The variational multiscale method

mrkmrk · November 7, 2021, 15:58

Hi,

Is there anyway to employ variational multiscale method [1] to solve the Navier-Stokes equations in ANSYS?

Is it correct that this formulation can model the transition from the laminar to turbulent flow regimes in a problem? I am modeling the blood flow through heart valves. In this problem, we know that we have both laminar and turbulent flow regimes in a cardiac cycle. I tried to model the flow using a laminar model as an approximation of the accurate solution. Is this a valid approach?

[1] https://en.wikipedia.org/wiki/Variat...tiscale_method

ghorrocks · November 7, 2021, 17:17

That looks like a method still in the research stage to me. I suspect you will need to be an expert in numerical methods to implement that, and if you are an expert in numerical methods then you will have written your own CFD solver to make best use of the features of the approach rather than use a commercial code. And then taking an experimental numerical method and applying it to a heart: with moving walls, complex rheology, laminar/turbulent transition and complex geometry....... I think I can safely say this is not realistic.

Simply put, you can be sure all numerical methods which are validated to work on a wide range of flows and can be implemented in a Navier Stokes solver like CFX are already in it.

So what is a realistic approach? If the Reynolds number is low then modelling the flow with a laminar is quite feasible. I used that exact model in my PhD thesis as a simple LES model. See my thesis, Chapter 6, for the justification of it and the results (it worked quite well): https://opus.lib.uts.edu.au/handle/10453/20133#

mrkmrk · November 9, 2021, 14:42

Dear Glenn,

Your help is much appreciated. Thank you for sharing your Ph.D. thesis with me.

LES seems to be the solution.

November 7, 2021, 15:58	The variational multiscale method	#1
mrkmrk Member David Join Date: Aug 2013 Posts: 72 Rep Power: 12	Hi, Is there anyway to employ variational multiscale method [1] to solve the Navier-Stokes equations in ANSYS? Is it correct that this formulation can model the transition from the laminar to turbulent flow regimes in a problem? I am modeling the blood flow through heart valves. In this problem, we know that we have both laminar and turbulent flow regimes in a cardiac cycle. I tried to model the flow using a laminar model as an approximation of the accurate solution. Is this a valid approach? [1] https://en.wikipedia.org/wiki/Variat...tiscale_method

November 7, 2021, 17:17		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143	That looks like a method still in the research stage to me. I suspect you will need to be an expert in numerical methods to implement that, and if you are an expert in numerical methods then you will have written your own CFD solver to make best use of the features of the approach rather than use a commercial code. And then taking an experimental numerical method and applying it to a heart: with moving walls, complex rheology, laminar/turbulent transition and complex geometry....... I think I can safely say this is not realistic. Simply put, you can be sure all numerical methods which are validated to work on a wide range of flows and can be implemented in a Navier Stokes solver like CFX are already in it. So what is a realistic approach? If the Reynolds number is low then modelling the flow with a laminar is quite feasible. I used that exact model in my PhD thesis as a simple LES model. See my thesis, Chapter 6, for the justification of it and the results (it worked quite well): https://opus.lib.uts.edu.au/handle/10453/20133# __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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November 9, 2021, 14:42		#3
mrkmrk Member David Join Date: Aug 2013 Posts: 72 Rep Power: 12	Dear Glenn, Your help is much appreciated. Thank you for sharing your Ph.D. thesis with me. LES seems to be the solution.