Synchronization of pitch and plunge motions during intermittency route to aeroelastic flutter

Abstract

Interaction of fluid forces with flexible structures is often prone to dynamical instabilities, such as aeroelastic flutter. The onset of this instability is marked by sustained large amplitude oscillations and is detrimental to the structure’s integrity. Therefore, investigating the possible physical mechanisms behind the onset of flutter instability has attracted considerable attention within the aeroelastic community. Recent studies have shown that in the presence of oncoming fluctuating flows, the onset of flutter instability is presaged by an intermediate regime of oscillations called intermittency. Further, based on the intensity of flow fluctuations and the relative time scales present in the flow, qualitatively different types of intermittency at different flow regimes have been reported hitherto. However, the coupled interaction between the pitch (torsion) and plunge (bending) modes during the transition to aeroelastic flutter has not been explored. With this, we demonstrate with a mathematical model that the onset of flutter instability under randomly fluctuating flows occurs via a mutual phase synchronization between the pitch and the plunge modes. We show that at very low values of mean flow speeds, the response is by and large noisy and, consequently, a phase asynchrony between the modes is present. Interestingly, during the regime of intermittency, we observe the coexistence of patches of synchronized periodic bursts interspersed amidst a state of desynchrony between the pitch and the plunge modes. On the other hand, at the onset of flutter, we observe a complete phase synchronization between the pitch and plunge modes. This study concludes by utilizing phase locking value as a quantitative measure to demarcate different states of synchronization in the aeroelastic response.

Experimental investigation on the synchronization characteristics of a pitch-plunge aeroelastic system exhibiting stall flutter

“…In field conditions, flow-field possesses random fluctuations, which give rise to 'noise-induced' instabilities 9 . These noise-induced instabilities can significantly alter the bifurcation route and the aeroelastic response dynamics [10][11][12][13] . It is thus very important to investigate the role of noise on the mode-coupling of aeroelastic systems and to understand the underlying mechanism through which the response dynamics is altered in the presence of the noise.…”

“…Addressing this end of the hitherto gap is the prime focus of this paper. Dynamic transitions in nonlinear systems (be it deterministic or stochastic) can be directly correlated with the transitions in relative phases and frequencies between the oscillators and their mutual synchronization [13][14][15][16] . Deriving impetus from the same, the present study focuses on experimental investigations on the nonlinear dynamics of stall flutter with and without the input noise, from the viewpoint of synchronization framework.…”

“…Synchronization is a well-known nonlinear phenomenon and has been widely reported in different nonlinear dynamical systems, such as cardiorespiratory systems 17 , electrochemical oscillators 18,19 , electronic circuits 20 , thermoacoustics 15,[21][22][23][24] , vortex-induced vibration systems 16,25 , and aeroelastic systems 13,26,27 . Synchronization phenomenon can be classified in a variety of forms, such as complete synchronization, lag synchronization, intermittent phase synchronization, imperfect phase synchronization, among others 13,14,[28][29][30] .…”

“…The response dynamics of such nonlinear dynamical systems show rich bifurcation behaviour with different phase relationships such as phase locking, phase drifting, phase slips 13,14,16,18,27,31 and a switch between in-phase to anti-phase synchronization, known as phase-flip bifurcation 19,20,32 ; see Section II for further details.…”

Synchronization framework for modeling transition to thermoacoustic instability in laminar combustors

“…They found different synchronization states including phase locking, intermittent phase locking, and phase drifting, corresponding to different dynamical states [28]. Recently, synchronization framework was introduced to model the transitions in aeroelastic system by Raaj et al [29].…”