# k-epsilon problem: non-physical turbulent viscosity production in coaxial free-jet

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 July 26, 2010, 09:45 k-epsilon problem: non-physical turbulent viscosity production in coaxial free-jet #1 New Member   Felipe B. Ch. Join Date: May 2010 Posts: 15 Rep Power: 8 What are some unexpected producers of turbulent viscosity when using k-epsilon? In our simulation, concentrically aligned free-jets are simulated for comparison with experimental data. In this figure, turbulent viscosity measured on the domain's centerline is shown in red, the axial velocity measured on the domain's centerline is shown in green, and the experimental axial velocity data which we seek to match is shown in orange. These curves are overlaid on top of the domain which is shown in blue. Why would k-epsilon produce the large amount of turbulent viscosity starting at about 40% of the length of the domain? Grid dependency in the direction of flow has been eliminated. Further simulation details: Fluent 2D Axisymmetric Incompressible Species Transport model Hydrogen-Air Concentric velocity-inlets: inner: Hydrogen, turbulence intensity 4% Concentric velocity-inlets: outer: Air, turbulence intensity of 3% Pressure inlet: Air, 1 atm Pressure outlet: 1 atm Very grateful for any advice or suggestions on how to remove/remedy this non-physical turbulent viscosity production. Last edited by Felipeb; July 26, 2010 at 10:02.

 July 26, 2010, 17:02 k, epsilon, rho plot #2 New Member   Felipe B. Ch. Join Date: May 2010 Posts: 15 Rep Power: 8 Below are plotted the constituent quantities comprising the turbulent viscosity in our simulation. The turbulent viscosity is defined as follows: From initial inspection of the plots, it looks like k is at fault. Why would k suddenly jump at X/D = 8 ? Any suggestions? Last edited by Felipeb; July 27, 2010 at 00:40.

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