CFD calculations on the unsteady aerodynamic characteristics of a tilt-rotor in a conversion mode

• Published in: Chinese journal of aeronautics Vol. 28; no. 6; pp. 1593 - 1605
• Main Authors: Li, Peng, Zhao, Qijun, Zhu, Qiuxian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2015
• Subjects: CFD; Conversion mode; Multi-layer moving-embedded grid; NACA0012翼型; Tilt-rotor; Unsteady flowfield; 中心差分格式; 网格系统; 转子; 转换模式; 非定常气动力; 非定常气动特性; 非定常计算; CFD; Conversion mode; Unsteady flowfield; Multi-layer moving-embedded grid; Tilt-rotor
• ISSN: 1000-9361
• DOI: 10.1016/j.cja.2015.10.009

In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver- sion mode, a virtual blade model （VBM） and an real blade model （RBM） are established respec- tively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map （AIM） is established to search corresponding donor elements in the present moving- embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data （SPMD） model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum- Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are val- idated by comparing the calculated results with available experimental data. Then, unsteady aero- dynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles （15°, 30°, 60°） and a whole conversion mode which converses from 0° to 90°, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these investigation results could provide a good foundation for tilt-rotor aircraft design in the future.