FIRST-PRINCIPLES FREE-VORTEX WAKE ANALYSIS FOR HELICOPTERS AND TILTROTORS

The development of high-fidelity models of the rotor wake is an issue of continuing, critical importance in the design of new helicopters and tiltrotors, as well as in the understanding of a wide range of problems in rotor aerodynamics, dynamics, and acoustics. This paper outlines a set of interrelated modeling methods developed over the last two decades that have yielded a unified free wake model suitable for the full range of current helicopter and tiltrotor designs. These methods, now embedded in the CHARM comprehensive analysis of rotorcraft aeromechanics, can produce high fidelity predictions of rotor performance, unsteady airloads, and noise as well as accurate predictions of rotor-induced flow fields and airframe loads over a wide range of aircraft configurations. An important feature of the wake modeling described here is that it is a first-principles analysis completely free of user-selected empirical parameters. This allows the model to be used as a design tool for analyzing future rotorcraft concepts as well as in flight simulations where wake characteristics vary with the flight condition. This paper describes the key technical elements of this model and provides numerous examples of its validation against challenging data sets for a wide range of rotorcraft applications. Results include new correlations with Tilt Rotor Aeroacoustics Model (TRAM) airloads measurements establishing that both helicopter and tiltrotor aeromechanics phenomena can be predicted accurately without adjusting the wake model.