CFD Online Discussion Forums - Estimate residence time per region

Hi,

I'm trying to solve a problem with my current simulation but I'm stuck, so maybe someone can help me out.

As you can see in the image, I have this pipe flow with a small jet hitting the main flow (right hand side) and then an outlet (left hand side). I put some arrows to help visualize the flow direction. The simulation is 3D, so this is only a slice for visualization purposes. The five colors in the image represent different regions, so the values of the scalar field shown are just categories (i.e. region 0, region 1, region 2, etc).

What I would like is to have an estimate of the residence time within each region. I have all fields available (i.e. U, phi, cell volume and so on) but I don't know how to go about estimating it.

The option of computing a residence time distribution (doing something like this: https://www.cfd.at/sites/default/fil...ExampleTen.pdf) by running a frozen flow simulation is not an option because I have this "region" scalar field on a regular and downsampled VTK file, so I do not have access to a mesh from which to run an OpenFOAM case from.

I have tried using phi (i.e. the flow rate, $\phi_i$ ), which is originally a surface field, to compute a phi volume vector field (using this utility https://openfoamwiki.net/index.php/C...rpolate-fields). Then I estimate the residence time for each cell ( $\tau_{i}$ ) as:

$\tau_i = \frac{vol_i}{ \lVert \phi_i \rVert}$

where

represents the volume of the

-th cell and $\lVert \phi_i \rVert$ is the magnitude of the flow rate vector of the

-th cell.

Then the total residence time for the region will be just the sum of the residence times of each cell in that region. However, the result was not a reasonable value.

Any ideas as to what I can do to estimate the residence time in each region?

Thanks in advance!