Ph.D. Thesis Proposal by

Advisor: Prof. J.V.R. Prasad

DEVELOPMENT OF A FINITE STATE COAXIAL ROTOR DYNAMIC INFLOW MODEL

9 a.m. Monday, December 5

Montgomery-Knight Building Room 317

ABSTRACT

Accurate modeling of rotor inflow dynamics in flight simulations is crucial for rotorcraft performance and handling qualities evaluations. While inflow predictions based on momentum theory give good results in hover, they do not produce the accuracy needed in forward flight. On the other hand, high-fidelity Computational Fluid Dynamics (CFD) models take up a significant amount of computational time to be feasible for use in real-time simulators. The finite state Peters-He inflow model satisfies both accurate inflow prediction and computational efficiency requirements. However, the inflow model is only applicable for single rotor configurations.

Recent published work on coaxial rotor configurations focus on performance related studies, which are not compatible for use in real-time rotor inflow simulations. The main challenge in coaxial rotor inflow modeling is to account for mutual aerodynamic interference effects between upper and lower rotors. While system identification approach can be used to obtain dynamic models associated with rotor inflows, this method is only feasible for small scale coaxial rotor Unmanned Aerial Vehicles (UAVs). For full scale vehicles such as the Sikorsky S-97 Raider, mathematical models to predict rotor inflows are still the desirable option.

In this work, a novel approach to formulate a coaxial rotor inflow model from first principles by superposition of upper and lower rotor pressure loadings is explored. By representing both rotors’ pressure and downwash with harmonic and radial expansion terms, a finite state coaxial rotor inflow model known as the Pressure Potential Superposition Inflow Model (PPSIM) is developed. Effects of both rotors mutual aerodynamic interferences are taken into account in PPSIM inflow equation. Steady hover inflow predictions from PPSIM match well with CFD results. In forward flight, corrections to PPSIM inflow equation to account for wake distortion effects are identified using GT-Hybrid (free-wake model) solutions. An analytical method is used to identify time delays associated with propagation of upper rotor inflow perturbations onto lower rotor. Time delay terms are incorporated into PPSIM and evaluation of its dynamic responses is performed.

Committee Members:

• Professor J.V.R. Prasad AE, Georgia Tech
• Professor Lakshmi N. Sankar AE, Georgia Tech
• Professor Marilyn J. Smith AE, Georgia Tech
• Professor Daniel P. Schrage AE, Georgia Tech
• Professor David A. Peters, Washington University in St. Louis