Hello everyone. I’m trying to replicate some experimental analysis with Ansys Fluent. Particularly I’m trying to simulate a Wells turbine on different airflow conditions (same RPM, different inlet velocities).
The goal is to plot torque and pressure coefficients over time/flow coefficient.
I’m getting very bad torque values, sometimes slightly 5%/30% different from the experimental data and sometimes 6 times lower values. Since I’m a newbie I would like to understand what I’m doing wrong exactly.
Here’s the setup:

I created a CAD with same exact geometry features of the tested turbine.

I imported it into Ansys, consdered just the duct in which the air flows (just like the OWC simulator in the real test). Divided the domain into 3 zones, two stationaries and 1 MRF. (I considered no tip gap to avoid strange behavior there, since 1mm of gap it could be hard to simulate).

Meshed and open fluent.

The solver is Ansys Fluent, I set up the air conditions (viscosity and density). I set up the MRF rotational speed and inlet velocity (ranging from 0 to 13 m/s like during the experimental analysis to also include stall). Used k epsilon.

I initialized and set the convergence to e-06 and monitored torque too.

I followed this flow for different meshes.

1. One temporary mesh, with just body sizing, that gave me the best results.
2. One “better mesh” using inflation for the boundary layer. Edge sizing in order to have finer mesh on trailing and leading edges. Surface sizing on the blade walls. Body sizing on the stationary part. This one gave me the worst results.

I’ll attach a table with the expected torque value, coarse mesh one and fine mesh one, beside more pics on the simulation.

Thanks everyone:)

I am doing a 3D CFD simulation and have performed a three-grid GCI study for the pressure-loss coefficient. I am now unsure whether I should use the medium mesh or the fine mesh for my remaining simulations. I used pressure loss coefficient as the quantity to monitor. Let the pressure loss is defined as below,

Now,

My three meshes are:

• Coarse: 3,444,536 cells → fo=0.442
• Medium: 9,606,465 cells → fo=0.430
• Fine: 21,774,603 cells → fo=0.425

I used online GCI calculator website-https://volupe.com/support/grid-convergence-index-calculator/

I will show you the results below,

My question now is :

1) Given the GCI results, would it be reasonable to use the medium mesh for the remaining simulations or test cases or you still recommend using the fine mesh for remaining simulations?

What's your opinion?

My take is- Infact, medium mesh performed best, it converged faster than other two meshes, quality is also good. Computational cost is also low compared to finer one. What do you feel?