**5. Conclusions**

The turbulent flow through a planar asymmetric diffuser was investigated numerically using LES with a high-order finite difference method to solve the equations for the resolved scales. Six resolutions were conducted for investigating the influence of mesh resolution in the turbulent diffuser flow. Four existing SGS models, a new one-equation dynamic model and a DNS were performed for LES of turbulent diffuser flow. The performance of five different SGS models was compared with published experiments and our DNS results. Firstly, LES on a coarse grid using the standard Smagorinsky model and well-designed wall-functions is able to predict the three-dimensional separated diffuser flow with fair accuracy at reasonable cost. Secondly, the ODM model and OVM model gave better agreemen<sup>t</sup> with experiments and DNS than the SM model, OM model and DSM model. Thirdly, unlike the ODM model, our OVM model, which does not require any test filtering and is not more expensive in terms of computational cost than the standard one-equation model, gave considerable improvement of the prediction accuracy even with moderate grid resolution in comparison with the four other SGS models.

**Author Contributions:** H.T. and Y.L. conceived the original ideal; H.T. wrote and edited the manuscript; and Y.L., X.L. and Y.F. supervised the study.

**Funding:** This research was funded by the project of Chinese National Natural Science Foundation (grant number: 51575220), the project of the Key Scientific and Technological Project of Jilin Province (grant numbers: 20160519008JH and 20170204073GX), and the project of National Key R&D Program of China (grant number: 2016YFB0101402).

**Acknowledgments:** The authors thank Takeo Kajishima and Kei Okabayashi for their help with the numerical method proposed and simulations conducted.

**Conflicts of Interest:** The authors declare no conflict of interest.
