Potential issue with unsteady force contribution in mod_liftlin.f90
I am referring to the following lines that appear in multiple places in the code (mod_liftlin.f90)
el%dforce = el%dforce &
- sim_param%rho_inf * el%area * ( &
el%Gamma_dt * el_nor + el%mag * el%dn_dt)
I am running a hover case and have tried with 15” and 30” rotors with experimental data. The thrust is very close to experiment, however the torque in my simulations is high, resulting in low FM relative to experiment. I discovered that if I remove the dn/dt term in the above equation, the torque reduces and the FM is much closer to the experimental values. In my correspondence with Alessandro, he pointed out that in a steady hover case, the dn/dt term is not supposed to contribute at all. I suggest that if the incorrect frame of reference is taken, the normal vectors are continuously changing as the rotor blades rotate, leading to a non-zero contribution of this dn/dt term. Could this be the case? For the purpose of replicating the issue, I am running the uncoupled version of DUST.