Numerical Simulation of Tiltrotor Flow Field during Shipboard Take-Off and Landing Based on CFD-CSD Coupling

Abstract

Due to the small tilt angle, a tiltrotor operates in non-axial flow conditions during shipboard take-off and landing. The non-uniformity of the blade’s air-load is high, resulting in structural deformation with high fluctuation frequency, affecting the rotor’s aerodynamic characteristics. A new computational fluid-dynamic computational structural dynamics (CFD-CSD) solver is proposed to analyze the effects of the blade’s elastic deformation on the aerodynamic characteristics. This method is suitable for the aeroelastic simulation of shipboard tiltrotor take-offs and landings. The CFD method uses the Reynolds-averaged Navier-Stokes (RANS) equations as the control equation, while the CSD solver is based on the Timoshenko beam model. The solvers are combined with a two-way loose coupling strategy to improve the solution efficiency. The reverse overset assembly technique (ROAT) is utilized to eliminate the effects of orphan mesh points after deformation. The simulation is conducted during take-off and landing at different heights and different tilt angles, using the XV-15 tiltrotor as an example. An analysis of the rotor’s air-load and the mutual interference of the vortex and wake indicates that when the tiltrotor takes off or lands with a small tilt angle, the wing shedding vortex causes the rotor’s wake to roll upward before it reaches the ship’s deck, producing strong thrust fluctuations. The elastic deformation of the blade reduces the fluctuations in the thrust amplitude. This phenomenon is more pronounced in areas of high fluctuations in the blade’s air-load.

Comparative Study of Soft In-Plane and Stiff In-Plane Tiltrotor Blade Aerodynamics in Conversion Flight, Using CFD-CSD Coupling Approach

“…The CFD analysis is based on the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and the CSD analysis is constructed based on the Timoshenko beam model. The coupling method was used in a previous study [19] for the simulation of tiltrotor flow field during shipboard take-off and landing. By analyzing the results of soft in-plane and stiff in-plane tiltrotor blades in conversion flight, this study found that the influence of the difference in the structural characteristics of the blades on the aerodynamic force is quite different in the first and last halves of the tilting action, being more significant in the first half than in the last half.…”