Abstract

In order to calculate the unsteady aerodynamic force of tilt-rotor in conversion mode, VBM (Virtual Blade Model), RBM (Real Blade Model) and HBM (Hybrid Blade Model) are established respectively. A new multi-layer moving-embedded grid technique is presented to reduce the numerical dissipation of the tilt-rotor wake. In this method, grid generated abound the rotor accounts for rigid blade motions and a new searching scheme is implemented to search suitable donor elements in moving-embedded grids to translate information between the viscous flow and inviscid flow zones. In these CFD methods, a dual-time method is employed to fulfil the calculation of unsteady flowfield of tilt-rotor, and a second-order centred difference scheme by introducing artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the SMPD model parallel acceleration technology adopted, according to the characteristics of the current grid system. The lift and drag distributions of NACA0012 airfoil, the dynamic pressure distributions on a typical rotor and the sectional pressure distributions on XV-15 tilt-rotor in hovering flight are calculated respectively, and the developed VBM and RBM model are validated by comparing the calculated results with available experimental data. Then, unsteady aerodynamic force and flowfield of XV-15 tilt-rotor in different modes, such as fixed conversion mode at different tilt angles (15-deg, 30-deg, 60-deg), and full conversion cases from 0-deg to 90-deg, are numerically simulated by the VBM/RBM/HBM respectively. By analyses and comparisons on the simulated results about unsteady aerodynamic forces of tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in conversion mode are obtained, and these investigated results could provide a good foundation for tilt-rotor aircraft design in the future.

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