Investigation Of Computational Modeling Techniques For Rotor Flowfields

Helicopters have obtained widespread utilization from the invention beginning in the military, civil transportation, first aid domain and so on, due to their mobile and nimble characteristics. The technology unceasingly renews, and has already experienced four generation's development to the present time. Modern helicopters request compact layout, high forward flight speed, maneuverability and low noise level, which result in more serious aerodynamic issues. Comparing with the fixed wing, rotor flowfields are more complex, include mainly the following characteristics. Firstly, the flowfileds simultaneously include transonic and incompressible regions; Secondly, the flowfields are typically unsteady, under the forward flight condition, the airflow speed relative to the blades of the advancing side increases, following phenomenons of transonic speed such as shock wave, on the other side, the relative speed decreases, the flow angle is comparatively high, usually lead to dynamic stall; Thirdly, the rotor produces intense tip vortex, which hover around the rotor, and make a strong impact on the aerodynamic characteristics of flight vehicle.After dozens of years'development, computational fluid dynamics has received practical application in aviation, as a result of the mentioned complexity above, its application to rotors is much less than fixed wings. The numerical method for rotor flow depends heavily on the wake simulation, along with the computer technology development, it's possible now to resolve the three dimensional time-dependent N-S equations for complex geometry. Considering viscosity effect, the N-S equations have the potential to achieve accurate description of the formation and transportation of vortex, which don't depend on any wake model. Rotor wake can be obtained as a part of solution, and the solution obtained by this method is also called First Principle Solution.Based on structured overlap grid and the 3-D copressible N-S equations, the dissertation studied the numerical simulation of rotor flowfields, and constructed the computation software of rotor and rotor airframe integration. The contents are mainly divided into following seven chapters to present.The first chapter is an introduction, which briefly introduces the research background, the present situation as well as the research work of this article.The second chapter presents the computational method, discusses the equation forms under inertial and non-inertial coordinates system, the low speed preconditioning method, dual time step and structured overlap grid, etc. Based on these methods, the simulation software are coded for flowfields of rotor and rotor airframe integration, this sofware directly solves the N-S equations coupling with SA or k-ωSST turbulence models, without any wake model, and in benefits of preconditoning and multigrid method the efficiency is comparatively high.The third chapter is for the verification and validation of simulation method. The preconditioning method are validated by the cases of NACA4412 and NLR7301 airfoil, and the time precision, the sub-iteration efficiency are confirmed by the simulation of 1-D duct flows, single vortex movement, 2-D oscillating airfoil, synthetic jet and flow control, rotor/stator etc, the other aspects such as grid convergence and time step study are also studied.The fourth chapter is for the simulation of hovering rotor, two types of rotor are simulated including Caradonna-Tung rotor and UH-60A rotor by solving the N-S equations under the non-inertial rotation coordinates system. The simulating efficiency and precision are testified, with reference to experiment data, the blade pressure distribution, velocity field and wake structures are studied in detail for this work.In the fifth chapter, the stall regulated wind turbines (NREL Phase VI) are simulated on the zero-yaw and yawed configurations. The former are solved under non-inertial rotating coordinate system and the latter under inertial coordinate system. Through the flow simulation, the load distribution of the blades are obtained and compared with the experimental results, the moments law and the performance of the wind turbines are analyzed.The sixth chapter is for the research of rotor body interaction. With the use of moving overlap grids and 3-D compressible N-S equations computation, the GIT model and the dauphin helicopter are simulated to study the rotor body interaction process. The simulation shows the wake convection and flow field evolution, which cause time dependent pressure oscillation of the airframe along with blade passage effect. The analysis for disturbance phenomenon and the behind physical mechanism is also performed in this chapter.The seventh chapter is concluding remarks, which summarize this dissertation's research work, and forecast the work in the future.