This paper presents a new approach for mitigating the unphysical delay in the Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) transition, often referred to as the gray area, which is a common issue for hybrid RANS–LES turbulence models such as delayed-detached eddy simulation. An existing methodology designed for improving the LES performance in complex flows is adapted and tested. This is based on reducing the numerical diffusion in critical areas for permitting a more accurate development of turbulence. The new formulation comprises both a two-dimensional sensitive velocity gradient model and an alternative definition of the subgrid length scale, which are tested both individually and in tandem, and compared with the other formulations commonly used for addressing the gray area. Four test cases are examined, a flat plate, two variants of the incompressible backward-facing step, and an open jet compressible case, all of which are selected to expose the adverse impact of numerical diffusion that this study seeks to address. Furthermore, the proposed changes are implemented in two different codes for the purpose of cross-validation. Encouraging results are observed, supporting the suitability of the new approach as a candidate for addressing the gray area issue in flows of this kind.

本文提出了一种减轻雷诺平均Navier-Stokes（RANS）向大涡模拟（LES）过渡（通常称为灰色区域）的非物理延迟的新方法对于混合RANS-LES湍流模型（例如延迟分离涡流仿真），这是一个常见问题。修改并测试了旨在改善复杂流中的LES性能的现有方法。这是基于减少关键区域中的数值扩散以允许更精确地产生湍流。新配方既包含二维敏感速度梯度模型，又包含子网格长度尺度的替代定义，它们分别进行了测试，并进行了串联测试，并与通常用于解决灰色区域的其他配方进行了比较。检查了四个测试用例，一块平板，不可压缩的朝后步骤的两个变体以及一个可喷射的可压缩开放式外壳，选择所有这些方法来揭示本研究试图解决的数值扩散的不利影响。此外，出于交叉验证的目的，建议的更改以两种不同的代码实现。观察到令人鼓舞的结果，支持了该新方法作为解决此类流程中的灰色区域问题的候选方法的适用性。