Efficient Method For Simulation Of Viscous Flows Past Helicopter Rotors And Active Flow Control

In present dissertation, efficient simulation of complex unsteady viscous flowsand active flow control based on synthetic jet technology are studied. By usingLU-SGS implicit method and introducing preconditioning method coupling withmultigrid scheme, an efficient and robust numerical method solving Navier-Stokesequations for flows at all speed is presented and investigated. Based on this method,the unsteady viscous flows past helicopter rotors in forward flight are simulated, andactive flow control over airfoils and rotor blades are conducted. At last, theaeroacoustic nosie generated by helicopter rotor and in hover and forward flight arepredicted by solving Navier-Stokes equations and Ffowcs Williams/Hawkingsequation with penetrable data surface. This dissertation develops an efficient analysismethod for aerodynamic and aeroacoustic design of advanced helicopter rotors andalso presents a new-concept flow control techniques based on synthetic jettechnology.The main research work and increasing contribution of this dissertation are listedas follows:1) An efficient, robust and accurate method for simulating steady/unsteadyflows at all speed is developed and applied to solve a variety of two-dimensional andthree-dimensional viscous flows. All methods are implemented within the frameworkof Finite-Volume method. Revised JST scheme and high-order AUSM+-up schemeare employed for spatial discretization. Improved LU-SGS scheme and fully implicitdual-time stepping method are utilized for time integral. Preconditioning method andmultigrid method is used as the highly efficient techniques for accelerating theconvergence of residual. To improve the efficiency and stability for viscous flows, aviscous correction is introduced into LU-SGS scheme and a Newton-like scheme isobtained. A fully implicit dual-time stepping method is developed to improve theefficiency of unsteady flow simulation and a prediction-correction method is proposedby predicting the initial flow field of sub-iteration with the direct LU-SGS method.2) To overcome the he difficult in solving compressible equations for low Machnumber flows, preconditioning method is investigated and successfully applied intoour code. The preconditioning scheme for explicit and implicit time steppingmethod and also for JST and AUSM+ scheme is derived and discussed. Coupling thespatial discretization with AUSM+-up scheme and time stepping usingpreconditioning method, efficient and accurate simulation of flows from extremelylow speed (Ma=10^-5) to supersonic speed has been realized.3) An implicit muligrid scheme for solving Navier-Stokes equations ispresented. It is proved by numerous examples that implicit multigrid method is moreefficient and robust than explicit multigrid method. Introducing preconditioningmethod, this paper develops a preconditioning multigrid method, and the flow chart ofthis general technique is presented and discussed.4) A chimera multigrid method and a fully implicit dual-time stepping method for simulating the viscous flows over helicopter rotors in forward flight is presented,and an efficient code named FORWARD is developed. To improve the efficiency androbustness of moving-over-set-grid technique, a revised method for searchingcontributing cell is proposed. A new technique for implementing multigrid cycle onmoving-over-set grid is also proposed. The flows past hovering rotor, non-lifting andlifting forward flight rotor are simulated. The computed pressure distribution iscompared with experimental data and good agreement has been achieved. It's shownthat the present method markedly improves the efficiency and reduces the CPU timeof numerical simulation of viscous flow past helicopter rotor in forward flight.5) Numerical analysis method for active flow control over airfoils withsynthetic jet is presented, and optimization method for control parameters based on"surrogate model" is proposed. By imposing unsteady blowing/suction boundarycondition on airfoil, the numerical method considering the interaction betweensynthetic jet and the flow around airfoil is developed. The simulations of stall controlover NACA0015 airfoil, YLSG107 high-lift airfoil and VR-7B rotor airfoil anddynamic stall over OA212R rotor airfoil are conducted. The income and mechanismof synthetic jet as well as the effect of control parameters are analyzed and discussed.In order to optimize the control parameters, a method based on "surrogate model" isproposed. The numerical examples for NACA0012 and VR-7B airfoil shows that thismethod is efficient and engineering applicable.6) Based on the developed efficient numerical method for flows over helicopterrotors, the active flow control on three-dimensional rotor blades is investigated.Three-dimensional unsteady blowing/suction boundary condition is developed anddefinitions of momentum coefficient, non-dimensional frequency and jet angle arepresented. The active flow control on hovering rotor and forward flight rotor forincreasing thrust and removing the chock wave/boundary layer interaction isnumerically studied.7) The RANS/FW-H_pds method is applied to predict the aeroacoustic noisegenerated by helicopter rotors in hover and forward flight for the first time. Thenear-filed noise is obtained by solving Reynolds-Averaged Naiver-Stokes equations,and far-field noise is predicted by solving Ffowcs Williams-Hawking equation.Numerical examples shows that RANS/FW-H_pds method can predict High-SpeedImpulsive noise more accurately and also this method can be used to predict theBlade-Vortex-Interaction noise.