yhy20081016 |
December 17, 2013 02:14 |
How to compute the viscous dissipation term
Hi, everybody. I am performing 2D unsteady CFD simulations on a cross-flow fan. I am using ANSYS FLUENT 12.1. I adopt the standard k-omega model to simulate turbulence.
I want to compute the viscous dissipation term. I cannot find this variable in FLUENT. Hence I exported the solution to Tecplot, and then write some equations to compute it.
I use the following equation to compute the viscous dissipation term: (This equation can be found in ANSYS FLUENT 12.0 Theory Guide, page 4-24 and 4-25)
viscous dissipation=
where
I use [Data]|[Alter]|[Specify Equations…] in Tecplot to implement these equations. The expressions which I type into Tecplot are listed as follows:
{duxdx}=ddx({x-velocity})
{duxdy}=ddy({x-velocity})
{duydx}=ddx({y-velocity})
{duydy}=ddy({y-velocity})
{viscous_heating2}=ddx({x-velocity}*({viscosity-eff}*({duxdx}*2)-2.0/3.0*{viscosity-eff}*({duxdx}+{duydy}))+{y-velocity}*({viscosity-eff}*({duxdy}+{duydx}))) + ddy({x-velocity}*({viscosity-eff}*({duydx}+{duxdy}))+{y-velocity}*({viscosity-eff}*({duydy}*2)-2.0/3.0*{viscosity-eff}*({duxdx}+{duydy})))
Finally, I display contour of the variable “viscous_heating2”. However, to my surprise, the minimum value of this variable is -679152, and the maximum value is 352578. This is weird – because the dissipation should be always positive. How could negative values occur?
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