An adaptive time integration approach for aeroelastic simulations using the unsteady vortex-lattice method and geometrically exact beams

In the context of aeroelastic simulations, the unsteady vortex-lattice method, strongly coupled with geometrically exact beams, represents a good balance between computational cost and accuracy. However, the computation of aerodynamic loads can still be very time-consuming. To reduce the wall time of aeroelastic computations using the unsteady vortex-lattice method and geometrically exact beams, we strive for a technique to reduce the number of time steps necessary to simulate a given physical time. This paper presents an approach to calculate and adapt the time step size, which can significantly reduce the total computation time without compromising the accuracy of the result. In order to achieve this, the time step size is adapted following the evolution of relevant physical quantities describing the system (ring circulations, aerodynamic forces, potential energy, kinetic energy). Limits for the minimum and maximum time step sizes are introduced by monitoring the geometry of the wake elements. This straightforward approach can easily be adapted to other aeroelastic frameworks using the unsteady vortex-lattice method. The high potential for computational acceleration is demonstrated in the application example of a NACA wing, the benchmark of the Pazy wing, and the NREL 5 MW reference wind turbine.