A novel approach for flutter prediction of pitch-plunge airfoils using an efficient one-shot method

In this work, the one-shot method previously developed for the solution of limit cycle oscillation problems is extended to predict flutter boundaries of aeroelastic systems. In essence, the one-shot method determines the aeroelastic response of wings and airfoils in a tightly-coupled fashion where both aerodynamic and structural dynamic problems are solved simultaneously using harmonic balance. This approach is superior to the frequency-based techniques previously reported in the literature such that it eliminates the need to sweep over a range of frequencies to determine flutter conditions. For each Mach number of interest, the values of flutter frequency and flutter velocity are determined as part of a single aeroelastic run. A method for identifying appropriate initial conditions is also presented. It is shown that the flutter onset point for given flow conditions can be accurately identified by prescribing a very small pitch amplitude treating flutter prediction as a response problem instead of the classical stability problem. Using this technique, three two-degree-of-freedom aeroelastic models, including a flat plate, the NACA 64A010 airfoil and the supercritical NLR 7301 airfoil, are studied under different flow conditions ranging from low-speed, inviscid flow to transonic, viscous, turbulent flow. The results are verified against reference results from the literature. In addition, two other established flutter methods are implemented in this work for verification purposes, and the efficiency and robustness of the one-shot method are investigated.