Theoretical and experimental study of unsteady rotor/body aerodynamic interactions

A systematic study is made of the unsteady interactions between a rotor and a body in order to assess the degree of sophistication necessary to accurately predict the unsteady pressure signatures on a helicopter fuselage due to the rotor and its wake. Experimental measurements and theoretical calculations were both made in order to clarify the nature of the unsteady interactions and to define the limitations of potential flow theory in modeling the various phenomena. An attempt is made to accurately model the geometry of vortex/surface interactions as well as to include the appropriate unsteady terms in the analysis. Unsteady pressure measurements from a series of wind tunnel experiments are also provided. Such data has allowed new conlusions on the nature of body pressure signatures which are due to blade passage effects, close wake interactions, and wake inmpingement on the fuselage. It is also concluded that the flowfield about the body is highly unsteady and cannot be modeled without the inclusion of the unsteady terms in the calculation of the local surface pressures and that theoretical modeling is still possible over most of the flow field using an unsteady inviscid analysis.