The Research Of Time-domain For Flutter Modal Analysis And Flutter Boundary Prediction Under Turbulence Excitation

Elastic deformation of an aircraft occurs under the effect of aerodynamic force, because of the aircraft structure's not being absolute rigid. Therefore, it's inevitable to take the aeroelastic problems into consideration during aircraft design. Aircraft flutter is often a catastrophic phenomenon, and thus, prediction of its onset is essential. Safety against flutter in full flight envelope for a newly developed aircraft must finally be guaranteed, by carrying out a series of flutter calculations and flight testing.The prediction of the flutter boundary is playing an important role in aircraft design. With the increase of flight speed, flutter is becoming more of a problem as its characteristics go more and more complicated, especially in supersonic flight. As to the flutter calculations and flight testing mentioned before, the principal purpose of them is to predict the flutter onset speed namely flutter boundary, precisely.The main research content of the flutter-boundary prediction, based on time domain signal analysis, is how to extrapolate from the known data points to the flutter boundary founded on the flutter stability criterion. And the criterion is established by the flutter modal parameters gained from the evaluation of the responses that measured in the process of wind-tunnel and flight tests.As for the wind-tunnel tests, it remains a challenge in active excitation control due to a great many restrictions. Hence, the random air turbulence is employed to excite the experimental model to produce the response used in the flutter-boundary prediction. This paper studies some methods of modal parameter identification in the time domain, and develops a set of method to predict the flutter boundary under the effect of turbulence. The main steps are as follows. First, we separate some order of the flutter modal; and then, free-decaying responses of the system will be extracted. Next, calculation of the modal parameters is required to establish the flutter stability criterion. Eventually, a curve fit about variation of the criterion with dynamic pressure or velocity will be plotted to extrapolate to the flutter boundary.Meanwhile, this paper performs error analysis on the flutter stability criterion, and conclusions are drown by comparison. Method adopted in the paper will be verified by numerical simulation and wind-tunnel test later in the paper, to prove its effectiveness and application in engineering. The researches and conclusions of this paper will have some guidance for engineering application.