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 mo...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.展开更多
A rotor CFD solver is developed for simulating the aerodynamic interaction phenomenon among rotor, wing and fuselage of a tilt rotor aircraft in its helicopter mode. The unsteady Navier-Stokes equations are discretize...A rotor CFD solver is developed for simulating the aerodynamic interaction phenomenon among rotor, wing and fuselage of a tilt rotor aircraft in its helicopter mode. The unsteady Navier-Stokes equations are discretized in inertial frame and embedded grid system is adopted for describing the relative motion among blades and nacelle/wing/fuselage. A combination of multi-layer embedded grid and 'extended hole fringe' technique is complemented in original grid system to tackle grid assembly difficulties arising from the narrow space among different aerodynamic components, and to improve the interpolation precision by decreasing the cell volume discrepancy among different grid blocks. An overall donor cell searching and automatic hole cutting technique is used for grid assembly, and the solution processes are speeded up by introduction of OpenMP parallel method. Based on this solver, flow fields and aerodynamics of a tilt rotor aircraft in hover are simulated with several rotor collective angles, and the corresponding states of an isolated rotor and rotor/wing/fuselage model are also computed to obtain reference solution. Aerodynamic interference influences among the rotor and wing/fuselage/nacelle are analyzed, and some meaningful conclusions are drawn. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.展开更多
基金supported by the National Natural Science Foundation of China(No.11272150)
文摘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.
文摘A rotor CFD solver is developed for simulating the aerodynamic interaction phenomenon among rotor, wing and fuselage of a tilt rotor aircraft in its helicopter mode. The unsteady Navier-Stokes equations are discretized in inertial frame and embedded grid system is adopted for describing the relative motion among blades and nacelle/wing/fuselage. A combination of multi-layer embedded grid and 'extended hole fringe' technique is complemented in original grid system to tackle grid assembly difficulties arising from the narrow space among different aerodynamic components, and to improve the interpolation precision by decreasing the cell volume discrepancy among different grid blocks. An overall donor cell searching and automatic hole cutting technique is used for grid assembly, and the solution processes are speeded up by introduction of OpenMP parallel method. Based on this solver, flow fields and aerodynamics of a tilt rotor aircraft in hover are simulated with several rotor collective angles, and the corresponding states of an isolated rotor and rotor/wing/fuselage model are also computed to obtain reference solution. Aerodynamic interference influences among the rotor and wing/fuselage/nacelle are analyzed, and some meaningful conclusions are drawn. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.
