Flutter Prediction of a Laminar Airfoil Applying a Corrected Doublet Lattice Method Based on Experimental Derivatives

Abstract

In this paper a stability analysis of a two dimensional laminar airfoil with two degrees-of-freedom is presented and compared to turbulent flow conditions. The process for the flutter calculations is introduced, containing a description of the structural parameters, the aerodynamic derivatives due to a pitch motion, which are identified experimentally and two DLM correction methods to determine the aerodynamic derivatives due to a heave motion. For the local pressure distributions the corrections include nonlinearities due to transonic flow as well as transitional effects. The resulting aerodynamic derivatives reflect the differences between laminar and turbulent flow as measured in the experiment. An influence of the mean angle-of-attack on the stability boundary is shown for free transition. A comparison of the flutter boundaries for free and fixed transition exhibits a lower transonic dip for free transition. One-degree-of-freedom flutter is found only for free transition.