THEORETICAL FLAP-LAG DAMPING WITH VARIOUS DYNAMIC INFLOW MODELS

The effects of dynamic inflow perturbations are incorporated into a flap-lag stability analysis of a rigid blade. The concept of equivalent Lock number, previously used to model the effect of quasi-steady inflow for flapping only, is extended to the case of coupled flap-lag motions by the addition of an equivalent profile drag coefficient. Plots of flap and lead-lag damping are presented for various inflow assumptions including: no dynamic inflow, quasi-steady momentum theory, unsteady momentum theory, empirical inflow, and equivalent Lock number and drag coefficient. The results show that dynamic inflow has a large effect on blade damping for the regressing mode. In some instances, this effect can be modeled by the equivalent Lock number and drag coefficient.