Study On Characteristics Of Nonlinear Flutter And Buffet Of Wings Of Aircraft

In this paper, the characteristics of nonlinear flutter and buffet of the airfoil with control surfaces and the wing of aircraft are systematically and thoroughly studied. The main contents are included as follows:(1) The phenomena of the nonlinear flutter of the airfoi 1 with control surfaces which stiffness is the hard spring and freeplay nonlinear are researched by way of the theory of the qusi-steady aerodynamics and the Hopf bifurcation. The aerodynamic derivatives of the 3-freedom-degree airfoil are derivated by way of the theory of the qusi-steady aerodynamics. The flluter boundary is determined by the theory of Hopf bifurcation.(2) Issues of the nonlinear flutter of the 3-D wing which stiffness is the hard spring and freeplay nonlinear are studied by using the mothod of finite element and the theories of the qusi-steady aerodynamics and the Hopf bifurcation. It is concluded that the characteristics of the nonlinear flutter of the 3-D wing is conformed to that of the airfoil by way of numerical simulation.(3) The solution of the unsteady compressible 3-D Navier-Stokes equations is studied by using implicit schemes and LU decompositions. The C (airfoil) and OH (wing) type grids are built with algebra method. The grids are fixed to airfoil or wing and are created only once in a computation, thus the computation efficiency is very high.(4) The 2-D compressible Navier-Stokes equations are adopted as the governing equations. The unsteady lift coefficients of airfoil are calculated by Navier-Stokes equations with the implicit LU-NND algorithm, Baldwin-Lomax turbulent model and C-type grids. The fluctuating values of lift coefficient are increased with the enlargement of incidence and Mach number. The buffet onset boundary is defined as the the beginning point where the fluctuating values of aerodynamic coefficients are increased suddenly. The buffet characteristics of supercritical airfoil DFVLR-R2 and conventional airfoil NACA 0012 are investigated. Theresults show that in the design Mach number range of supercritical airfoil, there are the larger buffet onset incidence and less buffet loads. When Mach number is larger than the design Mach number, the buffet onset incidence of supercritical airfoil decreases quickly and there are rather large buffet loads. In the NACA 0012 airfoil, there are much less buffet onset incidence, larger buffet loads and separated range.(5) The characateristics of nonlinear flutter of the transonic airfoil with the nonlinear stiffness is studied by using the 2-D compressible Navier-Stokes equations as the governing equations. Coupling the Navier-Stokes equations with the flutter equations with nonlinear structural stiffness functions solves the time histories of dynamic responses of airfoil. The calculated results shows that the influnces on flutter speed are much larger and limit cycle oscillations are very complicated because of both structural and aerodynamic nonlinear in the flutter system.(6) The characateristics of nonlinear flutter of the 3-D wing with one rotating axle of which rotating stiffness is the hard spring and freeplay nonlinear is studied by using the 3-D compressible Navier-Stokes equations as the governing equations. Coupling the Navier-Stokes equations with the flutter equations with nonlinear structural stiffness functions solves the time histories of dynamic responses of airfoil. The calculated results shows that the influences on flutter speed are much larger and limit cycle oscillations are very complicated because of both structural and aerodynamic nonlinear in the flutter system.