基于CFD/CSD耦合方法的旋翼气动弹性载荷计算分析

为提高直升机前飞状态下旋翼非定常气动弹性载荷的预估精度,在旋翼气动弹性综合分析方法中引入旋翼CFD模块,建立了一套基于CFD/CSD松耦合分析的计算方法和程序。为高效解决流固耦合方法中由于桨叶挥舞、扭转等弹性变形带来的旋翼贴体网格变形问题,采用基于代数变换方法的网格变形技术,桨叶运动变形量和旋翼气动力信息通过流固交接面传递。旋翼流场分析方法中,主控方程采用耦合S-A湍流模型的Navier-Stokes方程,围绕旋翼流场的网格采用结构嵌套网格方法生成,无黏通量计算采用Roe格式,时间推进采用双时间法。旋翼结构分析中,考虑旋翼配平,基于Hamilton变分原理和20自由度Timoshenko梁模型求解弹性旋翼非线性运动方程。分别对CSD和CFD方法进行验证,在此基础上,计算了SA349/2旋翼桨叶在前飞状态下的非定常气动力、挥舞弯矩、摆振弯矩和扭转力矩,并与飞行测试数据进行了对比。计算表明: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,精确捕捉桨叶表面压强峰值、激波位置等,表明本文发展的旋翼CFD/CSD耦合方法可以有效地运用到旋翼气动弹性载荷的预测分析中。

Computation analyses of aeroelastic loads of rotor based on CFD/CSD coupling method

In order to improve the prediction accuracy of the unsteady aeroelastic load of the rotor in forward flight of the helicopter,the rotor CFD module is introduced into the comprehensive analysis method for rotor aeroelastic,and then an analytical model and corresponding code based on CFD/CSD loose coupling method are established.In order to solve the deformation problem of blade body-fitted grid caused by aeroelastic deflections such as flapping and torsional motion in rotor CFD/CSD coupling process,the blade grids are deformed using algebraic method,and blade motion deformation and rotor aerodynamic force information are transferred through the interface between fluid and solid.In the analysis method for rotor flowfield,the Navier-Stokes equations coupled with S-A turbulence model are used as governing equations,and then the rotor moving-embedded grids are constructed.The Roe scheme is employed in spatial discretization,and a dual-time algorithm is adopted for temporal discretization.In the analysis of the rotor structure,considering the rotor trim,the nonlinear equations for motion of elastic rotor are solved based on Hamilton variational principle and 20 degree of freedom Timoshenko beam model.The CSD and CFD methods are validated.Based on aforementioned work,the aeroelastic loads on the SA349/2 rotor blade,mainly including unsteady aerodynamic loads and moment in flapping,lagging and torsion direction,are calculated and compared with flight test data.Comparisons of the CFD/CSD calculated results with flight test data demonstrate that the CFD/CSD coupling method has high accuracy in calculating the rotor unsteady aerodynamic load and structural load,and can capture the peak of pressure and shock position accurately.The method proposed could be effectively applied to prediction analysis of the aeroelastic loads of the rotor.