Unsteady aerodynamics of helicopter rotor hovering in dynamic ground effect

When a helicopter is hovering above a heaving, rolling and pitching ship deck, the lifting rotor is subjected to a dynamic ground effect. Existing models for helicopter rotor in ground effect use image rotor method based on vortex wake theory, which can not capture the unsteady aerodynamics due to such dynamic ground effect. In this paper, a finite state inflow model for hovering in ground effect is developed by treating both the rotor and the ground surface as pressure perturbations in the flow field. The ground perturbation potential coefficients are determined by imposing the non-penetration boundary condition at the ground surface. Analytical expressions for the [Af] and [L] matrices as well as mass flow parameter are modified to be functions of rotor height above the ground. It is seen that the effect of ground velocity and acceleration can be represented as additional forcing terms in the model. Numerical results are presented to illustrate dynamic ground effect.