UC Irvine

A Navier-Stokes Computational Fluid Dynamics (CFD) code is coupled with a Computa-

tional Structural Dynamics (CSD) code to study the flutter boundary of the NACA64A010

airfoil using Isogai’s structural model in transonic conditions. This model simulates aeroelas-

tic conditions on a sweptback wing. A well-known feature, only present in the inviscid flutter

boundary of this airfoil, is the existence of multiple flutter points for a fixed freestream Mach

number. The fully-turbulent flutter boundary has not been studied by many researchers us-

ing a Reynolds-Averaged Navier-Stokes approach. In the present study, the fully-turbulent

flutter boundary reveals the existence of multiple equilibrium positions for a narrow range

of flight conditions. The system moves away from the initial equilibrium position, finding a

new set of equilibrium points and oscillating around it. This new set of equilibrium points

reveals as stable or unstable for different structural properties of the wing.

We then proceed to study the effect of turbulent transition on flutter boundary. A laminar-

to-turbulent transition model is implemented in the CFD code and validated. The effect of

using a free-transition CFD code vs. a fully-turbulent approach is evaluated on three airfoils

with different characteristics for subsonic and transonic conditions. While free-transition

does not affect the pressure distribution at subsonic conditions, the transonic simulations

reveal a change in the shock-wave position when laminar-turbulent effects are included. The

effect of transition on the flutter boundary of the NACA64A010 airfoil at transonic conditions

is then investigated. A comparison between the free-transition, inviscid and fully-turbulent

flutter boundaries reveals similarities between the inviscid and free-transition elastic re-

sponses. Those similarities are due to the shift in the fully-turbulent shock-wave position,

when accounting for free-transition effects, moving closer to the inviscid shock location.