UDF residence time distribution

Many · January 21, 2016, 07:30

Hi CFD friends!

I am trying to compute residence time contours using UDF found in this forum

My questions are the following:

1. Changing the mesh, then the residence time contours change (at least the maximum of residence time). I guess this is not desirable. Anybody has an idea about why this is happening? I realized that mesh cells appear in the function...

I am wondering if achieving mesh independent results will fix this, it's to said, max_residence_time tends to real_max_residence_time as cell_size tends to zero

If not, I am not understanding the value of this UDF as residence time will be mesh-dependent...

2. Which values should I use for Schmidt number and mass diffusivity for water?

3. When I got convergent results, I just solve for the defined scalar in steady state. Is unsteady solution needed? In other words, have I switch to unsteady model just for solving the scalar transport?

I have asked in another threads and I have found no answer yet and it is quite urgent for me to understand this...

Thanks in advance for all your answers!

Many · January 21, 2016, 07:59

Just one more thing,

What happens if porous media is present in the model? How UDF can account for the effects of this?

January 21, 2016, 07:30	UDF residence time distribution	#1
Many Member Liam Join Date: Aug 2013 Posts: 40 Rep Power: 12	Hi CFD friends! I am trying to compute residence time contours using UDF found in this forum My questions are the following: 1. Changing the mesh, then the residence time contours change (at least the maximum of residence time). I guess this is not desirable. Anybody has an idea about why this is happening? I realized that mesh cells appear in the function... I am wondering if achieving mesh independent results will fix this, it's to said, max_residence_time tends to real_max_residence_time as cell_size tends to zero If not, I am not understanding the value of this UDF as residence time will be mesh-dependent... 2. Which values should I use for Schmidt number and mass diffusivity for water? 3. When I got convergent results, I just solve for the defined scalar in steady state. Is unsteady solution needed? In other words, have I switch to unsteady model just for solving the scalar transport? I have asked in another threads and I have found no answer yet and it is quite urgent for me to understand this... Thanks in advance for all your answers!

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January 21, 2016, 07:59		#2
Many Member Liam Join Date: Aug 2013 Posts: 40 Rep Power: 12	Just one more thing, What happens if porous media is present in the model? How UDF can account for the effects of this?