tracer recovery

Hi,

(I'm new to Feflow...)
for a simple model set up...
    --> 1 layer (confined)
    --> 2 wells: 1 injection, 1 extraction (set as well bc)
    --> tracer impuls at injection well (set as well bc, with time function)

I need to compute the tracer recovery in the extraction well. What would be the method of choise in Feflow?

[u]Additional question:[/u]
To assign the well bc's for the current model I assigned 50% of the fluxes to both, the nodes of the top and bottom slice (summing up to 100%). This is probably not the usual way...?

If I want to assign well bc's to a multi-layer model. To which nodes of the individual layers I specify the individual conditions? Or would be defining source/sink in material properties more appropriate?

Thank you, Torsten

You should run tests to figure out the best method for solving the transport equation however shock-front capturing may work well.

If you run as a 2d model with 2 slices and one layer, you will get concentration at the top and bottom of the layer, not in the middle.  You can average the top and bottom but it would be better to simulate the system with at least three slices (two layers) with one slice in the middle.  You will get results on the middle slice directly, and the model may behave more realistically. 

Specifying 50% from top and 50% from the bottom is sensible for the system you describe.  More from one elevation implies 3d flow which implies you need more layers to simulate vertical flow more realistically.

Wells in multilayer models can be handled in two ways.  FEFLOW allows automatic set up of a 1d vertical pipe element with large K that spans all the nodes the well is open to.  In this way, more water enters the pipe element where the K is larger.  You specify the pumping node at the bottom of the 1d pipe (or at the elevation of the pump).  You can also set up individual pumping nodes with rates specified according to the layers that each pumping node touches.  You might want to constrain the pumping node(s) so that they either stop pumping or switch to a 1st-kind bc if the saturation at the node falls below 1.

Source/sink BC is difficult to use but would work as long as the element its specified is saturated.  Not recommended for the problem you describe.

Pete

Thank you, Pete,

I didn't followed my thread after a longer while anymore until last week. Yes, it was a simple "2.5D"-case :) just to learn a bit about the switches in Feflow (not even thought as 3D).

Thanks for your suggestions - now I understood (????) the multilayer well BC thing. It seems to work well as a flow BC, but also seems to have problems to distribute the solute fast enough along the vertical well (in my case ~16 m). According to the manual 3 m^2 is the cross sectional area and 2e-6 m/s is the internal hydraulic conductivity in the well. Is that sufficient to describe a high conductive well tube or wouldn't be defining a high conductive 1D discrete element and tuning conductivity bit more well-alike?

Thx, Torsten

I am not sure I understand your question.  In reality, the inside of a well does not have a permeability.  What you are modeling is the combination of the well bore and its surroundings, so you are modeling that combination with a bulk conductivity.  The value you use depends on many things (mesh spacing, gradients, flow rates, model objectives, etc) and is often derived by calibration of the model.

Pete