基于CFD/CSD耦合方法的新型桨尖旋翼气动弹性载荷计算

Calculations on Aeroelastic Loads of Rotor with Advanced Blade-tip Based on CFD/CSD Coupling Method

为提高旋翼非定常气动弹性载荷的分析精度,在刚性旋翼计算流体力学（CFD）方法中引入计算结构动力学（CSD）方法,建立了一套适合于新型桨尖旋翼气动弹性载荷分析的CFD/CSD耦合方法。旋翼流场分析采用NavierStokes/Euler方程作为控制方程,围绕旋翼生成运动嵌套网格。在流场求解中,采用双时间法推进,通量计算采用Jameson中心格式,并采用B-L（Baldwin-Lomax）湍流模型。基于Hamilton变分原理和中等变形梁理论开展桨叶弹性运动变形分析,并发展了一套具有任意转角梁单元的新方法以提高新型桨尖旋翼的动力学分析精度。采用基于代数变换方法的网格变形策略,建立了一套CFD/CSD松耦合方法,桨叶运动变形和旋翼气动力信息通过流固交接面传递。首先分别对CSD和CFD模块进行了验证,然后计算了UH-60A旋翼在高速前飞状态下的气动弹性载荷,并与试验值进行了对比,最后重点对旋翼桨尖形状进行了参数分析。计算结果表明,相比于升力线理论和刚性旋翼CFD方法,CFD/CSD耦合方法可以显著提高旋翼非定常气动弹性载荷的分析精度,并能更准确地反映新型桨尖旋翼的气动弹性耦合效应;同时采用后掠桨尖在桨叶前行侧30°~90°方位角范围可以显著降低激波强度,有利于改善旋翼的气动特性。

Computational structural dynamics（CSD）is introduced into rigid rotor computational fluid dynamics（CFD）to enhance the accuracy of the unsteady aeroelastic load analysis of a rotor,and a CFD/CSD coupling method suitable for the aeroelastic analysis of a rotor with an advanced blade-tip is developed.The Navier-Stokes/Euler equations are adopted as the governing equations,and moving-embedded grids are generated around the rotor in forward flight.In the flowfield analysis,a dual time-stepping algorithm is employed in temporal discretization,while Jameson’s central scheme is adopted in spatial discretization and a B-L（Baldwin-Lomax）turbulence model is included.The blade motion analysis is conducted based on Hamilton’s variational principle and moderate deflection beam theory,and a new beam element method with an arbitrary junction angle is established to improve the accuracy of dynamics analysis on the rotor with an advanced blade-tip.The blade grid is deformed using algebraic transformation strategy,and a CFD/CSD loose coupling method is developed with blade motions and rotor airloads being transferred through the fluid-structure interface.The CSD and CFD modules are validated respectively,and the aeroelastic loads on a UH-60 Arotor in high speed forward flight condition are calculated and compared with test data.Then,parametric investigations are carried out with emphasis on blade-tip shapes.The calculated results indicate that the present CFD/CSD method is able to improve the prediction accuracy of unsteady aeroelastic loads on the rotor as compared with the lifting-line method and rigid rotor CFD method,and the aeroelastic coupling effect of the rotor with the advanced blade-tip can be analyzed more precisely.Meanwhile,it is shown that a swept blade-tip shape can reduce the strength of shock at the advancing side between 30°and 90°azimuth angles,resulting in improved aerodynamic characteristics of the rotor.