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Ph.D. Thesis Defense by
Yong-Boon Kong
Advisor: Prof. J.V.R. Prasad
DEVELOPMENT OF A FINITE STATE COAXIAL ROTOR DYNAMIC INFLOW MODEL
10 a.m. Thursday, May 10th, 2018
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. High-fidelity models such as free-wake or vortex particle method may not be computationally efficient for use in real-time flight simulations. The Pitt-Peters and Peters-He inflow models are reduced order models that provide good inflow predictions and satisfies real-time computational efficiency requirements. But these inflow models are only used in single rotor configurations. For coaxial rotor configuration, most published work focus on performance related studies, which are not compatible for use in real-time simulation of rotor induced inflows.
A novel approach to formulate a coaxial rotor inflow model from first principles by superposition of upper and lower rotor pressure potentials is explored. By representing both rotors' pressure and downwash in terms of harmonic and radial expansion terms, a finite state coaxial rotor inflow model known as the Pressure Potential Superposition Inflow Model (PPSIM) is developed. Steady hover inflow predictions from PPSIM match well with results obtained from high-fidelity models like GT-Hybrid and the Viscous Vortex Particle Method (VVPM), but differences in inflow distributions are observed in steady forward flight. Differences in transient responses between PPSIM and VVPM are also observed.
In view of this, system identification techniques are used to identify corrections to PPSIM inflow equations to account for real flow effects such as wake contractions/distortions, viscous diffusion and flow swirls. Average cost functions corresponding to the original and corrected PPSIM are compared for hover and various advance ratios against VVPM inflow results. In each comparison, the corrected PPSIM has the lower average magnitude and phase cost functions; indicating that it has a better match with VVPM frequency response data. Furthermore, since corrections are applied to PPSIM inflow equation directly, its state-space structure is preserved. This means that the corrected PPSIM can also be used for eigenvalue analysis as well as control law development in coaxial rotor aero-mechanics problems.
Committee Members:
Prof. J.V.R. Prasad, Advisor, AE, Georgia Institute of Technology
Prof. Lakshmi N. Sankar, AE, Georgia Institute of Technology
Prof. Marilyn J. Smith, AE, Georgia Institute of Technology
Prof. Daniel P. Schrage, AE, Georgia Institute of Technology
Prof. David A. Peters, Washington University in St. Louis
