upwind-high res. blending

k.vafiadis · July 27, 2012, 11:19

Hello, is there any difference if someone run a upwind advection scheme, and then:

run a high resolution (the upwind run will be the initial value) for both momentum and continuity
run a high resolution for continuity - upwind for momentum (the upwind run will be the initial value) and then a high resolution for both momentum and continuity (the high resolution for continuity - upwind for momentum will be the initial value).

even if they are coupled I think that they behave different when they use different schemes and that affects the way the simulation reach convergence

Felggv · July 27, 2012, 13:34

I believe you can find something about it in the section Wiki CFD here at this website.

Have you read the Ansys Help Documentation?

k.vafiadis · July 27, 2012, 13:56

I already read the documentation but I can't find something.
I would like any suggestions from the cfdonline community experience

I already run a simulation about this and I will post my conclusions!

ghorrocks · July 28, 2012, 08:07

The documentation describes all this. But for a fully converged steady state solution, in general it does not matter what the initial condition was. A good initial condition will converge faster, but the end result is the same. A small number of flows are bimodal (or multi-modal) and the intiial condition determines which final state they end up in.

But the final converged solution will be different if you use different advection schemes.

Note high res is not an available option for continuity. Continuity does not advection so has no need for an advection scheme. The high res option only applies to momentum and scalar equations. The important option for continuity is what P-V coupling is applied.

k.vafiadis · July 29, 2012, 09:23

I agree about the continuity equation. And thank you for your considerations! But what made me have this confusion was that:

solver control>equation class settings?equation class: continuity

has the option for an advection scheme and moreover it has the three choices used for advection in CFX, upwind, high resolution and specified blend factor.

My testing with this gives that the advection scheme for continuity does nothing...

July 27, 2012, 11:19	upwind-high res. blending	#1
k.vafiadis New Member Kyriakos Vafiadis Join Date: Feb 2011 Location: Kozani, Greece Posts: 29 Rep Power: 15	Hello, is there any difference if someone run a upwind advection scheme, and then: run a high resolution (the upwind run will be the initial value) for both momentum and continuity run a high resolution for continuity - upwind for momentum (the upwind run will be the initial value) and then a high resolution for both momentum and continuity (the high resolution for continuity - upwind for momentum will be the initial value). even if they are coupled I think that they behave different when they use different schemes and that affects the way the simulation reach convergence __________________ -- Kyriakos Vafiadis Mechanical Engineer, PhD candidate

July 27, 2012, 13:56		#3
k.vafiadis New Member Kyriakos Vafiadis Join Date: Feb 2011 Location: Kozani, Greece Posts: 29 Rep Power: 15	I already read the documentation but I can't find something. I would like any suggestions from the cfdonline community experience I already run a simulation about this and I will post my conclusions! __________________ -- Kyriakos Vafiadis Mechanical Engineer, PhD candidate

July 29, 2012, 09:23		#5
k.vafiadis New Member Kyriakos Vafiadis Join Date: Feb 2011 Location: Kozani, Greece Posts: 29 Rep Power: 15	I agree about the continuity equation. And thank you for your considerations! But what made me have this confusion was that: solver control>equation class settings?equation class: continuity has the option for an advection scheme and moreover it has the three choices used for advection in CFX, upwind, high resolution and specified blend factor. My testing with this gives that the advection scheme for continuity does nothing... __________________ -- Kyriakos Vafiadis Mechanical Engineer, PhD candidate Last edited by k.vafiadis; July 29, 2012 at 09:28. Reason: addes a picture

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July 27, 2012, 13:34		#2
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	I believe you can find something about it in the section Wiki CFD here at this website. Have you read the Ansys Help Documentation?

July 28, 2012, 08:07		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The documentation describes all this. But for a fully converged steady state solution, in general it does not matter what the initial condition was. A good initial condition will converge faster, but the end result is the same. A small number of flows are bimodal (or multi-modal) and the intiial condition determines which final state they end up in. But the final converged solution will be different if you use different advection schemes. Note high res is not an available option for continuity. Continuity does not advection so has no need for an advection scheme. The high res option only applies to momentum and scalar equations. The important option for continuity is what P-V coupling is applied.