Helicopter Rotor Unsteady Aerodynamics

Unsteady helicopter rotor aerodynamics are complicated. This paper reviews some of the fundamentals and newer developments of unsteady helicopter aerodynamics. Rotor flow is beautiful and complex. Visualizing rotor flow allows for an appreciation of the following theories and solution attempts as well as nature’s complexities. The flow through a helicopter rotor with forward motion is shown in Figure 1. The rotor is rotating horizontally along the right hand side. Notice the regular rake inlet and the regular rotational outlet! The next photo, Figure 2, shows a full size helicopter flying through five smoke streams. Once again, the regular inlet is transformed to a rotating flow field. This paper will discuss four areas of unsteady helicopter rotor aerodynamics. First, this paper discusses the classical harmonic solutions to rotational aerodynamics and their relationship to the fundamental Theodorsen solution. Second, modern solution techniques are discussed. Finally, the paper describes wake interactions and their noise production implications.