Transient and Quasi-steady Numerical Simulations of Tiltrotor Conversion Maneuvers

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. This is accomplished in two parts. 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. Ultimately this analysis showed that quasi-steady simulations were an efficient and accurate method for modeling transient maneuvers. Following the results from this analysis, the full XV-15 tiltrotor was studied using coupled CFD/CA quasi-steady and standalone CA transient maneuver simulations. It was found that 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 higher 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.