Aeroelastic Responses of Spring-suspended Airfoil Systems in Transonic Buffeting Flows

Abstract

Computer simulations are performed to determine the responses of a single DOF pitch airfoil system, as well as those of a two DOF pitch-and-heave system, in bueting ows. The bueting ow exhibits shock-wave oscillations of a unique frequency that occurs for some combinations of mean ow angle of attack and transonic Mach numbers. It was found that frequency lock-in may occur, depending on the relationship between the buet and structural frequencies. Following frequency lock-in the system response rapidly increases until reaching limit-cycle oscillations. Synchronization of the transonic aerodynamic buet phenomenon and the structural elastic modes provides a physical mechanism that may be responsible for some aircraft transonic LCO occurrences. It is distinctly dierent from a utter mechanism, leading to LCO, as discussed in the manuscript. Nomenclature a ∞ = speed of sound, m/s C L = airfoil lift coecient b = half chord length, m c = chord length, m f = frequency, Hz f = 2πf c/U ∞ = reduced frequencȳ f sb = 2πf c/U ∞ = shock-buet reduced frequency M ∞ = free-stream Mach number R ∞ = free-stream Reynolds number, based on chord t = physical time, s t = nondimensional time U ∞ = far-eld velocity, m/s Y + = dimensionless wall distance α ∞ = free-stream angle of attack, deg ∆C L = lift coecient peak-to-peak amplitude ∆t = nondimensional computational time step