T-tail flutter simulations with regard to quadratic mode shape components

Abstract

It is known that the dynamic aeroelastic stability of T-tails is dependent on the steady aerodynamic forces at aircraft trim condition. Accounting for this dependency in the flutter solution process involves correction methods for doublet lattice method (DLM) unsteady aerodynamics, enhanced DLM algorithms, unsteady vortex lattice methods (UVLM), or the use of CFD. However, the aerodynamic improvements along with a commonly applied modal approach with linear displacements results in spurious stiffness terms, which distort the flutter velocity prediction. Hence, a higher order structural approach with quadratic mode shape components is required for accurate flutter velocity prediction of T-tails. For the study of the effects of quadratic mode shape components on T-tail flutter, a generic tail configuration without sweep and taper is used. Euler based CFD simulations are applied involving a linearized frequency domain (LFD) approach to determine the generalized aerodynamic forces. These forces are obtained based on steady CFD computations at varying horizontal tail plane (HTP) incidence angles. The quadratic mode shape components of the fundamental structural modes for the vertical tail plane (VTP), i.e., out-of-plane bending and torsion, are received from nonlinear as well as linear finite element analyses. Modal coupling resulting solely from the extended modal representation of the structure and its influence on T-tail flutter is studied. The g-method is applied to solve for the flutter velocities and corresponding flutter mode shapes. The impact of the quadratic mode shape components is visualized in terms of flutter velocities in dependency of the HTP incidence angle and the static aerodynamic HTP loading.

Influence of Fluid Viscosity and Compressibility on Nonlinearities in Generalized Aerodynamic Forces for T-Tail Flutter

“…To study the effect of viscosity and compressibility on the aerodynamic response to structural deformation, the focus is set on an isolated HTP derived from a generic T-tail configuration described in [8,23]. This facilitates studying the aerodynamic response and its dependencies on the displacement amplitude, fluid viscosity, and fluid compressibility without aerodynamic interference effects.…”

“…The airfoil is a symmetric NACA 0012. Previous studies on the generic T-tail have revealed a minimum flutter speed at an incidence angle of 3.0° [23], for which reason this incidence angle was chosen for the presented studies. With a reference surface area of 16 m 2 and the reference values as listed in Table 1, this setting results in an up force and a positive lift coefficient of roughly 0.208 at Mach 0.4 and 0.259 at Mach 0.8.…”