Research On Aeroelastic Response Of Rotor With Swept Blade-Tip Based On CFD/CSD Coupling Method

High-accuracy analysis on aeroelastic response of rotor with advanced blade-tip shape remains andifficult issue in the field of helicopter aerodynamics and rotor dynamics, and Computational FluidDynamics (CFD)/Computational Structural Dynamics (CSD) coupling method can enhance theanalytical accuracy of rotor aeroelastic and has become an research hot spot. Researches on CFD/CSDcoupling method include unsteady rotor flowfield simulation, rotor dynamics analysis andhigh-efficient coupling strategy, which are quite challenging topics. To solve these difficulties, thepresent thesis starts from rotor moving-embedded grid generation methodology, dynamics analysismethod for rotor with advanced blade-tip, unsteady flowfield and aerodynamics characteristicssimulation method for helicopter rotor and high-efficient fluid/structure coupling strategy aredeveloped. Based on CFD/CSD coupling analysis on aeroelastic response of elastic rotor, parametricinvestigations on the effects of blade-tip shape and blade structural properties are carried out. Themain contents are:In Chapter one, the development of elastic rotor flowfield analysis is introduced. Both domestic andabroad research status and technical issues of rotor aerodynamics, rotor structural dynamics, rotorCFD/CSD coupling method and aerodynamics shapes of advanced blade-tip rotor are analyzed, andthe necessity and significance of conducting simulations on elastic rotor flowfield and aerodynamicscharacteristics based on CFD/CSD coupling method are pointed out.In Chapter two, grid system for unsteady rotor flowfield analysis is developed based onmoving-embedded grid method. Two dimensional airfoil grids, three dimensional blade grids andCartesian background grids are generated respectively. In order to accomplish CFD/CSD coupling,grid deformation strategy based on algebraic transformation is established and high-efficient donorelement searching and information interpolation in the moving-embedded grid system for elastic rotorare accomplished through Top Map and Inverse Map methods.In Chapter three, a finite element method for structural dynamics analysis of rotor blade isdeveloped. The element variation of strain energy, kinematic energy and virtual work of external loadsare derived based on Hamilton’s variational principles and moderate deflection beam theory, andmultiple intersection elements method is presented to handle rotor with advanced blade-tip. Blademodal analysis is conducted by calculating eigenvalues of blade equations of motion while propulsivetrim method and Newmark-Beta method are adopted in solving the rotor equations of motion inforward flight. On this basis, modal analysis on ADM rotor, Maryland beam in vacuum and UH-60A rotor are carried out and the aeroelastic responses of a model rotor are analyzed and compared withtest data, which validate the rotor dynamics method established in this thesis.In Chapter four, a CFD method is established to simulate the unsteady rotor flowfield based onRANS/Euler equations. The governing equations are discretized using Finite Volume Method (FVM),Jameson second-order central difference scheme is adopted in spatial discretization, dualtime-stepping method is employed in temporal discretization with Runge-Kutta algorithm used inpseudo-time step, and B-L turbulence model is used to simulate the viscous effect in vicinity of blade.The developed method is validated by analyzing Helishape7A rotor and Caradonna-Tung rotor, andthe calculated results demonstrate the validity of the developed method.In Chapter five, a fluid/structure coupling method suitable for elastic rotor flowfield simulation isestablished adopting CFD/CSD coupling strategy based on the aforementioned methods. Meanwhile,fluid/structure information is exchanged through high-efficient algebraic grid deformation method.The developed loose coupling strategy is verified through SA349/2and UH-60A rotor airloadsprediction. Parametric investigations of aerodynamics shape of UH-60A rotor with different blade-tipswept angles on rotor aeroelastic characteristics are carried out, as a result, new conclusions such asswept tip benefits the pressure distribution at tip region are drawn.In Chapter six, effects of structural properties on rotor aeroelastic response are analyzed using therotor CFD/CSD coupling method established. The rotor aeroelastic characteristics are investigated byvarying the torsional and flapping stiffness of UH-60A rotor blade and conclusions such as reducedtorsional stiffness could further improve the pressure distribution near tip region are arrived at.