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December 17, 2013, 02:14 |
How to compute the viscous dissipation term
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#1 |
Member
yehanyu
Join Date: Mar 2012
Location: Beijing, China
Posts: 48
Rep Power: 14 |
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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Tags |
dissipation, tecplot, turbulence, viscous |
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