A study of helicopter aerodynamics in ground effect

The flow around a helicopter is very complex; it becomes much more complex when it comes close to the ground. The presence of the ground changes the aerodynamic characteristics of the rotor and the flow environment becomes much more complex compared with that of flight out-of-ground effect (OGE) and hence the behavior of the rotor wake in the vicinity of the ground is challenging to predict. Under in-ground-effect(IGE) conditions, the wake collides with the ground and causes a significant perturbation to the flow near the blade. Significant interactions between the main rotor wake and the ground have been associated with the formation and passage of the ground vortex in forward flight. The presence of a ground vortex affects the handling qualities of the helicopter. The aim of this research is to capture the physics of the flow features and dynamics of ground effect flows around a rotorcraft, provide an understanding of the rotor wake/vortices near the ground, and generate rigorous models to accurately predict handling qualities, loads and moments acting on the rotor and the power requirements.; A free vortex method is used to model the flowfield. The presence of the ground is modeled using the method of images and the lifting-surface theory is used to model each rotor blade. An initial wake geometry is assumed which is allowed to develop in time until the flowfield becomes periodic. The rotor wake is assumed to consist of only the tip vortices and the inboard sheet and the root vortex are neglected. The solution is stepped in time using an Adams-Moulton scheme with a Runge-Kutta starting formula.; The wake structure after periodicity is reached is obtained for hover and different forward flight speeds. Also, the nature of the flowfield, as well as the formation of the ground vortex, is understood by obtaining the velocity contours on a longitudinal plane containing the rotor blade after periodicity is obtained. The unsteadiness in the velocities is quantified by obtaining the RMS deviation in velocities on different planes containing the tail rotor around the rotor disk simulating the various kinds of flight. Thrust and power requirements on the rotor disk have been predicted and have been successfully validated by comparison with experimental results obtained from Georgia Institute of Technology. A tail rotor has also been included in the current model to understand its implications on the wake structure and loads. The computational results have been validated against experimental results obtained at Georgia Institute of Technology and Empey and Ormiston.