Abstract
This study involves the unsteady analysis of the aerodynamic characteristics and the extraction of stability derivatives of an aerostat. The analysis of the effect of oscillations of the aerostat with respect to the wind variation is necessary for the model development and control of such a system. An unsteady analysis of the aerostat is presented in the current study. The combination of unsteady wind and unsteady motion of the aerostat is used for the analysis. Sinusoidal wind gust and sinusoidal oscillations along with the axial (surge) and vertical (heave) directions and about the pitch axis of the aerostat are considered. The aerostat model used for the current analysis is validated using experimental data available in the literature. The dynamic mesh feature used for the heave and surge oscillations and the mesh motion feature used for the pitching oscillation are validated using the NACA 0012 airfoil experimental data. The effect of phase shift between the wind gust and the aerostat motion, wind gust amplitude, angle of attack, and wind gust duration on the aerodynamic characteristics of the aerostat is studied. The stability derivatives of the aerostat are extracted using CFD simulations. The methodology used for the stability derivatives extraction is validated using experimental data of a prolate spheroid. From the results, the drag response is maximum for the 180-degree phase shift and the lift and moment responses have a lagging response for their 0-degree phase shift. Aerostat response is linear for gust amplitude variation, and drag response is less affected by the change in angle of attack. Stability derivatives involved in the longitudinal motion of the aerostat are extracted.