Aeroelastic Calculations Using CFD for a Typical Business Jet Model
Two time-accurate Computational Fluid Dynamics (CFD) codes were used to compute several flutter points for a typical business jet model. The model consisted of a rigid fuselage with a flexible semispan wing and was tested in the Transonic Dynamics Tunnel at NASA Langley Research Center where experimental flutter data were obtained from M(sub infinity) = 0.628 to M(sub infinity) = 0.888. The computational results were computed using CFD codes based on the inviscid TSD equation (CAP-TSD) and the Euler/Navier-Stokes equations (CFL3D-AE). Comparisons are made between analytical results and with experiment where appropriate. The results presented here show that the Navier-Stokes method is required near the transonic dip due to the strong viscous effects while the TSD and Euler methods used here provide good results at the lower Mach numbers.
Calculation of Airfoil Flutter by an Euler Method with Approximate Boundary Conditions
A numerical method is demonstrated for solving the steady and unsteady Euler equations on stationary Cartersian grids for the purpose of time-domain simulation of aeroelastic problems. Wall boundary conditions are implemented on nonmoving mean chord positions by assuming the airfoil being thin and undergoing small deformation, whereas the full nonlinear Euler equations are used in the flowfield for accurate resolution of shock waves and vorticity. The method does not require the generation of moving body-fitted grids and thus can be easily deployed in any fluid-structure interaction problem involving relatively small deformation of a thin body. The first-order wall boundary conditions are used in solving the full Euler equations, and the results are compared with the Euler solutions using the exact boundary conditions and known experimental data. It is shown that the first-order boundary conditions are adequate to represent airfoils of typical thicknesses with small deformation for both steady and unsteady calculations. Flutter boundaries are accurately predicted by this method for the Isogai wing model test case.
A review of some recent research on time-dependent aerodynamics
Time-dependent aerodynamics is primarily concerned with the pressure distributions developed by moving control surfaces, such as the oscillation of a trailing-edge flap, the rapid extension of a spoiler, or the pitching of a canard. Some recent experiments in time-dependent aerodynamics are reviewed. These include wind tunnel dynamic interference and its attenuation, the aerodynamics of an oscillating trailing-edge flap, the reduction of response to turbulence by active control, the aerodynamic characteristics of rapidly moving spoilers, and the time-dependent aerodynamic characteristics of supercritical wings. The paper concludes with a discussion of aeroelastic problems at subsonic and transonic speeds and with some buffeting measurements in a cryogenic wind tunnel.