ИСТИНА

In this paper we numerically analyse nonlinear flutter oscillations of elastic plate in a gas flow. In contrast to many other papers, we use direct Navier-Stokes equations for unsteady pressure calculations, instead of piston theory or other simplified aerodynamic theories. The primary interest lies in investigation of the region of low supersonic Mach numbers, 1<M<2, where several plate eigenmodes can be simultaneously unstable, and resulting oscillations are governed by nonlinear interaction of unstable modes. Two types of unstable plate behaviour have been obtained. First, at 0.7<M<1 the plate diverges. Second, at 1<M<1.67 single mode flutter occurs in three distinct forms: limit cycle in the first mode (1<M<1.33 and 1.5<M<1.67) or higher modes; limit cycle in the first and second modes being in internal 1:2 resonance (1.15<M<1.33 and 1.42<M<1.5), and non-periodic oscillations with several frequencies being in more complex ratio and a certain quasi-chaotic component (1.33<M<1.42). Amplitudes and spectra of each limit cycle type are analysed.