基于RANS/LES混合方法的分离流动模拟

飞行器在大迎角、快速俯仰机动时，流场中含有大尺度、非定常的涡结构，传统雷诺平均Navier-Stokes （RANS）模型不能准确模拟流场结构，根据国际上相关研究的发展趋势，需要采用混合RANS/大涡模拟（LES）模型来对复杂分离流动进行准确模拟。本文对基于分区混合与湍流尺度混合的双重RANS/LES混合计算模型进行发展与应用。通过典型简化模型的静、动态湍流大分离流动，测试和验证所采用的脱体涡模拟（DES）类方法，重点研究改进的延迟DES （IDDES）模型在动态问题应用中的正确性和有效性，并对所采用的数值模拟方法和相应的计算软件的可靠性、鲁棒性以及精度进行了考核验证。典型算例包括超声速圆柱底部流动、跨声速方腔流动、NACA0015机翼深失速分离涡模拟等。计算表明：发展的IDDES类混合计算模型可有效解决对数层不匹配的问题；对于定态非定常分离流动，DES、DDES、IDDES等模型计算结果差别不大，随着流动的非定常特性增强，IDDES模型的优势逐渐显现；对于动态非定常分离流动，则需要采用IDDES类模型。

Simulation of separated flow based on RANS/LES hybrid method

Aircraft maneuvering at high angle of attack and fast pitch leads to large-scale and unsteady vortices in the flow field. Since the traditional Reynolds-Averaged Navier-Stokes (RANS) model cannot accurately simulate the flow field structure, the hybrid RANS/LES model, based on the development trend of international research, is required to accurately simulate the complex separated flow. In this paper, the dual RANS/ Large Eddy Simulatio (LES) hybrid computational model based on zonal mixing and turbulence scale mixing is further developed and applied. Through large static and dynamic turbulent separation flow of typical simplified models, DES-based methods are tested and validated. The correctness and validity of Improved Delayed Detached-Eddy Simulation (IDDES) model in the application to dynamic problems are emphatically studied. The reliability, robustness and accuracy of the numerical simulation method and corresponding calculation software are also tested and verified. Typical examples include supersonic cylindrical bottom flow, transonic square cavity flow and deep stall separation eddy simulation of NACA0015 airfoil. The requirements of three flow types for turbulence simulation methods are provided: steady separated flow, static unsteady separated flow, and dynamic unsteady separated flow. The results show that for static separated flows, DES, DDES and IDDES models are equivalent for static unsteady separated flows, while IDDES models are required for dynamic unsteady separated flows. Meanwhile, the IDDES method developed in this paper can effectively solve the problem of log layer mismatch.