Discharge Output Options - Flux Calculations

[Chris.Huxley 1]

Question:

I need your help regarding TuflowFV output. I need to calculate flux (concentration/discharge) leaving estuary. So I need to know water velocity. I see there are Vx and Vy components. Are they for water or just above surface water?

 

 

Answer:

There are two elements to this question:

    1) What do the Vx and Vy components represent? For a 2D simulation, the Vx and Vy results define the depth averaged flow velocity x,y contributions. 

    2) How to calculate flux?  Modellers need not calculate these results from velocity and depth output. TUFLOW FV will automatically calculate and output flux results if the command "output == flux" is specified:

 

 

     output == flux                                       
            output interval == 900.                                        
     end output

 

 

 

Flux for all model parameters (e.g. flow, salinity) across all nodestrings within the model will be output to a csv file (simulation name_FLUX.csv).

Tutorial Module 3 (documented on the TUFLOW FV Wiki) includes a worked example of this output option (http://fvwiki.tuflow.com/index.php?title=Tutorial_Module03)

 

 

 

 

 

 

[adiyanti 0]

Thanks Chris,

I have more questions here.

1. I see both  _FLUX and _MASS outputs have the same unit: [conc].m³/s, the differences: the _FLUX is for each NS specified in 2dm file, _MASS is the whole domain. Is this correct?

2. My sim tstep is 1 min, are those discharge already converted to m³/s, or should it be read as unit in m³/minute ?. 

3. I need to calculate in and out fluxes which mass/cross-section area /unit time.  Is cross-section of each NS stored somewhere in the TFV output files? I understand the area of the whole domain is stored in .nc file, but not sure with cross-section area.

Thanks,

Yanti 

 

[Chris.Huxley 1]

Hi Yanti,

1. You're correct, _FLUX is for flow rate crossing each NS (eg. m³/s) and _MASS is the volume within the whole domain (eg. m³).

2. The  discharges are already converted to m³/s.

3. The Flux output should be the output you are after. If not, you can calculate your nodestring cross-section characteristics from the _spatial_nodestring.csv log file. The file summarises the cell x,y coordinate, elevation and face length for each nodestring in the model.   

 

 

You will need to switch on "Echo spatial" in the simulation control file for this log file to be written. The file will be written to the log folder (i.e. not the output folder)

 

Syntax Required:

     Echo spatial == 1

 

Module 3 of the TUFLOW FV tutorial models includes an example with this feature enabled: http://fvwiki.tuflow.com/index.php?title=Tutorial_Module03

Complete model files for this tutorial model can be downloaded from the TUFLOW website: http://www.tuflow.com/FV%20TutorialModel.aspx

 

Hope this helps,

Chris