共轴刚性旋翼气动干扰及操纵特性分析

Analysis of aerodynamic interaction andtrim characteristics of rigid coaxial rotor

建立了一套基于高效配平策略和嵌套网格技术的共轴刚性旋翼气动数值分析方法。流场求解采用雷诺平均Navier-Stokes方程,空间离散采用Roe-monotone upstream-centered schemes for conservation laws(MUSCL)格式,湍流模型为Spalart-Allmaras模型;配平计算中引入"差量修正"策略。分析了共轴刚性旋翼模型在不同飞行状态下的气动干扰现象和操纵特性。结果表明:所建立的配平方法在同等精度下,比传统方法可显著节省计算时间;共轴刚性旋翼间距较小,其气动干扰明显强于普通共轴旋翼;悬停状态下,由于受上旋翼下洗流影响,下旋翼总距较大但拉力较小;小速度前飞时气动干扰引起下旋翼气流不对称性增大,双旋翼周期变距差也变大;采用适当的升力偏置量,可以提高共轴刚性旋翼气动效率。

A numerical method based on high-efficient trim strategy and moving overset grid technique was developed to predict the aerodynamic characteristics of rigid coaxial rotor.To simulate the rotor＇s flow-field,the Reynolds-averaged Navier-Stokes equations were discretized by Roe-monotone upstream-centered schemes for conservation laws（MUSCL）scheme with Spalart-Allmaras turbulence model.A delta trim method was implemented.Researches on the aerodynamic interaction and trim characteristics of a coaxial rigid rotor model were conducted.Results indicated that the delta method consumed much less time than the conventional trim method with the same accuracy.The aerodynamic interaction of rigid coaxial rotor,with a smaller rotors＇distance,was much stronger than that of normal coaxial rotor.In hover condition,the lower rotor required greater collective pitch while providing less tensile force due to the upper rotor＇s downwash;in low speed forward flight,the aerodynamic interaction brought about a more asymmetrical airflow on the rotors＇disks,leading togreater difference of cyclic pitches.In addition,the rotor＇s power efficiency can be improved by aproper lift offset.