Different flow patterns in CFX and Fluent

avi@lpsc · April 2, 2012, 14:24

Hi Guys
I have some issues interpreting my results from two similar analysis, one in Fluent and other in CFX. Its a general compressible flow case of CD nozzle with supersonic diffuser attached to the exit of nozzle.
I will highlight the settings here:
Fluent: 2D axi case with density modeled as Ideal gas, Density based solver, 4 species properties given as polynomials, Pressure Inlet at Nozzle 33.5bar- Mass flow rate boundary imposed :8.65kg.s-Subsonic, Pressure outlet at Diffuser section attached to Nozzle exit 180millibar. Case Initialized with Pressure Inlet with lower value of axial velocity, Boundary layer in nozzle with Y plus approximately 10.Turbulence:SST K-omega, For this condition a converged solution shows the Nozzle mach Contour as - Full flow i.e no separation inside nozzle,No shock inside. (Maximum Mach Nbr: 8),

2. A similar case was ran in CFX with similar settings, Density: Ideal gas, Solver details : Default settings,Species Properties similar to Fluent,SST K-omega, Mass flow rate bc. A converged solution shows separated flow in nozzle and no full flow similar to Fluent results.

Grid Independent and Turbulence model study has already been conducted and all resulted in same flow pattern in Fluent i.e Nozzle full flow.

Similar GI study has also been done in CFX for with adapted grid in nozzle which shows separated flow with in nozzle.

So In a sense I am getting different results from two with similar simulations.I only uses density based solver of fluent for compressible flow problems. whether CFX solver is capable for this type of high speed flows. If it is,then what could be the possible reason for this differing results.

shall be thankful.

ghorrocks · April 4, 2012, 07:44

Are you sure the correct answer is no separation?

avi@lpsc · April 5, 2012, 02:41

Thanks for reply.

1D cal. shows flow will separate inside the nozzle, but point here is that even I performed both simulations in 3D, same grid, property settings same. I am getting full flow in Fluent and separated flow in CFX. What would be the possible reason for it , whether PBCS solvers are able to handle shock formation and separation better than density based solver of Fluent. Major facility change will be done based on this analysis, so I need a solution for this different results.

Shall be thankfull

avi@lpsc · April 6, 2012, 02:37

what for? ur also looking for answers to my query..

ghorrocks · April 15, 2012, 18:05

No, there is no general rule that PBCS solvers are better or worse at these type of flows.

avi@lpsc · April 16, 2012, 11:45

Thanks for reply..

Both CFX and Fluent DBS,PBCS are awesome. I have identified the problem.

ghorrocks · April 17, 2012, 01:22

What was the problem? What did you do to fix it?

April 2, 2012, 14:24	Different flow patterns in CFX and Fluent	#1
avi@lpsc New Member AMSharma Join Date: Apr 2012 Posts: 12 Rep Power: 14	Hi Guys I have some issues interpreting my results from two similar analysis, one in Fluent and other in CFX. Its a general compressible flow case of CD nozzle with supersonic diffuser attached to the exit of nozzle. I will highlight the settings here: Fluent: 2D axi case with density modeled as Ideal gas, Density based solver, 4 species properties given as polynomials, Pressure Inlet at Nozzle 33.5bar- Mass flow rate boundary imposed :8.65kg.s-Subsonic, Pressure outlet at Diffuser section attached to Nozzle exit 180millibar. Case Initialized with Pressure Inlet with lower value of axial velocity, Boundary layer in nozzle with Y plus approximately 10.Turbulence:SST K-omega, For this condition a converged solution shows the Nozzle mach Contour as - Full flow i.e no separation inside nozzle,No shock inside. (Maximum Mach Nbr: 8), 2. A similar case was ran in CFX with similar settings, Density: Ideal gas, Solver details : Default settings,Species Properties similar to Fluent,SST K-omega, Mass flow rate bc. A converged solution shows separated flow in nozzle and no full flow similar to Fluent results. Grid Independent and Turbulence model study has already been conducted and all resulted in same flow pattern in Fluent i.e Nozzle full flow. Similar GI study has also been done in CFX for with adapted grid in nozzle which shows separated flow with in nozzle. So In a sense I am getting different results from two with similar simulations.I only uses density based solver of fluent for compressible flow problems. whether CFX solver is capable for this type of high speed flows. If it is,then what could be the possible reason for this differing results. shall be thankful.

April 5, 2012, 02:41	Differing Results Fluent CFX /Fluent	#3
avi@lpsc New Member AMSharma Join Date: Apr 2012 Posts: 12 Rep Power: 14	Thanks for reply. 1D cal. shows flow will separate inside the nozzle, but point here is that even I performed both simulations in 3D, same grid, property settings same. I am getting full flow in Fluent and separated flow in CFX. What would be the possible reason for it , whether PBCS solvers are able to handle shock formation and separation better than density based solver of Fluent. Major facility change will be done based on this analysis, so I need a solution for this different results. Shall be thankfull

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April 4, 2012, 07:44		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Are you sure the correct answer is no separation?

April 6, 2012, 02:37		#4
avi@lpsc New Member AMSharma Join Date: Apr 2012 Posts: 12 Rep Power: 14	what for? ur also looking for answers to my query..

April 15, 2012, 18:05		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	No, there is no general rule that PBCS solvers are better or worse at these type of flows.

April 16, 2012, 11:45		#6
avi@lpsc New Member AMSharma Join Date: Apr 2012 Posts: 12 Rep Power: 14	Thanks for reply.. Both CFX and Fluent DBS,PBCS are awesome. I have identified the problem.

April 17, 2012, 01:22		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	What was the problem? What did you do to fix it?