When selecting dynamic stall model, there are some attached flow constants [A1, A2, b1, b2]. Where do they come from?
(1) For all dynamic stall models except IAG model(available since Bladed 4.14), the same defaut attached flow constants are adopted.
The attached flow constants [A1, A2, b1, b2] are adopted from the following work based on the flat plate.
Jones, R, The unsteady lift of a wing of finite aspect ratio, NACA Report NACA-TN-682, 1940.
The pressure lag time constant Tp, the separation time constant Tf, the vortex lift time constant Tv and the vortex travel time constant Tvl are from the following paper (see below table).
Leishman J. State-space model for unsteady airfoil behavior and dynamic stall. In30th Structures, structural dynamics and materials conference 1989 Apr 3 (p. 1319).
(2) For the attached flow constants in the IAG model, they are obtained from the default values adopted in the first generation IAG model.
Bangga, G., Lutz, T. and Arnold, M., 2020. An improved second-order dynamic stall model for wind turbine airfoils. Wind Energy Science, 5(3), pp.1037-1058.
The original source of the IAG constants list is as following:
The attached flow constants [A1, A2, b2] except for b1 are obtained from the Leishman paper, the same as above.
The pressure lag time constant Tp, the separation time constant Tf, the vortex lift time constant Tv are from the Leishman paper.
The attached flow constant b1 is tuned based on OSU experimental data for airfoil in the attached flow regime.
The vortex travel time constant Tvl is tuned based on OSU experimental data for airfoil in the separated flow regime post-stall.
Users are allowed to change these constants if they have reference data to tune them.