Torque coeff. value too low
 

I am doing the performance study of the Wells turbine through computation and experiment using Fluent. But in all of my calculations, the torque coefficient values are too low, when compared to the experimental ones, although the drag coefficients values agree both experimentally and numerically. Also in computation, it seems to be stalled too early at the rotational speeds/flow coefficients which result high torque coefficients in experiment. My residuals also do not go below 1e-2 after 10000 iterations or so. I am doing 3D computation with structured mesh and taking the drag coeff. as (0, 0, 1) and torque coeff. as (-1, 0, 0). Any help will be highly appreciated.