Expeditious Evaluation of the Dynamic Response of Natural Laminar Flow Configurations to Small Pitching Oscillations

Abstract

Modern aircraft designs tend towards attaining higher cruise velocities combined with lighter and more flexible structures. This intensifies the fluid-structure interactions raising the risks of flutter. Therefore, determining the aeroelastic stability boundaries for the whole range of flight conditions at an early stage of the design process is crucial to save unnecessary costs on later modifications. Nevertheless, time-accurately solving the dynamic response to structural perturbations is prohibited in terms of computational effort, mainly due to the wide range of flight conditions that needs to be considered (e.g. Mach amplitude, altitude, load, deformation mode shape and frequency). An efficient alternative to accomplish this task is by assuming small harmonic perturbations and applying the Linear Frequency Domain (LFD) [1] method to linearly evaluate the dynamic response of the flow. The small perturbation assumption is justified on the interest of capturing the flutter onset, which will occur at infinitesimal displacements, rather than solving the flutter effect. The LFD approach was extensively verified with the DLR TAU code for fully turbulent configurations with the Spalart-Allmaras (SA) turbulence model [1,2]. However, the increased demand for cost-efficient aircraft designs and the growing awareness for global warming effects have shifted the attention back towards natural laminar aircraft designs [3]. To adapt the design capabilities of the DLR TAU code to the current demands, the LFD solver was extended to account for free transition effects when transition is predicted by the DLR γ transition transport model which was successfully integrated to the negative SA turbulence model in [4]. This work is part of the multi-disciplinary project LamTA (Laminar Tailored Aircraft) which aims to investigate the maximum potential of laminar technologies to reduce the energy consumption in flight.