Transient and Quasi-steady Numerical Simulations of Tiltrotor Conversion Maneuvers

Abstract

The goal of this work is to characterize the ability of current numerical tools such as Comprehensive Analysis (CA) and computational fluid dynamics (CFD) to model the aeromechanics of a tiltrotor undergoing a transient conversion maneuver. First, a simplified model is used to quantify the differences in predicted loads between a simulation of a transient maneuver and those of several quasi-steady simulations. This analysis showed that quasi-steady simulations were an efficient and accurate method for modeling transient maneuvers. Next, the full XV-15 tiltrotor was studied using coupled CFD/CA quasi-steady and standalone CA transient maneuver simulations. Analysis and comparisons are made in terms of the rotor performance, trim, aerodynamic loads and interference, as well as the structural and vibrational loads. Nonlinear effects such as blade-wake interactions and aerodynamic interferences between the rotor and the wings were significant at the beginning and end of the conversion maneuver, respectively. As such, CA showed good agreement with CFD/CA at moderate airspeeds during conversion but struggled at low speeds and during cruise. Overall this work highlights the need for coupled CFD/CA analysis for capturing the complexities of tiltrotor conversion maneuvers. Coupled together, the simulations leverage the strengths offered by each tool and have the capability to accurately model the aerodynamic and structural dynamics of proprotors and tiltrotors at relevant operating conditions.