Verification & Validation

Check mass flow

It's always good to check the mass flow rate after CFD simulation. The solver tries to keep it satisfied, but sometimes a representative imbalance is obtain, showing that something has to be done in order to get more accurate results.

To do this, we will use FLUENT.

Highlight "Reports" in the left box. Then select "Fluxes" and click "Set Up...".

Note that "Mass flow rate" is already selected.

Here you can play around to see the mass balance through each boundaries. Since most of our boundaries are single circular element, it is expected that the imbalance at each boundary alone be zero. We will check the mass flow rate though two boundaries.

First, the external boundaries. In the "Flux Reports" window, locate and highlight "farfield1" and "farfield2" and hit "Compute". The mass flow rate though that boundary is now printed in the command window.

Note that 73.5kg/s get into out domain and virtually everything leaves. The imbalance is 7.4e-9kg/s which is negligible considering the total amount of flux in the system. Nice!

Now, let's check the imbalance inside the hub. For that we only have one boundary completely circling the zone, hub_inner (note that hub_outer is essentially the same boundary).

Proceed similarly as before and check the mass flow through the hub_inner boundary. You could also select hub_outer and the result would be almost identical.

Remember to deselect farfield1 and farfield2 before hitting compute!

You should get an imbalance of 3.42e-10kg/s which is essentially zero. Cool!

compare blade velocity (TSR?)  This is a BC, so it will essentially just check whether we had inputted the correct mathematical model into the tool.

Verification

Compare Cp with the expected

mesh refinements (different mesh. Summarize, don't need to show steps) Cp might be bad, refine the mesh and check.

Validation

check against FDRL data? Might have to re-scale, as it is a little larger, flow max at 7m/s and much greater rpm.... If you scale it up to xxx this is the results you'd get. Compare Cp, try using the actual wind speed and angular velocity.

Actually the angular velocity is coupled with the incoming velocity. To capture that with fluent, we would have to use 6DOF which is too complex. So a trick would be..... see jeremy email.

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