was 20m/s based on an inlet duct area of 0.004m2. The turbulence intensity (I) was set at 10% or 0.1. No sensitivity analysis has been carried out on this parameter. The turbulent length scale was set at 0.0028m and this was calculated based on an approximate relationship between the length scale and the physical size of the inlet duct. The length scale being set as 0.07 times a cross sectional duct dimension. In this case the duct dimension used was 0.04m. No sensitivity study was carried on this parameter. From these parameters the values of the Reynolds stresses and the turbulence dissipation rate, ε, specified at the inlet were derived. The turbulent kinetic energy, k, was derived based on equation 1.

The derived Reynolds stresses were then calculated as shown by equation 2 and the derived turbulence dissipation rate was derived according to equation 3.


where


The simulations were carried out with a zero underflow component. The underflow was therefore represented using a wall boundary. An outflow boundary condition was used to represent the cyclone overflow.


Application of Physical Models

The RSM with standard Fluent wall functions, after Launder and Spalding 12 was applied in this case. Using the standard wall function approach, the viscosity affected inner region near the wall is not resolved. Instead, semi-empirical formulas are used to bridge the viscosity affected region between the wall and the fully turbulent region and this obviates the need to modify the turbulence models to account for the presence of the wall. Further details of this approach can be found in the Fluent User Guide 9. The simulations were isothermal, steady state and incompressible. The flow and turbulence within a cyclone are determined principally by the main flow and are less sensitive to boundary layer effects. This was recently demonstrated by Slack et al. 13 who compared the axial and tangential velocity predictions obtained by the CFD model described here with those of an LES turbulence model of the same cyclone with a computational mesh that consisted of 640,000 cells. The LES and fine mesh simulation results were only marginally more accurate than the coarse mesh simulation when compared with experimental data.


Numerical Accuracy

In the AC, the flow profile in the radial direction was monitored using the x-y plotting function along a series of line surfaces distributed evenly throughout the chamber domain. The x-y plot generated was written to a file such that the change in the profile was monitored with the increase in the number of solution iterations.

The residual plotting option was also activated.

The solution process continued until the scaled residual values exhibited no significant change and there were no further significant changes in the radial flow profiles with iteration as shown by the recorded x-y plot files. These coupled with mass flux reporting were the key quantitative solution convergence criteria.

A mesh sensitivity study was not undertaken at this stage.


CFD Results

The results of the CFD analysis are presented in direct comparison with the experimental data in the following section.


Image017.jpg


Image019.jpg


Image021.jpg


© copyright ERCOFTAC 2004


Contributors: Chris Carey - Fluent Europe Ltd

Site Design and Implementation: Atkins and UniS


Front Page

Description

Test Data

CFD Simulations

Evaluation

Best Practice Advice