An analytical study of unsteady rotor/fuselage interaction in hover and forward flight

An analytical study of the coupled rotor/fuselage aerodynamic environment is presented. Results from the analysis are used to help understand the nature of interactional phenomena on helicopters. Two analytical methods have been developed, and results from these models are compared with experimental measurements on a representative rotor/body model. The first method is a simplified analysis that treats the fuselage as an planar surface. This model is very computationally efficient, and is particularly useful for studying the pressure on the upper surface of the fuselage induced by the rotor and its wake. The second, and more comprehensive, model is the MURFI (Maryland Unsteady Rotor/Fuselage Interaction) model and consists of an unsteady source panel representation of the fuselage coupled with a lifting line rotor model and several different wake models. This analysis is more computationally expensive than the simplified model, but is capable of studying the entire coupled rotor/fuselage flowfield. In addition, the latter model is also used for the prediction of the effects of the fuselage on the rotor flowfield.;A new helicopter free-wake methodology is also presented. The new model overcomes the well known instability of traditional free-wake methods in hover and in low-speed flight. In addition, the new method achieves this capability without an appreciable increase in computational effort. This model is particularly useful for interactional aerodynamics since the most severe wake/fuselage interactions occur in the hover and low-speed flight regime.;Using these analytical models, results are shown that clearly demonstrate the capability of potential flow analyses to predict interactional effects, provided that all of the pertinent unsteady terms are included in the analysis. In particular, it is shown that the unsteady terms due to the time-rate-of-change of the surface source elements are very important to prediction of the surface pressure response. The analysis has also provided an improved understanding of the effects of the fuselage on the rotor loads and performance.