Time-Linearized Analysis of Motion-Induced and Gust-Induced Airloads with the DLR TAU Code

Abstract

This paper provides an overview about the time-linearized analysis of motion-induced and gust-induced airloads with the DLR flow solver TAU. Time-linearized CFD methods to compute an aircraft’s aerodynamic response to sinusoidal oscillations promise a reduced computational effort while retaining the fidelity of the RANS flow characteristics. Two approaches are presented: a system identification method which excites the nonlinear steady background flow state with a broad-band pulse signal of small amplitude resulting in the aerodynamic frequency response function, and the DLR TAU linear frequency domain (LFD) solver which solves the linearized and Fourier transformed unsteady RANS equations for the first harmonic of the aerodynamic response. Both methods are validated with forced-motion pitching oscillations of the 2-d NACA 64A010 airfoil in comparison to the response of the fully nonlinear solver. Furthermore, the pulse method and LFD method are extended for sinusoidal gust encounters.