Viscous flux

9mile · September 24, 2010, 14:59

Hello all.
I got question about visous flux evaluation.
Mostly the central differencing method is used for the viscous flux.
I just got wondered why the central differencing is useful.
Some books said that the reason comes from "elliptic property of the viscous flux".
Can anyone give some more specific explanation from either mathematical or physical point of view?

Hamidzoka · September 25, 2010, 01:53

this mainly comes form the mechanism of voscous flux.
viscous fluxes are diffusive.
diffusive motions are random motions in each directions. for example in a 2-d domain a diffusive flux like viscousity can go up-down-righ or left and thus they are affected by both upstream and downstream points. therefore central difference is more physical since it considers up-down-right and left points.
but for example if you make an upwind differnce scheme, you force the diffusive flux to be affected just by upsteam points and this means that diffusive flux is not modeled properly according to its nature.

regards

9mile · September 25, 2010, 09:17

Dear Hamidzoka.

That's what i want to hear.

Thanks.

September 24, 2010, 14:59	Viscous flux	#1
9mile New Member Neo Join Date: Mar 2009 Posts: 18 Rep Power: 17	Hello all. I got question about visous flux evaluation. Mostly the central differencing method is used for the viscous flux. I just got wondered why the central differencing is useful. Some books said that the reason comes from "elliptic property of the viscous flux". Can anyone give some more specific explanation from either mathematical or physical point of view?

September 25, 2010, 09:17	Thanks for reply	#3
9mile New Member Neo Join Date: Mar 2009 Posts: 18 Rep Power: 17	Dear Hamidzoka. That's what i want to hear. Thanks.

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September 25, 2010, 01:53		#2
Hamidzoka Senior Member Hamid Zoka Join Date: Nov 2009 Posts: 293 Rep Power: 18	this mainly comes form the mechanism of voscous flux. viscous fluxes are diffusive. diffusive motions are random motions in each directions. for example in a 2-d domain a diffusive flux like viscousity can go up-down-righ or left and thus they are affected by both upstream and downstream points. therefore central difference is more physical since it considers up-down-right and left points. but for example if you make an upwind differnce scheme, you force the diffusive flux to be affected just by upsteam points and this means that diffusive flux is not modeled properly according to its nature. regards