Wing flutter computations using an aerodynamic model based on the Navier-Stokes equations

The flutter characteristics of the first AGARD standard aeroelastic configuration for dynamic response, Wing 445.6, are studied using an unsteady Navier-Stokes algorithm to investigate a previously noted discrepancy between Euler flutter characteristics and experimental data. The algorithm, which is a three-dimensional, implicit, upwind Euler/Navier-Stokes code (CFL3D Version 2.1), was previously modified for the time-marching, aeroelastic analysis of wings using the unsteady Euler equations, These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time integration with the governing flow equations. The aeroelastic method is extended and evaluated for applications that use aerodynamics based on the Navier-Stokes equations, A bl ief description of the aeroelastic method and time-marching calculations are presented that verify this method for Navier-Stokes calculations. A linear stability analysis and a time-marching aeroelastic analysis are used to determine the flutter characteristics of the isolated 45-deg swept-back wing, Effects of fluid viscosity, structural damping, and number of modes in the structural model are investigated, For the linear stability analysis, the unsteady generalized aerodynamic forces of the wing are computed for a range of reduced frequencies using the pulse transfer-function approach, The flutter characteristics of the wing are determined using these unsteady generalized aerodynamic forces in a traditional velocity-incremental damping (V-g) analysis, This stability analysis is used to determine the flutter characteristics of the wing at freestream Mach numbers of 0.96 and 1.141, using the generalized aerodynamic forces generated by solving the Euler equations and the Navier-Stokes equations. Time-marching aeroelastic calculations are performed at a freestream Mach number of 1.141 using the Euler and Navier-Stokes equations to compare with the linear V-g flutter analysis method. The V-g analysis, which is used in conjunction with the time-marching analysis, indicates that the fluid viscosity has a significant effect on the supersonic flutter boundary for this wing, whereas the structural damping and number of modes in the structural model have a lesser effect.