Nonlinear Response of Airfoil Section with Control Surface Freeplay to Gust Loads

Abstract

A nonlinear response analysis of a typical airfoil section with control surface freeplay excited by periodic gust loads in low subsonic flow is presented along with a companion wind-tunnel test program. The analytical model uses Peters's finite state model for the two-dimensional aerodynamic flow over the airfoil (Peters, D. A., Finite-State Airloads for Deformable Airfoils on Fixed and Rotating Wings, Symposium on Aeroelasticity and Fluid/Structure Interaction, American Society of Mechanical Engineers, Winter Annual Meeting, Nov. 1994, rev. 3, May 1996). Results for a single harmonic gust and a continuous frequency sweep gust have been computed and measured for flow velocities below the flutter speed. A theoretical and experimental chaotic response phenomenon for the nonlinear structural model was observed. These results further confirm some conclusions about limit cycle oscillations and complement our earlier theoretical and experimental studies of self-excited oscillations. The experimental investigation has been carried out in the Duke University wind tunnel using a rotating slotted cylinder gust generator. The fair to good quantitative agreement between theory and experiment verifies that the present analytical approach has reasonable accuracy and good computational efficiency for nonlinear gust response analysis in the time domain.