适用于倾转旋翼机气动分析的新型嵌套网格方法

New embedded grid method for aerodynamic analyses of tiltrotor aircraft

为克服围绕复杂倾转旋翼机生成高质量一体化结构网格的困难,将分块网格策略与嵌套网格方法融合,提出并建立了一套适用于倾转旋翼机气动干扰分析的新型嵌套网格生成方法。该方法中,将整体网格按照倾转旋翼机结构特性进行了分块生成,在保证插值精度的基础上降低了网格规模。为高效连接不同部件网格,首先,引入Inverse-Map方法来辅助部件网格定位,采用新颖的多向投影方法保证了部件间洞边界的连续性;其次,基于独立挖洞嵌套策略完成机身与背景网格的组合,并使用了相应的辅助计算坐标进行背景边界网格标识。在贴体网格区域采用基于S-A(Spalart-Allmaras)湍流模型可压缩RANS(雷诺平均NavierStokes)方程求解流场,背景网格区域采用欧拉方程,并运用了SPMD(single program,multiple data)模式的并行加速技术,建立了适合倾转旋翼机气动干扰特性分析的高效混合CFD方法。采用Robin直升机机身作为数值算例,验证了CFD方法的有效性。在此基础上着重对倾转旋翼机在悬停、过渡和前飞巡航模式下的干扰流场进行了数值分析研究,分别得出了悬停状态下倾转旋翼机典型的"喷泉效应"干扰现象、过渡状态下的非定常气动干扰特性以及巡航状态下的部件气动变化特性,计算结果表明建立的新型嵌套网格方法能够较好地表征倾转旋翼机外形特性,并能够有效地用于倾转旋翼机的气动特性分析,加速比能超过5.0。

To overcome the difficulties in generating high quality integrative structured grids around the tiltrotor aircraft, the multi-block grid strategy and embedded grid method were combined to establish a new embedded grid generation method, which was suitable for aerodynamic interaction analyses of tiltrotor aircraft. On the basis of keeping the interpola- tion accuracy, the whole grid system composed of the multi-block grids was used to reduce the size of the grids. Firstly, the Inverse-Map method was introduced for auxiliary localiza- tion, and the new multi-directional projection method was proposed to ensure the continuityof the hole boundaries among the multi-block grids. Then, the independent embedded grid strategy was used in completing the combination of the airframe and background grids, and the assistant coordinates were adopted in the identification of the background boundary grids. Compressible RANS （Reynolds averaged Navier-Stokes） equations with S-A （Spal- art-Allmaras） turbulence model were employed in the body-fitted region, and Euler equa- tions were chosen to simulate the background region. In the present method, the SPMD （single program, multiple data） model parallel acceleration technology was adopted to im- prove the computational efficiency. On this basis, Robin airframe was taken as the numerical example to verify the validity of the present CFD method. Then the interaction flowfields of tiltrotor aircraft in different modes were investigated emphatically, and several simulated re- sults （special fountain effect phenomenon in hover, special flowfield in conversion mode, and variations of the aerodynamic characteristics of the tiltrotor aircraft in cruise） were obtained. The proposed embedded grid method and the numerical method were demonstrated to be effective in investigating the aerodynamic configuration of the tiltrotor aircraft, laying a good foundation for an- alyzing aerodynamic characteristics of the tiltrotor aircraft, with the speedup greater than 5.0.