Modeling reversing tidal flow

[bv169]

Hello,

I am modeling a domain with reversing tidal flow. In previous models without a strong tidal influence, I used the traditional inlet/outlet options. I am now trying to determine the best way to model a reversing tidal flow during the simulation. The inlets will be forced with velocity profiles from real ocean observations. Would it be best to force all sides of the domain with the velocity profiles (therefore the inlet would act as an outlet when the flow is negative?), or to continue using a pressure outlet with backflow. If going with this option, should the backflow be setup with the velocity profile? The boundary conditions are forced every 60 seconds with new data profiles from the field experiment. Also open to other suggestions for most accurately modeling this! 

Thanks!

[Rob]

Are you looking at tide, wave or current effects? For the former the rate of change is usually fairly slow, unless you're modelling the Channel Islands? 

[bv169]

Tides and currents, turbulence in the upper ocean off the coast of Scotland. There was an oscillating/reversing semi-diurnal (twice-a-day) tide. 

[Rob]

I know - I've been diving in it! The rocks at the SW end of Lismore make for some interesting current/tide/wind interactions. 

The problem with forcing all boundaries is that doesn't allow the solver to adjust flow within the domain, but with transient you might get away with it. With VOF you can only set a boundary as wet/dry unless using the open channel conditions, but that may not match well with the defined profiles. CFD also must solve for the flow speed, so whilst a tidal effect may take hours the flow speed v cell size typically results in (very) sub 1s time step. 

What is the purpose of the model as we'd often model turbine systems with more "generic" data or for sea defence type applications might use specialist (nonAnsys) tools. 

[bv169]

Cool! Have not been myself, just get to analyze the data and model it.

For the first iteration just going to model the velocity, (no temp/density). The purpose is to expand the model we used prevously in a different location (simpler flow dynamics), to a new location and basically validate that its able to model and predict sub-mesoscale ocean processes. We also MHD runs to look at magnetics.