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Negative Densities

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Old   April 24, 2005, 08:14
Default Negative Densities
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Hi All,

My run is coming out by giving -ve densities found in more than 100 cells. The fluid is air with f(T,P) setting. Domain size is 1km. shape is spherical. Velocity inlet is given by pressure UV explicit method. I use MARS scheme.

Kindly guide.


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Old   April 24, 2005, 21:32
Default Re: Negative Densities
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Play with the relaxation factors. Reduce them even then if it doesnt work,then reduce the time step it will surely work
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Old   May 8, 2005, 06:17
Default Re: Negative Densities
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My technique! The combination of relaxation factors helps me for various compressible steady problems: velocity=0,2; pressure=0,1; turbulence=0,5; density and turb.visc.=0,5; and for entalphy you can keep ones by default. However, if the solution doesn't converge you have to issue the relaxation factor for entalphy equal 0,1. And reduce the values of residual tolerance to 10e-6 for pressure, 10e-18 for temperature, and others to 10e-2. If this combination doesn't work you should go on a transient solver! For transient problems only time step reducing delivers from negative density!
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