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首页> 外文期刊>Journal of the American Helicopter Society >Unsteady Aerodynamic Modeling with Time-Varying Free-Stream Mach Numbers
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Unsteady Aerodynamic Modeling with Time-Varying Free-Stream Mach Numbers

机译：随时间变化的自由流马赫数的非定常空气动力学建模

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The development of a reduced-order unsteady airfoil theory is described for application to subsonic compressible flows with variable free-stream Mach number. The airfoil theory, which is suitable for application to most types of blade element based comprehensive helicopter rotor analyses, is developed for arbitrary, time-dependent combined variations in angle of attack and Mach number. The approach is validated using computational fluid dynamics (CFD) solutions based on the Euler equations. The results show that blade element unsteady aerodynamic theories generally give good results only if the local Mach number variations are small in amplitude and vary slowly in time (i.e., a nearly quasi-steady assumption). However, helicopter rotor problems involve significant non-steady variations in local Mach number at the blade element level and so violate the quasi-steady Mach number assumptions. The new model is developed using linear indicial theory as a basis, and shows excellent agreement with direct CFD solutions for a wide range of flow conditions. For supercritical flows, nonlinearities associated with the formation and movement of shock waves are observed in the CFD solutions, which are responsible for nonlinearities in the lift and pitching moment. The estimation of the pitching moment is found to be particularly challenging because it is sensitive to these nonlinear phenomena. Overall, the new approach provides significant improvements in sectional airloads predictions over existing methods that might be used in various types of comprehensive helicopter rotor analyses.
机译：描述了降阶非定常翼型理论的发展，以应用于具有可变自由流马赫数的亚音速可压缩流。机翼理论适用于大多数类型的基于叶片元素的综合直升机旋翼分析，适用于迎角和马赫数的任意随时间变化的组合变化。使用基于欧拉方程的计算流体动力学（CFD）解决方案验证了该方法。结果表明，仅当局部马赫数变化幅度较小且时间变化缓慢时（即近似准稳态假设），叶片元件非稳态空气动力学理论通常才能给出良好的结果。但是，直升机旋翼问题涉及叶片元素水平上局部马赫数的显着非稳态变化，因此违反了准稳态马赫数假设。该新模型是使用线性指数理论作为基础开发的，并且在广泛的流动条件下与直接CFD解决方案显示出极好的一致性。对于超临界流，在CFD解决方案中观察到与冲击波的形成和运动相关的非线性，这是引起升力和俯仰力矩的非线性的原因。发现俯仰力矩的估计特别具有挑战性，因为它对这些非线性现象很敏感。总体而言，与可能在各种类型的综合直升机旋翼分析中使用的现有方法相比，新方法在截面空载预测方面提供了显着改进。

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